My original point was that- AFAIK- both RGB and YPbPr component allocate the same bandwidth to each of the three channels, i.e. there is no trade-off (nor any need for that trade off)
There are versions of Component that do allocate full bandwidth to the two colour difference channels. However, that is the exception rather than the norm. It's probably clearer if I use the industry nomenclature.
RGB gives full bandwidth to each colour channel. It is expressed as 4:4:4.
Colour Difference Component is expressed 4:2:2. That is the Luma channel at full bandwidth, but each of the colour difference channels are half bandwidth. IOW, they have been compressed in a lossy format because the data resolution in the colour portion of the image is less important than the Luma as you correctly surmised.
So, what's recorded on disc or tape is two full bandwidth signals. One is the Luma. The other is comprised of two half-bandwidth colour channels recorded sequentially, i.e. Cb then Cr in the same time interval as the Luma channel data for that particular field or frame of image. 4+2+2= 8 versus 4+4+4= 12 In effect, the signal has been shrunk by 1/3rd.
Just like JPEG and MP3, if the data is gone then the data is gone. Whether we notice it is a different question.
From what you said, am I right in thinking you're saying that the Y, Pb and Pr three-component signals are used because the industry revolves (or revolved around that format)? As you say, DVD compresses pictures in YUV/YPbPr format so that it can subsample the chroma, so maybe it makes more sense.
I think others have mentioned that DVD came after Colour Difference Component. The data storage format was already in place, so it made sense to use it on DVD.
Just seems strange that there are two different three-component signals output by consumer equipment (i.e. YPbPr and RGB) with no clear reason why both exist (or why the former is used in the US, but the latter seems more common over SCART in Europe).
To add to and compliment Nigel's information about RGB, the reason for the use of Component was that it would allow the use of higher bandwidth versions of the same signal via the same sockets.
Colour Difference Component support everything from baseband video (SD 480i/576i @ 50/60Hz) through progressive scan 480p/576p right up to 1080p @ 60Hz. The same isn't true of RGB SCART. It was never designed for anything much better than 576i/50Hz, and it certainly wasn't designed to cope with progressive scan. Hence, the stream of DVD players with progressive scan needed a TV with a Component input. Lots of American TVs have this feature. Very few Europe TVs did. But nearly all decent video projectors sold in the UK had a wideband Component input.
DVD and almost all broadcasts are 4:2:0, not 4:2:2. If Y = 720x576, Cb and Cr = 360x288. Hence half the raw datarate of three full resolution signals.
RGB SCART fast blanking is for "pixel" accurate punching in of RGB teletext-like data into a composite video signal. It's not just a "plausible" explanation - it's what it was designed for.
There was never any question of delivering RGB video to consumers - from the 1960s to today, consumer video has always been based on luma plus colour difference, and those colour difference signals have always been of a lower bandwidth.
Colour Difference Component support everything from baseband video (SD 480i/576i @ 50/60Hz) through progressive scan 480p/576p right up to 1080p @ 60Hz. The same isn't true of RGB SCART. It was never designed for anything much better than 576i/50Hz, and it certainly wasn't designed to cope with progressive scan.
That's only because Component was modified to add higher resolutions (original versions were SD only), RGB SCART never was modified as there was no reason to - by the time HD came to the UK HDMI was the connection of choice.
Progressive scan doesn't really make any difference, it's simply a question of the set been designed to accept it, and nothing to do with either RGB or Component.
RGB obviously supports resolutions well above that used for Component, as on all the ultra hires monitors going back years - but as I said, there was no point in upgrading RGB SCART when analogue connections were obsolete for HD.
Comments
RGB gives full bandwidth to each colour channel. It is expressed as 4:4:4.
Colour Difference Component is expressed 4:2:2. That is the Luma channel at full bandwidth, but each of the colour difference channels are half bandwidth. IOW, they have been compressed in a lossy format because the data resolution in the colour portion of the image is less important than the Luma as you correctly surmised.
So, what's recorded on disc or tape is two full bandwidth signals. One is the Luma. The other is comprised of two half-bandwidth colour channels recorded sequentially, i.e. Cb then Cr in the same time interval as the Luma channel data for that particular field or frame of image. 4+2+2= 8 versus 4+4+4= 12 In effect, the signal has been shrunk by 1/3rd.
Just like JPEG and MP3, if the data is gone then the data is gone. Whether we notice it is a different question.
I think others have mentioned that DVD came after Colour Difference Component. The data storage format was already in place, so it made sense to use it on DVD.
To add to and compliment Nigel's information about RGB, the reason for the use of Component was that it would allow the use of higher bandwidth versions of the same signal via the same sockets.
Colour Difference Component support everything from baseband video (SD 480i/576i @ 50/60Hz) through progressive scan 480p/576p right up to 1080p @ 60Hz. The same isn't true of RGB SCART. It was never designed for anything much better than 576i/50Hz, and it certainly wasn't designed to cope with progressive scan. Hence, the stream of DVD players with progressive scan needed a TV with a Component input. Lots of American TVs have this feature. Very few Europe TVs did. But nearly all decent video projectors sold in the UK had a wideband Component input.
RGB SCART fast blanking is for "pixel" accurate punching in of RGB teletext-like data into a composite video signal. It's not just a "plausible" explanation - it's what it was designed for.
There was never any question of delivering RGB video to consumers - from the 1960s to today, consumer video has always been based on luma plus colour difference, and those colour difference signals have always been of a lower bandwidth.
Cheers,
David.
That's only because Component was modified to add higher resolutions (original versions were SD only), RGB SCART never was modified as there was no reason to - by the time HD came to the UK HDMI was the connection of choice.
Progressive scan doesn't really make any difference, it's simply a question of the set been designed to accept it, and nothing to do with either RGB or Component.
RGB obviously supports resolutions well above that used for Component, as on all the ultra hires monitors going back years - but as I said, there was no point in upgrading RGB SCART when analogue connections were obsolete for HD.