Need tech info on YCbCr display inputs.

potatohead

I was musing over a HDTV display driver for Propeller. Clearly the digital and patent / DRM encumbered HDMI is out. There is always VGA, but I've noted many sets don't have VGA, but most all of them do have YCbCr display inputs.

These have some advantages where effective use of memory is concerned. Being able to put intensity in one bitplane, with color in another opens up some interesting doors. Say color at half resolution, or maybe only double buffering the intensity, leaving the color single buffered. Intensity only displays are easy, and I think the driver wouldn't have to do color burst.

Don't know, but want to.

Can anybody link me to some solid info on this input type? It seems a complete mess, with it being everything from a component NTSC standard resolution signal, to a full on analog HDTV path. Arrgh!!!

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Lawson

I am by no means an expert, but I like to have a high level understanding of things I use. So I remember things.

My understanding is that YCbCr component video is very similar to RGB component video which is, on a signal level, almost the same as VGA. Detail two, is my old computer monitor has 5 BNC connectors for RGB video. In it's manual it stated that it could display RGB with seperate H and V sync lines, RGB with a composite sync on the H sync line, or RGB with a composite sync multiplexed onto the green. I suspect that YCrCb is similar to this last scenario in that a composite sync signal is multiplexed onto the "Y" component video line.

My guess is that any current VGA object would display *something* if it was modified to place a composite sync signal on the "Y" component.

Optimally I think connecting the Y:Cb:Cr components to a 4:2:2 resistor DAC would work really well. The extra resolution of the "Y" component would provide for a sync level while simultaneously allowing more colors.

My 10 bits,
Marty

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Paul Baker

These should get you started:
http://en.wikipedia.org/wiki/YCbCr······· defines the different implementations of the colorspace
http://en.wikipedia.org/wiki/Rec._709··· defines the format used for HDTV

You may have to refer to the external references to get all the needed information.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

OwenS

Just a nickpick: YCbCr refers simply to the digital colourspace, not the analog one. The analog one is YPbPr - though theyre mostly identical. Theres also YUV - which is pretty much identical digitally.

YPbPr puts the synchronization on green. You want an identical number of resistors for each component - slight differences have an annoying propensity to cause miscolouring. And it doesn't work very well unless you have 8 bits per component - you end up with a horrible mess.

YUV/YCbCr are best used when you can preprocess the graphics ahead of time - films, videos, etc, since you can perform the chroma subsampling ahead of time (Video compression is usually YUV, with one chroma (UV) sampling for each luma (Y) sampling. This is obviously not the best for generated content.

Your better off using an external converter chip.