Mtpaint is a graphic editing program which uses the GTK+ toolkit. It can create and edit indexed palette or 24bit RGB images, offers basic painting and palette manipulation tools. It also handles JPEG, JPEG2000, GIF, TIFF, WEBP, BMP, PNG, XPM formats.

LodePNG is a PNG image decoder and encoder, all in one, no dependency or linkage required. It's made for C (ISO C90), and has a C++ wrapper with a more convenient interface on top.

Collection of graphics images created to test PNG applications like viewers, converters and editors. As far as that is possible, all formats supported by the PNG standard are represented.

libimagequant is a small, portable C library for high-quality conversion of RGBA images to 8-bit indexed-color (palette) images. This library can significantly reduces file sizes and powers pngquant and other PNG optimizers.

WebP is a new image format that provides lossless and lossy compression for images. WebP lossless images are 26% smaller in size compared to PNGs. WebP lossy images are 25-34% smaller in size compared to JPEG images at equivalent SSIM index. WebP supports lossless transparency (also known as alpha channel) with just 22% additional bytes. Transparency is also supported with lossy compression and typically provides 3x smaller file sizes compared to PNG when lossy compression is acceptable for the red/green/blue color channels.

Gifsicle is a command-line GIF image manipulation tool that:

• Provides a batch mode for changing GIFs in place.

• Prints detailed information about GIFs, including comments.

• Control over interlacing, comments, looping, transparency, etc.

• Creates well-behaved GIFs: removes redundant colors, only uses local color tables, etc.

• Shrinks colormaps and change images to use the Web-safe palette.

• Optimizes GIF animations, or unoptimizes them for easier editing.

Two other programs are included with Gifsicle: gifview is a lightweight animated-GIF viewer, and gifdiff compares two GIFs for identical visual appearance.

Developer's Image Library (DevIL) is a library to develop applications with support for many types of images. DevIL can load, save, convert, manipulate, filter and display a wide variety of image formats.

Jp2a is a small utility that converts JPEG images to ASCII.

pngquant is a PNG compressor that significantly reduces file sizes by converting images to a more efficient 8-bit PNG format with alpha channel (often 60-80% smaller than 24/32-bit PNG files). Compressed images are fully standards-compliant and are supported by all web browsers and operating systems.

Features:

1. High-quality palette generation using a combination of vector quantization algorithms.

2. Unique adaptive dithering algorithm that adds less noise to images than the standard Floyd-Steinberg.

3. Easy to integrate with shell scripts, GUIs and server-side software.

4. Fast mode for real-time processing/large numbers of images.

This is a tiny, header-only C++ library for manipulating INI files.

Libjpeg implements JPEG image encoding, decoding, and transcoding. JPEG is a standardized compression method for full-color and gray-scale images. It also includes programs that provide conversion between the JPEG format and image files in PBMPLUS PPM/PGM, GIF, BMP, and Targa file formats, as well as lossless JPEG manipulations such as rotation, scaling or cropping:

1. cjpeg

2. djpeg

3. jpegtran

4. rdjpgcom

5. wrjpgcom

libyuv is an open source project that includes YUV scaling and conversion functionality. It can:

• Scale YUV to prepare content for compression, with point, bilinear or box filter.

• Convert to YUV from webcam formats for compression.

• Convert to RGB formats for rendering/effects.

• Rotate by 90/180/270 degrees to adjust for mobile devices in portrait mode.

Picket is a screen color picker that includes a magnifier and supports custom formats for representing color values..

libspng is a simple C library for loading Portable Network Graphics (PNGs), intended as an easy-to-use replacement for libpng.

OptiPNG is a PNG optimizer that recompresses image files to a smaller size, without losing any information. This program also converts external formats (BMP, GIF, PNM and TIFF) to optimized PNG, and performs PNG integrity checks and corrections.

OpenJPEG is an implementation of JPEG 2000 codec written in C language. It has been developed in order to promote the use of JPEG 2000, a still-image compression standard from the Joint Photographic Experts Group (JPEG). Since April 2015, it is officially recognized by ISO/IEC and ITU-T as a JPEG 2000 Reference Software.

This package provides a C interface to the VIGRA C++ computer vision library. It is designed primarily to ease the implementation of higher-level language bindings to VIGRA.

swappy is a command-line utility to take and edit screenshots of Wayland desktops. Works great with grim, slurp and sway. But can easily work with other screen copy tools that can output a final PNG image to stdout.

JBIG2 is designed for lossy or lossless encoding of bilevel (1-bit monochrome) images at moderately high resolution, and in particular scanned paper documents. In this domain it is very efficient, offering compression ratios on the order of 100:1.

This is a decoder only implementation, and currently is in the alpha stage, meaning it doesn't completely work yet. However, it is maintaining parity with available encoders, so it is useful for real work.

A pretty small png library. Currently all documentation resides in pnglite.h.

Libpng is the official PNG (Portable Network Graphics) reference library. It supports almost all PNG features and is extensible.

Libicns is a library for the manipulation of Mac OS IconFamily resource type files (ICNS). icns2png and png2icns are provided to convert between PNG and ICNS. icns2png will extract image files from ICNS files under names like "Foo_48x48x32.png" useful for installing for use with .desktop files. Additionally, icontainer2png is provided for extracting icontainer icon files.

FreeImage is a library for developers who would like to support popular graphics image formats like PNG, BMP, JPEG, TIFF and others.

Converseen is an image batch conversion tool. You can resize and convert images in more than 100 different formats.