Magick::Image Class

Quick Contents

• BLOBs
• Constructors
• Image Manipulation Methods
• Image Attributes
• Low-Level Image Pixel Access

Image is the primary object in Magick++ and represents a single image frame (see design ). The STL interface must be used to operate on image sequences or images (e.g. of format GIF, TIFF, MIFF, Postscript, & MNG) which are comprised of multiple image frames. Individual frames of a multi-frame image may be requested by adding array-style notation to the end of the file name (e.g. "animation.gif[3]" retrieves the fourth frame of a GIF animation.  Various image manipulation operations may be applied to the image. Attributes may be set on the image to influence the operation of the manipulation operations. The Pixels class provides low-level access to image pixels. As a convenience, including <Magick++.h> is sufficient in order to use the complete Magick++ API. The Magick++ API is enclosed within the Magick namespace so you must either add the prefix " Magick:: " to each class/enumeration name or add the statement " using namespace Magick;" after including the Magick++.h header.

The preferred way to allocate Image objects is via automatic allocation (on the stack). There is no concern that allocating Image objects on the stack will excessively enlarge the stack since Magick++ allocates all large data objects (such as the actual image data) from the heap. Use of automatic allocation is preferred over explicit allocation (via new) since it is much less error prone and allows use of C++ scoping rules to avoid memory leaks. Use of automatic allocation allows Magick++ objects to be assigned and copied just like the C++ intrinsic data types (e.g. 'int '), leading to clear and easy to read code. Use of automatic allocation leads to naturally exception-safe code since if an exception is thrown, the object is automagically deallocated once the stack unwinds past the scope of the allocation (not the case for objects allocated via new ).

Image is very easy to use. For example, here is a the source to a program which reads an image, crops it, and writes it to a new file (the exception handling is optional but strongly recommended):

#include <Magick++.h> 
#include <iostream> 
using namespace std; 
using namespace Magick; 
int main(int argc,char **argv) 
{ 
  InitializeMagick(*argv);

  // Construct the image object. Separating image construction from the 
  // the read operation ensures that a failure to read the image file 
  // doesn't render the image object useless. 
  Image image;
  try { 
    // Read a file into image object 
    image.read( "girl.gif" );

    // Crop the image to specified size (width, height, xOffset, yOffset)
    image.crop( Geometry(100,100, 100, 100) );

    // Write the image to a file 
    image.write( "x.gif" ); 
  } 
  catch( Exception &error_ ) 
    { 
      cout << "Caught exception: " << error_.what() << endl; 
      return 1; 
    } 
  return 0; 
}

The following is the source to a program which illustrates the use of Magick++'s efficient reference-counted assignment and copy-constructor operations which minimize use of memory and eliminate unnecessary copy operations (allowing Image objects to be efficiently assigned, and copied into containers).  The program accomplishes the following:

1. Read master image.
2. Assign master image to second image.
3. Resize second image to the size 640x480.
4. Assign master image to a third image.
5. Resize third image to the size 800x600.
6. Write the second image to a file.
7. Write the third image to a file.

#include <Magick++.h> 
#include <iostream> 
using namespace std; 
using namespace Magick; 
int main(int argc,char **argv) 
{ 
  InitializeMagick(*argv);

  Image master("horse.jpg"); 
  Image second = master; 
  second.resize("640x480"); 
  Image third = master; 
  third.resize("800x600"); 
  second.write("horse640x480.jpg"); 
  third.write("horse800x600.jpg"); 
  return 0; 
}

During the entire operation, a maximum of three images exist in memory and the image data is never copied.

The following is the source for another simple program which creates a 100 by 100 pixel white image with a red pixel in the center and writes it to a file:

#include <Magick++.h> 
using namespace std; 
using namespace Magick; 
int main(int argc,char **argv) 
{ 
  InitializeMagick(*argv);
  Image image( "100x100", "white" ); 
  image.pixelColor( 49, 49, "red" ); 
  image.write( "red_pixel.png" ); 
  return 0; 
}

If you wanted to change the color image to grayscale, you could add the lines:

image.quantizeColorSpace( GRAYColorspace ); 
image.quantizeColors( 256 ); 
image.quantize( );

or, more simply:

 image.type( GrayscaleType );

prior to writing the image.

BLOBs

While encoded images (e.g. JPEG) are most often written-to and read-from a disk file, encoded images may also reside in memory. Encoded images in memory are known as BLOBs (Binary Large OBjects) and may be represented using the Blob class. The encoded image may be initially placed in memory by reading it directly from a file, reading the image from a database, memory-mapped from a disk file, or could be written to memory by Magick++. Once the encoded image has been placed within a Blob, it may be read into a Magick++ Image via a constructor or read() . Likewise, a Magick++ image may be written to a Blob via write() .

An example of using Image to write to a Blob follows:
 

#include >Magick++.h> 
using namespace std; 
using namespace Magick; 
int main(int argc,char **argv) 
{ 
  InitializeMagick(*argv);

  // Read GIF file from disk 
  Image image( "giraffe.gif" );
  // Write to BLOB in JPEG format 
  Blob blob; 
  image.magick( "JPEG" ) // Set JPEG output format 
  image.write( &blob );

  [ Use BLOB data (in JPEG format) here ]

  return 0; 
}

likewise, to read an image from a Blob, you could use one of the following examples:

[ Entry condition for the following examples is that data is pointer to encoded image data and length represents the size of the data ]

Blob blob( data, length ); 
Image image( blob );

or

Blob blob( data, length ); 
Image image; 
image.read( blob);

some images do not contain their size or format so the size and format must be specified in advance:

Blob blob( data, length ); 
Image image; 
image.size( "640x480") 
image.magick( "RGBA" ); 
image.read( blob);

Constructors

Image may be constructed in a number of ways. It may be constructed from a file, a URL, or an encoded image (e.g. JPEG) contained in an in-memory BLOB . The available Image constructors are shown in the following table:
 
 

