Chatter with Keylight

[Danny Princz]

what is your source footage…DV?

who is that masked man…

[Darby Edelen]

[rendernyc] “what is your source footage…DV?”

If your source footage is DV, you might try blurring the U & V channels (chroma) as DV has a 4:1:1 compression rate.

You have 4 times as much information in the luminance channel as in one of the chroma channels, which can be problematic for keying (done based on chroma). The ideal is to use a different format with a lower chroma compression, but if you’ve already shot the footage and you can’t get back into the greenscreen then you can try this:

Use the Channel Combiner effect (Channels > Channel Combiner) and change the ‘From’ field to RGB to YUV. Then apply a Channel Blur (Blur & Sharpen > Channel Blur) and play with settings for the U and V channels (correspond to the G and B channels in the Channel Blur). Blurring these channels will blur the chroma without touching the luma in your footage, blur it too much and the colors will ‘spill’ over the edges of the footage, blur it too little and you will still have blocky chroma channels… Play with the values =)

After you’ve applied the Channel Blur you need to get your footage looking normal again, so use the Channel Combiner effect again and change ‘From’ to YUV to RGB.

This isn’t ideal, but can provide for a better key from DV footage.

[Franky Torres]

Dope,

I am assuming, that you then apply the keylight at the end of the pipeline after converting it back to RGB. Is this assumption correct?

[Darby Edelen]

Yes. The RGB->YUV, Channel Blur, YUV->RGB is a pre-process that should make the actual keying process friendlier with DV.

You still need to key in order to have a… erm… key.