15 April 2010 - 21:06#25: Color Correction Basics IV – Manipulating Color Balance with Color Wheels

Show/Hide Embed Code

In last week’s episode, we chnaged the color balance of a shot with curves. This week we’ll do the same thing with the color wheels.

Download 480p | 720p

If you really want to learn about color correction, I strongly recommend Steve Hullfish’s “The Art and Technique of Digital Color Correction”

(Disclaimer: If you buy the book from the link above, I’ll get a small kickback from Amazon.)

7 Comments

  • udosauer

    A vectorscope does NOT show any luma information by definition. It is a XY-plot of Cb and Cr.

  • avidscreencast

    Udo,

    as always you are correct albeit not too polite about it ;)

    The thing is, if you're talking in an HSL context, you change the
    Luminance (L) and it will have an effect on the vectorscope, as Cb =
    (some factor) * (B-Y) — right? So S as well as L affect the
    vectorscope, which is what I meant. Or am I totally missing the point?

  • udosauer

    Hello Christian, never intended to be unpolite, sorry for that. You are not exactly right. First of all the HSL colorspace does not really apply to digital video. There is the R'G'B' (nonlinear, gamma corrected RGB) and Y'CbCr which is derived from R'G'B'. And these are the colorspace avids colorcorrection works with. If you use the term “luminance” you have to be very, very carefully and should explain which “luminance” you mean. I can really recommend this document by Charles Poynton: http://poynton.com/PDFs/YUV_and_luminance_harmf… and his great book “Digital Video and HDTV”. And again if you make changes in the luma (Y') channel you won't see any changes on your vectorscope.

  • avidscreencast

    Hi Udo,

    again, thanks for explaining this to me.

    Maybe I still don't really get it: I guess you're right if I change
    only the luma channel. But as Cb is basically B-Y, if I change Y,
    shouldn't this affect Cb as well?

    This is something I have wondered about for a while. I also always
    thought the length of the vectors in the vectorscope to be saturation
    only (probably BS, because it relies one the HSL metaphor), but then
    again the vectors change if I play around with Setup/Gamma/Gain.
    That's why I thought luma plays into the vectors as well, using the
    explanation above to keep my brain from spinning ;)

  • avidscreencast

    BTW, if this is explained in the PDF above, just reply RTFM. I'll
    print it out and actually read it some time ;)

  • udosauer

    Okay i'll try to write very slowly :-)
    Y', Cb and Cr are derived from R'G'B' values. Something like Y'=a*R' + b*G' + c*B'. Cb= d*R' + e*G' + f*B' … If this conversion is done, it's done. if you change Y' you won't change Cb or Cr. Forget about B-Y. Always remember that Y'CbCr is R'G'B' in another form. If you do color correction you do it 99,9% in the R'G'B' color space. So if increase the gain to R', G' and B' the result in Y', Cb and Cr depends on the colors in your picture. If you have a black and white movie you won't see any changes on your vectorscope, because there's no color. Some operations (like changing hue, saturation or luma) can be computed in Y'CbCr colorspace very easily. There's another very good document by Charles Poynton “Color FAQ”: http://www.poynton.com/ColorFAQ.html

  • u00a0Great work you write very clean…..Thanks for a nice post