Image Constructors

Signature	Description
const std::string &imageSpec_	Construct Image by reading from file or URL specified by imageSpec_. Use array notation (e.g. filename[9]) to select a specific scene from a multi-frame image.
const Geometry &size_, const Color &color_	Construct a blank image canvas of specified size and color
const Blob &blob_	Construct Image by reading from encoded image data contained in an in-memory BLOB . Depending on the constructor arguments, the Blob size , depth , magick (format) may also be specified. Some image formats require that size be specified. The default ImageMagick uses for depth depends on the compiled-in Quantum size (8 or 16).  If ImageMagick's Quantum size does not match that of the image, the depth may need to be specified. ImageMagick can usually automagically detect the image's format. When a format can't be automagically detected, the format (magick ) must be specified.
const Blob &blob_, const Geometry &size_
const Blob &blob_, const Geometry &size, size_t depth
const Blob &blob_, const Geometry &size, size_t depth_, const string &magick_
const Blob &blob_, const Geometry &size, const string &magick_
const size_t width_,  const size_t height_, std::string map_, const StorageType type_, const void *pixels_	Construct a new Image based on an array of image pixels. The pixel data must be in scanline order top-to-bottom. The data can be character, short int, integer, float, or double. Float and double require the pixels to be normalized [0..1]. The other types are [0..MaxRGB].  For example, to create a 640x480 image from unsigned red-green-blue character data, use    Image image( 640, 480, "RGB", 0, pixels ); The parameters are as follows:   width_ Width in pixels of the image. height_ Height in pixels of the image. map_ This character string can be any combination or order of R = red, G = green, B = blue, A = alpha, C = cyan, Y = yellow M = magenta, and K = black. The ordering reflects the order of the pixels in the supplied pixel array. type_ Pixel storage type (CharPixel, ShortPixel, IntegerPixel, FloatPixel, or DoublePixel) pixels_ This array of values contain the pixel components as defined by the map_ and type_ parameters. The length of the arrays must equal the area specified by the width_ and height_ values and type_ parameters.

Image Manipulation Methods

Image supports access to all the single-image (versus image-list) manipulation operations provided by the ImageMagick library. If you must process a multi-image file (such as an animation), the STL interface , which provides a multi-image abstraction on top of Image, must be used.

Image manipulation methods are very easy to use.  For example:

Image image; 
image.read("myImage.tiff"); 
image.addNoise(GaussianNoise); 
image.write("myImage.tiff");

adds gaussian noise to the image file "myImage.tiff".

The operations supported by Image are shown in the following table:
 

