Open Source C Library for Advanced Image Processing

Getting Started with LibGD

The recommended way to install LibGD is using CMake. Please use the following command for smooth installations

$ make install 

Clone the latest sources using the following command

$ git https://github.com/libgd/libgd.git 

Generate & Modify Images via C

The LibGD library provides the capability to create and manipulate images with ease. It allows using the creation of images in BMP, GIF, TGA, WBMP, JPEG, PNG, TIFF, WebP, XPM file formats with just a couple of lines of C code. One great feature of the library is that it lets you create images on the fly. The library is known for creating images on the fly that can be used on Web pages. It enables you to programmatically create an image, color it, draw on it, and save it to disk with ease.

    gdImagePtr im;
    int black, white;
    FILE *out;
    // Create the image
    im = gdImageCreate(100, 100);
    // Allocate background
    white = gdImageColorAllocate(im, 255, 255, 255);
    // Allocate drawing color
    black = gdImageColorAllocate(im, 0, 0, 0);
    // Draw rectangle
    gdImageRectangle(im, 0, 0, 99, 99, black);
    // Open output file in binary mode
    out = fopen("rect.jpg", "wb");
    // Write JPEG using default quality
    gdImageJpeg(im, out, -1);
    // Close file
    fclose(out);
    // Destroy image
    gdImageDestroy(im);
    

Image Resizing via C Library

The open source LibGD library enables computer programmers to resize their images on the fly using C commands inside their applications. To start you need to provide the complete path and name of the image for loading. Once it is done you need to provide the width and height of your new image and the output location of your choice where you want to save it. Please make sure all the provided information is correct other than the library not accepting it and throwing an exception.

    int main (int argc, char *argv[]) {
	FILE *fp;
	gdImagePtr in, out;
	int w, h;

	/* Help */
	if (argc<=4) {
		printf("%s  input.jpg  output.jpg  width  height\n", argv[0]);
		return 1;
	}

	/* Size */
	w = atoi(argv[3]);
	h = atoi(argv[4]);
	if (w<=0 || h<=0) {
		fprintf(stderr, "Bad size %dx%d\n", h, w);
		return 2;
	}

	/* Input */
	fp = fopen(argv[1], "rb");
	if (!fp) {
		fprintf(stderr, "Can't read image %s\n", argv[1]);
		return 3;
	}
	in = gdImageCreateFromJpeg(fp);
	fclose(fp);
	if (!in) {
		fprintf(stderr, "Can't create image from %s\n", argv[1]);
		return 4;
	}

	/* Resize */
	gdImageSetInterpolationMethod(in, GD_BILINEAR_FIXED);
	out = gdImageScale(in, w, h);
	if (!out) {
		fprintf(stderr, "gdImageScale fails\n");
		return 5;
	}

	/* Output */
	fp = fopen(argv[2], "wb");
	if (!fp) {
		fprintf(stderr, "Can't save image %s\n", argv[2]);
		return 6;
	}
	gdImageJpeg(out, fp, 90);
	fclose(fp);

	/* Cleanups */
	gdImageDestroy(in);
	gdImageDestroy(out);

	return 0;
}
    

Crop, Flip, Convert or Rotate Images via C API

The LibGD library has provided complete support for programmatically cropping and Flipping images using C commands. The library has provided multiple functions for flipping the image, such as flipping the image horizontally or vertically as well as both. Same like flipping you can also easily rotate it according to your own needs. Once done you can save the images with ease. It also provides support for converting PNG and JPEG images to other supported file formats.

   int main(int argc, char **argv)
{
	gdImagePtr im;
	FILE *in, *out;

	if (argc != 3) {
		fprintf(stderr, "Usage: png2avif infile.png outfile.avif\n");
		exit(1);
	}
	printf("Reading infile %s\n", argv[1]);
	in = fopen(argv[1], "rb");
	if (!in) {
		fprintf(stderr, "Error: input file %s does not exist.\n", argv[1]);
		exit(1);
	}
	im = gdImageCreateFromPng(in);
	fclose(in);
	if (!im) {
		fprintf(stderr, "Error: input file %s is not in PNG format.\n", argv[1]);
		exit(1);
	}
	out = fopen(argv[2], "wb");
	if (!out) {
		fprintf(stderr, "Error: can't write to output file %s\n", argv[2]);
		gdImageDestroy(im);
		exit(1);
	}
	fprintf(stderr, "Encoding...\n");
	gdImageAvifEx(im, out, 100, 0);
	printf("Wrote outfile %s.\n", argv[2]);
	fclose(out);
	gdImageDestroy(im);

	return 0;
}

Image Loading from Buffer in Memory

The open source library LibGD allows software developers to load an entire image to buffer in memory inside their own C applications. Once the image is loaded developers can easily perform different operations on the image, such as reading the image from the buffer, modifying the image, saving the image to a particular location, and so on. Once done please remember to free the buffer with normal memory management functions.