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Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-01, 05:06

How about variations in the color burst amplitude? :) I couldn't get my sync separator IC working properly, so I ended up doing some minor surgery on my CGA card's composite output resistors, replacing them with pots. I'm quoting from SMPTE-170M: "A gated and filtered signal derived from subcarrier …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-30, 20:44

By the way, I have a Tandy 1000 TX on which I can do some tests, if desired. Oh, awesome! Can you try running http://www.reenigne.org/misc/chart.com on it and take pictures of the results? (It cycles through all 8 possible CGA mode/palette combinations on a keypress.) It would be good to get …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-30, 19:51

because of the reduced chroma amplitude in the new card there's almost no relative delay between the pixel clock and the chroma signals, so the two cards do differ in hue by about 13 degrees. Why is the delay a function of the chroma amplitude? Because the final output signal is a weighted sum of …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-30, 14:00

I was referring to the high-contrast single-pixel transitions, such as on the leading and trailing edges of the wings. In the KQ1 booter most of the transitions from one solid color to another are at least a couple of pixels wide. No doubt it's more noticeable with the sharp pixels of a digital …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-30, 04:10

With default hue in Blue Angels the edge artifacts don't stand out because the colors are similar, but after changing the hue there are single-pixel edges with high contrast. It's a bit strange looking, like some kind of filter was applied to the image. Shouldn't transitions be more gradual in …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-30, 01:29

with cga=new, colors are the same as in the previous patch or cga2ntsc; with cga=old, the hue once again looks like it does in upatched DOSBox, i.e. 15 degrees away. Essentially the same effect as the -15 degree hack in current SVN. That seemed odd to me at first but I rechecked the numbers and yes …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-30, 01:17

1. In mode 6 / white foreground, there's now a distinct difference between the new and old CGA types: with cga=new, colors are the same as in the previous patch or cga2ntsc; with cga=old, the hue once again looks like it does in upatched DOSBox, i.e. 15 degrees away. Essentially the same effect as …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-30, 00:18

Looks like another not configurable game: I, Damiano: The Wizard of Partestrada When you say "not configurable" do you mean that the automatic detector doesn't choose composite mode by default? (Because its only heuristic is 640x200 mode with palette 15 and color burst enabled and this is a 320x200 …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-30, 00:13

The colors generally look good; but the colored edges, such as on the castle bricks or door handles, take some getting used to. Maybe this is cause of too high saturation too? No, it's just a consequence of using a notch/bandpass filter to separate Y and C - whenever there is a vertical boundary …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-29, 21:30

I noticed a minor bug in the way I'm computing the zero point of hue. The line: double hue_adjust = (-(45-22.5+33)+hue_offset+pixel_clock_delay)*tau/360.0; should read: double hue_adjust = (-(90-33)+hue_offset+pixel_clock_delay)*tau/360.0; The previous cga2ntsc/composite_test code has a similar bug. …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-29, 06:13

Here's my "160 colour" patch so far. I realized that it actually only uses at most 64 distinct colours in 2bpp modes, so with a bit more work it might be possible to use a (1,4,7,8,7,4,1) kernel instead of the (1,1,1,1) one - this would smooth out the edges of some of the colour transitions a bit. …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-28, 19:06

i mean that it is designed specially for composite mode. For rgb it would have solid colors and checkerboards (different checkerboards). But never everything with vertical lines that doesn't look nice on rgb. They also produce nice colors in composite, actually even better than mode 6 in my opinion …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-27, 22:52

Here's a patch that fixes the score line for Bruce Lee. It's still a line higher with this patch than it is on my XT, but I suspect that some real BIOSes may do the same thing as DOSBox here. For one thing, the score line is now in the same place in RGB and composite modes (which it isn't on my XT …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-27, 20:10

The sky and mountains in Bruce Lee (composite colors #11 and #6, respectively) appear a lot lighter and less saturated than in any decoding method shown here so far, possibly for the same reasons as color #8. That might just be the camera - a lot of the lighter blues seem to come out much whiter in …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-27, 15:34

I've uploaded an archive containing (full-resolution) photos of all the CGA composite colours in all graphics mode/palette register combinations to http://www.reenigne.org/misc/cga_composite_calibration.zip . The program that generates these is http://www.reenigne.org/misc/chart.com (it won't work …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-27, 15:19

If you use the start of the sync pulse as the reference point, then the shorter sync signal makes no difference (except for choking off the color burst), and horizontal centering will be exactly as in the 40 column mode. If you use the end of the sync pulse as the reference point, it will make a …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 20:04

In any case, 80 column text should be shifted to the right, while all other modes should be shifted to the left. I could imagine that switching from black to color 6 in 80 column text mdoe would then shift the whole picture to the left as well on some monitors. On my TV, there is no noticable …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 19:52

I'm talking about the CRTC's HSYNC signal, not the composite hsync pulse. The CRTC's HSYNC signal doesn't directly control any monitors though, so that's not the only thing you need to (and hence horizontal position) though - just that shift register which is used to generate the actual HSYNC pulse …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 19:20

I'm having trouble correlating what you've written to the point I made. For one thing, I'm looking at mode 4, which means color burst is enabled; and for another, I haven't mentioned anything about text. Ah, sorry - I thought you were talking about robertmo's Quest for the Time-Bird screenshots. In …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-25, 19:02

80 column text is more complicated, because the sync period is too short, as you mentioned: the complete active display area (characters/graphics plus overscan) is now ($71+1-$0A)*8=832 pixels wide That's not right - the width of the hsync pulse comes from the shift register (clocked with LCLK) not …

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