Should a B/W mode have been standard?

[kool kitty89]

Should a luma only (disabled colorburst) mode have been a standard feature for home computers (and similar devices) outputting composite video? (and/or RF -which uses composite, or S-video)

 

I'm thinking mainly in terms of a manual switch that allows color to be disabled by hardware, on systems outputting separate chroma and luma signals, it's as simple as disabling the chroma line, but even on systems with such, a separate composite video line was usually used rather than combining Y/C externally. On other machines, it's only composite video output in general, so that chip would have to disable color internally (be it a RGB video encoder, or the video chip natively outputting video).

 

The obvious reason to support this is clear, undegraded grayscale video on composite monitors. (or only RF noise hindering RF displays) With something like the C64, one could simply plug the luma connector staight into a composite video jack, but that's not often an option for other platforms. For platforms (like the Amiga and ST) with RGB standard, but composite video as the cheaper option, this would be very important as well, as users would have the option for crisp, RGB quality grayscale graphics (especially if software specifically adapted to this mode -otherwise some colors would end up looking identical). That still wouldn't help for ST users with the monochrome highres monitor unless those were made to specifically support a lower resolution.

For any users with B/W TVs or B/W composite monitors, such modes would be preferable in general, as any luma degridation from composite video would be eliminated.

 

With Y/C monitors such as the C64 had, it's less of an issue as luma is separate as standard, and one can simply turn color intensity down to get a clear image, but in composite video, the luma signal degrades even with good comb filtering, and horrible dot crawl at worst.

 

 

I know CGA had specific grayscale modes, disabling colorburst, but not an option to configure such in any video mode, so it was only good for applications catering to those modes.

 

 

Such a feature would add to cost, but it seems like a rather minimal addition if planned from the start. For any machines that commonly provided separate chroma and luma anyway, it would be even simpler. For others, it would mean adding such a feature onboard the video chip, or using encoders with separate Y/C outputs instead of just composite video.

[Herbarius]

A related anecdote: I found out, when I connect my C64 to the TV via RF instead of using the S-Video cable, and then tune my TV so it is only slightly off from the frequency, just before the picture from the C64 "disappears" into static it suddenly gets to luma only. There's no color and, what's even more remarkable, there's no (visible) interference, the display is crystal clear, as opposed to the "swirly lines" all over the place normally when using the RF output.

Seems to depend on the television, this "trick" wasn't possible with my old one, but with my new one it works consistently (both CRTs, PAL).

 

However, I haven't tested if you'll be able to hear sound that way. It's very possible you can't.

Edited February 26, 2010 by Herbarius

[kool kitty89]

A related anecdote: I found out, when I connect my C64 to the TV via RF instead of using the S-Video cable, and then tune my TV so it is only slightly off from the frequency, just before the picture from the C64 "disappears" into static it suddenly gets to luma only. There's no color and, what's even more remarkable, there's no (visible) interference, the display is crystal clear, as opposed to the "swirly lines" all over the place normally when using the RF output.

Seems to depend on the television, this "trick" wasn't possible with my old one, but with my new one it works consistently (both CRTs, PAL).

 

However, I haven't tested if you'll be able to hear sound that way. It's very possible you can't.

 

That's interesting. Still though, that immage would at best look liek the composite signal with the color turned down on the TV, the luma would still be degraded and have artifacts (namely dot crawl). The better the comb filter in the TV, the less visible the artifacts. Chroma is much less degraded by comparison, hence why the C64 uses composite video as the S-video chroma sourse. (late models did have dedicated chroma as well, but would need different cables to take advantage of that)

 

The worst possible artifacts can be seen by using a composite to S-video splitter (technically it actually using a s-video to composite adaptor improperly -reversed) and you see the full extent of the degridation in luma. (horrible full screen checkerboarding dot crawl, even with color turned off) I think the same will happen if you plug composite video into the C64 monitors luma input. I first discovered this by using a crappy 3rd party nintendo multi av cable; as it turns out many such cables simply put the composite line on the s-video Y/C pins for craptacular video output, real Nintendo cables are tougher to find.

