Adobe After Effects - Keylight problem

Author

Keylight problem – noisy dark parts?

massepasse@adobeforums.com

2006-12-06, 8:14 pm

Hello,

I have a green screen clip (on a person) which I am trying to key out the background with Keylight (AE 7.0). The shot is perfectly lit in a pro studio, shot on HD. I apply Keylight and pull the green, no problem at all. I fill out the Alpha channel I bit
with the matte tools, and I use the rest of the settings to fine tune it. It looks perfect, EXCEPT for one thing: I get a lot of moving noise in the subject’s brown pants and in his black jacket, like its crawling?? (I read that this problem has been brou
ght up before in this forum but no actual answer was given?)

Any clue, anyone??

Thanks!
/Matt

Andrew_Yoole@adobeforums.com

2006-12-06, 8:15 pm

Keylight has been upgraded recently - see this thread:

<http://www.adobeforums.com/cgi-bin/webx/.3bc26d70/1>

massepasse@adobeforums.com

2006-12-06, 8:15 pm

Thanks for your answer, but I have upgraded and it didn’t solve the problem with crawling noise in dark parts. Hmmm, any more tips?

Thanks,
Matt

Philo_Calhoun@adobeforums.com

2006-12-06, 8:15 pm

Here is a post from Jeff Binks for a similar question asked (now in the archive):

Hi there,

Because of the way Keylight works it doesn't add noise to an image, however, if the spill removal has to work particularly hard it may emphasize the noise which already exists in the image. Essentially it is using the non screen colour channels (so say th
e R & B channels if its a green screen shot) to define how the screen colour channel (G in prev example) is formed. Thus if there is large amounts of noise in the B channel, it may become emphasised in the G channel through this process.
If this is the root of the problem then you will see it happening in regions where there are fairly large amounts of screen colour spill on the foreground subject, or where the foreground subject is of a similar colour to the screen.

There are a number of methods for dealing with this, a few common ones I've given below:

1. Reshoot with more separation between screen and subject, both physically and in lighting strategy, to reduce spill. Ensure wardrobe does not use colours similar to screen, if necessary change screen colour. If possible use a less compressed format than
dv.

2. Brute force post approach - use the grain removal tool to smooth out the grain seen in the various channels. Disadvantages include softening, the need to reapply grain for realism and so forth

3. Change Keylight colour replacement methods (drop down menu) to see if this improves anything. If necessary isolate regions where high grain seen using inside masks, hicon mattes and/or separate key passes.

4. Use keylight to pull mask, but not spill remove, so set to intermediate result output and use a separate spill removal tool.

HTH, like the guys have said, if you can show us some footage it'll help us figure out your problem is occurinng, as what I'm referring to here may not even be the issue you are seeing.

Kind Regards,
Jack

The Foundry, UK

silversurfer@adobeforums.com

2006-12-06, 8:15 pm

"Shot on HD"

HD...what? What codec? HDCAM? XDCAM? DVCProHD? HDV?

All respect to Jack...Keylight is not the only solution...especially if you shot HDV. Let's see some ftg.

- Joey