Image Image Manipulation Methods

Method	Signature(s)	Description
adaptiveThreshold	size_t width, size_t height, size_t offset = 0	Apply adaptive thresholding to the image. Adaptive thresholding is useful if the ideal threshold level is not known in advance, or if the illumination gradient is not constant across the image. Adaptive thresholding works by evaluating the mean (average) of a pixel region (size specified by width and height) and using the mean as the thresholding value. In order to remove residual noise from the background, the threshold may be adjusted by subtracting a constant offset (default zero) from the mean to compute the threshold.
addNoise	NoiseType noiseType_	Add noise to image with specified noise type.
addNoiseChannel	const ChannelType channel_, const NoiseType noiseType_	Add noise to an image channel with the specified noise type. The channel_ parameter specifies the channel to add noise to.  The noiseType_ parameter specifies the type of noise.
affineTransform	const DrawableAffine &affine	Transform image by specified affine (or free transform) matrix.
annotate	const std::string &text_, const Geometry &location_	Annotate using specified text, and placement location
	string text_, const Geometry &boundingArea_, GravityType gravity_	Annotate using specified text, bounding area, and placement gravity. If boundingArea_ is invalid, then bounding area is entire image.
	const std::string &text_, const Geometry &boundingArea_, GravityType gravity_, double degrees_,	Annotate with text using specified text, bounding area, placement gravity, and rotation. If boundingArea_ is invalid, then bounding area is entire image.
	const std::string &text_, GravityType gravity_	Annotate with text (bounding area is entire image) and placement gravity.
blur	const double radius_ = 1, const double sigma_ = 0.5	Blur image. The radius_ parameter specifies the radius of the Gaussian, in pixels, not counting the center pixel.  The sigma_ parameter specifies the standard deviation of the Laplacian, in pixels.
blurChannel	const ChannelType channel_, const double radius_ = 0.0, const double sigma_ = 1.0	Blur an image channel. The channel_ parameter specifies the channel to blur. The radius_ parameter specifies the radius of the Gaussian, in pixels, not counting the center pixel.  The sigma_ parameter specifies the standard deviation of the Laplacian, in pixels.
border	const Geometry &geometry_ = "6x6+0+0"	Border image (add border to image).  The color of the border is specified by the borderColor attribute.
cdl	const std::string &cdl_	color correct with a color decision list. See http://en.wikipedia.org/wiki/ASC_CDL for details.
channel	ChannelType channel_	Extract channel from image. Use this option to extract a particular channel from  the image.  alphaChannel   for  example, is useful for extracting the alpha values from an image.
charcoal	const double radius_ = 1, const double sigma_ = 0.5	Charcoal effect image (looks like charcoal sketch). The radius_ parameter specifies the radius of the Gaussian, in pixels, not counting the center pixel.  The sigma_ parameter specifies the standard deviation of the Laplacian, in pixels.
chop	const Geometry &geometry_	Chop image (remove vertical or horizontal subregion of image)
colorize	const unsigned int opacityRed_, const unsigned int opacityGreen_, const unsigned int opacityBlue_, const Color &penColor_	Colorize image with pen color, using specified percent opacity for red, green, and blue quantums.
colorMatrix	const size_t order_, const double *color_matrix_	apply color correction to the image.
comment	const std::string &comment_	Comment image (add comment string to image).  By default, each image is commented with its file name. Use  this  method to  assign a specific comment to the image.  Optionally you can include the image filename, type, width, height, or other  image  attributes by embedding special format characters.
compare	const Image &reference_	Compare current image with another image. Sets meanErrorPerPixel , normalizedMaxError , and normalizedMeanError in the current image. False is returned if the images are identical. An ErrorOption exception is thrown if the reference image columns, rows, colorspace, or matte differ from the current image.
composite	const Image &compositeImage_, ssize_t xOffset_, ssize_t yOffset_, CompositeOperator compose_ = InCompositeOp	Compose an image onto the current image at offset specified by xOffset_, yOffset_ using the composition algorithm specified by compose_.
	const Image &compositeImage_, const Geometry &offset_, CompositeOperator compose_ = InCompositeOp	Compose an image onto the current image at offset specified by offset_ using the composition algorithm specified by compose_ .
	const Image &compositeImage_, GravityType gravity_, CompositeOperator compose_ = InCompositeOp	Compose an image onto the current image with placement specified by gravity_ using the composition algorithm specified by compose_.
contrast	size_t sharpen_	Contrast image (enhance intensity differences in image)
convolve	size_t order_, const double *kernel_	Convolve image.  Applies a user-specified convolution to the image. The order_ parameter represents the number of columns and rows in the filter kernel, and kernel_ is a two-dimensional array of doubles representing the convolution kernel to apply.
crop	const Geometry &geometry_	Crop image (subregion of original image)
cycleColormap	int amount_	Cycle image colormap
despeckle	void	Despeckle image (reduce speckle noise)
display	void	Display image on screen. Caution: if an image format is not compatible with the display visual (e.g. JPEG on a colormapped display) then the original image will be altered. Use a copy of the original if this is a problem.
distort	const DistortImageMethod method, const size_t number_arguments, const double *arguments, const bool bestfit = false	Distort image.  Applies a user-specified distortion to the image.
draw	const Drawable &drawable_	Draw shape or text on image.
	const std::list<Drawable > &drawable_	Draw shapes or text on image using a set of Drawable objects contained in an STL list. Use of this method improves drawing performance and allows batching draw objects together in a list for repeated use.
edge	size_t radius_ = 0.0	Edge image (hilight edges in image).  The radius is the radius of the pixel neighborhood.. Specify a radius of zero for automatic radius selection.
emboss	const double radius_ = 1, const double sigma_ = 0.5	Emboss image (hilight edges with 3D effect). The radius_ parameter specifies the radius of the Gaussian, in pixels, not counting the center pixel.  The sigma_ parameter specifies the standard deviation of the Laplacian, in pixels.
enhance	void	Enhance image (minimize noise)
equalize	void	Equalize image (histogram equalization)
erase	void	Set all image pixels to the current background color.
extent	const Geometry &geometry_	extends the image as defined by the geometry, gravity, and image background color.
	const Geometry &geometry_, const Color &backgroundColor_
	const Geometry &geometry_, const GravityType &gravity_	extends the image as defined by the geometry, gravity, and image background color.
	const Geometry &geometry_, const Color &backgroundColor_, const GravityType &gravity_
flip	void	Flip image (reflect each scanline in the vertical direction)
floodFill- Color	ssize_t x_, ssize_t y_, const Color &fillColor_	Flood-fill color across pixels that match the color of the target pixel and are neighbors of the target pixel. Uses current fuzz setting when determining color match.
	const Geometry &point_, const Color &fillColor_
	ssize_t x_, ssize_t y_, const Color &fillColor_, const Color &borderColor_	Flood-fill color across pixels starting at target-pixel and stopping at pixels matching specified border color. Uses current fuzz setting when determining color match.
	const Geometry &point_, const Color &fillColor_, const Color &borderColor_
floodFillOpacity	const long x_, const long y_, const unsigned int opacity_, const PaintMethod method_	Floodfill pixels matching color (within fuzz factor) of target pixel(x,y) with replacement opacity value using method.
floodFill- Texture	ssize_t x_, ssize_t y_,  const Image &texture_	Flood-fill texture across pixels that match the color of the target pixel and are neighbors of the target pixel. Uses current fuzz setting when determining color match.
	const Geometry &point_, const Image &texture_
	ssize_t x_, ssize_t y_, const Image &texture_, const Color &borderColor_	Flood-fill texture across pixels starting at target-pixel and stopping at pixels matching specified border color. Uses current fuzz setting when determining color match.
	const Geometry &point_, const Image &texture_, const Color &borderColor_
flop	void	Flop image (reflect each scanline in the horizontal direction)
frame	const Geometry &geometry_ = "25x25+6+6"	Add decorative frame around image
	size_t width_, size_t height_, ssize_t x_, ssize_t y_, ssize_t innerBevel_ = 0, ssize_t outerBevel_ = 0
fx	const std::string expression, const Magick::ChannelType channel	Fx image.  Applies a mathematical expression to the image.
gamma	double gamma_	Gamma correct image (uniform red, green, and blue correction).
