Working with Black-and-White and Color Images - GIMP 2.6 for Photographers: Image Editing with Open Source Software - page 338

4.4.6 Using the Sample Colorize Function to
Color an Image
You can find yet other methods to color an image in the Colors menu. These
filters are found in the image window under Colors > Map . They allow you
to colorize black-and-white images by mapping a color source image or a
gradient from foreground and background colors. Therefore, you must first
select both colors with the Color Picker from the Toolbox. We will have a closer
look at the Sample Colorize filter. However, the Gradient Map filter (gradient
from the foreground and background color) and, especially, the Alien Map
filter offer some rather special effects.
When you select the Sample Colorize filter, a window opens that is split in
two sections. On the left below Destination you can see what the image looks
like after editing, and on the right below Sample the image is in the original
condition. When you're editing, even color images are turned into black-and-
white images and can only be colorized with one color or a gradient.
First, select the Get Sample Colors button to colorize an image. Then
determine the sample color by double-clicking on the corresponding area in
the image under Destination . You will have to determine yourself which area
corresponds to the area with the desired color in the example image. The
image in the preview is then colorized with the assigned color.
Below the two images are two color gradients with triangles that can
be used as sliders. The sliders can be used as in the tonality correction. By
moving the sliders, you can control the brightness, tonality, and intensity of
the colors. If the color transition is too severe, check the Use subcolors and
Smooth samples boxes.
When you are satisfied with the result, click on the Apply button. The
applied filter settings will be transferred to the image.
In my experience, the program is rather instable; it crashed several times
when I worked with a sample color from the image. However, colorizing with a
gradient did work reliably. As previously mentioned, the program works with
a gradient selected from the foreground and background color.
For this purpose, select the entry in the menu at the top right next to
Sample . You may also select a reverse gradient. The image will be colorized
instantaneously by the gradient. The gradient can be modified with the sliders
below the preview images.
It could be interesting to deactivate the Hold intensity box. The intensity
of the colors will be the same as the preselected colors in the gradient at first.
But now you have complete freedom to change all settings. Go ahead and
experiment with it.