Doom9's Forum - View Single Post

Dimwitted · 13th April 2005, 20:19

Sorry, I don't think you understood my question.

I've written some filters to process the Cb and Cr information in order to do better greenscreen compositing using (PAL) DV footage in After Effects.

However, the camera that we're using - the Canon XM2 - like most DV cameras, stores the Y, Cb and Cr data in the range 0-255. Consequently, when the codec presents the RGB data to After Effects (which, as you correctly observe, requires RGB input) you can get "luma leakage": because one or more of the R, G or B values that correspond to the YCbCr values would need to be less than zero or greater than 255, when you re-convert the RGB data back to YCbCr for processing, artifacts that ought to be confined to the chroma channels can appear in Y.

Additionally, converting back and forth introduces quantization error.

Hence, I would like to find a method (presumably using Avisynth) that will output an uncompressed (RGB) AVI file, in which R contains the Y, G contains the Cb, and B contains the Cr data from the original DV AVI.

13th April 2005, 20:19	#3 \| Link
Dimwitted Registered User Join Date: Apr 2005 Posts: 5	Sorry, I don't think you understood my question. I've written some filters to process the Cb and Cr information in order to do better greenscreen compositing using (PAL) DV footage in After Effects. However, the camera that we're using - the Canon XM2 - like most DV cameras, stores the Y, Cb and Cr data in the range 0-255. Consequently, when the codec presents the RGB data to After Effects (which, as you correctly observe, requires RGB input) you can get "luma leakage": because one or more of the R, G or B values that correspond to the YCbCr values would need to be less than zero or greater than 255, when you re-convert the RGB data back to YCbCr for processing, artifacts that ought to be confined to the chroma channels can appear in Y. Additionally, converting back and forth introduces quantization error. Hence, I would like to find a method (presumably using Avisynth) that will output an uncompressed (RGB) AVI file, in which R contains the Y, G contains the Cb, and B contains the Cr data from the original DV AVI.