Photoshop is an image-editing program – its images are composed of a grid of pixels and closely approximate continuous-tone photographs. Photoshop provides tools and commands used to edit images on a pixel-by-pixel basis.

In general, most operations in Photoshop are of the following form:

1.  Use a tool or a command to select pixels within the image.

2.  Perform an action on the selected pixels to change their color.