[Tig] ProRes444 necessary when grading BW

David HJ. Lindberg david.hj.lindberg at gmail.com
Sun Mar 17 16:43:52 GMT 2013


What the clients wants is bw which I guess it's true bw, true gray.
Although are there any benefits with saving just a few percent of the
colors in the picture, even if it's not that noticeable?

"21.26% red, 71.52% green, 7.22% blue."
This got me thinking, when adding bw effects where you can adjust
parameters like the red, green and blue channel does that mean we're
adjusting the percent of how much of the different channels is affecting
the bw effect?

Thanks for answering on a Sunday.


2013/3/17 Bob Friesenhahn <bfriesen at simple.dallas.tx.us>

> On Sat, 16 Mar 2013, David HJ. Lindberg wrote:
>
>  In my case I'm coming from colored raw files converted to colored
>> ProRes444
>> which I then will grade to black and white. But now I understand that 444
>> would give me more grey values per pixel than 422 would.
>>
>
> 444 would not give you more actual grey values but it may provide more
> perceptually gray values than 422 if the gray is allowed to include a tiny
> bit of color (not-apparent to the non-expert viewer).  This assumes a
> full-bandwidth luma channel, which is available in both 444 and 422.  Is
> black and white true gray or is it really highly desaturated color?
>
> If RGB samples are all the same (R=G=B) then the image can be processed in
> RGB-form as 'grey' and will remain as such as long as all of the channels
> receive the same treatment.  It is more efficient to use just one channel
> for grey though.
>
>
>  "but a matrix of RGB in a roughly 70/20/10 mix."
>> Do you mean it's 70% of the green channel and 20, 10 of either red and
>> blue? If so, which is 20 and which is 10?
>>
>
> 21.26% red, 71.52% green, 7.22% blue.
>
> This formula is only important when converting from RGB to Re.709 grey
> ('luma').  It has no importance if all the pixels are pure grey.  You can
> apply it repeatedly to grey pixels and still get the same answer.
>
> Bob
> --
> Bob Friesenhahn
> bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/**
> users/bfriesen/ <http://www.simplesystems.org/users/bfriesen/>
> GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
>



-- 
David HJ. Lindberg
My films: http://vimeo.com/davidhjlindberg
My blog: http://davidhjlindberg.blogspot.com/


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