VOGONS

Search

Common searches

Search results

Display options

Display options

Re: Some of your video modes are incorrect.

Posted on 2015-03-25, 13:37

However the screenshot you take with Ctrl+F5 is SUPPOSED TO save the actual pixels, Says who? And that's not all. Mode 00 is supposed to be a text mode, just like Mode 01, except with black and white instead of 16 colors. But DosBox shows BOTH modes in color. On real CGA hardware, this bit has no …

Re: CGA Composite Mode under DOSBOX

Posted on 2012-11-15, 08:00

Is it possible to recreate the composite signal by using the RGBI output from the monitor connector? I am not just talking about a straight color to color conversion, which can be done, but to allow for artifacting. In theory, yes. It would not be easy though, because the RGBI output doesn't …

Re: CGA Composite Mode under DOSBOX

Posted on 2012-11-14, 19:03

Except for the border color, both method will yield same visual results on non-composite monitors. Would the same also applies for composite output? (Old, New, Tandy & PCJr) Yes, they should give the same results on composite output. At least for CGA (both types), the composite output is generated …

Re: CGA Composite Mode under DOSBOX

Posted on 2012-06-29, 05:27

I have never seen old CGA captures, so I don't know for sure about it. I do actually have an old CGA and a capture card, so I'll have a go at creating some. The captures are at http://www.reenigne.org/misc/old_cga_captures.zip . I used my chart.com program, so each screen shows a different graphics …

Re: CGA Composite Mode under DOSBOX

Posted on 2012-06-06, 14:22

It's not "roundabout", it's called modular design. :disapproving: Keeping the composite signal generation and the decoding separate allows me to reuse the decoding portion for other signal sources such as Apple II or NES. Sorry, didn't mean to come across so critically. But I'd have thought the …

Re: CGA Composite Mode under DOSBOX

Posted on 2012-06-05, 22:44

Here's the relevant portion for new CGA I'm not sure how you even get any artifact colour from that algorithm. Presumably you're taking the generated luma, inPhase and quadrature, combining them and then decoding the signal again? Seems like a bit of a roundabout way to do it... Since you mentioned …

Re: CGA Composite Mode under DOSBOX

Posted on 2012-06-05, 18:43

It turns out that the result is much better if I set the chroma amplitude twice as high. Which would indicate that the problem lies more with my algorithm than with any particular idiosyncracy in the CGA. Though I wouldn't know where the factor two would come from. Is your algorithm giving the same …

Re: CGA Composite Mode under DOSBOX

Posted on 2012-06-05, 18:02

Then I output, for testing purposes, just the artifact color part of 320x200 graphics with chroma color amplitude set to zero to see what the "pure artifact color" at that screen position would be. I realized that any time there is a color error, the color is too close to the artifact color . I'm …

Re: CGA Composite Mode under DOSBOX

Posted on 2012-06-05, 17:27

Like VileRancour, I'm still having trouble getting some color combinations right in 320x200 mode with new CGA and PCjr (i.e. Adventure in Serenia ). Has anyone ever checked what the actual resistor values built on the card for R/G/B are? I know the ones from the logic diagrams, but maybe they …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-06-05, 17:07

Hmm, thought I did something similar... if you look at my attempts, the solid colors (patterns 0,5,10,15) aren't shifted. Though I applied the offset to phases[6] rather than pixel_clock_delay. Attached is a comparison of the results against the colors from the captures: the trouble with Below the …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-06-05, 03:43

Oh, fascinating! So the color burst phase relative to the pixel clock is completely different for the three machines PCjr, CGA and Tandy 1000. That explains the inability to make the Below The Root title screen look right - because the hues of the artifact colours are shifted relative to the hues of …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-10, 04:56

but the result is somewhat different - see the screenshot attached. Yep, that makes sense since the algorithm as initially calibrated takes black to black and white to white, so turning down the brightness will turn white to grey. I bet NewRisingSun is also adjusting the contrast when adjusting the …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-10, 03:20

Trying to mess around with adjustable saturation/brightness, for testing. What would be a good algorithm for brightness control? There are various models for calculating brightness, but we'd want something that produces similar results to NewRisingSun's Championship Golf images (top of page 17 in …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-01, 21:30

You'll have to do more than one multiplication for S-Video or RGB inputs anyway. Since all modern TVs, and European TVs since 1980 or so, have to be able to handle RGB signals, applying contrast to the RGB signals will be the easiest way to take care of all possible inputs. True, that's a good …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-01, 20:15

I = average(sin(t*2*pi*3.57MHz)*C) Q = average(cos(t*2*pi*3.57MHz)*C) I don't understand that. Why average? Average over time to implement the notch/bandpass filter. I should have left that bit out - it's not relevant to the issue of I and Q linearity. doubling composite (the active picture part, …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-01, 17:34

Don't forget that the color burst signal generated by the CGA card is a square wave and not the NTSC standard sine wave, so there's an additional factor of sqrt(2). SMPTE-170M speaks of peak-to-peak amplitude for the color burst, not RMS. It also says the color burst is supposed to be a sine wave. …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-01, 14:43

That is why if it is possible to make saturation proper for games without any disadvantages of it, it should be done the userfriendly way. If there were any evidence that it was standard practice to set the saturation one way for mode 4 games and another way for mode 6 games, I would agree with you …

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-05-01, 13:39

You can make it this way: f12 - toggles emulated monitor type (composite, rgb, auto) f11 - toggles hue/brightness/contrast/saturation/cgaversion ctrl-alt-f11/ctrl-alt-12 - adjusts what was chosen by f12 (as alt-f11/f11 the way it is now is hard to tell which option goes which direction without …

Page 27 of 31

Go to top of page Go to top of page
Close window
Close window