On Thu, Aug 31, 2017 at 10:44 PM, Ben Hutchinson wrote:

The Levels control (the dialog box you get with Ctrl+L) has a bug. When you select Value for the channel, it is supposed to have a histogram which is based on all of the color channels combined. However, this bug causes the Value channel for the histogram to only consider the green channel. The result is that when you select either Value or Green for the color channel, you get identical histograms. The levels sliders themselves work correctly. It's just the histogram that has the problem.

This bug is present in the latest beta/development version (at the time I wrote this email) of Gimp.
That is version 2.9.4 commit 5afea2f Note that I'm using the Windows version of Gimp, not the Linux version (not sure if there are any differences between these 2 in functionality).

First, make sure you can reproduce it (ie, here it is the red channel, and I never noticed that).

Second: https://bugzilla.gnome.org/enter_bug.cgi?product=GIMP Perhaps attach a screenshot or not. If you can figure out how to fix it, patches for stuff like this are usually well received.

Also, this is kind of funny to me. I wonder how far back this oddity goes.

carol

On Thu, Aug 31, 2017 at 10:44 PM, Ben Hutchinson wrote:

The Levels control (the dialog box you get with Ctrl+L) has a bug. When you select Value for the channel, it is supposed to have a histogram which is based on all of the color channels combined. However, this bug causes the Value channel for the histogram to only consider the green channel. The result is that when you select either Value or Green for the color channel, you get identical histograms. The levels sliders themselves work correctly. It's just the histogram that has the problem.

Early gimp (gimp-1.0.0 thru gimp-1.0.3 iirc) had some breakage on the red channel. You could start with a grayscale image, convert it to RGB and using levels (at least, maybe other tools) change an image of blacks, whites and grays to an image of reds.

Here is a tutorial that utilized this bug: https://web.archive.org/web/20010107023700/http://at8.abo.fi:80/~mwikholm/com/gimp/tutor/glass/

I suspect that it has always been this way.

Let me know if you file a bug report about it. This is just great!

carol