[PD] Colour in Digital Video

Andrew Brouse brouse at music.mcgill.ca
Fri Dec 21 09:43:40 CET 2007

Hello Matju et al,

You really shouldn't take my comments personally, they aren't meant to be 
at all. I do like you personally and respect the work that you do.

My comments were meant to provide useful information to all those who are 
developing and working with Digital Video in Pd. For what it's worth, the 
references I pointed to are standard fare for all video engineers, whether 
on computers or not.

I find it really sad the amount of bitterness, bickering, infighting and 
acrimony in parts of the Pd community. The energy that goes into this is 
energy that doesn't go into making Pd and associated projects better 
tools. I find that really sad.

That's all I have to say,


On Fri, 21 Dec 2007, Mathieu Bouchard wrote:

> On Wed, 12 Dec 2007, Andrew Brouse wrote:
>> To further complicate things, our response to brightness and colour is not
>> linear and so those perceptual curves have to be taken into account during
>> that mapping into video signals (chroma and luma).
> Oh and also all those "absolutely perceptual" systems are just discarding the 
> genetic diversity of the universe (as well as the non-genetic diversity!). 
> One man's metamers is another one's yuck. ;)
>> Most video digitisation systems also use 'chroma sub-sampling'
> Yes, we know about it, but I don't think that it's so relevant to colours 
> unless using the YUV image type in GEM or PDP. (In GridFlow, YUV images are 
> not subsampled, and also, Claude is so far only talking about individual 
> colours, as float triplets)
>> This uses that fact that we are more sensitive to differences in brightness 
>> than variations in colour.
> But this is not counting the fact that we could be standing close enough to 
> the screen to actually see that much chroma resolution. No explanation of 
> subsampling ever talks about that.
>> The YCbCr (corresponds the YUV colour space of our perception) video 
>> representation uses this technique which makes it more compact while giving 
>> approximately equal quality to an larger RGB representation.
> In order to say that, you have to define quality to correspond to some idea 
> of how one should look at a screen in order to justify the subsampling. But 
> people don't watch a screen from the same distance.
>> Anyone working with colour video systems should know and read Charles 
>> Poynton's writing on this subject - he is the acknowledged expert. If you 
>> only have one book on your shelf it should be his "Digital Video and HDTV".
> Hey. Colours are nice, but art in general is a lot more important. If I'd 
> have only one book on my shelf it should be something else than a treatise of 
> colorimetry.
>> [you can also be amazed, amused or angered by the way he vacillates
>> between 'color' and 'colour' in his writing...]
> None of the above...
> _ _ __ ___ _____ ________ _____________ _____________________ ...
> | Mathieu Bouchard - tél:+1.514.383.3801, Montréal QC Canada

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