 

I immagine the reson for the more visible artifacting in "fake" s-video is due to bypassing any sort of comb filter.

 

 

That said, doing the opposite: plugging the luma line from s-video (or component video) into a composite video input will result in crisp, artifact free grayscale video. I've doen this with component video for fun on occasion (with a TV lacking component inputs), usually my gamecube as the dot crawl is especially visible. Actually, pretty much any high red console does that (DC, PS2, Xbox, and current gen consoles), the interlacing makes things the worst though SNES,-N64, and Genesis in 240p show almost no visible dot crawl in composite, mainly blurriness; NES has nasty dot crawl while scrolling though. (all of them have aweful dot crawl through a composite to s-video bypass though)

[desiv]

Now, I had an RGB monitor for my Amiga 500 back in the day. But, when I recently rebought a 500, I picked one up with no monitor or modulator. So the only output was monochrome composite.

 

I hooked that up and it looked really nice, albeit monochrome.

Then I picked up a cheap A520 modulator, and I had color, but I used a switchbox for my Workbench, because the 520 is a crappy modulator and the picture was so much better in monochrome on the TV. Now, for games, I went color. But for text, it makes a huge difference.

 

My guess is very few people did that for long tho. They would just buy an RGB monitor.

 

desiv

[kool kitty89]

Now, I had an RGB monitor for my Amiga 500 back in the day. But, when I recently rebought a 500, I picked one up with no monitor or modulator. So the only output was monochrome composite.

 

I hooked that up and it looked really nice, albeit monochrome.

Then I picked up a cheap A520 modulator, and I had color, but I used a switchbox for my Workbench, because the 520 is a crappy modulator and the picture was so much better in monochrome on the TV. Now, for games, I went color. But for text, it makes a huge difference.

 

My guess is very few people did that for long tho. They would just buy an RGB monitor.

 

desiv

Hmm, why is the composite video output monochrome, I thought the Amiga output a color composite video signal standard? (it's grayscale right, not monochrome as in the ST's 640x400 mode -which has it's own video line and used a different monitor, but that's a bit of a different issue)

If you used a PAL machine on an NTSC set, or vice versa, that would explain the lack of color, but otherwise it seems rather odd.

 

Anyway there are a number of reasons for video not looking good on a TV, the primary ones would be the dot pitch, phosphor persistance, and beam precision. (of course adjusting the video controls ont eh TV can alter things, like the brightness and black level or contrast -plus the color and hue options for color) And even on a b/w set, the luma signal will be degraded by the chroma signal in compsote video, worse if that monitor/tv lacks a comb filter. (I think it's worse for NTSC than PAL, but I'm not sure)

A good luma singal should produce a b/w immage comparable to the RGB immage on the same monitor or TV. (easy to compare on monitors with both RGB and composite inputs or TVs with both as well -the latter bing common in europe)

 

 

This is off from my main topic, but thinking about the ST in particular, it had the monochrome mode and mono monitor in the lower cost bundle, but that was stuck in the monochrome (1-bit per pixel) highres graphics mode. Had the mono monitor being variable sync and supported the lower res standard modes, it could have been able to display all color software as well, albeit in grayscale. (that how my first VGA DOS PC was in the early 90s as a little kid, just a grayscale VGA monitor)

 

In any case, soem things would be tough to use or see in grayscale if the colors used had similar luma levels, but if software specifically supported a grayscale mode that would fix that problem. But that would matter mode in the context of the example of a dedicated b/w monitor, with a common composite video monitor (or TV), oen could always use color in lower quality. (the more text heavy programs could be optimized to be grayscale friendly anyway -most of which probably already are)

 

 

 

 

BTW the thing that really triggered this though came from playing around with the video output on my gamecube (as I mentioned above) witht he composite video having significant dot crawl on a TV (which does have a pretty good comb filter by general comparison) lacking component video inputs, I decided to see how the luma signal from component video compared (which I already knew was compatible with composite/s-video luma). So I turned off color (or as low as it goes) and plugged in the luma line from YPbPr to compare, and it was indeed much nicer to look at: a perfect, crisp grayscale picture as I would have expected. (granted s-video should have similar quality luma)

The polar opposite is a composite video signal sent into a tv or monitor, bypassing the comb filter (like passed into s-video inputs, I think the same mught occur by plugging composite video into the luma input on a Y/C monitor liek the C64 used), then the dot crawl encompassed th entire screen.

