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 GraphicsMagick.dll depending on your system.
The API is divided into a number of categories:
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.
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