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GraphicsMagick has a number of functions that allow you to read, manipulate, write, or display an image. These functions are accessible through the various tools or the object-oriented Perl interface, PerlMagick. However, you can also access the functions directly from your program through the Magick Application Programmer Interface. To invoke the functions, write your program in your favorite language while making calls to the Magick image functions and link with `libGraphicsMagick.a`, `libGraphicsMagick.so`, or `Magick.dll` depending on your system.

The API is divided into a number of categories:

  GraphicsMagick Methods to Constitute an Image
  GraphicsMagick Methods to Composite an Image
  GraphicsMagick Image Methods
  Methods to Count the Colors in an Image
  Methods to Reduce the Number of Unique Colors in an Image
  Methods to Segment an Image with Thresholding Fuzzy c-Means
  Methods to Resize an Image
  Methods to Transform an Image
  Methods to Shear or Rotate an Image by an Arbitrary Angle
  Methods to Enhance an Image
  GraphicsMagick Image Effects Methods
  GraphicsMagick Special Effects Methods
  GraphicsMagick Image Decoration Methods
  Image Text Attributes Methods
  Methods to Annotate an Image
  Methods to Paint on an Image
  Methods to Draw on an Image
  Image Vector Drawing Methods
  GraphicsMagick Methods to Create Image Thumbnails
  Methods to Interactively Display and Edit an Image
  Methods to Interactively Animate an Image Sequence
  Methods to Get or Set Image Pixels
  Working with Image Lists
  GraphicsMagick Cache Views Methods
  Image Pixel FIFO
  Methods to Read or Write Binary Large OBjects
  Methods to Read or List GraphicsMagick Image formats
  Methods to Compute a Message Digest for an Image
  GraphicsMagick Registry Methods
  GraphicsMagick Error Methods
  GraphicsMagick Memory Allocation Methods
  GraphicsMagick Resource Consumption Methods
  GraphicsMagick Progress Monitor Methods

Here is a sample program to get you started. To find out about all the functions that are available, read the source code. Each function is delineated with a full rows of percent signs with comments describing the parameters required for the function and what it does. For ease in finding a function, they are sorted in alphabetical order.

Here is a full example of a program, `demo.c`, which reads multiple input files (possibly animation files) specified on the command line, resizes the image frames to 106x80, and writes the resulting animation to disk.

    #include <stdio.h>
    #include <string.h>
    #include <time.h>
    #include <sys/types.h>
    #include <magick/api.h>

    int main(int argc,char **argv)
    {
      ExceptionInfo
        exception;

      Image
        *image,
        *images,
        *resize_image,
        *thumbnails;

      ImageInfo
        *image_info;

      int
        i;

      /*
        Initialize the image info structure and read the list of files
        provided by the user as a image sequence
      */
      InitializeMagick(*argv);
      GetExceptionInfo(&exception);
      image_info=CloneImageInfo((ImageInfo *) NULL);
      images=NewImageList();
      for (i=1; i< argc-1; i++)
        {
          (void) strcpy(image_info->filename,argv[i]);
          printf("Reading %s ...", image_info->filename);
          image=ReadImage(image_info,&exception);
          printf(" %lu frames\n", GetImageListLength(image));
          if (exception.severity != UndefinedException)
            CatchException(&exception);
          if (image)
            (void) AppendImageToList(&images,image);
        }

      if (!images)
        {
          printf("Failed to read any images!\n");
          exit(1);
        }
      /*
        Create a thumbnail image sequence
      */
      thumbnails=NewImageList();
      while ((image=RemoveFirstImageFromList(&images)) != (Image *) NULL)
        {
          resize_image=ResizeImage(image,106,80,LanczosFilter,1.0,&exception);
          DestroyImage(image);
          if (resize_image == (Image *) NULL)
            {
              CatchException(&exception);
              continue;
            }
          (void) AppendImageToList(&thumbnails,resize_image);
        }
      /*
        Write the thumbnail image sequence to file
      */
      if (thumbnails)
        {
          (void) strcpy(thumbnails->filename,argv[argc-1]);
          printf("Writing %s ... %lu frames\n", thumbnails->filename,
                 GetImageListLength(thumbnails));
          WriteImage(image_info,thumbnails);
        }

      /*
        Release resources
      */
      DestroyImageList(thumbnails);
      DestroyImageInfo(image_info);
      DestroyExceptionInfo(&exception);
      DestroyMagick();
      return(0);
    }

Now we need to compile. On Unix, the command would look something like this:

       gcc -o demo demo.c -O `GraphicsMagick-config --cppflags --ldflags --libs`

As a usage example, with the input files in1.gif, in2.png, and in3.jpg, create the animation file out.miff:

       demo in1.gif in2.png in3.jpg out.miff

The resulting animation may be played on an X11 display using 'gm animate out.miff'.

The GraphicsMagick-config script reproduces the options which were used to compile the GraphicsMagick utilities. Using compatible options ensures that your program will compile and run.

Another example is smile.c. Compile and execute it to display a smiley face on your X server.

Image manipulation software that works like magic.