[desiv]

The Amiga 1000 had color composite I believe.

The Amiga 500/2000 had monochrome (shades of grey) composite.

I think the 3000 was monochrome as well. Not sure about the 4000.

 

They said, I believe, it was to cut costs; but I'm guessing it was so they could sell the A520 modulator or monitors.

(or genlocks)

 

desiv

[kool kitty89]

Huh, that's weird, I thought at least the earlier model A500s had built-in RF and color composite video, that must have made it rather annoying to buyers getting it mainly as a game system and had TVs or VCRs with composite video inputs. (or already had a composite monitor) It really is a swap with the ST then, with early STs only having monochrome (highres) and RGB onboard, and later models having composite video and built-in RF available. (only the STM/STFM models, those with RF modualtors onboard, had composite video on the AV port iirc, other models had RGB and highres monochrome only)

[Herbarius]

It's nice to see someone actually tries to figure this stuff out!

 

Anyway there are a number of reasons for video not looking good on a TV, the primary ones would be the dot pitch, phosphor persistance, and beam precision. (of course adjusting the video controls ont eh TV can alter things, like the brightness and black level or contrast -plus the color and hue options for color)

Yes, before I got an S-Video cable for the C64 and still if I'm using the 2600 - I want to do an S-Video mod eventually, but I don't trust my soldering yet - I see that reducing contrast and/or color saturation on the TV will make a clearer picture... However I had no idea if its a technical or rather psychological issue... If the interference really is reduced or if you just don't notice it that much anymore.

Of course unfortunately, both controls make for a dull (or colorless, respectively) picture if reduced too far and even on their lowest setting the picture is far from artifact-free.

[kool kitty89]

RF is a separate problem too, even on the best modulators on good TVs (with fine tuning or good auto tuning) ghosting still seems to be a problem, though static and scrolling lines can be minimal. (the cables you use effect this as well, in some cases, I've found using composite video RCA cables greatly increases noise, especially on a Sega Genesis)

 

As far as composite video artifacting, turning the sharpness down or filtering on tends to hide that, but that's not fixing the problem, just masking it with blurriness. I've noticed that darkening the black level (I think that would be contrast on some sets, terminology varies) seems to reduce the visible RF artifacts, especially any snow or lines. On my old 1988 Zenith Advanced System 3, turnign the "picture" (I think brightness) up too high results in distortion and added bleeding (especially of whites), even the scanlines seem to bleed together, so I have to make sure that's not to high. (even at low levels there is sometimes some warping of the immage unless I turn it way down, but then it's too dim)

 

The visibility of dot crawl shoudl be dependent on the comb filter (outside of adjusting sharpness), but even the best comb filters don't remove it completely.

 

 

I still think that Amiga thing is odd. It would have made more sense for the original A1000 to lack RF and maybe onboard composite color, but to remove it on the more home computer/lower-end market that the A500 was aimed at really doesn't make too much sense. (lacking composite video color might have coincidentally reduced complaints by some about default workbench looking "unprofessional" too -any graphics artists should be using RGB monitors anyway, so that wouldn't be an issue)

I knew about removing RF on late models, but I thought that was for late models, not starting with the first A500s, and I hand't heard about the lack of color in composite either.

Edited March 1, 2010 by kool kitty89

[Herbarius]

Mhh, I remember my father had his Amiga 500 hooked up to our color TV once or twice...