The Gallery
Paint Tools
When it comes to color tools, the color palette is among the more useful. Think of it like the palette that you use for making ordinary paintings. Choosing colors from the color dialog is much too ineffective, and you can't be that sure that you get the same color each time.
Gradients
The Gradient Editor is the key to making smooth color transitions, and it is used as a base for many kinds of important operations in Gimp. You can use gradients to blend two images through layer masks, or as a distort map image. The Gradient Editor allows you to create your own gradients where you'll have absolute control over all parameters, so this is a very useful tool for advanced image manipulation.
Color
If you want to learn to use an image manipulation program like Gimp to its full capacity, you must learn how colors work in the digital world and to understand the different color Color Models and Pre-press chapters.
It is essential to understand that different color models/devices have different gamut areas. An RGB monitor can display many more colors than a printer (CMYK) can. Finally, you can perceive more colors with your eyes than a monitor can display. The image below visualizes these facts.
Image Menu
The Image menu commands execute most operations in either RGB or HSV color space.
The Equalize command can be used enhance contrast and to find "hidden" colors in old, fading photos.
Invert will make a color image look like a photo negative. This means that if you have a slide scanner, scan the negative film and "develop" it to positive images using the Invert command. With the Posterize command you can reduce the number of colors/shades in an image, making it less naturalistic.
Color balance is a useful color correction tool if your image has distorted colors, or if you want to change the colors, like we have done with the blue duck.
Hue-Saturation is perhaps an even better tool for correcting color problems. It's also a great tool for changing colors. As you can see, our yellow truck has turned blue without any change in the other colors in the image. Curves is another color control tool. Here, we have turned day into night, or is it the other way around?
Levels is an excellent tool for enhancing 3-D effects by adding highlights or shadow. You can also use it the other way around and make the image flat, using less contrast when it comes to color, highlights and shadows. Desaturate takes away the color information, but you are still in RGB space. Desaturate is excellent when you want to accentuate a certain part of the image. If the surroundings are desaturated, the colored part will catch the viewer's focus.
Normalize, Contrast Auto-stretch and Auto-stretch HSV are three ways of enhancing faded or dull color photos.
Compose and Decompose in the Image/Channel Ops menu let you compose and decompose images to and from different color models. The RGB original to the left has been used for all decompose operations. All decomposed images are grayscale images, because they are representation of the color models' different channels.
Modes
The color images shown here are a necessary complement to their black-and-white counterparts, which are shown in the Modes chapter.
Comparing Modes
A layer containing a green leaf pattern was combined with the portrait layer. These images show the difference between Color and Hue mode.
Channels
These figures show the result of adding color to a channel. The yellow channel would look like the black-and-white image to the right if you copied and pasted it to a new image. If the yellow image had been a regular layer, it would look like the gray image (after desaturation).
This duotone image was created using a blue and a yellow channel.
Plug-ins
Plug-ins, commonly referred to as filters are an important part of Gimp. Many filters use color transformation, or affect the colors in the image in other ways.
Artistic Filters
All of the artistic filters affect color. However, only the Newsprint filter changes the way that color is used. The Newsprint filter separates colors either to RGB or to CMYK mode in order to build the half-tone pattern of an AM-screening printer.
Color Filters
Naturally, color filters must be shown in color. This section should be your companion when you read the color filters chapter.
Adjust Fgrd. - Bkgrd is a simple color-rotating filter
Alien Map is a psychedelic color-rotating filter that rotates and phase displaces colors using cosine and sine functions. Alien Map only works in RGB color space.
Alien Map2 has nearly the same functions as Alien Map, but this filter also works in HSV color space. Here we have aged a green spring leaf prematurely.
Color Mapping is a more "advanced" implementation of Adjust Fgrd. - Bkgrd.
Color Exchange lets you exchange one color to another. You can set the width of the desired color spectrum, i.e. how many shades should be exchanged for the specified color.
The Colorify effect is like putting a transparent color slide on top of your image.
Filter Pack is the darkroom filter. It's perfectly suited for adjusting miscolored photographs.
The Gradient Map filter will map an image against a gradient in the Gradient Editor.
Max RGB will only display the color that has the highest or lowest value.
If you want to colorize an old black-and-white photo, then Sample Colorize is the tool to use. You use a sample (a color photo) as source for colorizing an old black-and-white photo.
But you can also use a gradient, as we have done by coloring the baby's shirt.
Instead of inverting the colors like in the right-click|Image|Colors|Invert command, the Value Invert filter will invert the brightness value of each pixel.
Edge Detect
And with the Log filter you can make instant cartoon pictures.
Light Effects
Most of the light effects such as Flare FX, GFlare and Super Nova produce color lens/light effects.
Render
Most of the render filters affect color in one way or another. Here are some examples of the outcome of the fantastic IFS Compose filter.
