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Added alpha support to Color To Alpha (allows repeated use)

This commit is contained in:
Seth Burgess 2000-03-19 01:47:15 +00:00
parent c4f941f793
commit bcd9899101
2 changed files with 13 additions and 2 deletions
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6
ChangeLog
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@ -1,3 +1,9 @@
2000-03-18 Seth Burgess <sjburges@gimp.org>
* plug-ins/common/colortoalpha.c: Fixed handling of previously
existing alpha, so it can be run successively now (much more
useful)
2000-03-18 <tigert@guadec1.enst.fr>
* pixmaps/linked.xpm: another icon for the L&C&P dialog.. to be

9
plug-ins/common/colortoalpha.c
View File

@ -212,8 +212,10 @@ colortoalpha (float *a1,
float c2,
float c3)
{
float alpha1, alpha2, alpha3;
float alpha1, alpha2, alpha3, alpha4;
alpha4 = *a4;
if ( *a1 > c1 )
alpha1 = (*a1 - c1)/(255.0-c1);
else if ( *a1 < c1 )
@ -250,13 +252,16 @@ colortoalpha (float *a1,
{
*a4 = alpha3;
}
*a4 *= 255.0;
if ( *a4 < 1.0 )
return;
*a1 = 255.0 * (*a1-c1)/ *a4 + c1;
*a2 = 255.0 * (*a2-c2)/ *a4 + c2;
*a3 = 255.0 * (*a3-c3)/ *a4 + c3;
*a4 *= alpha4/255.0;
}
/*
<clahey> so if a1 > c1, a2 > c2, and a3 > c2 and a1 - c1 > a2-c2, a3-c3, then a1 = b1 * alpha + c1 * (1-alpha) So, maximizing alpha without taking b1 above 1 gives a1 = alpha + c1(1-alpha) and therefore alpha = (a1-c1)/(1-c1).