[opendtv] Re: RGB mania
- From: "Alan Roberts" <roberts.mugswell@xxxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 14 Jan 2005 15:02:32 -0000
601 covers all ways of doing it. It gives a set of digital equations for
generating YUV signals from digital RGB, and acknowledges the limitations of
quantised systems. It's a well thought out paper and gets all the maths
right. It was, indeed first formulated when only composite signals were
being digitised, but it's been through many revisions and covers it all,
including an 18 MHz 960-pixel version (as used in the D5), and 4:4:4
(i.e.RGB) as well.
I have it on authority from the manufacturers that camera processing often
uses much more than 10-bit processing. The HDW900, at the top of the
quality tree, has 12-bit linear RGB adcs and internal processing is 22-bits
in each of R G and B. That's one reason why it dissipates so much power. The
HDW750 consumes 2/3 of that by using 10-bit non-linear adcs (i.e. pre-knee)
and fewer internal bits (although I don't know exactly how many) using
processing tricks to keep up the image quality.
Alan
----- Original Message -----
From: <jeroen.stessen@xxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Friday, January 14, 2005 2:06 PM
Subject: [opendtv] Re: RGB mania
> Hello,
>
> Alan Roberts wrote:
> > Not quite right Jeroen. ITU.601 etc all include specifications for the
> > coding of RGB as well as YUV signals. They form a closed set.
>
> Okay... I was under the false impression that 601 was invented
> at a time when all RGB->YUV and YUV->RGB conversions were still
> done by analog matrix circuits, and that storage and signal
> processing were to be done only on the (cheaper) YUV 4:2:2
> signals. Then it would not be necessary to specify anything for
> digital RGB signals, if they did not exist at the time...
>
> > At no point is there any flexibility in the coding of Y, since
> > it normally doesn't exist in analogue these days.
>
> Huh ? So the situation has been reversed, all matrices are now
> digital... Then I hope that the signals are 10 bits or better !
> What helps is if the gain RGB->Y and Y->RGB (for monochrome
> signals) is always exactly 1.00, to avoid quantisation of grey.
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