rbt@sftig.UUCP (R.Thomas) (09/03/85)
> Inputs: RGB analog and sync signals, digital > RGBI, NTSC composite. > > Jere M. Marrs > Tektronix, Inc. OK. I give up. Will somebody please explain what the difference between the various color input types are. What is the difference between RGBI digital, RGB analog, and NTSC composite, and all the rest. (The Apple RGB Color card produces something called XRGB, what's that?) Thanks for any light you can shed! Rick Thomas ihnp4!attunix!rbt
brian@sdcsvax.UUCP (Brian Kantor) (09/04/85)
In article <577@sftig.UUCP> rbt@sftig.UUCP (R.Thomas) writes: >OK. I give up. Will somebody please explain what the difference between the >various color input types are. What is the difference between RGBI digital, >RGB analog, and NTSC composite, and all the rest. >Rick Thomas ihnp4!attunix!rbt Quickly: Analog inputs allow you to have continuous shades displayed of the input signal - for monochrome, you get shades of grey; for RGB analog you can vary the three input Red Green and Blue inputs and get just about every color possible. (Analog signals generally vary from 0 = black to 1 = full on volts). Digital inputs allow no shading - either the signal is full on or its off, and so with the color or brightness. Digital RGB therefore allows you the primary colors, mixtures of any two of them, and black and white. RGBI adds an intensity input to (typically) cut brightness in half for all colors. This gives you pastel shades of the primary and secondary colors, and adds a single shade of grey. NTSC (National Television Standards Council) (also known as Never Twice the Same Color) is a method of encoding analog color and brightness signals using a complex combination of amplitude and phase relationships into a single signal. It is inherently limited in resolution when compared with RGB analog, and so is not used for medium or high resolution displays. It also tends to be less stable, as the phase relationships are delicate. Composite signals usually refer to the inclusion of synchronizing signals combined with the video. Sync can also be sent separately. Composite sync with vertical, horizontal, and color is customary with NTSC, a separate sync source is common with RGB. A small confusion exists here, in that a separate sync feed that contains both vertical and horizontal sync, rather than two separate sync feeds, can also be called composite sync. To top it all off, it is real common to feed composite sync on top of the green signal to an RGB monitor in order to reduce the number of pieces of coaxial cable running around underfoot. Hope this helps some. Brian Kantor UC San Diego Computer Graphics Lab decvax\ brian@ucsd.arpa akgua >--- sdcsvax --- brian ucbvax/ Kantor@Nosc
ron@brl-tgr.ARPA (Ron Natalie <ron>) (09/04/85)
> OK. I give up. Will somebody please explain what the difference between the > various color input types are. What is the difference between RGBI digital, > RGB analog, and NTSC composite, and all the rest. (The Apple RGB Color > card produces something called XRGB, what's that?) > RGB ... red, green, blue. A separate wire for color signal. There may be a separate sync signal or it may be overlaid on one of the color signals. RGB analog is just that. The Sony profeel monitors put schmidt triggers on the RGB inputs which shape them into either zero or one values. NTSC is what your TV set use (nick named Never The Same Color). It is the method of composing all the colors into a single video signal that is also compatible with Black and White monitors. They do this by making the primary signal the black and white intensity, and then have some side signals for the color. Look up "color" in Foley and Van Dam. -Ron
peterh@tekgvs.UUCP (Peter Hildebrandt) (09/06/85)
In article <577@sftig.UUCP> rbt@sftig.UUCP (R.Thomas) writes: >What is the difference between RGBI digital, >RGB analog, and NTSC composite, and all the rest. (The Apple RGB Color >card produces something called XRGB, what's that?) > >Thanks for any light you can shed! > >Rick Thomas >ihnp4!attunix!rbt TTL or RGB digital refers to a video source of three signals, RED, GREEN, and BLUE, each of which has a digital signal level (0 or 5 Volts). RGBI digital adds a fourth bit, INTENSITY, which is also a digital signal. Hence, RGB digital gives eight colors, whereas RGBI digital produces 16. RGB analog is also a video source consisting of three signals, RED, GREEN, and BLUE, but in this case, the signals are analog voltages from 0 to 1 volt. With analog RGB, you can theoretically get an infinite number of colors on the screen, but most analog systems are limited by the size of the digital to analog converter inside. NTSC composite is standard composite video, combining the red, green, and blue signals into one. Most video cassette recorders output NTSC composite. NTSC video is usually output through a RCA phono jack on microcomputers. Generally, the signal quality is degraded when the signals are combined for NTSC video, and therefore, any kind of RGB is preferable. Peter Hildebrandt Tektronix Laboratories