GBR Format Guide

Available Conversions

About GBR Format

GBR (GIMP Brush) is a raster image format created by the GIMP project (GNU Image Manipulation Program) for storing custom brush definitions. The format stores single brush images that are used as stamp patterns when painting in GIMP. GBR files come in two versions: Version 1 supports grayscale brushes only, while Version 2 extends support to full RGBA color brushes with alpha transparency. Each GBR file contains a header with brush metadata (name, dimensions, spacing) followed by raw pixel data. The format uses the .gbr file extension and is natively recognized by GIMP and compatible open-source image editors. GBR brushes define the shape and texture of each paint stroke, allowing artists to create effects ranging from simple circular dots to complex textured patterns, natural media simulations, and decorative stamps.

History of GBR

The GBR format was developed alongside GIMP, the GNU Image Manipulation Program, which was first released in 1996 by Spencer Kimball and Peter Mattis as a free and open-source alternative to commercial image editors like Adobe Photoshop. The brush format was designed to provide GIMP users with a simple, efficient way to define custom brush tips for the painting tools. The original Version 1 format supported only grayscale brush data, where each pixel defined the brush opacity at that point. As GIMP evolved and users demanded more creative flexibility, Version 2 was introduced to support full-color RGBA brushes, enabling colored and textured brush stamps with transparency. The GBR format became a cornerstone of the GIMP ecosystem, with thousands of community-created brush sets shared freely online. Many digital artists and hobbyists rely on GBR brushes for illustration, photo retouching, texture creation, and graphic design work within the GIMP environment.

Technical Details

GBR files use a simple binary structure consisting of a header followed by raw pixel data. The header contains: a 4-byte field for the total header size, a 4-byte version number (1 for grayscale, 2 for RGBA), a 4-byte width, a 4-byte height, a 4-byte bytes-per-pixel value (1 for grayscale, 4 for RGBA), and a variable-length null-terminated brush name string. The pixel data follows immediately after the header and is stored uncompressed in row-major order. For Version 1 (grayscale) brushes, each pixel is a single byte representing opacity (0=transparent, 255=opaque). For Version 2 (color) brushes, each pixel consists of four bytes in RGBA order. The format does not support layers, animation, metadata standards (EXIF, XMP), or compression. The spacing value in the header determines the distance between brush dabs when painting continuously, expressed as a percentage of the brush width.

Common Applications

GBR brushes are primarily used within GIMP for digital painting, illustration, photo retouching, and texture creation. Artists create custom brush tips to simulate natural media such as watercolor, charcoal, pencil, and ink effects. Graphic designers use GBR brushes for decorative elements, borders, patterns, and stamp effects in their compositions. Photo editors employ specialized brushes for retouching tasks like skin smoothing, dodge and burn effects, and selective adjustments. The GIMP community actively shares GBR brush packs for specific purposes including foliage, clouds, hair, fabric textures, grunge effects, and geometric patterns. Converting GBR files to standard image formats like PNG, JPG, or WebP is useful when extracting brush tip images for preview galleries, documentation, web display, or use in other applications that do not natively support the GBR format.

Advantages and Disadvantages