LinuxQuestions.org
Did you know LQ has a Linux Hardware Compatibility List?
Go Back   LinuxQuestions.org > Forums > Linux Forums > Linux - Software
User Name
Password
Linux - Software This forum is for Software issues.
Having a problem installing a new program? Want to know which application is best for the job? Post your question in this forum.

Notices



Reply
 
Search this Thread
Old 07-08-2010, 09:58 AM   #1
KonfuseKitty
LQ Newbie
 
Registered: Jul 2010
Distribution: Ubuntu 10.10
Posts: 22

Rep: Reputation: 0
Exclamation GIMP: most if not all colour/value transfer functionality is broken


I'm a photographer making the switch from Mac to Linux, and currently trying to make GIMP do the work. Alas, there's a serious problem that runs deep: the colour/value processing functionality does not work as it should. You can prove this for yourself with 3 easy experiments:

1.

Open any photo of a decent size and duplicate it into a new layer. Zoom in to 300% or 400% to better see the effects. Desaturate this new layer using the Hue-Saturation command. Set the layer's blending, transfer mode to Value. You won't fail to notice that the desaturation has seriously affected the Value, something that should not happen. The value should have remained the same.

2.

Revert the image to its original and again duplicate it into a new layer. Now we'll approach the problem from the other end and pretend we want to reduce colour noise by blurring the colours only, leaving luma Values the same. So apply a strong blur to the new layer and change the blending mode to Color. Again, the luminance is seriously affected, giving the image an appearance of a greater degree of mottled grain. This should not have happened, the luminance should have remained the same, only the colours should have become smoother and perhaps more muted.

3.

To satisfy ourselves that this is not merely a problem with layers, we tackle the problem in yet another way. Revert the image again, but this time don't duplicate into a new layer, apply a strong blur to the image directly. Now pull down the Fade command from the Edit menu and set the transfer mode to Color, leaving the percentage at 100%. It's no better, the luminance is as badly affected as it was with the layer method.

This leads me to my question: is there an easy way to report this as a bug? I've looked at the Gimp Bugzilla page and can't make sense of it. Would someone experienced here care to repeat the tests and do the report? We could treat it as sharing the workload...

Last edited by KonfuseKitty; 07-08-2010 at 10:05 AM. Reason: Gimp version is 2.6.8, from Ubuntu 10.04 Software Center
 
Old 07-08-2010, 10:04 AM   #2
pixellany
LQ Veteran
 
Registered: Nov 2005
Location: Annapolis, MD
Distribution: Arch/XFCE
Posts: 17,802

Rep: Reputation: 729Reputation: 729Reputation: 729Reputation: 729Reputation: 729Reputation: 729Reputation: 729
I will look into this as soon as I have time.

Meanwhile, is it possible that GIMP just does not work they way you are used to? (eg if you are accustomed to Photoshop)
 
Old 07-08-2010, 10:08 AM   #3
KonfuseKitty
LQ Newbie
 
Registered: Jul 2010
Distribution: Ubuntu 10.10
Posts: 22

Original Poster
Rep: Reputation: 0
Thanks!

Quote:
Originally Posted by pixellany View Post
Meanwhile, is it possible that GIMP just does not work they way you are used to? (eg if you are accustomed to Photoshop)
I've thought of this, but I don't think it applies. Processing algorithms are at stake, not "the interface I'm used to". If I'm wrong, it should be quite easy to refute what I'm saying.

Last edited by KonfuseKitty; 07-08-2010 at 10:10 AM. Reason: can't spell...
 
Old 07-10-2010, 12:24 PM   #4
pixellany
LQ Veteran
 
Registered: Nov 2005
Location: Annapolis, MD
Distribution: Arch/XFCE
Posts: 17,802

Rep: Reputation: 729Reputation: 729Reputation: 729Reputation: 729Reputation: 729Reputation: 729Reputation: 729
I'm having trouble coming up with anything conclusive on this. I did note two things:

1. There is a "desaturate" tool that offers the choice of preserving lightness or luminosity. Each gives very different results. Thus, the GIMP definition of these two terms could be different in GIMP.

2. To reduce color noise it seemed more effective to me to set the mode of the top layer to "value" and then blur the bottom layer.

I'm afraid I'm not very scientific when it comes to GIMP (or Photoshop)---I just keep hacking until it looks right...
 
Old 07-10-2010, 09:23 PM   #5
John VV
Guru
 
Registered: Aug 2005
Posts: 13,479

Rep: Reputation: 1803Reputation: 1803Reputation: 1803Reputation: 1803Reputation: 1803Reputation: 1803Reputation: 1803Reputation: 1803Reputation: 1803Reputation: 1803Reputation: 1803
gimp now uses 1 of 3 different methods for desat.
1) lightness
2) luminosity
3) average

pick one i normally use #2
 
Old 07-11-2010, 01:36 AM   #6
pixellany
LQ Veteran
 
Registered: Nov 2005
Location: Annapolis, MD
Distribution: Arch/XFCE
Posts: 17,802

Rep: Reputation: 729Reputation: 729Reputation: 729Reputation: 729Reputation: 729Reputation: 729Reputation: 729
The "desaturate" tool is all or nothing---in other dialogs having a controllable saturation, it seems to work on lightness (Which maybe explains the issue in the OP.)
 
Old 07-11-2010, 02:05 AM   #7
KonfuseKitty
LQ Newbie
 
Registered: Jul 2010
Distribution: Ubuntu 10.10
Posts: 22

Original Poster
Rep: Reputation: 0
In my experience, if your tests are giving you inconsistent results, you're probably working on an image that isn't very noisy. Try stretching the tonal range or pick a noisier file. The problem is very obvious when the noise is obvious.

I've tried all 3 modes of the Desaturate command and the results are as bad as in the tests I've posted. I create a new layer from the image, desaturate that layer, and set its transfer mode to Value. If everything worked as it should, you should see nothing, there should be no effect. Yet, the effect is very pronounced, with each of the 3 modes different, but none correct. The Desaturate command may be working correctly, but the Value transfer mode definitely isn't. It's difficult to make judgements here because the fact that the user has a choice of 3 algorithms actually serves to put the ball in the user's court: don't complain, you chose the algorithm. Well, one way or another, the right algorithm isn't available.

One good thing is that the new version coming up will apparently be using GEGL routines for more of its processing, so there's hope that might fix it.
 
  


Reply

Tags
gimp


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
LXer: Gimp Paint Studio [Gimp Optimized for Drawing and Painting] LXer Syndicated Linux News 0 05-04-2009 02:30 PM
LXer: Bring Out the GIMP Part 1: GIMP Basics LXer Syndicated Linux News 0 06-30-2007 06:16 PM
Changing colour of images with Gimp or Paint Shop Pro rblampain Programming 14 02-25-2007 06:17 PM
How do I change the colour themes Firefox and Gimp? anticuchos Suse/Novell 2 09-09-2005 12:15 AM
printing on HP PhotoSmart from Gimp 2.2, gimp-print drivers needed? pearman Debian 2 08-05-2005 05:19 AM


All times are GMT -5. The time now is 02:38 PM.

Main Menu
Advertisement
My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
identi.ca: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration