Editing X PixMap (section)

==== Many-color encoding ====

One tool is known to use only '''a''' to '''p''' for 16 colors, switching to '''aa''' up to '''dp''' for 64 colors, but still reading single character encodings for 64 colors; compare [[Base64]].

With more colors the codes use more characters, e.g. '''aa''' up to '''pp''' for 16 × 16 = 256 colors. This is less useful for text editors, because a string '''ab''' could be actually the middle of two adjacent pixels '''dabc'''. Spaces are allowed as color code, but might be a bad idea depending on the used text editor. Without control codes, backslash, and quote (needed in XPM1 and XPM3) 128 − 33 − 2 = 93 [[ASCII]] characters are available for single character color codes.

Simplified example: 90 US-ASCII characters could be arranged into nine non-overlapping sets of 10 characters. Thus unambiguous strings of nine characters could set the color of each pixel by its XPM palette index with up to 10<sup>9</sup> = {{val|1000000000}} colors (compare to [[GIF]], which supports only 256).

For XPM2 it is clear how many lines belong to the image – two header lines, the second header line announcing the number of color codes (2 lines in the example above) and rows (height 4 in the example above), e.g. 2 + 2 + 4 = 8 lines.