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change the LUT function for the contrast. Fixes the buggy behaviour as

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2006-02-24  Simon Budig  <simon@gimp.org>

	* app/base/lut-funcs.c: change the LUT function for the contrast.
	Fixes the buggy behaviour as described in bug #319872 and
	bug #332068 and makes the behaviour consistent with the standard
	contrast formula. However, I am leaving the bug open to discuss
	further improvements.

	Untabbified.
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Simon Budig 2006-02-24 01:04:48 +00:00 committed by Simon Budig
parent 3343baa84c
commit 78c41aa68f
2 changed files with 77 additions and 102 deletions
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10
ChangeLog
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@ -1,3 +1,13 @@
2006-02-24 Simon Budig <simon@gimp.org>
* app/base/lut-funcs.c: change the LUT function for the contrast.
Fixes the buggy behaviour as described in bug #319872 and
bug #332068 and makes the behaviour consistent with the standard
contrast formula. However, I am leaving the bug open to discuss
further improvements.
Untabbified.
2006-02-23 Sven Neumann <sven@gimp.org>
* libgimpbase/gimpwire.[ch]: added utility functions to send

41
app/base/lut-funcs.c
View file

@ -43,8 +43,7 @@ brightness_contrast_lut_func (B_C_struct *data,
gint channel,
gfloat value)
{
gfloat nvalue;
gdouble power;
gdouble slant;
/* return the original value for the alpha channel */
if ((nchannels == 2 || nchannels == 4) && channel == nchannels -1)
@ -56,42 +55,8 @@ brightness_contrast_lut_func (B_C_struct *data,
else
value = value + ((1.0 - value) * data->brightness);
/* apply contrast */
if (data->contrast < 0.0)
{
if (value > 0.5)
nvalue = 1.0 - value;
else
nvalue = value;
if (nvalue < 0.0)
nvalue = 0.0;
nvalue = 0.5 * pow (nvalue * 2.0 , (double) (1.0 + data->contrast));
if (value > 0.5)
value = 1.0 - nvalue;
else
value = nvalue;
}
else
{
if (value > 0.5)
nvalue = 1.0 - value;
else
nvalue = value;
if (nvalue < 0.0)
nvalue = 0.0;
power = (data->contrast == 1.0) ? 127 : 1.0 / (1.0 - data->contrast);
nvalue = 0.5 * pow (2.0 * nvalue, power);
if (value > 0.5)
value = 1.0 - nvalue;
else
value = nvalue;
}
slant = tan ((data->contrast + 1) * G_PI_4);
value = (value - 0.5) * slant + 0.5;
return value;
}