I am working on re-writing an old game, and have faced some issues with the older images that were used, the first thing we done was convert all the old images and set the alpha channel on black pixels so they are transparent, and then built our image libraries. However, the animated images have had some conversion issues it appears the edges of the images were not all set to true black so the conversion never set the transparency on these pixels. The value on the edges varies between R0 G0 B1-16 we have seen but we can't be sure as there is 1000s of images.
If we use additive blending it allows us to blend without showing the noisy outline but the additive blending does not display the images exactly how they should be to reproduce the old style of the game of course.
Question is, what options are available to either fix the image, or render it properly at run time using a HLSL.
I am hesitant to run a conversion on the known black ranges as we might miss a lot out and extending the range might set stuff we should set wrongly. Has anyone faced this before and how did you solve it?