Free graphics software

- GIMP

GIMP is a cross-platform image editor available for GNU/Linux, OS X, Windows and more operating systems. It is free software, you can change its source code and distribute your changes.

Whether you are a graphic designer, photographer, illustrator, or scientist, GIMP provides you with sophisticated tools to get your job done. You can further enhance your productivity with GIMP thanks to many customization options and 3rd party plugins.
 
GIMP provides the tools needed for high quality image manipulation. From retouching to restoring to creative composites, the only limit is your imagination.
Original Artwork Creation

GIMP is used for producing icons, graphical design elements, and art for user interface components and mockups.
Programming Algorithms

GIMP is a high quality framework for scripted image manipulation, with multi-language support such as C, C++, Perl, Python, Scheme, and more!
 
GIMP provides top-notch color management features to ensure high-fidelity color reproduction across digital and printed media. It is best used in workflows involving other free software such as Scribus, Inkscape, and SwatchBooker.

GIMP provides extensibility through integration with many programming languages including Scheme, Python, Perl, and more. The result is a high level of customization as demonstrated by the large number of scripts and plug-ins created by the community.

- Faststone

FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor. It has a nice array of features that include image viewing, management, comparison, red-eye removal, emailing, resizing, cropping, retouching and color adjustments. Its innovative but intuitive full-screen mode provides quick access to EXIF information, thumbnail browser and major functionalities via hidden toolbars that pop up when your mouse touches one of the four edges of the screen. Other features include a high quality magnifier and a musical slideshow with 150+ transitional effects, as well as lossless JPEG transitions, drop shadow effects, image annotation, scanner support, histogram and much more. It supports all major graphic formats (BMP, JPEG, JPEG 2000, animated GIF, PNG, PCX, PSD, EPS, TIFF, WMF, ICO, CUR and TGA) and popular digital camera RAW formats (CR2, CR3, CRW, NEF, NRW, PEF, RAF, RWL, MRW, ORF, SRW, X3F, ARW, SR2, SRF, RW2 and DNG).

- Photoscape

PhotoScape is a fun and easy photo editing software that enables you to fix and enhance photos.

Key Features:

• Viewer: View photos in your folder, create a slideshow

• Editor: resizing, brightness and color adjustment, white balance, backlight correction, frames, balloons, mosaic mode, adding text, drawing pictures, cropping, filters, red eye removal, blooming, paint brush, clone stamp, effect brush

• Batch editor: Batch edit multiple photos

• Page: Merge multiple photos on the page frame to create one final photo

• Combine: Attach multiple photos vertically or horizontally to create one final photo

• Animated GIF: Use multiple photos to create a final animated photo

• Print: Print portrait shots, carte de visites(CDV), passport photos

• Splitter: Slice a photo into several pieces

• Screen Capture: Capture your screenshot and save it

• Color Picker: Zoom in on images, search and pick a color

• Rename: Change photo file names in batch mode

• Raw Converter: Convert RAW to JPG

• Paper Print: Print lined, graph, music and calendar paper

• Face Search: Find similar faces on the Internet 

PhotoScape is provided free of charge.

- Krita

Krita is a professional FREE and open source painting program. It is made by artists that want to see affordable art tools for everyone.

• concept art

• texture and matte painters

• illustrations and comics

Krita is a free and open-source raster graphics editor designed primarily for digital painting and animation purposes. It features OpenGL-accelerated canvas, colour management support, an advanced brush engine, non-destructive layers and masks (similar to Adobe Photoshop), group-based layer management, vector artwork support and switchable customisation profiles. It is written in Qt and runs on Windows and Unix-like OSes (including Linux and macOS). 

- Paint.NET

Paint.NET is image and photo editing software for PCs that run Windows. It features an intuitive and innovative user interface with support for layers, unlimited undo, special effects, and a wide variety of useful and powerful tools. An active and growing online community provides friendly help, tutorials, and plugins.

Every feature and user interface element was designed to be immediately intuitive and quickly learnable without assistance. In order to handle multiple images easily, Paint.NET uses a tabbed document interface.

