Editing 2D computer graphics (section)

====Extended color models====
Text, shapes and lines are rendered with a client-specified color. Many libraries and cards provide [[color gradient]]s, which are handy for the generation of smoothly-varying backgrounds, shadow effects, etc. (See also [[Gouraud shading]]).  The pixel colors can also be taken from a texture, e.g. a [[digital image]] (thus emulating rub-on [[screentone]]s and the fabled ''checker paint'' which used to be available only in [[cartoon]]s).

Painting a [[pixel]] with a given color usually replaces its previous color. However, many systems support painting with [[Transparency (graphic)|transparent]] and [[translucent]] colors, which only modify the previous pixel values.  
<!--should elaborate: modify by mixing (weighted average) or by filtering (multiplication) -->
The two colors may also be combined in more complex ways, e.g. by computing their [[bitwise operation|bitwise]] [[exclusive or]].  This technique is known as ''inverting color'' or ''color inversion'', and is often used in [[graphical user interface]]s for highlighting, rubber-band drawing, and other volatile painting&mdash;since re-painting the same shapes with the same color will restore the original pixel values.  <!-- limitations -->