Originally Posted by itigap
First I want to thank you for sharing in this thread. I stumbled today upon this thread and find it very interesting as I am tyring to better understand the anatomy of a video signal path and the processing and signal transformations that take place along the way.
Basic to this is an understanding of the signal itself. I have always been a bit confused between YPbPr and RGB and these seem to be the two major forms when talking HDTV and DVD.
I guess what I want to know is where the color decoder and other processing functions (deinterlacing and scaling and noise reduction) come in along the way as a signal gets transformed from YPbPr (or is it YCbCr?) to being finaly displayed as RGB driving a screen? One reason I ask is if I choose to have a signal transformed external to a display into RGB, then what processing functions, if any, are left for the display to perform.
Component video is YCbCr/YPbPr. Technically, YPbPr refers to component video in the analog domain, and YCbCr in the digital domain, but you will find that many devices and articles on the internet come up with wacky labeling conventions and strange reasonings. Regardless, it's just a label.
What a display does with what it's fed will really depend on the display. Some RPTVs for instance will take an RGB input, and then convert it back to component to do all kinds of "color processing" features before going back to RGB (in other words screwing everything up). Some don't.
Also I think there is some confusion in terminology often used on this forum (at least I am still a little confused) regarding the video signals transported via 3 wire "component" cables. Are these signals always analog?, digital?, can be either?, and does the term "component" necessarily refer to just YPbPr or is RGB also a "component" signal?
Those are going to be analog, and almost always component (YPbPr). Rarer but out there is analog RGB, you'll find that most often on professional equipment, and may be 3-5 cables depending on what the sync is(RGBhv, RGBs, or RGsB). RGB is not a component video signal, and shouldn't be referred to as that. I'm not really sure where the terminology 'component' video originally came from, but it is a Color Opponent colorspace, as opposed to an RGB space.
Finally how does this terminology fit with signals conveyed over HDMI? I suspect if HDMI can carry some of the same signals that are caried via "component" cables, then those signals are also "component" signals just carried via HDMI connections. Is this correct terminology.
Correct. HDMI is capable of sending YCbCr, which is digital component video. It is also capable of sending digital RGB (which is also what DVI sends, but DVI usually does not send YCbCr, but it can). But yes, component video is not just analog component video. Note that all your digital content is basically exclusively encoded in component video, digitally of course. What is written on your DVDs, HD-DVDs, BRD etc is all YCbCr, not RGB.
The only reason component video exists and is used is to allow for chroma subsampling, which throws away color data which we ostensibly can't really see. RGB is superior in this sense, but more wasteful, which is why all the consumer content uses subsampled component video to save space. At some point, this component video content needs to be de-matrixed into RGB again so it can be displayed, and so what you choose to output (RGB or component) will move where the location of this color decoding is happening. For instance, if you output component, some other device like the display has to de-matrix that to RGB. If you output RGB, then obviously it has already beedn de-matrixed into RGB. Ideally, this is a simple process and is easy to do correctly, but for a whole host of reasons including incompetence, it may not be done correctly. You'll want to check color decoding with colorbars or a color decoder check pattern to see that things are properly decoded. And returning to some of those RPTVs that turn everything into component and do their "special feature" color functions, sometimes they'll just mess everything up anyway. :-/
I really appreciate you clearing this up for me so I migh finally properly understand the terminology and plan an appropriate signal path.
Again you rock! Thanks for helping us all.
I try, but it's confusing.