THIS IS A WORK IN PROGRESS!

BricsCAD and AutoCAD rely on 256 indexed colours. Lots of people like to work with black backgrounds, staring to white during a working day is less relaxed for the brains. So people draw yellow lines on the black screen and find out that they can't be seen when printed on white paper. Similar, very light blue on black is hardly visible on white.

Processing, converting, colour information is crucial for optimizing representation in PDF's or paper. Information can be used to change colours in CTB (Colour TaBles) files for printing.

The subject is hard, wanted is an approach to optimize visibility. To limit complexity: RGB "Truecolor" is not discussed. And the tip of the day: Don't use these colours unless you understand the consequences.

More specific, we want a mapping of 256 (0-255) screen colours to 256 paper colours as a base for CTB files.

The table of index colours

• There used to be a colorwheel drawing. Here it is: http://images.autodesk.com/adsk/files/colorwh.dwg.

• A proper guide can be found here: http://www.niwa.nu/2013/05/math-behind-colorspace-conversions-rgb-hsl/

• The subject of Hue can be found here: https://en.wikipedia.org/wiki/Hue#Defining_hue_in_terms_of_RGB

• CTB-files are compressed stuff and so far I am not able to properly write data to CTB. A link for uncompressing data can be found here: http://www.noliturbare.com/plot-print/print-ctbs-and-more

• It is pretty hard to obtain a list of RGB values of all indexed colours, so here it is: