But…. The problem is that to get that black and white balance, Avid looks to the highest and lowest luminance pixels to balance. And what often happens, especially with noisy codecs, is that there is a lot of noise below "black". Those points get balanced and brought o zero IRE. This often results in raised blacks, a strong shift towards blue on the lower end, etc.
As far as the mids, or gamma, you can achieve a quick balance here with the "cast removal" tool. Click it on anything in the scene that you feel should be neutral, and it will balance that part of the scene. If you do this in curves you get an immediate idea of where things are out of balance.
--- In Avid-L2@yahoogroups.com, Dan McCabe <danlist@...> wrote:
>
> Thanks for the explanation Dennis.
>
> Dennis' explanation is more what I was trying to find out.
>
> The demo was an Avid User's group in New England (actually at
> Avid) with some local colorists including one from Frontline. The
> focus was less on artistic uses of grading and more on dealing
> with troublesome doc footage shot on all kinds of gear relatively
> quickly. Auto-contrast and auto color were both billed as
> ballpark first steps not the final word. Understanding the
> principles behind auto contrast was easy, auto color balance less
> so. Part of what was surprising was that the repeated use of
> auto color in Curves, hitting it two or three times in a row, led
> to slightly different results.
>
> D.
>
> On Sat, Mar 31, 2012, at 06:39 PM, Dennis Degan wrote:
>
>
> On Mar 31, 2012, at 2:57 PM, Dan McCabe wrote:
> > Anyone know how auto-color balance works in the CC? Saw an Avid
> CC
> correction demo this week and it was never really explained.
> I say:
> I can tell you how auto balance works in general. A color
> imbalance
> may exist in scenes that contain unequal RGB gains and ped
> levels.
> IOW, 'white' isn't really neutral white and 'black' may contain a
> bias
> towards one or more colors). These imbalances are usually caused
> by
> the lack of proper camera white- and black-balance when the scene
> was
> shot. Auto-balance compares the relative levels of R,G, and B in
> the
> overall scene and adjusts the gain and ped of the 3 color
> channels in
> order to minimize any color bias at the white and black levels.
> Since
> auto-balance cannot take into account any errors in gamma (it
> cannot
> measure gamma nor many other parameters), the use of auto balance
> is
> fairly crude and limited. All it sees is the relative peak and
> pedestal differences between red, green, and blue. Using that
> information, auto-balance then adjusts peak and ped levels of the
> 3
> color channels in order to minimize measurable color bias in the
> blacks and whites. Its use is not intended to replace a serious
> careful color grading done by an experienced specialist.
> Dennis Degan, Video Editor-Consultant-Knowledge Bank
> NBC Today Show, New York
>
> __._,.
> [nc3=3848643]
>
>
>
> [Non-text portions of this message have been removed]
>
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