GNOME Bugzilla – Bug 353639
Gaussian Blur preview can show artifactual color bands
Last modified: 2006-09-11 12:09:40 UTC
Please describe the problem: When you try to use the filter Gaussian Blur on a selected area, a color appear from nowhere... Steps to reproduce: 1. Create a new document without background 2. Use the elipse tool and filled the selection with white 3. Use the Gaussian Blur filter on the selection Actual results: A pink color appear on the form Expected results: A normal gaussian blur limited by the selection Does this happen every time? Yes Other information: Yes, I have an screenshot I can send you. It's a different problem than the one present in 2.2.11 where the gaussian blur where adding grayish to the form
Created attachment 71949 [details] Screenshot of the bug
I suspect that this is a duplicate of bug #343047, I just don't understand why the artefact is pink. If it were black I'd resolve this as a duplicate. Was pink the background color before you cleared the image?
(In reply to comment #2) > I suspect that this is a duplicate of bug #343047, I just don't understand why > the artefact is pink. If it were black I'd resolve this as a duplicate. Was > pink the background color before you cleared the image? > No, my Gimp was freshly installed and by following the step shown in the bug declaration, it happen each time. I suspect that when the previous bug concerning the black artefact have been resolved, something else have been modified.
It looks like this is actually a preview bug, not a gaussian blur bug. I can replicate it in HEAD, if I set things up as shown in the screenshot attached in comment 1, and then scroll horizontally one pixel at a time -- sometimes I see a band of anomalous color -- yellow, cyan, or magenta -- at the left edge of the preview. I don't see any problems with the actual result of the gaussian blur in the image itself, though. Changing summary to reflect the problem as I see it, and confirming. If my understanding is incomplete, we can continue to refine the summary.
(In reply to comment #4) > It looks like this is actually a preview bug, not a gaussian blur bug. I can > replicate it in HEAD, if I set things up as shown in the screenshot attached in > comment 1, and then scroll horizontally one pixel at a time -- sometimes I see > a band of anomalous color -- yellow, cyan, or magenta -- at the left edge of > the preview. I don't see any problems with the actual result of the gaussian > blur in the image itself, though. > > Changing summary to reflect the problem as I see it, and confirming. If my > understanding is incomplete, we can continue to refine the summary. > You are right after testing, it's only the preview that is not working properly and I got a yellow artefact also when I scroll horizontally. I tried some other filters and every time a preview is shown, I got the problem. Maybe I could look at the source and help in correcting the bug ? But I have no idea how to do it... sylvain.lamontagne@gmail.com
Umm, there's no need to quote when replying to a comment in Bugzilla. Anyway, you're welcome to try to figure it out. The problem might be in the function gimp_drawable_preview_draw_area() in libgimp/gimpdrawablepreview.c, but more likely it's one level down, in the function gimp_preview_area_mask() in libgimipwidgets/gimppreviewarea.c. The code there, as you will see if you look at it, is pretty difficult.
That would explain why I didn't notice the problem. I was testing the 2.2 plug-in on gimp-2.3. If the problem is indeed in the preview widget, then it is likely already fixed in the HEAD branch and we should consider to backport that change. Note that this is just a guess. Before we jump to the conclusion that the error is in the preview widget, someone should try the test case given in comment #1 using the gauss plug-in from gimp 2.2.13 running under a recent gimp 2.3.
You missed the part in comment #4 where I said that I was able to replicate it in HEAD.
Fixed in both branches: 2006-09-11 Sven Neumann <sven@gimp.org> * libgimp/gimpdrawablepreview.c (gimp_drawable_preview_draw_area): fixed calculation of offset into the source buffer (bug #353639).