create color table from a jpeg

[altenbach]

OK, here's the (seemingly?) correct way to read LUT files into a 256 element color map (LabVIEW 2014).

See if it works for you. 😄

[GerdW]

Hi Christian,

thanks for correcting me.

It was a (kind of) copy&paste error: I looked at those LUT files using a hex editor presenting byte offsets in hexadecimal. Ofcourse you need to use 0x100=0d256 instead of 0d100 when reshaping the array.

Background: Several years ago I worked with an ultrasonic microscope. The software for that scope used similar (or even the same) color files for generating images - back then I also used my own LabVIEW routine to convert measurement results to nice(r) images and also had to load such LUT files. Back then those files also had a filesize of 768 bytes (768 = 3*256 = 256 * RGB), so all you have to do when loading them is to recognize the order the bytes are written in such files (either "RGB, RGB, RGB…" or "RRR…, GGG…, BBB…").

[altenbach]

In summary:

• The *.lut files sometimes have a variable size header that I did no investigate further. (e.g. some are 800bytes)
• We need to get the last 768 bytes from the file and discard the beginning if the file ls longer than that.
• The color arrangement is not [RGBRGBRGB...RGBRGBRGB] but [RRR....RRRGGG...GGGBBB...BBBB], each stretch is 256 bytes.

In any case, this website has a nice collection of color tables and I might actually use some of those. Great find. Thanks!