Usually only found on expensive or complicated professional software, layers form the basis for a rich image composition experience. You may think of them as a stack of transparency slides that, when viewed together at the same time, form one image.

Many special effects are included for enhancing and perfecting your images. Everything from blurring, sharpening, red-eye removal, distortion, noise, and embossing are included. Also included is our unique 3D Rotate/Zoom effect that makes it very easy to add perspective and tilting.

Paint.NET includes simple tools for drawing shapes, including an easy-to-use curve tool for drawing splines or Bezier curves. The Gradient tool, new for 3.0, has been cited as an innovative improvement over similar tools provided by other software. The facilities for creating and working with selections is powerful, yet still simple enough to be picked up quickly. Other powerful tools include the Magic Wand for selecting regions of similar color, and the Clone Stamp for copying or erasing portions of an image. There is also a simple text editor, a tool for zooming, and a Recolor tool.

- Darktable

Darktable is an open source photography workflow application and raw developer. A virtual lighttable and darkroom for photographers. It manages your digital negatives in a database, lets you view them through a zoomable lighttable and enables you to develop raw images and enhance them.

Raw is the unprocessed capture straight from the camera’s sensor to the memory card, nothing has been altered. There are multiple alternatives in the open source world for raw development (ufraw, dcraw, rawtherapee) but darktable tries to fill the gap between the excellent existing free raw converters and image management tools (such as e.g. ufraw, rawstudio, f-spot, digikam, shotwell). It focuses on the workflow to make it easier for the photographer to quickly handle the thousands of images a day of shooting can produce. It’s also one of the very few FOSS projects able to do tethered shooting.

The user interface is built around efficient caching of image metadata and mipmaps, all stored in a database. The main focus lies on user interaction, both in terms of a smooth interface design as well as processing speed. High quality output is also one of our goals.

All editing is fully non-destructive and only operates on cached image buffers for display. The full image is only converted during export. Raw image loading is done using rawspeed, high-dynamic range and standard image formats such as jpeg are also supported. The core operates completely on floating point values, so darktable can not only be used for photography but also for scientifically acquired images or output of renderers (high dynamic range).

- Digikam

digiKam is an advanced open-source digital photo management application that runs on Linux, Windows, and MacOS. The application provides a comprehensive set of tools for importing, managing, editing, and sharing photos and raw files.

You can use digiKam’s import capabilities to easily transfer photos, raw files, and videos directly from your camera and external storage devices (SD cards, USB disks, etc.). digiKam organizes photos, raw files, and videos into albums. But the application also features powerful tagging tools that allow you to assign tags, ratings, and labels to photos and raw files. You can then use filtering functionality to quickly find items that match specific criteria.

In addition to filtering functionality, digiKam features powerful searching capabilities that let you search the photo library by a wide range of criteria. You can search photos by tags, labels, rating, data, location, and even specific EXIF, IPTC, or XMP metadata. You can also combine several criteria for more advanced searches. digiKam rely on Exiv2 library to handle metadata tag contents from files to populate the photo library.

digiKam can handle raw files, and the application uses the excellent LibRaw library for decoding raw files. The library is actively maintained and regularly updated to include support for the latest camera models.

The application provides a comprehensive set of editing tools. This includes basic tools for adjusting colors, cropping, and sharpening as well as advanced tools for, curves adjustment, panorama stitching, and much more. A special tool based on Lensfun library permit to apply lens corrections automatically on images.

- Pixelitor

Pixelitor is an open source image editor that supports layers, layer masks, text layers, filters, multiple undo etc. It requires Java 8 or higher. As of 4.2.3, it has more than 110 image filters and color adjustments, some of which are unique to Pixelitor. Some of the gradients can also be found only here.

Note that Pixelitor is intended to be powerful rather than simple. You should have some experience with image editors in order to use it, because there isn't much documentation available yet, and many concepts (layers, blending modes, cropping, Gaussian blurring, unsharp masking, histograms, etc.) are the same.