Diff swallows black color in added areas

[cburgmer]

In a diff with two unequal images, added pixels in black are not distinguishable. They are swallowed by the otherwise black background, the result of the diff of same pixels.

Test case: http://jsfiddle.net/cburgmer/79pr2/4/

[B2F]

I had another case where the diff image's pixels are not distinguishable, the difference is there and correctly detected (a subtle one), but the resulting image is all black, probably the same issue.

[B2F]

I can confirm the issue. Here is the example:

As you can see the lines are off by few pixels, I was able to highlight the imagediff pixels in gimp with the pixel color selection in gimp.

[B2F]

I've fixed the problem with a options.lightness for imagediff.diff, I should post a pull request this week end.

[B2F]

Here are some screenshots illustrating the fix, all taken with Succss (The CSS regression testing tool I'm doing).

With the default value 25 it is now visible but still subtle depending on your screen type and settings.

The above uses options.lightness manually set to 100.

And with the maximum boost 255 everywhere, area of differences are now obvious.

I also factorised the rgb color diffing code and tested it for diffUnequal (with option.align set to 'top') as well:
.

Please review my pull request #51.

While the previous PR can be used per project, another, much better and stable pull request is in the work.