CGTalk - Difference matting with alpha as output

View Full Version : Difference matting with alpha as output

polarize

07-13-2003, 05:40 PM

Hi,

I need help with a part of a graphic where one color turn´s smoothly into another. The colordifference is too great to handle it with the colorrange.
But i have a second file where the part which i need as selection has another color.

So is it possible to use the difference of this 2 pictures to create a selction or an alpha?

THX in advice

polarize

Ian Jones

07-14-2003, 02:53 AM

Yes it certainly is possible. Granted that you don't have too much image compression or digital camera artifacts.

I don't have much experience with difference matte's but what I would do in photoshop is put both image's into their own respective layers then I would make the upper one's blending mode "difference". This will output the area's of difference between the two images. Merge these two layers together then desaturate and use this new greyscale image as an alpha channel for your original image. This process will require quite a lot of tweaking and editing I would imagine.

You'll have to edit the contrast of the reulting alpha channel and maybe edit levels to adjust the edges of this aalpha matte. In a similar way to spill suppression with traditional blue-screening.

I hope that helps.

polarize

07-14-2003, 08:49 PM

nice technique - it worked fine :applause:

Ian Jones

07-15-2003, 12:45 PM

Cool... was a bit of a shot in the dark, but I'm glad it worked!

CGTalk Moderation

01-15-2006, 04:00 PM

This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.