	double gammaRed_, double gammaGreen_, double gammaBlue_	Gamma correct red, green, and blue channels of image.
gaussianBlur	const double width_, const double sigma_	Gaussian blur image. The number of neighbor pixels to be included in the convolution mask is specified by 'width_'.  For example, a width of one gives a (standard) 3x3 convolution mask. The standard deviation of the gaussian bell curve is specified by 'sigma_'.
gaussianBlurChannel	const ChannelType channel_, const double radius_ = 0.0, const double sigma_ = 1.0	Gaussian blur an image channel. The channel_ parameter specifies the channel to blur. The number of neighbor pixels to be included in the convolution mask is specified by 'width_'.  For example, a width of one gives a (standard) 3x3 convolution mask. The standard deviation of the gaussian bell curve is specified by 'sigma_'.
haldClut	const Image &reference_	apply a Hald color lookup table to the image.
implode	const double factor_	Implode image (special effect)
inverseFourierTransform	const Image &phaseImage_, const bool magnitude_	implements the inverse discrete Fourier transform (DFT) of the image either as a magnitude / phase or real / imaginary image pair.
label	const string &label_	Assign a label to an image. Use this option to  assign  a  specific label to the image. Optionally you can include the image filename, type, width, height, or scene number in the label by embedding  special format characters. If the first character of string is @, the image label is read from a file titled by the remaining characters in the string. When converting to Postscript, use this  option to specify a header string to print above the image.
level	const double black_point, const double white_point, const double mid_point=1.0	Level image. Adjust the levels of the image by scaling the colors falling between specified white and black points to the full available quantum range. The parameters provided represent the black, mid (gamma), and white points.  The black point specifies the darkest color in the image. Colors darker than the black point are set to zero. Mid point (gamma) specifies a gamma correction to apply to the image. White point specifies the lightest color in the image.  Colors brighter than the white point are set to the maximum quantum value. The black and white point have the valid range 0 to MaxRGB while mid (gamma) has a useful range of 0 to ten.
levelChannel	const ChannelType channel, const double black_point, const double white_point, const double mid_point=1.0	Level image channel. Adjust the levels of the image channel by scaling the values falling between specified white and black points to the full available quantum range. The parameters provided represent the black, mid (gamma), and white points. The black point specifies the darkest color in the image. Colors darker than the black point are set to zero. Mid point (gamma) specifies a gamma correction to apply to the image. White point specifies the lightest color in the image. Colors brighter than the white point are set to the maximum quantum value. The black and white point have the valid range 0 to MaxRGB while mid (gamma) has a useful range of 0 to ten.
magnify	void	Magnify image by integral size
map	const Image &mapImage_ , bool dither_ = false	Remap image colors with closest color from reference image. Set dither_ to true in to apply Floyd/Steinberg error diffusion to the image. By default, color reduction chooses an optimal  set  of colors that best represent the original image. Alternatively, you can  choose  a  particular  set  of colors  from  an image file with this option.
floodFillAlpha	const ssize_t x_, const ssize_t, const unsigned int  alpha_, const Color &target_, const bool invert_	Floodfill designated area with a replacement alpha value.
medianFilter	const double radius_ = 0.0	Filter image by replacing each pixel component with the median color in a circular neighborhood
mergeLayers	LayerMethod noiseType_	handle multiple images forming a set of image layers or animation frames.
minify	void	Reduce image by integral size
modifyImage	void	Prepare to update image. Ensures that there is only one reference to the underlying image so that the underlying image may be safely modified without effecting previous generations of the image. Copies the underlying image to a new image if necessary.
modulate	double brightness_, double saturation_, double hue_	Modulate percent hue, saturation, and brightness of an image. Modulation of saturation and brightness is as a ratio of the current value (1.0 for no change). Modulation of hue is an absolute rotation of -180 degrees to +180 degrees from the current position corresponding to an argument range of 0 to 2.0 (1.0 for no change).
motionBlur	const double radius_, const double sigma_, const double angle_	Motion blur image with specified blur factor. The radius_ parameter specifies the radius of the Gaussian, in pixels, not counting the center pixel.  The sigma_ parameter specifies the standard deviation of the Laplacian, in pixels. The angle_ parameter specifies the angle the object appears to be coming from (zero degrees is from the right).
negate	bool grayscale_ = false	Negate colors in image.  Replace every pixel with its complementary color (white becomes black, yellow becomes blue, etc.).  Set grayscale to only negate grayscale values in image.
normalize	void	Normalize image (increase contrast by normalizing the pixel values to span the full range of color values).
oilPaint	size_t radius_ = 3	Oilpaint image (image looks like oil painting)
opacity	unsigned int opacity_	Set or attenuate the opacity channel in the image. If the image pixels are opaque then they are set to the specified opacity value, otherwise they are blended with the supplied opacity value.  The value of opacity_ ranges from 0 (completely opaque) to MaxRGB . The defines OpaqueOpacity and TransparentOpacity are available to specify completely opaque or completely transparent, respectively.
opaque	const Color &opaqueColor_, const Color &penColor_	Change color of pixels matching opaqueColor_ to specified penColor_.
ping	const std::string &imageSpec_	Ping is similar to read except only enough of the image is read to determine the image columns, rows, and filesize.  The columns , rows , and fileSize attributes are valid after invoking ping.  The image data is not valid after calling ping.
	const Blob &blob_
process	std::string name_, const ssize_t argc_, char **argv_	Execute the named process module, passing any arguments via an argument vector, with argc_ specifying the number of arguments in the vector, and argv_ passing the address of an array of null-terminated C strings which constitute the argument vector. An exception is thrown if the requested process module does not exist, fails to load, or fails during execution.
quantize	bool measureError_ = false	Quantize image (reduce number of colors). Set measureError_ to true in order to calculate error attributes.
raise	const Geometry &geometry_ = "6x6+0+0",  bool raisedFlag_ =  false	Raise image (lighten or darken the edges of an image to give a 3-D raised or lowered effect)
read	const string &imageSpec_	Read image into current object
	const Geometry &size_, const std::string &imageSpec_	Read image of specified size into current object. This form is useful for images that do not specify their size or to specify a size hint for decoding an image. For example, when reading a Photo CD, JBIG, or JPEG image, a size request causes the library to return an image which is the next resolution greater or equal to the specified size. This may result in memory and time savings.
	const Blob &blob_	Read encoded image of specified size from an in-memory BLOB into current object. Depending on the method arguments, the Blob size, depth, and format may also be specified. Some image formats require that size be specified. The default ImageMagick uses for depth depends on its Quantum size (8 or 16).  If ImageMagick's Quantum size does not match that of the image, the depth may need to be specified. ImageMagick can usually automagically detect the image's format. When a format can't be automagically detected, the format must be specified.
	const Blob &blob_, const Geometry &size_
	const Blob &blob_, const Geometry &size_, size_t depth_
	const Blob &blob_, const Geometry &size_, size_t depth_, const string &magick_
	const Blob &blob_, const Geometry &size_, const string &magick_
	const size_t width_, const size_t height_, std::string map_, const StorageType type_, const void *pixels_	Read image based on an array of image pixels. The pixel data must be in scanline order top-to-bottom. The data can be character, short int, integer, float, or double. Float and double require the pixels to be normalized [0..1]. The other types are [0..MaxRGB].  For example, to create a 640x480 image from unsigned red-green-blue character data, use   image.read( 640, 480, "RGB", CharPixel, pixels ); The parameters are as follows:   width_ Width in pixels of the image. height_ Height in pixels of the image. map_ This character string can be any combination or order of R = red, G = green, B = blue, A = alpha, C = cyan, Y = yellow M = magenta, and K = black. The ordering reflects the order of the pixels in the supplied pixel array. type_ Pixel storage type (CharPixel, ShortPixel, IntegerPixel, FloatPixel, or DoublePixel) pixels_ This array of values contain the pixel components as defined by the map_ and type_ parameters. The length of the arrays must equal the area specified by the width_ and height_ values and type_ parameters.
