mherman@alias.UUCP (Michael Herman) (11/18/89)
In article <46900048@uxe.cso.uiuc.edu> mcdonald@uxe.cso.uiuc.edu writes: > >>Well, not quite. A standard NTSC image does not contain the digital >>equivalent of 24 bits per pixel. What is a reasonable number of bits to use? Some people claim they are producing *NTSC-quality* video with 16-bit video ouput boards. They are configured as 6-6-4 or 5-6-5 bits/component. What do people think?
pierce@radius.UUCP (Pierce T. Wetter III) (11/19/89)
mherman@alias.UUCP (Michael Herman) writes: >> >>>Well, not quite. A standard NTSC image does not contain the digital >>>equivalent of 24 bits per pixel. >What is a reasonable number of bits to use? >Some people claim they are producing *NTSC-quality* video with 16-bit >video ouput boards. They are configured as 6-6-4 or 5-6-5 bits/component. >What do people think? I think that Sony, whose Trinitron is about the highest quality monitor I've had the pleasure to use, tells us that the monitor electronics is only accurate to about 5 bits per channel, so 16 bits is pretty good if not better than normal televison. There are additional problems with NTSC as well but I'm not sure I want to go in to them. Heres a fun fact, though: Broadcast NTSC is specced for a gamma of 2.2 and most TVs have a gamma of 2.8. Pierce
rick@hanauma.stanford.edu (Richard Ottolini) (11/20/89)
In article <630@alias.UUCP> mherman@alias.UUCP (Michael Herman) writes: >In article <46900048@uxe.cso.uiuc.edu> mcdonald@uxe.cso.uiuc.edu writes: >>Well, not quite. A standard NTSC image does not contain the digital >>equivalent of 24 bits per pixel. Sun TAAC group says 2 bits per pixel is adequate for color animation. For actual digital processing, that is still-frame and decompressed, the amount approachs 24 bits per pixel. Storage amounts and digital processing are different issues with different optimal answers in this debate.
john@cfa250.harvard.edu (John Roll) (11/20/89)
The problem with trying to figure out the # of bits per pixel that are needed to reproduce NTSC quality video on a workstation is that the NTSC picture is encoded in a different color space. The usual RGB color repersentation that we use for computer graphics display is over done. When the NTSC spec was created the television (analog hackers) engineers shoehorned the color broadcast singal into the already defined black and white broadcast system. They did this by limiting the sugnal to those colors and bandwidths that the eye could percieve. The signal is not an RGB signal because the eye descriminates the changes in colors at different bandwidths. Black and White is the most sensative. (~8MHz). The color portion of the picture is sent along the IQ color axis. I is the purple color at the bottom of an NTSC test pattern and Q is the more anber white color. These signals make up the color picture and are sent as "sub-carrier" modulations of the BW signal. Any way these signals are sent at much lower frequencies. To obtain NTSC quality from RGB 24 bits are indeed needed. (fact) To obtain NTSC quality from another scheme MUCH less bandwidth is needed. Example: YRB color syncronized coding used in the New Media Graphics VideoWindows digital video board. 12 bits per pixel at 8MHz Endcode The BW as 7 bits lumanance at 8MHz Multiplex the two chroma channels to obtain two 4MHz streams. 8 bits R-Y at 4MHz 8 bits B-Y at 4MHz This will give FULL NTSC color and spatial resution in a more compact form than RGB. Other schemes are even better but more difficult to handle in a DSP (for post processing of the video signal). If the signal were encoded in its native braodcast format YIQ 10 bits at 8 MHZ 7 bits Luma Multiplex I and Q to obtain 8 bits at 1.6 and 3.9 MHz respectivly DISCALIMER: I am a past employee of New Media Graphics. This answer is off the top of my head all flames ignored. For a serious explaination see "The Television Engineers Handbook" 1000 pages of fine print but really covers the subjects of color space representaion and signal encoding (recomended reading for all CG Engineers). John@cfa needs of the human ~v