Has anyone tried to save a render as a jpeg2000 with RGBA?
I can get it to save OK but when I take the image back into Blender via an image input node, I can’t get the alpa channel to appear correctly.
When I plug the alpha channel of the RGBA image into a viewer node, I would expect to see all black where the background would be and all white where the object (e.g. default cube) would be.
I get this fine with png.
With jpeg 2000, I instead get a black and white version of the image - not the alpha channel.
Am I missing something? I’m simply selecting ‘Jpeg 2000’ in the format tab and switching to ‘RGBA’.
Load your newly rendered Jpeg 2000 file into the ‘Image’ node.
Important: link the ‘Alpha’ channel from ‘Image’ node to the ‘Image’ channel of the ‘Viewer’ node.
You should now see the issue in the viewer node (click ‘Backdrop’ to see a larger version in the background).
Instead of getting pure black (transparent) or pure white (solid) masking, there are shades of gray. Looks likes it saves the luminance channel or something instead of the alpha channel.
For comparison, link up the alpha channel from the ‘Render Layer’ node to a ‘Viewer’ node. Or perform the same steps above but saving as a PNG - you will see the alpha channel properly showing.
You might want to contact Campbell Barton on this one, he brought Blender jpeg2000 support to Blender, or just put it in the bug tracker and get it assigned to him.
Yup, sod’s law - couldn’t get anyone to verify it was a bug until today. Made an entry into the bug tracker (#19280).
Worse case scenario, there should be a workaround. Save your render file that requires the transparency channel (RGBA) in PNG format instead of JPEG2000.
Assuming this will soon be fixed in 2.5, load the PNG via the compositor and save out again as Jpeg 2000.
Or save the PNG file out as Jpeg2000 in an image editing program like GIMP.