reduceNoise	const double order_	reduce noise in image using a noise peak elimination filter.
randomThreshold	const Geometry &thresholds_	Random threshold the image. Changes the value of individual pixels based on the intensity of each pixel compared to a random threshold. The result is a low-contrast, two color image. The thresholds_ argument is a geometry containing LOWxHIGH thresholds. If the string contains 2x2, 3x3, or 4x4, then an ordered dither of order 2, 3, or 4 will be performed instead. This is a very fast alternative to 'quantize' based dithering.
randomThresholdChannel	const Geometry &thresholds_, const ChannelType channel_	Random threshold an image channel. Similar to randomThreshold() but restricted to the specified channel.
roll	int columns_, ssize_t rows_	Roll image (rolls image vertically and horizontally) by specified number of columns and rows)
rotate	double degrees_	Rotate image counter-clockwise by specified number of degrees.
sample	const Geometry &geometry_	Resize image by using pixel sampling algorithm
scale	const Geometry &geometry_	Resize image by using simple ratio algorithm
segment	double clusterThreshold_ = 1.0, double smoothingThreshold_ = 1.5	Segment (coalesce similar image components) by analyzing the histograms of the color components and identifying units that are homogeneous with the fuzzy c-means technique. Also uses quantizeColorSpace and verbose image attributes. Specify clusterThreshold_ , as the number  of  pixels  each cluster  must exceed the cluster threshold to be considered valid. SmoothingThreshold_ eliminates noise in the  second derivative of the histogram. As the value is  increased, you can  expect  a  smoother second derivative.  The default is 1.5.
shade	double azimuth_ = 30, double elevation_ = 30, bool colorShading_ = false	Shade image using distant light source. Specify azimuth_ and elevation_ as the  position  of  the light source. By default, the shading results as a grayscale image.. Set colorShading_ to true to shade the red, green, and blue components of the image.
shadow	const double percent_opacity = 80, const double sigma_ = 0.5, const ssize_t x_ = 0, const ssize_t y_ = 0	simulate an image shadow
sharpen	const double radius_ = 1, const double sigma_ = 0.5	Sharpen pixels in image.  The radius_ parameter specifies the radius of the Gaussian, in pixels, not counting the center pixel.  The sigma_ parameter specifies the standard deviation of the Laplacian, in pixels.
sharpenChannel	const ChannelType channel_, const double radius_ = 0.0, const double sigma_ = 1.0	Sharpen pixel quantums in an image channel  The channel_ parameter specifies the channel to sharpen..  The radius_ parameter specifies the radius of the Gaussian, in pixels, not counting the center pixel.  The sigma_ parameter specifies the standard deviation of the Laplacian, in pixels.
shave	const Geometry &geometry_	Shave pixels from image edges.
shear	double xShearAngle_, double yShearAngle_	Shear image (create parallelogram by sliding image by X or Y axis).  Shearing slides one edge of an image along the X  or  Y axis,  creating  a parallelogram.  An X direction shear slides an edge along the X axis, while  a  Y  direction shear  slides  an edge along the Y axis.  The amount of the shear is controlled by a shear angle.  For X direction  shears,  x  degrees is measured relative to the Y axis, and similarly, for Y direction shears  y  degrees is measured relative to the X axis. Empty triangles left over from shearing the  image  are filled  with  the  color  defined as borderColor.
solarize	double factor_ = 50.0	Solarize image (similar to effect seen when exposing a photographic film to light during the development process)
splice	const Geometry &geometry_	splice the background color into the image
spread	size_t amount_ = 3	Spread pixels randomly within image by specified amount
stegano	const Image &watermark_	Add a digital watermark to the image (based on second image)
sparseColor	const ChannelType channel, const SparseColorMethod method, const size_t number_arguments, const double *arguments	Sparse color image, given a set of coordinates, interpolates the colors found at those coordinates, across the whole image, using various methods.
statistics	ImageStatistics *statistics	Obtain image statistics. Statistics are normalized to the range of 0.0 to 1.0 and are output to the specified ImageStatistics structure. The structure includes members maximum, minimum, mean, standard_deviation, and variance for each of these channels: red, green, blue, and opacity (e.g. statistics->red.maximum).
stereo	const Image &rightImage_	Create an image which appears in stereo when viewed with red-blue glasses (Red image on left, blue on right)
swirl	double degrees_	Swirl image (image pixels are rotated by degrees)
texture	const Image &texture_	Layer a texture on pixels matching image background color.
threshold	double threshold_	Threshold image
transform	const Geometry &imageGeometry_	Transform image based on image and crop geometries. Crop geometry is optional.
	const Geometry &imageGeometry_, const Geometry &cropGeometry_
transparent	const Color &color_	Add alpha image to image, setting pixels matching color to transparent.
trim	void	Trim edges that are the background color from the image.
unsharpmask	double radius_, double sigma_, double amount_, double threshold_	Sharpen the image using the unsharp mask algorithm. The radius_ parameter specifies the radius of the Gaussian, in pixels, not counting the center pixel. The sigma_ parameter specifies the standard deviation of the Gaussian, in pixels. The amount_ parameter specifies the percentage of the difference between the original and the blur image that is added back into the original. The threshold_ parameter specifies the threshold in pixels needed to apply the diffence amount.
unsharpmaskChannel	const ChannelType channel_, const double radius_, const double sigma_, const double amount_, const double threshold_	Sharpen an image channel using the unsharp mask algorithm. The channel_ parameter specifies the channel to sharpen. The radius_ parameter specifies the radius of the Gaussian, in pixels, not counting the center pixel. The sigma_ parameter specifies the standard deviation of the Gaussian, in pixels. The amount_ parameter specifies the percentage of the difference between the original and the blur image that is added back into the original. The threshold_ parameter specifies the threshold in pixels needed to apply the diffence amount.
wave	double amplitude_ = 25.0, double wavelength_ = 150.0	Alter an image along a sine wave.
write	const string &imageSpec_	Write image to a file using filename imageSpec_ . Caution: if an image format is selected which is capable of supporting fewer colors than the original image or quantization has been requested, the original image will be quantized to fewer colors. Use a copy of the original if this is a problem.
	Blob *blob_	Write image to a in-memory BLOB stored in blob_. The magick_ parameter specifies the image format to write (defaults to magick ). The depth_ parameter species the image depth (defaults to depth ). Caution: if an image format is selected which is capable of supporting fewer colors than the original image or quantization has been requested, the original image will be quantized to fewer colors. Use a copy of the original if this is a problem.
	Blob *blob_, std::string &magick_
	Blob *blob_, std::string &magick_, size_t depth_
	const ssize_t x_, const ssize_t y_, const size_t columns_, const size_t rows_, const std::string &map_, const StorageType type_, void *pixels_	Write pixel data into a buffer you supply. The data is saved either as char, short int, integer, float or double format in the order specified by the type_ parameter. For example, we want to extract scanline 1 of a 640x480 image as character data in red-green-blue order:   image.write(0,0,640,1,"RGB",0,pixels); The parameters are as follows:   x_ Horizontal ordinate of left-most coordinate of region to extract. y_ Vertical ordinate of top-most coordinate of region to extract. columns_ Width in pixels of the region to extract. rows_ Height in pixels of the region to extract. map_ This character string can be any combination or order of R = red, G = green, B = blue, A = alpha, C = cyan, Y = yellow, M = magenta, and K = black. The ordering reflects the order of the pixels in the supplied pixel array. type_ Pixel storage type (CharPixel, ShortPixel, IntegerPixel, FloatPixel, or DoublePixel) pixels_ This array of values contain the pixel components as defined by the map_ and type_ parameters. The length of the arrays must equal the area specified by the width_ and height_ values and type_ parameters.
resize	const Geometry &geometry_	Resize image to specified size.

