Given the symptoms: 1) Occurs during resizing using factors that are not powers of 2 (i.e., 2, 4, 8, etc.). Comment #2 2) The thatched pattern is the color (254, 254, 254), where pure white is (255, 255, 255). Attachment to Comment #1 3) Only occurs for pure white (255, 255, 255) starting image. Comment #3
I would strongly suspect that this is not a bug, but a rounding error inherent in filter. It just happens that only images starting from pure white end up with rounding errors large enough to change a pixel value by one. The Lanczos filter actually takes on negative values at places, so that might be enough to put a resampled pixel one value below where it should be when the scaling isn't a nice power of 2. In other words, this is a limitation of the filter, not a programming bug. -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to gimp in Ubuntu. https://bugs.launchpad.net/bugs/648379 Title: Artifacts when scaling down with Sinc Lanczos3 Status in “gimp” package in Ubuntu: New Bug description: Binary package hint: gimp Scaling down a solid white field with the Sinc algorithm causes a weird thatched-pattern to appear. I've seen this before but now have an easy way to reproduce. I'm not sure whether the resolutions matter, but here's how I'm currently reproducing: 1. Create a new RGB image filled with solid white, size 5616x3744 (size of 5D Mark II images, what I was editing when I found it) 2. Scale down to 1200x800 using "Sinc (Lanczos3)" Interpolation 3. There will now be a weird thatched-pattern in the image, even though it should be completely #ffffff pixels I attached the resulting image, saved as a PNG. ProblemType: Bug DistroRelease: Ubuntu 10.10 Package: gimp 2.6.10-1ubuntu3 ProcVersionSignature: Ubuntu 2.6.35-22.33-generic 2.6.35.4 Uname: Linux 2.6.35-22-generic x86_64 Architecture: amd64 CheckboxSubmission: fdbdfcded0c0bb479a6b52e9ec5af131 CheckboxSystem: edda5d4f616ca792bf437989cb597002 Date: Sun Sep 26 14:32:20 2010 EcryptfsInUse: Yes InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release amd64 (20100429) ProcEnviron: PATH=(custom, user) LANG=en_US.UTF-8 SHELL=/bin/bash SourcePackage: gimp To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gimp/+bug/648379/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : [email protected] Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp
