Bug 506510

Summary: Gaussian and Directional Blur don't affect alpha
Product: [Applications] kdenlive Reporter: nuxttux
Component: Video Effects & TransitionsAssignee: Jean-Baptiste Mardelle <jb>
Status: REPORTED ---    
Severity: normal    
Priority: NOR    
Version First Reported In: 25.04.1   
Target Milestone: ---   
Platform: Flatpak   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description nuxttux 2025-07-02 21:49:27 UTC 
Kdenlive 25.04.02

SUMMARY
Gaussian Blur and Directional Blur are constraint to visible pixels when blurring.
The blur does not spill into alpha channel of image or title clips.

STEPS TO REPRODUCE
1. Create Title clip, add red text, leave background transparent.
2. Add title clip to timeline.
3. Apply Gaussian blur with Sigma & Vertical Sigma ~80. 
4. Increase Gaussian blur Sigma & Vertical Sigma to ~320

OBSERVED RESULT
The text will blur inwards, pulling in the alpha (dark) onto the text.
Once blur reaches ~320, the red text will turn white.

EXPECTED RESULT
For the text to blur outwards and all-over. For the blur to reflect the blurred image colors.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 6.13.0
Qt Version: 6.9.0

ADDITIONAL INFORMATION
Although the red text won't turn white with the Directional Blur, it will turn black as the alpha gets pulled in and the blur remains contained within the visible pixels.