I am using gimp for windows 7. I have an image of a color gradient line (top is black middle white, bottom black) and I want to use gimp to extend the bottom of the line. Meaning, I want to make the black part of the line longer than it is. How can I do this? I do not want to effect the sizes of the other colors on the line.
To resize the canvas in Gimp, you can use the Canvas Size Dialog. Maybe this link will be of help: http://docs.gimp.org/en/gimp-image-resize.html
You can set the Width and the Height of the canvas. The default units are pixels but you can choose different units, e.g. percent. If the Chain to the right of the Width and Height is not broken, both Width and Height keep the same relative size to each other. If you break the Chain by clicking on it, you can set Width and Height separately. Information about the size in pixels and the current resolution are always displayed below the Width and Height fields.
In the link, see the last example Figure 15.65. Canvas enlarged (all layers changed):