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Colour-space concerns: monitoring HD on SD monitors


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#1 Jack Kelly

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Posted 17 April 2008 - 12:01 PM

Hi there,

I have a nice Sony PVM-14L4 monitor which I feed via component YCbCr from my Blackmagic Decklink HD Extreme card. When I'm editing HD projects, the Decklink card down-converts the HD to SD while I'm editing so I can still use my SD monitor to edit and grade HD projects. However, should I be worried about colour-space issues (i.e. HD uses rec.709 whilst SD uses rec.601)?

To confuse matters further, as I understand it... rec.709 and rec.601 are standards for the digital encoding of HD and SD video (respectively). i.e. there's no such thing as "rec.709" or "rec.601" once you're in analogue land.

In other words... do I not need to worry about colour space issues when monitoring HD on my SD CRT because my monitor is being driven by an analogue (YCbCr) connection?

I'm confused, I admit it!

Any help would be greatfuly received!

Many thanks,
Jack
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#2 Walter Graff

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Posted 17 April 2008 - 12:35 PM

Nothing to worry about. You're seeing colors the way they were meant if your monitor is set up properly.
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#3 John Sprung

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Posted 17 April 2008 - 01:39 PM

All the up/down converters that I know of convert correctly for the difference between the 601 and 709 luminance equations and matrices.

This was a subject of discussion a little over ten years ago, when the HD standards were in the works. At that time, I wrote a little assembly language program that would take a .BMP file and apply to it the equivalent of encoding as 601 and decoding as 709, and vice versa. Those test images were widely circulated, and the converter makers decided that getting 601/709 right was a nice bullet point to have in their feature lists, so they all did it.

I'll have to try to find that stuff again.




-- J.S.
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