User:Terrywallwork/Trash/Puzzle

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Hi all,

I have been working with the Blender Node system and generally have lots of fun. However I hit upon a problem which I have been unable to solve.

Below is the blend file I am referring to. This file as made with Blender 2.49.

File:TerryWallwork - Blender 2.49 - GreenScreenReplaceIssue.blend

The file above has had all of the pictures packed into it and all the paths within it have been made relative. So you should be able to open the file in Blender and press F12 to render and see the node setup as I have it and how the pictures look when run through the node system.

[edit] The (Possible) Bug

I was experimenting with making a green screen replacement node setup. Which basically allows me to take an image taken in front of a green screen and replace all the bits that are green with another image. In the case of the above blend file it was a mans head in front of a green screen background. The green background being replaced with a checked pattern.

Below is a screenshot of the node setup:

Click image to see a larger version.

The resultant rendered image that I get from the node setup is shown below:

Click image to see a larger version.

As can be seen above the background image (the chequered background) is combined with the foreground (the mans face). Unfortunately for reasons I am not sure of you can see that the chequered background image appears to be leaking through to the foreground image.

As you can see in squares 7 (chequered background with black foreground knockout) and 15 (foreground image with black background knocked out). These 2 images are added together at square 12. This should result in the 2 images being added together to form a solid image of the combined background and foreground. However squares 13 and 14 both show that the image that result is transparent looking.

So to check that I wasn't misunderstanding how this works I outputted both the background image and foreground image (squares 10 and 11) and then took the files that those nodes outputted and added them manually in squares 16 through 20. When doing this it results in a properly combined foreground and background image which is not transparent. This is despite the fact that these images should be identical to those in squares 5, 9 and 12.

So the question, is this a bug, a misunderstanding of how this should work or something else?

Any help appreciated!