Image Attributes

Image attributes are set and obtained via methods in Image. Except for methods which accept pointer arguments (e.g. chromaBluePrimary) all methods return attributes by value.

Image attributes are easily used. For example, to set the resolution of the TIFF file "file.tiff" to 150 dots-per-inch (DPI) in both the horizontal and vertical directions, you can use the following example code:

string filename("file.tiff"); 
Image image; 
image.read(filename); 
image.resolutionUnits(PixelsPerInchResolution); 
image.density(Geometry(150,150));   // could also use image.density("150x150") 
image.write(filename)

The supported image attributes and the method arguments required to obtain them are shown in the following table:
 

Image Attributes

Function	Type	Get Signature	Set Signature	Description
adjoin	bool	void	bool flag_	Join images into a single multi-image file.
antiAlias	bool	void	bool flag_	Control antialiasing of rendered Postscript and Postscript or TrueType fonts. Enabled by default.
animation- Delay	size_t (0 to 65535)	void	size_t delay_	Time in 1/100ths of a second (0 to 65535) which must expire before displaying the next image in an animated sequence. This option is useful for regulating the animation of a sequence  of GIF images within Netscape.
animation- Iterations	size_t	void	size_t iterations_	Number of iterations to loop an animation (e.g. Netscape loop extension) for.
attribute	string	const std::string name_	const std::string name_, const std::string value_	An arbitrary named image attribute. Any number of named attributes may be attached to the image. For example, the image comment is a named image attribute with the name "comment". EXIF tags are attached to the image as named attributes. Use the syntax "EXIF:<tag>" to request an EXIF tag similar to "EXIF:DateTime".
background- Color	Color	void	const Color &color_	Image background color
background- Texture	string	void	const string &texture_	Image file name to use as the background texture. Does not modify image pixels.
baseColumns	size_t	void		Base image width (before transformations)
baseFilename	string	void		Base image filename (before transformations)
baseRows	size_t	void		Base image height (before transformations)
borderColor	Color	void	const Color &color_	Image border color
boundingBox	Geometry	void		Return smallest bounding box enclosing non-border pixels. The current fuzz value is used when discriminating between pixels. This is the crop bounding box used by crop(Geometry(0,0)).
boxColor	Color	void	const Color &boxColor_	Base color that annotation text is rendered on.
cacheThreshold	size_t		const size_t	Pixel cache threshold in bytes. Once this threshold is exceeded, all subsequent pixels cache operations are to/from disk. This is a static method and the attribute it sets is shared by all Image objects.
channelDepth	size_t	const ChannelType channel_	const ChannelType channel_, const size_t depth_	Channel modulus depth. The channel modulus depth represents the minimum number of bits required to support the channel without loss. Setting the channel's modulus depth modifies the channel (i.e. discards resolution) if the requested modulus depth is less than the current modulus depth, otherwise the channel is not altered. There is no attribute associated with the modulus depth so the current modulus depth is obtained by inspecting the pixels. As a result, the depth returned may be less than the most recently set channel depth. Subsequent image processing may result in increasing the channel depth.
channels	size_t		const size_t	NUmber of pixel channels.
chroma- BluePrimary	double x & y	double *x_, double *y_	double x_, double y_	Chromaticity blue primary point (e.g. x=0.15, y=0.06)
chroma- GreenPrimary	double x & y	double *x_, double *y_	double x_, double y_	Chromaticity green primary point (e.g. x=0.3, y=0.6)
chroma- RedPrimary	double x & y	double *x_, double *y_	double x_, double y_	Chromaticity red primary point (e.g. x=0.64, y=0.33)
chroma- WhitePoint	double x & y	double*x_, double *y_	double x_, double y_	Chromaticity white point (e.g. x=0.3127, y=0.329)
classType	ClassType	void	ClassType class_	Image storage class.  Note that conversion from a DirectClass image to a PseudoClass image may result in a loss of color due to the limited size of the palette (256 or 65535 colors).
clipMask	Image	void	const Image &clipMask_	Associate a clip mask image with the current image. The clip mask image must have the same dimensions as the current image or an exception is thrown. Clipping occurs wherever pixels are transparent in the clip mask image. Clipping Pass an invalid image to unset an existing clip mask.
colorFuzz	double	void	double fuzz_	Colors within this distance are considered equal. A number of algorithms search for a target  color. By default the color must be exact. Use this option to match colors that are close to the target color in RGB space.
colorMap	Color	size_t index_	size_t index_, const Color &color_	Color at colormap index.
colorMapSize	size_t	void	size_t entries_	Number of entries in the colormap. Setting the colormap size may extend or truncate the colormap. The maximum number of supported entries is specified by the MaxColormapSizeconstant, and is dependent on the value of QuantumDepth when ImageMagick is compiled. An exception is thrown if more entries are requested than may be supported. Care should be taken when truncating the colormap to ensure that the image colormap indexes reference valid colormap entries.
colorSpace	ColorspaceType colorSpace_	void	ColorspaceType colorSpace_	The colorspace (e.g. CMYK) used to represent the image pixel colors. Image pixels are always stored as RGB(A) except for the case of CMY(K).
columns	size_t	void		Image width
comment	string	void		Image comment
compose	CompositeOperator	void	CompositeOperator compose_	Composition operator to be used when composition is implicitly used (such as for image flattening).
compress- Type	CompressionType	void	CompressionType compressType_	Image compression type. The default is the compression type of the specified image file.
debug	bool	void	bool flag_	Enable printing of internal debug messages from ImageMagick as it executes.
defineValue	string	const std::string &magick_, const std::string &key_	const std::string &magick_, const std::string &key_,  const std::string &value_	Set or obtain a definition string to applied when encoding or decoding the specified format. The meanings of the definitions are format specific. The format is designated by the magick_ argument, the format-specific key is designated by key_, and the associated value is specified by value_. See the defineSet() method if the key must be removed entirely.
defineSet	bool	const std::string &magick_, const std::string &key_	const std::string &magick_, const std::string &key_, bool flag_	Set or obtain a definition flag to applied when encoding or decoding the specified format. . Similar to the defineValue() method except that passing the flag_ value 'true' creates a value-less define with that format and key. Passing the flag_ value 'false' removes any existing matching definition. The method returns 'true' if a matching key exists, and 'false' if no matching key exists.
density	Geometry   (default 72x72)	void	const Geometry &density_	Vertical and horizontal resolution in pixels of the image. This option specifies an image density when decoding a Postscript or Portable Document page. Often used with psPageSize.
depth	size_t (8-32)	void	size_t depth_	Image depth. Used to specify the bit depth when reading or writing  raw images or when the output format supports multiple depths. Defaults to the quantum depth that ImageMagick is compiled with.
endian	EndianType	void	EndianType endian_	Specify (or obtain) endian option for formats which support it.
directory	string	void		Tile names from within an image montage
file	FILE *	FILE *	FILE *file_	Image file descriptor.
fileName	string	void	const string &fileName_	Image file name.
fileSize	off_t	void		Number of bytes of the image on disk
fillColor	Color	void	const Color &fillColor_	Color to use when filling drawn objects
fillPattern	Image	void	const Image &fillPattern_	Pattern image to use when filling drawn objects.
fillRule	FillRule	void	const Magick::FillRule &fillRule_	Rule to use when filling drawn objects.
filterType	FilterTypes	void	FilterTypes filterType_	Filter to use when resizing image. The reduction filter employed has a sigificant effect on the time required to resize an image and the resulting quality. The default filter is Lanczos which has been shown to produce high quality results when reducing most images.
font	string	void	const string &font_	Text rendering font. If the font is a fully qualified X server font name, the font is obtained from an X  server. To use a TrueType font, precede the TrueType filename with an @. Otherwise, specify  a  Postscript font name (e.g. "helvetica").
fontPointsize	size_t	void	size_t pointSize_	Text rendering font point size
fontTypeMetrics	TypeMetric	const std::string &text_, TypeMetric *metrics		Update metrics with font type metrics using specified text, and current font and fontPointSize settings.
format	string	void		Long form image format description.
gamma	double (typical range 0.8 to 2.3)	void		Gamma level of the image. The same color image displayed on two different  workstations  may  look  different due to differences in the display monitor.  Use gamma correction  to  adjust  for this  color  difference.
