the 'Overlay-Mode' bug

Esper · **Joined:** Jul 17, 2012 **Posts:** 2770

'Overlay' is the same as 'Soft Light' because of a bug

as this is just a simple formula, would it be possible for me to edit the bug on my own in my Gimp program ?

if so how ?

and in before anybody says Overlay is correct in G'MIC :mrgreen:

i know but i would rather have it in my layers-tab

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

It's not just the matter of changing the formula in GIMP file, Esper.

AFAIK, the formula for Overlay mode in GIMP is all right (pegtop's formula, IIRC). The problem is much bigger.
It is non-linear color conversion in GIMP. To that extent, ALL blend modes in GIMP are 'legacy' bugs and somewhat incorrect.
GEGL uses linear color conversion and gets Overlay mode correctly (as well as other blend modes),
you can downgrade to 2.8.0 where GEGL operations is/was still available under 'Colors' menu or wait for 2.10 release (with GIMP fully ported to GEGL).
Edit. Finally, found the thread I started 2 months ago, where I used Overlay mode made with GEGL in 2.8.0.

If you want to do it yourself, you can apply this patch to override "gfloat comp" in the gimpoperationoverlaymode.c and then compile it for Windows.

Code: Select all

diff --git a/app/operations/gimpoperationoverlaymode.c b/app/operations/gimpoperationoverlaymode.c
index 611cf4e..70365ee 100644
--- a/app/operations/gimpoperationoverlaymode.c
+++ b/app/operations/gimpoperationoverlaymode.c
@@ -112,9 +112,19 @@ gimp_operation_overlay_mode_process (GeglOperation       *operation,
 
           for (b = RED; b < ALPHA; b++)
             {
-              gfloat comp = in[b] * (in[b] + (2.0 * layer[b]) * (1.0 - in[b]));
+               gfloat comp;
+              
+              if (in[b] < 0.5) {
+                  comp = 2.0 * in[b] * layer[b];
+              } else {
+              comp = 1.0 - 2.0 * (1.0 - layer[b]) * (1.0 - in[b]);
+              }              
+              
+            //  gfloat comp = in[b] * (in[b] + (2.0 * layer[b]) * (1.0 - in[b]));
+
 
               out[b] = comp * ratio + in[b] * (1.0 - ratio);
+
             }
         }
       else

Other options are
A. returning 'Use GEGL' ops as GIMP menu item to current 2.8.4 version but that would probably require rebuilding GIMP from the source code
B. finding such a 'Overlay-mode-bug-free' build somewhere.
C. using 2.9 custom builds (Partha's for one) but 2.9 is still not very good for production

Graechan · **Posted:** Sun Mar 10, 2013 10:59 pm **(#3)**

Esper have you thought of trying one of GMIC's layer mode's, theres a new one called vivid-light. also there easy to use set input layers to active and below, set output to new layers then select the layer you want to set the layer mode to i.e.it should have another layer below it

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

Graechan wrote:

Esper have you thought of trying one of GMIC's layer mode's, theres a new one called vivid-light. also there easy to use set input layers to active and below, set output to new layers then select the layer you want to set the layer mode i.e.it should have another layer below it

Esper wrote:

and in before anybody says Overlay is correct in G'MIC :mrgreen:

i know but i would rather have it in my layers-tab

Esper · **Joined:** Jul 17, 2012 **Posts:** 2770

thanks K1te

i dont want to go back to 2.8 and i have no idea how to compile, whatever that actually means in my case as a windows user

waiting for Gimp 2.10 is all good, but as far as i understand, its in the somewhat far future

so no Overlay mode for me, except in G'MIC

i do not find all of this overly sensible, especially as coders probably like thinking logically
but whatever

Graechan · **Posted:** Sun Mar 10, 2013 11:26 pm **(#6)**

Woops! Esper I didn't notice you have already ruled out gmic, but for the sake of getting it right it's either that or leave it till 2.10 comes along

Esper · **Joined:** Jul 17, 2012 **Posts:** 2770

seems so, thanks Graechan

K1TesseraEna · **Joined:** Sep 22, 2012 **Posts:** 2089 **Location:** US

Esper wrote:

i dont want to go back to 2.8 and i have no idea how to compile, whatever that actually means in my case as a windows user

i do not find all of this overly sensible, especially as coders probably like thinking logically
but whatever

well, it's a C programming language so you need a compiler to make it work on Windows/Linux/Mac, but if this is not much of a problem, it's not worth a headache of setting a compiler environment on your system, unless you also want to build GIMP from the git source code to get a newest version with fixed bugs or new features long before the next stable version official release.

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