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Alpha premultiplied are badly diplayed in image viewer
Closed, ArchivedPublicTO DO


Resolution: New

The display of alpha-pre-multiplied pictures in "Draw Image with Alpha" mode is made as is the image was not pre-multiplied and so is incorrect.

* open the linked .blend file
* render
* in image editor, make sure you are in "Draw Image with Alpha" mode
-> you can see that the edges of the "Render Result" are badly composed with the background of the viewer, they are dark.
Actually if the image is not premultiplied, as in "Viewer Node", composition is OK.

Note: on the contrary the display when "Draw Image with Alpha" is off is correct (but this time it is the display of the non-premul image that is wrong).

Event Timeline

Ton Roosendaal (ton) changed the task status from Unknown Status to Unknown Status.Jul 20 2006, 1:00 PM

I originally thought that as well but I completely disagree now.

The scenario is that it is entirely likely an artist is hand crafting their own alpha and performing their own over operations using math nodes.

In this scenario, much like predivide, the artist would require the granularity to set the viewing option based on their crafted image.

The same would go for log transforms or any other custom image crafting.

It is impossible for the compositor to know these things, and would require some nasty manual flag setting in the nodes.

In all cases, it would be manual.