Hi, I sent this simple fix to mitch, however I'm too impatient to wait for mitch to check his inbox, So I'm now passing it onto this mailing list. Basically it fixes over/underflow in the Levels op; with the attached image, the bug gives the appearance of a triangle wave repeating gradient, instead of a readjusted single gradient for the channel being adjusted. ---------- Forwarded message ---------- From: David Gowers <00ai99@xxxxxxxxx> Date: Jan 31, 2008 5:45 PM Subject: GIMP Levels operation To: Michael Natterer <mitch@xxxxxxxx> I've just found a bug in the Levels op -- if the selected low/hi input endpoints of a channel are (low -> more than the lowest non-empty histogram entry; or high ->less than the highest non-empty histogram entry for the channel) then underflow/overflow happens. Adjusting any of the input range sliders to fall into that range will show this behaviour up. Using the channels dialog to disable all but one channel also helps. I would say you have simply forgotten to clip the input values before mapping them to output values. *pokes around* indeed, I've attached a very short patch that performs correct clipping. With this patch, GEGL levels op matches old levels behaviour in all tests I could contrive.
Attachment:
testimage.png
Description: PNG image
Index: app/gegl/gimpoperationlevels.c
===================================================================
--- app/gegl/gimpoperationlevels.c (revision 24754)
+++ app/gegl/gimpoperationlevels.c (working copy)
@@ -87,6 +87,8 @@
else
value = (value - low_input);
+ value = CLAMP (value, 0.0, 1.0 );
+
if (gamma != 0.0)
{
if (value >= 0.0)
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