[Digikam-devel] [Bug 290442] New: Unsharp mask with radius less than 1.0 burns images

[Tap at people.homeip.net]

https://bugs.kde.org/show_bug.cgi?id=290442

           Summary: Unsharp mask with radius less than 1.0 burns images
           Product: digikam
           Version: 2.4.1
          Platform: Compiled Sources
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: Image Editor
        AssignedTo: digikam-devel at kde.org
        ReportedBy: Tap at people.homeip.net


Version:           2.4.1 (using KDE 4.5.5) 
OS:                Linux

When I try to use a radius less than 1 with the Unsharp mask method in the
digiKam Image Editor, the image becomes noticeably brighter and shows channel
clipping in bright areas. I do not know the math involved but the GIMP does not
share this behavior -- it simply sharpens the image as requested.

I am using digiKam 2.4.1 but this bug was also evident in 1.9.0.

Reproducible: Always

Steps to Reproduce:
1. Select an image in the lighttable and press F4 to open the Image Editor

2. Go to Enhance > Sharpen...

3. Set the following parameters, for example:
   radius 0.3
   amount 0.8
   threshold 0.00

4. Click OK and compare the before and after images.

Actual Results:  
The image becomes noticeably brighter.

Expected Results:  
The image should become sharper on a fine scale, but not noticeably brighter.

OS: Linux (i686) release 2.6.32.41-smp
Compiler: gcc

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