Perhaps I am misunderstanding this proposal, but the ramifications
seem to be more confusing than the present method. And while I realize
that GIMP does not make any guarantees about retaining the colors of
transparent pixels, its current behavior is quite useful for editing
files destined for applications which employ the alpha channel in
unconventional ways. It also offers a few other atypical benefits, but
mainly it is consistent and easy to comprehend what is happening.
Currently, erasing on a layer having an alpha channel only affects the
alpha channel, the color values remain the same. If a special case
were to be created such that transparent erasures (alpha < 1/256)
result in changes to color values, what then is to happen when color
depths are increased such that the minimum non-zero alpha becomes
1/65556 (16-bit per color), or even lower (32-bit or floating point)?
Erasures of an 8-bit PNG image using these higher color depths will
reveal not the original image, but instead some unassociated color and
this might cause some problematic "fringing".
If erasing is to be changed such that color channels are painted, is
this to be offered as a tool option which can be disabled? And if
erasures are done with an tool opacity less than 100%, would the
option be provided to decide whether the color channels are painted at
100% background or instead blend with the underlying color at the
tool's opacity level? or would using the tool's transparency level
make more sense?
If the eraser's color is to blend with the existing color channels,
should blend modes be enabled for the eraser tool?
If a PNG is loaded as a layer, should the "image background color" be
updated to the PNG file's background color? or should it remain what
it was originally? If a JPEG is loaded as a layer, should the "image
background color" be set to white? Maybe every layer should be
assigned its own background color?
Should gradients be using the "image background color" or the "second
color in a color slot history"?
I don't mean to stomp on the idea of an image background color
completely but I do think some of the deeper consequences need to be
addressed in detail, and the options being presented to, and removed
from, the user weighed.
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