rgb to yuv and back
by Matt Clark
on
Oct 1, 2008 at 5:08:29 pm
I was just checking out Andrew Shanks tutorial on 'smoothing the dv jaggies" - link is below. In this video he has some pal footage that he takes from rgb colorspace and converts it to yuv to blur (smooth) the blue and green channels and then uses colorspace to bring it back into rgb. I'm working with ntsc footage shot in HDV P24. Any reason I need to do this colorspace change? Curious as to why he does it...
Re: rgb to yuv and back by moody glasgow on Oct 1, 2008 at 6:29:50 pm
If you plan on keying your HDV footage, then yes you should try it. It is a good technique to soften the blockiness of DV footage. I've found that if you try to key DV footage without addressing the blockiness, you tend to get steppy edges in your key.
Re: rgb to yuv and back by moody glasgow on Oct 1, 2008 at 7:45:59 pm
Since DV is 4:1:1, you want to preserve the Y channel, since that has the most info. So if you go from rgb to yuv, you can effectively blur the blue and green without affecting the Y.
Simply put, DV cameras shoot YUV colorspace, and if you are working in RGB you need to convert to YUV so you can preserve the overall image quality.
Re: rgb to yuv and back by Matt Clark on Oct 1, 2008 at 8:26:54 pm
ok- I see. Thanks for your response. Maybe you can answer this for me this as well... I am using a JVC HD110 to shoot HDV 24P and capture to Final Cut Pro. Should I immediately convert that to ProRes HQ after I capture from the camera so that any image processing I do to it will not recompress it?
Re: rgb to yuv and back by Andrew Shanks on Oct 10, 2008 at 2:22:46 am
It has already been asnwered, but yes you are trying to retain the Y part of the original signal (as it is the only uncompressed part of the video signal in DV and any other formats that aren't 4:4:4, ...therefore the only channel that doesn't get the jaggies). Converting it allows you to leave the Y part of the signal as is while blurring the UV parts, then you convert it back RGB at the end (as Shake composites in RGB space).
Re: rgb to yuv and back by Matt French on Nov 5, 2008 at 5:59:58 am
Check the Shake Tutorials and there is a great tutorial on keying DV footage and why you are doing it. There is also a good example of how to key hair shot with DV footage (basically, ColorSpace RGB>YUV, lumakey on the fine hair, roto just the hair and keep Inside and use the same roto to either Outside or combine this matte with your main key).
