Mindset 16 color mode, via composite, vs CGA composite

[falter]

I've posted a few pics around of Mindset sample artwork, which I find really impressive. Others seem to as well. However every now and again I get a comment back: "bah, CGA composite could do that". But I don't think it really could, could it? I mean yes, you could get 16 colors, but it was via artifacting, not because the machine actually could generate 16 colors straight up. Am I wrong on that? Whenever I look at CGA composite art or games, it always looks blurry and color fringy to me like the Apple.

Below I have two pics. The girl with the crystal ball is from the Mindset. The one on the right is a CGA rework of Commander Keen. I find Keen looks kinda blurry by comparison, although the Mindset photo is dimmed a bit from composite capture. Obviously it would be even sharper with RGB.

 

[reenigne]

I hadn't come across Mindset before but a quick Google search says that it can do 16 colours from a palette of 512. Whereas the 15 colours in the mode that most CGA composite games (including Commander Keen) use are fixed. This probably accounts for most of the difference - I expect that if the Mindset was programmed with the same palette that CGA uses, and then to display an image, the output would look very similar to what you'd get from displaying that image on a CGA's composite output. The distinction between "direct" and "artifact" colours exists only within the CGA card - a composite monitor or TV can't distinguish between them as at the level of a composite signal there is only phase, amplitude and DC offset corresponding to hue, saturation and brightness respectively.

 

[VileR]

While it's nice to see my Keen image used as an example of CGA, the Mindset is definitely more flexible. Having 16 "direct" colors in true graphics mode makes all the difference: CGA can do either 2 or 4, depending on the horizontal resolution; for a given palette/mode combination, the total number of solid composite colors it can produce (direct and artifacted) always adds up to 16. If you use the same artifacting technique on the Mindset, I'd expect 256 possible composite colors, like on a Tandy 1K or an enhanced PCjr; and if your 16 base colors can be customized, then your 256-color composite "palette" becomes programmable as well, which enhances your possibilities even further.

 

[Eudimorphodon]

The Mindset claims to offer 16 colors out of a 512 color palette in composite mode. (I’ve never touched the machine but I think the way this is implemented is a lot like the Atari 800’s palette, where a smaller set of possible chroma options is combined with a pretty wide range of luminance values.) And these are “true” colors in the sense that the bit pattern in video ram is abstracted from what gets thrown out the back of the computer; you could, say, fade a picture in and out just by hitting the palette. With CGA the bit pattern (IE, the luma) is directly getting interpreted as the color, ala an Apple II, so there’s no palette banging tricks possible.

 

[VileR]

With CGA the bit pattern (IE, the luma) is directly getting interpreted as the color, ala an Apple II, so there’s no palette banging tricks possible.

That's true for CGA mode 6 if you keep the default base colors (black and white), but not if you change the white to some other color with intrinsic chroma information. Or if you just use mode 4 and pick non-B&W colors as your bit pattern's building blocks. CGA's got nothing on the Mindset, but it still beats the Apple II at composite.

 

[falter]

Mindset can do 16 out of 512 in both composite and RGB. I've now confirmed this with demo programs and art software like Mindset Designer. There doesn't seem to be any 'enabling' factor with composite output - the main reason it seems to be there is because it's useful for tasks Mindset later came to specialize in - video titling, animation, etc - anything that required genlocking to an external source.

It's a pity they couldn't or didn't go further - I'm guessing to offer more than 16 colors at once would have required expensive changes with the video display chip, as well as tons more memory?

That's one thing I find weird about the Mindset - they were offering a machine with a base RAM of just 32k in 1984. Even for 1984 that seems rather light. (Yes, technically they had 64k but half of that was video RAM).

 

[Eudimorphodon]

Mindset can do 16 out of 512 in both composite and RGB

I find that kind of baffling, to be honest, because isn’t its RGB output RGBI digital? Unless you’re doing horrid things like subpixel dithering or some other form of PWM how do you get 512 colors out of 16 digital options?

… Digging around I found a tech note that seems to indicate that the “Professional” video production add-on for the Mindset *did* do RGB analog? Are these things being conflated to the standard Mindset?

 

[Eudimorphodon]

I find that kind of baffling, to be honest, because isn’t its RGB output RGBI digital? Unless you’re doing horrid things like subpixel dithering or some other form of PWM how do you get 512 colors out of 16 digital options?

Okay, I'm not wrong. On page 4-4 of the Mindset software development guide it's crystal clear that the 512 colors thing does not apply to the (standard?) RGB out. According to the manual the palette registers are 16 bits wide of each of the 16 color "slots", and of those 16 bits nine of them apply to the composite palette (three bits each for Red-Green-Blue), one of them indicates if the color is "visible" when using a chroma-key device, and four completely separate bits define the RGBI color for that slot. They are completely separate entities.

The color palette specifies the actual color corresponding to each numeric color value. Each 16-bit word in the color palette specifies the content of red, green, and blue (RGB) for a single color. The 4 most significant bits of each word define the color for an RGB color monitor, while the 9 least significant bits define the color for a color television (see Figure 4-1).
...
(Diagram)
...
When using an RGB color monitor, the system uses bits 12, 13, and 14 to define the blue, green, and red components of a color and bit 15 to define high or low intensity for that color. For example, a value of 0000 for these 4 bits produces black, 0100 produces red, and 1111 produces intense white.

According to these specs the Mindset's RGB output is exactly as capable as, say, 200 line EGA or a Tandy 1000. So...

Mindset can do 16 out of 512 in both composite and RGB. I've now confirmed this with demo programs and art software like Mindset Designer.

What monitor/hardware setup are you showing 512 distinct RGB colors on?

