On NTSC Video, Blue Blurring, Chroma Subsampling 308
NEOGEOman writes "Something I've been fascinated with for a long time is video signals. On my website I've spent over six years collecting video and other hacks for game consoles. I've recently put together the fourth revision of my video signal primer and it's expanded to six pages now, including strange subjects like chroma subsampling, horizontal colour resolution and rather interesting revelation: your eyes suck at blue."
Once again, Europe is ahead (Score:3, Informative)
Re:It's Christmas, why do you lie? (Score:1, Informative)
Which means that we - the people - have to take drastic measures to bypass it: Hardware [psxtune.com] or Software [dvdregionx.com]
suck egg (-nog) MPAA.
False positive (Score:4, Informative)
You may want to read a report on misbehaving censorware [atari.org]. Blocking the the article as "pornography" is misbehavior. If your company's business has anything remotely to do with video production or video games, ask your IT department to review gamesx.com (the site on which the article is hosted) and consider whitelisting it.
Obvious Physics (Score:5, Informative)
It's well known; as our eyes drift to the blue and red end of the spectrum, we lose our sensitivity, off by many orders of magnitude from say, yellow. This is why you see blue, and more commonly, red, lights as "night" light sources.
The general reasoning: our eyes evolved with a single primary light source: the Sun. Which has quite the yellow tinge to it. Our eyes adapted to this, and as such, gave yellow the highest sensitivity and drifted off in a rough bell curve [ndt-ed.org] from there.
It was an interesting article, and certainly put the RGB sensitivity into perspective, but ... it's not entirely new or surprising, either. Nor does the human eye really respond at RGB -- its response curves (beta, gamma, and rho) more closely correspond to blue, green/yellow, and yellow/orange.
That all being said, thanks for letting us meet Traci. ;)
Irises and Pupils (Score:3, Informative)
Beyond that, I also remember reading that it's actually the brain that does all of the color (and gamma) correction; nothing in the eye's machinery--it's all done in the (pre?) processing.
SCART != RGB (Score:5, Informative)
Not necessarily.
SCART connectors are huge chunky things that can handle a number of video formats, including RGB, S-Video and Composite (maybe others too). But that's not the same as saying that a given SCART cable or socket will support all those formats. Many cheaper cables only support Composite (fewer wires means cheaper cost). And on some high-end TVs with multiple SCART inputs, only some of those will support RGB.
So if you're playing your PS2 or whatever through a SCART cable, the TV might be using the SVideo or Composite signal rather than RGB.
The lesson is, be sure to check your TV inputs, and always buy good quality cables!
It's NOT RGB. (Score:4, Informative)
NTSC video uses the YIQ color space, very similar to YUV (used in PAL, JPEG, DVD, & stuff). Y is the brightness, which gets the highest resolution, and I & Q (or U & V) are the chroma values, which can be greatly subsampled because they have no effect on brightness (when everything's working correctly).
Most lossy image compression formats involve first transforming the image to the yuv color space. The RGB->YUV transform is also used by many paint programs for things like estimating differences between colors for color reduction & such.
First match on google for "YIQ YUV":
http://astronomy.swin.edu.au/~pbourke/colour/conv
The limits of NTSC (Score:3, Informative)
JPEG also relies on this. But JPEG could provide considerably more compression if it didn't introduce those highly visible high-frequency artifacts.
Re:Uhm... (Score:3, Informative)
You can alternatively try http://nfgman.ath.cx - it's the same server, different name.
If you looked at the image on an oscilscope.... (Score:3, Informative)
Re:SCART != RGB (Score:3, Informative)
"Using it instead of RGB makes your DVD player cheaper by about $0.02 and that's significant savings! On the other hand the price of your TV goes up with the extra equipment needed to decode this component signal."
This complains too much of the cost of converting component to RGB and no explaination is given to why it costs more to integrate comp->RGB into the TV than it would in the DVD player.
Where the conversion to RGB happens doesn't matter that much that I can tell, and it really doesn't raise the cost of the TV, it is cheaper than being composite or s-video compatible, which is dirt cheap in TVs. While separate transcoders cost $80 or more, to be integrated in a TV, I really doubt it costs any more because most of that circuitry is there anyway.
I do share the disgust over Macrovision.
Another thing to keep in mind is that the digital broadcast video standards are 720x480 for NTSC, when output as progressive scan RGB, a lot of digital display devices assume that RGB at 480 scan lines is 640x480, which is worse than the component / RGB difference can ever be.
hopefully going away... (Score:3, Informative)
I *hope* this will continue to the point where Y'CbCr can be dropped entirely (there isn't much use for it aside from chroma subsampling), as well as interlacing. These things cause serious problems in computing... Every time you see stair-step artifacts, improper telecine, mis-matched black levels, banding in gradients, or black rectangles in screenshots of media players, you can thank interlacing and Y'CbCr color space.
(but they *are* quite effective as compression algorithms, and also clever hacks, in their time - how *else* are you going to send full-color motion video in 6MHz of radio bandwidth using 1950's technology?)
Other advantages to Y'CbCr (Score:4, Informative)
First, a 4:2:0 Y'CbCr is half the bandwidth of 4:4:4 RGB. We're a long way away from having half the processing power required, bandwidth, storage, etcetera simply not mattering. My RAID is 2 TB formatted, but I regularly have projects that take up over 50% of the space.
Second, Y'CbCr is a better native space for video processing, since the channels align better with what we want to filter. Luma filters like gamma or contrast are more than 3x faster in Y'CbCr than in RGB, since only one channel needs to be processed. Saturation is more than 6x faster in 4:2:0, since only two channels, each at 25% bandwidth, need to be processed. Plus a lot of filters have to convert from RGB to another color space to run. Y'CbCr is closer to those other spaces, and often doesn't require any conversion. You can say whatever you will about Moore's law, the difference between 4 and 8 real-time layers will matter for a while. Even the audio guys, who have it a lot easier, still run into performance limits with enough simultaneous tracks and such.
Lastly, our entire video infrastructure is build around subsampled Y'CbCr. Never underestimate the lock-in of standards like this. If computer people couldn't kill interlaced video in HDTV, they're never going to kill subsampling for lots of applications. Color video has always been Y'CbCr, and that's how everyone works and thinks for decades now.
That said, Hollywood is likely to pick a >8-bit RGB solution for digital projection. For digital projection, bandwidth is a non-issue, and quality, and quality like that of film. Film guys live in RGB. Plus, it's a win for that industry to have digital cinema be as INCOMPATIBLE with consumer digital video tech as possible, in order to reduce the ease of piracy, and to maintain an advantage of the theatrical experience over home theater.
FWIW, I'm a member of the SMPTE groups working on both video compression and digital cinema.
Re: ABBE Numbers... (Score:2, Informative)
Glass has the best ABBE numbers , but most people these days go for plastic lenses. The cheap CR-39 lenses actually have the best rating of the plastics, but they're also big, thick, and heavy. My guess is that a lot of people are wearing polycarbonate lenses, because they're light, have a relatively high index, and are VERY impact resistant. Downside? Really crappy ABBE number. I just switched to trivex lenses which have a slightly better ABBE number and there is a noticeable difference. (similar to polycarb in safety and thickness, can be drilled for rimless frames, but much better lens characteristics)