colo-hex

[Peter Rolf <indiego@gmx.net>]

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Hi,

there is a small bug in colo-hex, which leads to slightly wrong colors 
(at max. -0.390625%).
In line 41 of both mark related files there is

\newdimen\hexcolorfraction \hexcolorfraction=\dimexpr(1pt/256)
.
This should be 255 (#fractions) instead of 256 (#values); I made the 
same error a quite while ago. If I patch the files, I get the correct 
color in case of mark ii, but mark iv still gives the wrong one (remade 
the formats). Mh, strange.

Here the output of my beloved 'tabbyCalc' (result of operation is always 
in next line, which is then used for next operation):

1/255
 0,0039215686*255
 0,999999993

1/256
 0,00390625*255
 0,99609375-1*100
 -0,390625

I attached a small test file, which hopefully 'shows' (depends on your 
monitor) the difference. The border line goes from the lower left to the 
upper right corner; you have to look 'closely'. :D
I case of pdftex you can also peek into the eps file to see the color 
values (before and after patching). No such help for mkiv. I have no 
clue why mkiv still gives the wrong color...


Best wishes,  Peter


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\setupcolors[state=start]
\setupcolor[hex]

%% fraction=  1/255*65536= 257.004
%\newdimen\hexcolorfraction \hexcolorfraction=\dimexpr1pt/255\relax% = 257sp

\definecolor[testcolor] [r=0.87843,g=0.87451,b=0.89020] % RGB(224,223,227))
\definecolor[testcolorHEX] [h=E0DFE3]% same as HEX (currently transformed to RGB(223,222,226) )
\definecolor[testcolor] [r=1,g=1,b=1] % RGB(224,223,227))
\definecolor[testcolorHEX] [h=FFFFFF]% same as HEX (currently transformed to RGB(223,222,226) )


\startMPpage
    path p;
    p:= unitsquare xyscaled(5cm,5cm);
    fill (point 0 of p -- point 1 of p -- point 2 of p --cycle)
    withcolor \MPcolor{testcolorHEX}; % bottom right part of the square
    fill (point 0 of p -- point 3 of p -- point 2 of p --cycle)
    withcolor \MPcolor{testcolor}; % top left part
\stopMPpage


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