 

[Eudimorphodon]

That's true for CGA mode 6 if you keep the default base colors (black and white), but not if you change the white to some other color with intrinsic chroma information. Or if you just use mode 4 and pick non-B&W colors as your bit pattern's building blocks. CGA's got nothing on the Mindset, but it still beats the Apple II at composite.

Yeah, I guess that is indeed true. When I think of composite color on CGA it's generally just the standard (effectively) "160x200 composite mode" that most of the early PC games used back in the day. That you have the option of mixing "pure" color artifacting on top of separately generated chroma certainly gives the sufficiently ingenious a lot more additional options, but I guess I don't really know if anyone leveraged that before modern demos.

(Back in the 80's I was cursed with a Princeton Graphics MAX-12 and my knockoff CGA card didn't have a composite port, so any game with artifact colors was nothing but jailbars for me...)

 

[falter]

Kids can actually hear that sound on their darn smartphones? Which already make everything sound like it is trying to rape my ear?

Okay, I'm not wrong. On page 4-4 of the Mindset software development guide it's crystal clear that the 512 colors thing does not apply to the (standard?) RGB out. According to the manual the palette registers are 16 bits wide of each of the 16 color "slots", and of those 16 bits nine of them apply to the composite palette (three bits each for Red-Green-Blue), one of them indicates if the color is "visible" when using a chroma-key device, and four completely separate bits define the RGBI color for that slot. They are completely separate entities.



According to these specs the Mindset's RGB output is exactly as capable as, say, 200 line EGA or a Tandy 1000. So...



What monitor/hardware setup are you showing 512 distinct RGB colors on?

Hm.. I might be wrong then. I was certain I'd run designer on my 5154, and it allowed me to switch through several different 16 color pallettes. I'll check this out again. I've been switching back and forth between composite and RGB so much, and i have this Taxan monitor that can do both analog and digital RGB in between, plus 3 different models of Mindset.. I think I'm getting confused.

 

[falter]

I find that kind of baffling, to be honest, because isn’t its RGB output RGBI digital? Unless you’re doing horrid things like subpixel dithering or some other form of PWM how do you get 512 colors out of 16 digital options?

… Digging around I found a tech note that seems to indicate that the “Professional” video production add-on for the Mindset *did* do RGB analog? Are these things being conflated to the standard Mindset?

Where did you find that tech note? On bitsavers? It might help me solve a mystery. When I got my two other models of Mindset - the Video Production System and the Professional Video Graphics system, I was getting zero out of them on power up.. just the fan - a solid blue screen on RGB for one and nothing on the other, and nothing on composite for both. I discovered the LO BIOS roms matched the LO BIOS EPROM in my working Mindset, but the HI did not. So I burned two EPROMs with the correct HI BIOS info, and suddenly they were both starting up. I don't know if BIOS can change the RGB output type.. I'd assume not. Just wondering if that was my original problem. The VPS works fine for both RGB and composite, but the PVGS does not - composite is perfect, but RGB, the horizontal sync seems to be messed up. You can make out bits of what should be the output but it doesn't assemble properly into an image. I've tried a couple different RGB monitors and settings but nothing worked. I thought maybe the PVGS was using a different frequency than standard or the 640x400 mode just doesn't work with my monitors. But I wonder if maybe it's putting out analog? I would think i wouldn't get anything though, or worse. I have that Taxan monitor, and someone was kind enough to send me a cable for it.. if the PVGS is putting out analog I might try that as the cable is for one of the analog ports.

 

[falter]

Okay - I get confused about analog and RGB. I dug around on bitsavers and found this about the pinouts on the VPS and the PVGS:



The VPS looks like what I'd expect for digital RGB. but the PVGS on the right looks quite different.

This comes from this Application note. I'm wondering if this different pinout is the source of my issue syncing the PVGS properly.

 

[falter]

Ah... I see my mistake with the Taxan. I don't think it actually does anything but digital RGB.. I thought the Apple II mode implied analog, which is what I think the Apple RGB card uses. But this was set up for the Taxan RGBII card you can install in an Apple II, which is digital.

 

[Eudimorphodon]

Okay - I get confused about analog and RGB. I dug around on bitsavers and found this about the pinouts on the VPS and the PVGS:

This is the tech note I was referring to and, yeah, the PVGS, if this note is to be believed, takes a completely different RGB monitor than the plain Mindset. The double asterisks next to the R-B-G signals are explained as indicating a “1v peak” analog signal, and it’s also chucking out composite sync instead of separate H/V.

If this note is correct the apropos monitor for this system would be an NTSC frequency analog RGB monitor like the Commodore 1084 set up to work with an Amiga.

 

[falter]

This is the tech note I was referring to and, yeah, the PVGS, if this note is to be believed, takes a completely different RGB monitor than the plain Mindset. The double asterisks next to the R-B-G signals are explained as indicating a “1v peak” analog signal, and it’s also chucking out composite sync instead of separate H/V.

If this note is correct the apropos monitor for this system would be an NTSC frequency analog RGB monitor like the Commodore 1084 set up to work with an Amiga.

They did mention the Zenith ZVM-135 somewhere. I have one of those and IIRC it does both digital and analog RGB. Weird that they'd do that though with one machine. But it may explain the larger daughter board in the RGB port area.

 

[Eudimorphodon]

But it may explain the larger daughter board in the RGB port area

I would hazard a guess that what the analog output on the PVS does is take the nine bits that are usually used for the Composite palette and slap a three bit DAC in front of each color group and pump it out the back. The probable reason they use composite sync is because it looks at least like the PVS supports RGB overlay, which means getting sync off the genlock feed.

 

[falter]

Well.. this settles it.



Alright. Now to pull out my ZVM-135, make up a cable and see what it can do.