HIPS - how do you handle transparency?

[keflavich]

I have tried HIPSing some png images with transparency, and they're coming out black. Can we / how does HIPS support transparency?

[keflavich]

The source code looks like it's trying to handle transparency correctly, e.g. with

reproject/reproject/utils.py

Line 327 in 204bfd9

def as_transparent_rgb(data, footprint=None):

. And indeed, transparency is handled correctly at some level, since there is transparency, but I'm seeing things like this:

where the black pixels should be transparent. I'll try to hunt down the bug.

[keflavich]

I can't see where this is happening, but I'm continually reproducing it; alpha=0 is being transformed to alpha=255. My best guess is that the problem lies in these lines:

reproject/reproject/utils.py

Lines 341 to 345 in 204bfd9

	if data.shape[0] == 3:
	array[:3] = data
	array[3] = 255
	else:
	array[...] = data

but I can't see how the wrong logic would be adopted, i.e., how the input RGBA file would accidentally get the alpha layer dropped.

[astrofrog]

@keflavich - is this still an issue if you upgrade pillow?

[keflavich]

Yes, version 11.3 fixes it. 11.2 had the problem.