Some filters / operations should provide clipping to float values superior to 1.0

Submitted by Thomas Manni (@tmanni)

Link to original bug (#737925)

Description

We can observe this bug using some filters / operations on a layer mask :

1. create an image (i use template 640x480, 8-bit gamma integer precision)

2. fill the background layer with pure red

3. create a new white layer above the background layer

4. add some content to this layer (i use Filters > Render > Noise > Solid Noise... with default parameters) and create a layer mask on it using grayscale copy of layer

5. with the layer mask selected, use Colors > Brightness-Contrast... and increase the Contrast slider

Cyan color appears on the canvas preview ; clicking "OK" to apply the operation give the expected result : cyan color disappears, certainly due to the float to integer conversion. But if you repeat the exact same procedure with a floating point precision image, applying the operation changes nothing : cyan color stays visible (no float to integer conversion, layer mask keeps values superior to 1.0)

I was able to reproduce this behavior with :

• Colors > Levels
• Colors > Exposure
• Filters > Enhance > Unsharp Mask

Version: git master