Simplify Background::class manipulator

[olivervogel]

For the calls of the Background bg manipulator Intervention Image has already an own method blendTransparency() to set the background color of the image.

This patch simplifies the Background::class manipulator in that way and replaces the manual individual steps with the mentioned method.

[ADmad]

While looking into this I found that setting bg doesn't work when for e.g. using fit=fill and the using w and h larger than the original image dimensions. The extra area if always white since the default background color for Image::pad() is ffffff. Before merging this change, changing the background color to 'ffffff00' for Image::pad() fixed this issue but after merging this the background color is "skewed".

Before merging this PR using bg=blue I get

After this merge

[ADmad]

Problem seems to occur only when blue color is involved. If I use red or green the results appear same before and after this patch.

[olivervogel]

I think the definition of the default background color in Image::pad() and other methods could have been implemented more logically in Intervention Image. Unfortunately a breaking change.

See Intervention/image#1391 (comment)

[ADmad]

I think the definition of the default background color in Image::pad() and other methods could have been implemented more logically in Intervention Image.

Yes, ffffff does not seem like a good default, null or transparent would be better.

The problem I described above only occurs when using imagick, not gd. So to summarize, when using imagick and blue as the blending color, the resulting background color is off (PHP 8.4 and imagick 3.7.0 ).

[olivervogel]

The problem I described above only occurs when using imagick, not gd. So to summarize, when using imagick and blue as the blending color, the resulting background color is off (PHP 8.4 and imagick 3.7.0 ).

I'm not sure but maybe it's better to revert my changes.

[ADmad]

I'll try to look into it a bit more over the weekend and then decide. Will also try to submit a test case / minimal example for the issue.

[ADmad]

I am going to revert this. The blending color is only used when outputting to image format which does not support transparency. But when bg is specified that color should replace the transparent area.