geometry	Geometry	void		Preferred size of the image when encoding.
gifDispose- Method	size_t { 0 = Disposal not specified, 1 = Do not dispose of graphic, 3 = Overwrite graphic with background color, 4 = Overwrite graphic with previous graphic. }	void	size_t disposeMethod_	GIF disposal method. This option is used to control how successive frames are rendered (how the preceding frame is disposed of) when creating a GIF animation.
iccColorProfile	Blob	void	const Blob &colorProfile_	ICC color profile. Supplied via a Blob since Magick++/ and ImageMagick do not currently support formating this data structure directly.  Specifications are available from the International Color Consortium for the format of ICC color profiles.
interlace- Type	InterlaceType	void	InterlaceType interlace_	The type of interlacing scheme (default NoInterlace ). This option is used to specify the type of  interlacing scheme  for  raw  image formats such as RGB or YUV. NoInterlace means do not  interlace, LineInterlace uses scanline interlacing, and PlaneInterlace uses plane interlacing. PartitionInterlace is like PlaneInterlace except the  different planes  are saved  to individual files (e.g.  image.R, image.G, and image.B). Use LineInterlace or PlaneInterlace to create an interlaced GIF or progressive JPEG image.
iptcProfile	Blob	void	const Blob & iptcProfile_	IPTC profile. Supplied via a Blob since Magick++ and ImageMagick do not currently  support formating this data structure directly. Specifications are available from the International Press Telecommunications Council for IPTC profiles.
label	string	void	const string &label_	Image label
magick	string	void	const string &magick_	Get image format (e.g. "GIF")
alpha	const bool	void	const bool alphaFlag_	Image supports transparency (alpha channel)
matteColor	Color	void	const Color &matteColor_	Image matte (frame) color
meanError- PerPixel	double	void		The mean error per pixel computed when an image is color reduced. This parameter is only valid if verbose is set to true and the image has just been quantized.
modulusDepth	size_t	void	size_t depth_	Image modulus depth (minimum number of bits required to support red/green/blue components without loss of accuracy). The pixel modulus depth may be decreased by supplying a value which is less than the current value, updating the pixels (reducing accuracy) to the new depth. The pixel modulus depth can not be increased over the current value using this method.
monochrome	bool	void	bool flag_	Transform the image to black and white
montage- Geometry	Geometry	void		Tile size and offset within an image montage. Only valid for montage images.
normalized- MaxError	double	void		The normalized max error per pixel computed when an image is color reduced. This parameter is only valid if verbose is set to true and the image has just been quantized.
normalized- MeanError	double	void		The normalized mean error per pixel computed when an image is color reduced. This parameter is only valid if verbose is set to true and the image has just been quantized.
orientation	OrientationType	void	OrientationType orientation_	Image orientation.  Supported by some file formats such as DPX and TIFF. Useful for turning the right way up.
packets	size_t	void		The number of runlength-encoded packets in the image
packetSize	size_t	void		The number of bytes in each pixel packet
page	Geometry	void	const Geometry &pageSize_	Preferred size and location of an image canvas. Use this option to specify the dimensions and position of the Postscript page in dots per inch or a TEXT page in pixels. This option is typically used in concert with density . Page may also be used to position a GIF image (such as for a scene in an animation)
pixelColor	Color	ssize_t x_, ssize_t y_	ssize_t x_, ssize_t y_, const Color &color_	Get/set pixel color at location x & y.
profile	Blob	const std::string name_	const std::string name_, const Blob &colorProfile_	Get/set/remove a named profile . Valid names include "*", "8BIM", "ICM", "IPTC", or a user/format-defined profile name.
quality	size_t (0 to 100)	void	size_t quality_	JPEG/MIFF/PNG compression level (default 75).
quantize- Colors	size_t	void	size_t colors_	Preferred number of colors in the image. The actual number of colors in the image may be less than your request, but never more. Images with less unique colors than specified with this option will have any duplicate or unused colors removed.
quantize- ColorSpace	ColorspaceType	void	ColorspaceType colorSpace_	Colorspace to quantize colors in (default RGB). Empirical evidence suggests that distances in color spaces such as YUV or YIQ correspond to perceptual color differences more closely than do distances in RGB space. These color spaces may give better results when color reducing an image.
quantize- Dither	bool	void	bool flag_	Apply Floyd/Steinberg error diffusion to the image. The basic strategy of dithering is to  trade  intensity resolution  for  spatial  resolution  by  averaging the intensities  of  several  neighboring  pixels. Images which  suffer  from  severe  contouring  when  reducing colors can be improved with this option. The quantizeColors or monochrome option must be set for this option to take effect.
quantize- TreeDepth	size_t	void	size_t treeDepth_	Depth of the quantization color classification tree. Values of 0 or 1 allow selection of the optimal tree depth for the color reduction algorithm. Values between 2 and 8 may be used to manually adjust the tree depth.
rendering- Intent	RenderingIntent	void	RenderingIntent render_	The type of rendering intent
resolution- Units	ResolutionType	void	ResolutionType units_	Units of image resolution
rows	size_t	void		The number of pixel rows in the image
scene	size_t	void	size_t scene_	Image scene number
signature	string	bool force_ = false		Image MD5 signature. Set force_ to 'true' to force re-computation of signature.
size	Geometry	void	const Geometry &geometry_	Width and height of a raw image (an image which does not support width and height information).  Size may also be used to affect the image size read from a multi-resolution format (e.g. Photo CD, JBIG, or JPEG.
strip	void	strips an image of all profiles and comments.
strokeAntiAlias	bool	void	bool flag_	Enable or disable anti-aliasing when drawing object outlines.
strokeColor	Color	void	const Color &strokeColor_	Color to use when drawing object outlines
strokeDashOffset	size_t	void	double strokeDashOffset_	While drawing using a dash pattern, specify distance into the dash pattern to start the dash (default 0).
strokeDashArray	const double*	void	const double* strokeDashArray_	Specify the pattern of dashes and gaps used to stroke paths. The strokeDashArray represents a zero-terminated array of numbers that specify the lengths (in pixels) of alternating dashes and gaps in user units. If an odd number of values is provided, then the list of values is repeated to yield an even number of values.  A typical strokeDashArray_ array might contain the members 5 3 2 0, where the zero value indicates the end of the pattern array.
strokeLineCap	LineCap	void	LineCap lineCap_	Specify the shape to be used at the corners of paths (or other vector shapes) when they are stroked. Values of LineJoin are UndefinedJoin, MiterJoin, RoundJoin, and BevelJoin.
strokeLineJoin	LineJoin	void	LineJoin lineJoin_	Specify the shape to be used at the corners of paths (or other vector shapes) when they are stroked. Values of LineJoin are UndefinedJoin, MiterJoin, RoundJoin, and BevelJoin.
strokeMiterLimit	size_t	void	size_t miterLimit_	Specify miter limit. When two line segments meet at a sharp angle and miter joins have been specified for 'lineJoin', it is possible for the miter to extend far beyond the thickness of the line stroking the path. The miterLimit' imposes a limit on the ratio of the miter length to the 'lineWidth'. The default value of this parameter is 4.
strokeWidth	double	void	double strokeWidth_	Stroke width for use when drawing vector objects (default one)
strokePattern	Image	void	const Image &strokePattern_	Pattern image to use while drawing object stroke (outlines).
subImage	size_t	void	size_t subImage_	Subimage of an image sequence
subRange	size_t	void	size_t subRange_	Number of images relative to the base image
textEncoding	string	void	const std::string &encoding_	Specify the code set to use for text annotations. The only character encoding which may be specified at this time is "UTF-8" for representing Unicode as a sequence of bytes. Specify an empty string to use the default ASCII encoding. Successful text annotation using Unicode may require fonts designed to support Unicode.
tileName	string	void	const string &tileName_	Tile name
totalColors	size_t	void		Number of colors in the image
type	ImageType	void	ImageType	Image type.
verbose	bool	void	bool verboseFlag_	Print detailed information about the image
view	string	void	const string &view_	FlashPix viewing parameters.
virtualPixelMethod	VirtualPixelMethod	void	VirtualPixelMethod virtualPixelMethod_	Image virtual pixel method.
x11Display	string (e.g. "hostname:0.0")	void	const string &display_	X11 display to display to, obtain fonts from, or to capture image from
xResolution	double	void		x resolution of the image
yResolution	double	void		y resolution of the image

