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Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 18:42

If... we take the average propagation delays from the datasheet (with 0 for the missing minimums) it goes down to 18ns or 23 degrees. Correcting for some arithmetic errors and using the correct type of flip-flop (74S series is faster than 74LS) gets us 14ns. Additionally taking into account that …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 17:48

Looking at the mode 4 palette, some of the colors have little difference in the two brightest levels. Perhaps there is excessive clamping at the upper end? It's not excessive clamping - that's just the way the old CGA's composite generation works when the color burst is disabled: colours 1-6 become …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 17:45

What exactly is a HCLK and LCLK? I'm asking because I don't quite understand how this translates to high-resolution text mode, although I have read that it makes the color burst unusable. HCLK is a 1.79MHz signal (the CRTC clock in 80-column text mode) and LCLK is a 895KHz signal (the CRTC clock in …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 17:09

By any chance, could you provide a build with screenshots enabled? win32 zlib and libpng are giving me a headache, but if I could look at the indexed png screenshots it might help me come up with a fix. Here's my recipe for getting DOSBox built with screenshots enabled: Make two directories, one …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 04:23

mode 6 games work as well (no difference between old and new CGA when color register is set to white): This isn't anything to do with composite decoding, but I think the text at the top of the screen in Bruce Lee is wrong - it's twice as wide in the screenshot at http://www.mobygames.com/game/pc- …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-24, 22:54

Which reminds me: the CGA wikipedia article painfully needs updating in this regard. At least the 1501981 (haven't checked the earlier schematics) bases both the pixel clock and the color burst on the OSC signal (pin B30 in IO PORT becoming +14 MHz on sheets 3, 4 and 5, with S174 U4/U5 dividing …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-24, 04:32

I think this should be adjustable, probably as another config file option - games with composite CGA support continued coming out well after that (e.g. Dragon Wars was a 1990 release that did artifacting in 320x200). There's no knowing what developers used, especially if there was an overlap in CGA …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-23, 21:37

For example, composite color 8 is almost always used as brown, on CGA composite and Apple II double hi-res alike, yet looks more like a yellowish green with standard NTSC. I just checked on my TV-connected CGA card, and composite colours 8 and 13 are definitely a more reddish hue than chroma …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-23, 15:29

If all composite monitors deviate from the NTSC standard in a similar way (which they do), at least the last part of that statement will turn out to be untrue. For example, composite color 8 is almost always used as brown, on CGA composite and Apple II double hi-res alike, yet looks more like a …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-23, 04:45

I remember on some CGA monitor theres a button that 'i-believe' were designed to fiddling with mode 4. One push will remove all blue-signal, this will change appearace as if using pallete 0 (black, green, red, brown/yellow). Another push will forcibly add blue-signal, but its also affecting black …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-23, 04:35

It looks what NewRisingSun wants to achieve by making colours prettier by making red more reddish and brown more brownish or providing knobs for people to regulate like reenigne suggest is simply not possible, cause game programmers were using one color as more then one color even in one game. As a …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-22, 15:58

Do you want me to produce pictures with my algorithm? Yes please, if it's not too much trouble. By the way, I just noticed when taking the luma signal from the comb filter instead of the notch filter, the dark gray is no longer solid even when post-filtering the luma to get rid of vertical bands. …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-22, 05:04

Why use a resonant bandpass filter at all in the comb-filter-less design? Why not just use a notch filter for chroma, then subtract the chroma signal obtained in that manner from the composite signal to obtain luma? Don't they amount to the same thing? (Assuming the filters are exactly matched). …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-21, 16:49

For what it's worth, as promised earlier, a picture from the game without and with comb-filtered grays. One more question about comb filters: what happens when you alternate black and white lines? On that screenshot (and the one on MobyGames) it appears that doing this gives you black and white …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-20, 21:05

Blue Angels: Formation Flight Simulation[/i] uses the dark gray I mentioned earlier. I'll post screenshots later. I found the ones on MobyGames. It definitely looks much better there than it does on DOSBox at the moment. Between that and Karateka I'm convinced - there were monitors which applied a …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-20, 19:05

Could the boundary condition have anything to do with that ? It's not just the boundary - look at the rightmost white vertical line in the lower door in each pair of doors - the same lack of fringing shows up there too. The boundary values should be the values corresponding to whatever colour is in …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-20, 19:01

Given the sheer number of Apple II (and a few CGA) games using the technique, I would assume so. I saw the "Mask of the Sun" example that TeaRex posted at http://www.vogons.org/viewtopic.php?t=12319&postdays=0&postorder=asc&start=140 but I think the horizontal lines there are just dithering between …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-20, 17:28

Of course, that's a heck of a lot of settings, which probably wouldn't be popular with developers to implement, maintain and mostly, explain in a documentation. (Implementation would be the least problem, as code for all aspects already exists.) Yep - so it's a classic 3-way engineering tradeoff: …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-20, 16:00

It's seen like the dark cyan is swaped with light green. Also, the gray color is darker and darker gray is black. You're not comparing like with like there - the colours between the CGA composite and the PCjr versions were never the same and were never supposed to be because the sets of colours …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-20, 15:37

But it won't necessarily make for particularly pretty colors. In particularly, people will continue to pester the developers about brown being too greenish or red being too pinkish, depending on the hue setting. See pictures, all at a hue setting of ±0°. You would not need any fancy non-linear …

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