PDA

View Full Version : bright pixels


sherridge101
02-25-2008, 02:24 PM
Hi all,

When I attached a Contrast Lum node and tweak the value to 0.9 I get extra bright red pixels (see attached) and when I set the value to 1.1 I get extra blue pixels. The images are 32Bit.

Cheers,

Steve

sherridge101
02-25-2008, 04:02 PM
Changing the soft clip to anything other than 0 removes the bright pixels.

Hugh
02-28-2008, 11:34 AM
Are you doing your CC on an unpremultiplied image?


It could be that your alpha is slightly dodgy compared to your colour. Some CG renderers add a certain amount of dithering to the colour channels but not to the alpha. This causes all sorts of problems around the edges when you MDiv. Chuck an MDiv onto your render. You should see colour straight up to the white (where the alpha is 0) without any suddenly brighter or darker pixels. If you turn on "Ignore Zero", the white bits around the edge should go black, and you shouldn't have any odd bright or dark pixels.

If you do, then your renderer is doing something funky (I've found that Lightwave is a culprit in this kind of thing before), and you'll have to do some funkiness to fix up the edges...

sherridge101
02-29-2008, 04:01 PM
Cheers Hugh,

I didn't realize it was the premultiplied thang. We bought exrpro a while back to sort this thing in photoshop. Cheers for the advice.

The help files for Shake say to add the MDiv file, carry out your colour correction and then to add a MMut node.

Cheers again.

Steve

CGTalk Moderation
02-29-2008, 04:01 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.