Color Video
The first color television system was developed in the U.S. by RCA in the 1940's and 1950's, before Europe's PAL and SECAM systems. It was named NTSC after the National Television Standards Committee. It used analog vacuum-tube technology which was the state of the art at the time. For what it was it worked remarkably well until broadcasters in the U.S. went digital in 2009.
The main reason it worked so well was because there was ONE STANDARD which everyone was expected to adhere to, particularly manufacturers of broadcasting and receiving equipment. You didn't have manufacturers adopting their own proprietary standards which viewers were expected to adapt or not adapt to.
There is something every broadcaster has known for decades and it is just as applicable in today's world of web-based video as it was in 1950. Today there are millions of videos on YouTube, Vimeo or wherever, being viewed by a potential audience of millions. As producers of these videos we have NO CONTROL over how each of these potentially millions of viewers has adjusted, or not adjusted, his monitor. All we can do is set a standard and hope the viewer's device complies with that standard.
Where NTSC fell short was that viewers didn't have a viable way of adjusting their receivers. Viewers were left to simply guess at the correct settings for brightness, contrast, hue and saturation. In 1978 CBS labs developed a color bar signal which won a technical Emmy award. It was widely used to calibrate studio monitors. The user could adjust hue and saturation by disabling the red and green channels and displaying only the blue channel. Many monitors had a button which would show a blue-only display. The problem was that it required bandwidth to broadcast the signal, and broadcasters would rather broadcast revenue-generating programming with that bandwidth than a test signal.
Much of the technology in today's digital video has its antecedents in analog NTSC video developed in the 1940's and 1950's, such as the concept of a luminance channel and two color-difference signals, with the color-difference signals having a lower resolution/bandwidth than the luminance signal which carries the detail. Gamma correction was used to compensate for the transfer characteristics of CRT phosphors and was set at 2.2. I've read a lot of cruft about gamma correction but that is the historical reason it exists.
We're dealing with the RGB data which is ultimately delivered to the viewer's monitor. It is then up to the user to make sure his monitor is properly calibrated.
Today in 2017 we have one standard for web video: sRGB. As noted above, it uses the same coefficients as bt.709 and 2.2 gamma. As also noted above, not all encoders flag their color space — in fact many videos aren't flagged at all — and even if they were, the players/decoders don't necessarily read those flags and do the right thing with them. The best we can do as producers is to make our videos sRGB compliant.
My monitor calibration program with its USB sensor is one of the best investments I have ever made. The main parameters I use are 6500° K color temperature and 2.2 gamma. Many of these programs have a preset for sRGB.
The main reason it worked so well was because there was ONE STANDARD which everyone was expected to adhere to, particularly manufacturers of broadcasting and receiving equipment. You didn't have manufacturers adopting their own proprietary standards which viewers were expected to adapt or not adapt to.
There is something every broadcaster has known for decades and it is just as applicable in today's world of web-based video as it was in 1950. Today there are millions of videos on YouTube, Vimeo or wherever, being viewed by a potential audience of millions. As producers of these videos we have NO CONTROL over how each of these potentially millions of viewers has adjusted, or not adjusted, his monitor. All we can do is set a standard and hope the viewer's device complies with that standard.
Where NTSC fell short was that viewers didn't have a viable way of adjusting their receivers. Viewers were left to simply guess at the correct settings for brightness, contrast, hue and saturation. In 1978 CBS labs developed a color bar signal which won a technical Emmy award. It was widely used to calibrate studio monitors. The user could adjust hue and saturation by disabling the red and green channels and displaying only the blue channel. Many monitors had a button which would show a blue-only display. The problem was that it required bandwidth to broadcast the signal, and broadcasters would rather broadcast revenue-generating programming with that bandwidth than a test signal.
Much of the technology in today's digital video has its antecedents in analog NTSC video developed in the 1940's and 1950's, such as the concept of a luminance channel and two color-difference signals, with the color-difference signals having a lower resolution/bandwidth than the luminance signal which carries the detail. Gamma correction was used to compensate for the transfer characteristics of CRT phosphors and was set at 2.2. I've read a lot of cruft about gamma correction but that is the historical reason it exists.
We're dealing with the RGB data which is ultimately delivered to the viewer's monitor. It is then up to the user to make sure his monitor is properly calibrated.
Today in 2017 we have one standard for web video: sRGB. As noted above, it uses the same coefficients as bt.709 and 2.2 gamma. As also noted above, not all encoders flag their color space — in fact many videos aren't flagged at all — and even if they were, the players/decoders don't necessarily read those flags and do the right thing with them. The best we can do as producers is to make our videos sRGB compliant.
My monitor calibration program with its USB sensor is one of the best investments I have ever made. The main parameters I use are 6500° K color temperature and 2.2 gamma. Many of these programs have a preset for sRGB.
No comments:
Post a Comment