# [fpc-devel] Correlation between TFPColor and RGB values (possible inconsistencies)

JoshyFun joshyfun at gmail.com
Wed Feb 17 17:30:30 CET 2010

```Hello Graeme,

Wednesday, February 17, 2010, 2:57:07 PM, you wrote:

GG> Yes, that is always ideal, but I can only work with what I know and what I
GG> can find on the internet. If you have a link on the internet that defines
GG> color values in 48bit, then please do post it here. I have search for the
GG> last 30 minutes and haven't found a single link.

You will not find nothing quite sure as 24 bits is quite closer to our
color perception capability.

GG> All colors I could find are defined as 24-bit RGB values (certified values
GG> and color names created by companies like Microsoft, HP, Adobe, W3C, Exif
GG> etc.), so that is what I based my calculations on. Using ratios to do the
GG> upscaling calculation seems to be the most common conversion method too -
GG> as per the links I found on the internet (wikipedia and many websites like
GG> Adobe or other photographic websites).

The problem is that for each 24 bit colors there are 16.1 million
equivalent colors in 48 bits so any test like:

Pixel[x,y]=clMaroon;
if Pixel[x,y]=clMaroon then blah, blah...

will only be true 1/16000000 times, so that compare is not logical due
different bases.

Any other discussion about the low byte of 48 bit colors is useless
because:

\$8001 is in 24 bits the same as \$80FF in 24 bits, and there is not
proper upscaling, as clMaroon is not \$8080 nor \$8000, nor \$80FF. It is
a 48 bits value defined by somebody using any upscaling or downscaling
technique.

Colorimetric is a "dangerous" field for programmers. We are used to
think in RGB values, but once you work a bit with temperature or
different codifications like YUV, YUY, CMYK or any other you end
knowing that 2+2=2.12321+-2*pi when the wind blows from the north :)

GG> But yes I understand the most accurate would be to only downscale - but I
GG> can't find color name definitions in 48-bit color.

As 24 bit versions of clXXXX colors are compatible with Delphi any 48
bit definition is valid from my point of view.

--
Best regards,
JoshyFun

```