On Sun, 3 Jul 2011, Chris McCormick wrote:
Despite reading several posts in the archive and the source code in g_all_guis.c I am embarrassed to say that I am completely stumped by the problem of extracting the individual RGB components from the IEM saved color value in the .pd file, as ints between 0 and 255.
as a reference, [#to_iem] supports both iem colour formats, the 18-bit format for files, and the 24-bit format for messages. Such a patch is very simple :
http://gridflow.ca/svn/trunk/abstractions/%23to_iem.pd http://gridflow.ca/help/%23to_iem-help.html
But it does the opposite conversion of what you are trying to do.
What I am doing (in the case where the saved value is negative) is: iemcolor = -1 - iemcolor; r = (iemcolor & 0x3f000) >> 14; g = (iemcolor & 0xfc0) >> 4; b = (iemcolor & 0x3f) << 2;
this is the 18 bit iem format that you are trying to convert to a 3*8 bit component format. You are correctly extracting blue and green, where the shift is 0*6-2 for blue, 1*6-2 for green, but it has to be 2*6-2 for red.
For the 24 bit iem format, instead, you have to shift by 0*8, 1*8, 2*8.
-2 is the difference between 6 bits per component and 8 bits per component.
Note that those conversions scale in a crude way, such that 63 is scaled to 252, instead of the maximum 255. If you want to scale more appropriately to fill the whole range, you need to post-process those components a little bit(s) :
r = r | (r>>6) g = g | (g>>6) b = b | (b>>6)
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