Tools used to perform image editing can be accessed via the toolbox, through menus and dialogue windows. They include filters and brushes, as well as transformation, selection,
layer and masking tools. GIMP's developers have asserted that it has, or at least aspire to it having, similar functionality to Photoshop, but has a different user interface.
Color There are several ways of selecting colors, including palettes, color choosers and using an eyedropper tool to select a color on the canvas. The built-in color choosers include
RGB/
HSV/
LAB/
LCH selector or scales, water-color selector,
CMYK selector and a color-wheel selector. Colors can also be selected using hexadecimal color codes, as used in HTML color selection. GIMP has native support for indexed color and
RGB color spaces; other color spaces are supported using decomposition, where each channel of the new color space becomes a black-and-white image. CMYK,
LAB and
HSV (
hue,
saturation,
value) are supported this way. Color blending can be achieved using the Blend tool, by applying a
gradient to the surface of an image and using GIMP's color modes. Gradients are also integrated into tools such as the brush tool, when the user paints this way the output color slowly changes. There are a number of default gradients included with GIMP; a user can also create custom gradients with tools provided. Gradient plug-ins are also available.
Selections and paths GIMP
selection tools include a rectangular and circular selection tool, free select tool, and fuzzy select tool (also known as magic wand). More advanced selection tools include the select by color tool for selecting contiguous regions of color—and the scissors select tool, which creates selections semi-automatically between areas of highly contrasting colors. GIMP also supports a quick mask mode where a user can use a brush to paint the area of a selection. Visibly this looks like a red colored overlay being added or removed. The foreground select tool is an implementation of
Simple interactive object extraction (SIOX), a method used to perform the extraction of foreground elements, such as a person or a tree in focus. The Paths Tool allows a user to create vectors (also known as
Bézier curves). Users can use paths to create complex selections, including around natural curves. They can paint (or "stroke") the paths with brushes, patterns, or various line styles. Users can name and save paths for reuse.
Image editing There are many tools that can be used for editing images in GIMP. The more common tools include a paint brush, pencil, airbrush, eraser and ink tools used to create new or blended pixels. The Bucket Fill tool can be used to fill a selection with a color or pattern. The Blend tool can be used to fill a selection with a color gradient. These color transitions can be applied to large regions or smaller custom path selections. GIMP also provides "smart" tools that use a more complex algorithm to do things that otherwise would be time-consuming or impossible. These include: • Clone tool, which copies pixels using a brush • Healing brush, which copies pixels from an area and corrects tone and color • Perspective clone tool, which works like the clone tool but corrects for distance changes • Blur and sharpen tools • The Smudge tool can be used to subtly smear a selection where it stands • Dodge and burn tool is a brush that makes target pixels lighter (dodges) or darker (burns)
Layers, layer masks and channels An image being edited in GIMP can consist of many
layers in a stack. The user manual suggests that "A good way to visualize a GIMP image is as a stack of transparencies," where in GIMP terminology, each level (analogous to a transparency) is called a layer. Each layer in an image is made up of several channels. In an
RGB image, there are normally 3 or 4 channels, each consisting of a red, green and blue channel. Color sublayers look like slightly different gray images, but when put together they make a complete image. The fourth channel that may be part of a layer is the
alpha channel (or layer mask). This channel measures opacity where a whole or part of an image can be completely visible, partially visible or invisible. Each layer has a layer mode that can be set to change the colors in the image. Text layers can be created using the text tool, allowing a user to write on an image. Text layers can be transformed in several ways, such as converting them to a path or selection. Since GIMP 3.2, there are "link layers", which are linked duplicates to external source files. Link layers automatically update changes that are made to the source files.
Automation, scripts and plug-ins using Mathmap plug-in GIMP has approximately 150 standard effects and filters, including Drop Shadow, Blur, Motion Blur and Noise. GIMP operations can be automated with
scripting languages. The Script-Fu is a
Scheme-based language implemented using a
TinyScheme interpreter built into GIMP. GIMP can also be scripted in
Perl,
Python (Python-Fu), or
Tcl, using interpreters external to GIMP. New features can be added to GIMP not only by changing program code (GIMP core), but also by creating plug-ins. These are external programs that are executed and controlled by the main GIMP program. MathMap is an example of a plug-in written in
C. There is support for several methods of sharpening and blurring images, including the blur and sharpen tool. The
unsharp mask tool is used to sharpen an image selectively – it sharpens only those areas of an image that are sufficiently detailed. The Unsharp Mask tool is considered to give more targeted results for photographs than a normal sharpening filter. The Selective Gaussian Blur tool works in a similar way, except it blurs areas of an image with little detail. GIMP-ML is an extension for machine learning with 15 filters.
GEGL The
Generic Graphics Library (
GEGL) was first introduced in GIMP 2.6 to improve how the software processes images. Initially GIMP used GEGL for high bit-depth color operations, helping reduce data loss when adjusting colors. GIMP 2.8 was limited to 8-bit color, which is much lower than the 12-bit or higher depth that most digital cameras produce. GIMP 2.10 introduced full support for high bit-depth color, and hardware acceleration was enabled through OpenCL for some tasks. GIMP 3.0 introduces non-destructive filters, allowing users to apply effects without permanently changing the original image. This means they can be edited, toggled on or off, or removed after being applied. Third-party filters are also supported, though they will not be retained if the necessary plugins are missing.
CTX CTX is a
rasterizer for vector graphics introduced in GIMP 3.0. It allows certain simple shapes, such as lines and circles, to be converted into vector objects.
File formats GIMP supports importing and exporting with a large number of different
file formats. GIMP's native format
XCF is designed to store all information GIMP can contain about an image; XCF is named after the e
Xperimental
Computing
Facility at
UC Berkeley where GIMP was authored. Import and export capability can be extended to additional file formats by means of plug-ins. XCF file size is extended to more than 4 GB since 2.9.6 and new stable tree 2.10.x. == Professional reviews ==