Low-Level Image Pixel Access

Image pixels (of type Quantum ) may be accessed directly via the Image Pixel Cache .  The image pixel cache is a rectangular window into the actual image pixels (which may be in memory, memory-mapped from a disk file, or entirely on disk). Two interfaces exist to access the Image Pixel Cache. The interface described here (part of the Image class) supports only one view at a time. See the Pixels class for a more abstract interface which supports simultaneous pixel views (up to the number of rows). As an analogy, the interface described here relates to the Pixels class as stdio's gets() relates to fgets(). The Pixels class provides the more general form of the interface.

Obtain existing image pixels via getPixels(). Create a new pixel region using setPixels().

In order to ensure that only the current generation of the image is modified, the Image's modifyImage() method should be invoked to reduce the reference count on the underlying image to one. If this is not done, then it is possible for a previous generation of the image to be modified due to the use of reference counting when copying or constructing an Image.

Depending on the capabilities of the operating system, and the relationship of the window to the image, the pixel cache may be a copy of the pixels in the selected window, or it may be the actual image pixels. In any case calling syncPixels() insures that the base image is updated with the contents of the modified pixel cache. The method readPixels() supports copying foreign pixel data formats into the pixel cache according to the QuantumTypes. The method writePixels() supports copying the pixels in the cache to a foreign pixel representation according to the format specified by QuantumTypes.

The pixel region is effectively a small image in which the pixels may be accessed, addressed, and updated, as shown in the following example:

Image image("cow.png"); 
// Ensure that there are no other references to this image.
image.modifyImage();
// Set the image type to TrueColor DirectClass representation.
image.type(TrueColorType);
// Request pixel region with size 60x40, and top origin at 20x30 
ssize_t columns = 60; 
Quantum *pixel_cache = image.getPixels(20,30,columns,40); 
// Set pixel at column 5, and row 10 in the pixel cache to red. 
ssize_t column = 5; 
ssize_t row = 10; 
Quantum *pixel = pixel_cache+row*columns+column; 
*pixel = Color("red"); 
// Save changes to underlying image .
image.syncPixels();
  // Save updated image to file.
image.write("horse.png");

The image cache supports the following methods:
 

Image Cache Methods

Method	Returns	Signature	Description
getConstPixels	const Quantum *	const ssize_t x_, const ssize_t y_, const size_t columns_, const size_t rows_	Transfers pixels from the image to the pixel cache as defined by the specified rectangular region.  The returned pointer remains valid until the next getPixel, getConstPixels, or setPixels call and should never be deallocated by the user.
getConstMetacontent	const void*	void	Returns a pointer to the Image pixel meta-content corresponding to a previous getPixel(), getConstPixels(), or setPixels() call.   The returned pointer remains valid until the next getPixel, getConstPixels, or setPixels call and should never be deallocated by the user. The pixel meta-content represent an array of type void, with each entry corresponding to an x,y pixel position.
getMetacontent	void*	void	Returns a pointer to the Image pixel meta-content corresponding to the pixel region requested by the last getConstPixels , getPixels , or setPixels call. The returned pointer remains valid until the next getPixel, getConstPixels, or setPixels call and should never be deallocated by the user.
getPixels	Quantum *	const ssize_t x_, const ssize_t y_, const size_t columns_, const size_t rows_	Transfers pixels from the image to the pixel cache as defined by the specified rectangular region. Modified pixels may be subsequently transferred back to the image via syncPixels. The returned pointer remains valid until the next getPixel, getConstPixels(), or setPixels() call and should never be deallocated by the user.
setPixels	Quantum *	const ssize_t x_, const ssize_t y_, const size_t columns_, const size_t rows_	Allocates a pixel cache region to store image pixels as defined by the region rectangle.  This area is subsequently transferred from the pixel cache to the image via syncPixels.  The returned pointer remains valid until the next getPixel, getConstPixels, or setPixels call and should never be deallocated by the user.
syncPixels	void	void	Transfers the image cache pixels to the image.
readPixels	void	QuantumTypes quantum_, unsigned char *source_,	Transfers one or more pixel components from a buffer or file into the image pixel cache of an image. ReadPixels is typically used to support image decoders. The region transferred corresponds to the region set by a preceding setPixels call.
writePixels	void	QuantumTypes quantum_, unsigned char *destination_	Transfers one or more pixel components from the image pixel cache to a buffer or file. WritePixels is typically used to support image encoders. The region transferred corresponds to the region set by a preceding getPixels or getConstPixels call.