color spill node anti aliaised to black not alpha:(

Support Compositing and Post Processing
1

I have an image on a greenscreen type background that I’m compositing and the color spill node really helps get rid of the outline of the green but it seems that rather than antialiaise to alpha it antialises to black so that I get a faint dark outline (less than when it was green though) around the foreground object. Using view nodes etc I can see that the issue seems to be creaping in in the spill node, do I need to set some transparancy here manually with another node first?

I have a green screen image input node ->Difference Key Matte (green)->color spill (green) then alpha over the background image

Am I missing a node?

Thanks

2

The yafaray forum guys pointed me to this plugin :eek: http://paprmh.googlepages.com/greenscreen so perhaps I’m just trying to reinvent a wheel here

3

De spill is often neutral grey, its still there (in pro renders) but not as obvious.

4

Actually, the greenscreen plugin won’t do you any good here because it does not have transparency capabilities… but my RGBscreen plugin will:
final: … alpha mask:
[ATTACH]96464[/ATTACH] [ATTACH]96463[/ATTACH]
The problem with the dark outline may be due to the fact that when you remove green from a pixel, it also will make it seem darker because almost 60% of a pixels perceived brightness (luminosity) comes from the green channel. (RGBscreen has the ability to help compensate for this btw…)
[ATTACH]96465[/ATTACH]
BTW: the above final pics are RGBA pngs so you can try compositing with them…

5

Paprmh, congrats on some excelent plugins. Will you be doing a re-make for 2.5?

6

I believe that all of the updated plugins ( for 2.49 ) will work in 2.50… sorta :confused:

The problem is that in 2.50 there is no way to access the plugin buttons yet - but if you set up a plugin in 2.49, save, and then open the blend in 2.50 it will work. Since the main developers are quite busy doing more important things & there seems to be little to no love for seq plugins from them, I don’t see seq plugins being a viable option in the near future for 2.5+

7

That makes me sad. Sometimes I dont want to build node trees just to key. Fingers crossed for plugins (against all hope).

8

Thanks paprmh, I seem my problem now and I don’t think I’ll get it much better, using the channel key I can get a good effect but the anti aliaised spill is due to keeping the shadow alive, if I adjust the channel sliders I can get rid of the outline but at the cost of the shadow.

I need yafaray to support blenders “accept shadow” feature to fudge this.

Looks like this http://www.dwyer-family.net/3D/viperontable3.png . not too bad but not perfect. In your pics above, you have lightened the shadow, if you darken the shadow again, can you keep the edges clean still?

9

This isn’t going to solve your problem but it may cast some light on blue/green screen keying. Most compositing packages i.e. AE, Fusion etc. allow you to stipulate whether or not your input image has a pre-multiplied alpha channel. If the input images’s alpha is premulted, you will get that outline on your comp until you tell the node that the input is pre-multiplied. (Pre multiplication refers to the process of multiplying the color values of a pixel by its alpha values to generate a legally additive image). If your input image is a Blender rendered image, try using the premult button on the render panel. Hope this helps.

10

It’s a yafaray image so I’m using an image node with a png.

from what you say, perhaps I should have two streams come from the input node, handle the shadow in one and the outline AA issue in the other. I can split it out but when I re-merge it back together I end up with basically the same thing… or, If I do cut the shadow really clean the I lose the blur effect on it and if I artifically blur it I get a lightened halo around the viper …

I really want to do this with a yafaray render too…