Colour space

[absence]

Does it make any sense to talk about colour space on the Amiga, or do you get different colours depending on Amiga model, OCS/ECS/AGA vs. RTG, whether you use the RGB port directly, RGB port converted to VGA (multisync), TV modulator, scan doubler, etc.? I'm asking because I wonder what colour profile to use when displaying ILBM files on a PC. SRGB is probably sensible if the colours on a real Amiga depends on a lot of different factors, but the Amiga video hardware did have a pretty close relationship with the TV standards, so I'm not sure if it would make sense to use PAL or NTSC colour spaces. Has anyone researched or knows anything about this?

[Jope]

I'd say PAL colour space is a good starter. Not basing it on any science, just feeling. :-)

[absence]

I'm resurrecting the thread to ask if anyone knows what kind of phosphors were used in typical video monitors used with Amigas, like the Commodore 1084 or later multisync ones. Is it something like EBU or SMPTE-C? Or something different entirely?

[Shadowfire]

absence-

The early amigas had a 12-bit color space (4 red, 4 green, 4 blue). AGA (CD32, A1200, A4000) amigas had a 24-bit color space. All video was generated internally in digital RGB format, and converted to analog RGB by a video hybrid IC.

Therefore, the exact color generated when viewing a composite signal was determined by the characteristics of the hybrid IC.

From amiga-hardware.com:

The 1084 is a usually a variation of the Philips CM8833 monitor; the 1084S-D was made by Daewoo (as was the 1084D, probably). The display tubes used in these monitors were made by Orion, Toshiba, Hitachi, and Samsung.

Since the AGA and OCS/ECS amigas used totally different video hybrid IC's, there is no way to know for sure if they output the exact same color for a given RGB value except with an oscilloscope. DENISE(digital rgb) -> HYBRID IC(analog rgb) -> MONITOR RGB DRIVE

If the composite output of the system was used, the color path would be DENISE(rgb) -> HYBRID IC(analog rgb) -> ENCODER(composite) -> MONITOR COMPOSITE DECODER(analog rgb) -> MONITOR RGB DRIVE. This, of course, adds all the hairy issues of stuffing all the color and sync signals onto one wire, then extracting them. I will say with 99.99% certainty that the colors will be *slightly* different when taking this path.

Most (all?) of the internal scandoubler/flickerfixers tapped the digital output of the Denise chip for their data, so there was no loss of color information, however such devices have their own RAMDACs and would likely have a slightly different output than the HYBRID IC.

Hope this helped.

[absence]

Originally Posted by Shadowfire

absence-
Since the AGA and OCS/ECS amigas used totally different video hybrid IC's, there is no way to know for sure if they output the exact same color for a given RGB value except with an oscilloscope. DENISE(digital rgb) -> HYBRID IC(analog rgb) -> MONITOR RGB DRIVE

I guess you are right, even though ideally there shouldn't be any difference. I haven't heard about an official colour space matrix for Amiga, so the hybrid IC ought to do the same operations for all three colour channels.

Originally Posted by Shadowfire

If the composite output of the system was used, the color path would be DENISE(rgb) -> HYBRID IC(analog rgb) -> ENCODER(composite) -> MONITOR COMPOSITE DECODER(analog rgb) -> MONITOR RGB DRIVE. This, of course, adds all the hairy issues of stuffing all the color and sync signals onto one wire, then extracting them. I will say with 99.99% certainty that the colors will be *slightly* different when taking this path.

Since it uses the output of the hybrid IC, the result would in theory be the same. RGB to YUV/YIQ (without quantisation) and modulation aren't lossy operations on paper, but with reduced colour bandwidth, luma/chroma cross-talk, phase errors and what not, there is a difference not only in colour but also luma. Therefore I don't worry too much about composite.

In all cases, assuming the RGB channels are treated the same way during DAC, it's probably up to the display device. I know quite a lot of Amiga users had 1084, but I don't know if its colour space (phosphors) is that of PAL/SECAM (EBU) or NTSC (SMPTE-C), or something else entirely. I do know that the monitor itself handles both 50 and 60 Hz signals on its RGB input, but not if the composite/CVBS decoder supports all of PAL, SECAM and NTSC. If it does, it's possible that all of them have the same colour space (SMPTE-C being the most likely?), but since the power supply is internal, they can't ship the same monitor to all territories anyway, so both tubes and decoding circuits could vary. There is also the possibility of phosphor type variations from monitor to monitor due to different manufacturers, but since the 1084 is rumored to be a decent video monitor (not sure how it holds up against expensive professional monitors though), I'm hoping there is some degree of standard conformance.

Does anyone know if a 1084 bought in Europe can handle NTSC on its CVBS input or vice versa? Or if there are markings on the tube itself suggesting PAL/EBU or NTSC/SMPTE-C? Mine is in unfortunately in storage at my parents' place far away.

[Jope]

PAL 1084s do PAL and NTSC 1084s do NTSC when fed a composite or s-video signal.. The tubes are probably different in each, at least my PAL and NTSC 1702 monitors had tubes that looked different to each other.