Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-23, 04:45

by

by reenigne

in DOSBox Patches

in DOSBox Patches

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

by

by reenigne

in DOSBox Patches

in DOSBox Patches

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

by

by reenigne

in DOSBox Patches

in DOSBox Patches

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

by

by reenigne

in DOSBox Patches

in DOSBox Patches

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

by

by reenigne

in DOSBox Patches

in DOSBox Patches

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

by

by reenigne

in DOSBox Patches

in DOSBox Patches

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

by

by reenigne

in DOSBox Patches

in DOSBox Patches

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

by

by reenigne

in DOSBox Patches

in DOSBox Patches

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

by

by reenigne

in DOSBox Patches

in DOSBox Patches

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

by

by reenigne

in DOSBox Patches

in DOSBox Patches

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

by

by reenigne

in DOSBox Patches

in DOSBox Patches

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 …

---

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-20, 15:15

by

by reenigne

in DOSBox Patches

in DOSBox Patches

If we're doing our band-limiting by just averaging over 4 consecutive pixels (as the current DOSBox implementation does, I think) and we limit ourselves to graphics modes we can just enumerate all the colour possibilities directly in the palette. There are only 64 of them Having thought about this …

---

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-19, 22:51

by

by reenigne

in DOSBox Patches

in DOSBox Patches

A gated and filtered signal derived from subcarrier, called the burst, shall be added in the horizontal blanking interval of each line, excluding the nine-line vertical sync interval, as a synchronizing signal and amplitude reference for the chrominance signals. Now you've got me wondering if I was …

---

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-19, 20:51

by

by reenigne

in DOSBox Patches

in DOSBox Patches

In any case, the CGA does not generate proper video levels, and having gone back and forth between several ways of dealing with this, I think for emulation purposes, the best way is to just normalize everything so that black really is at 0/0/0 and white is at 1/1/1. Agreed. I still want to figure …

---

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-19, 20:39

by

by reenigne

in DOSBox Patches

in DOSBox Patches

As Qbix noted, the precalculation produces 80 colors (16 hues * 5 luminance levels for each); the line-drawing handler then determines the palette index for each pixel by doing some averaging over adjacent pixels. Having thought about this some more - I think there's a slight variation on this …

---

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-19, 19:18

by

by reenigne

in DOSBox Patches

in DOSBox Patches

As it should. If your purpose of performing the band-limiting is to replicate the blur on a monochrome monitor, then you would be right, and you would have to linearize the signals before applying a linear transformation. But when the NTSC standard was first developed, that was exactly the idea - …

---

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-19, 16:48

by

by reenigne

in DOSBox Patches

in DOSBox Patches

No, that's entirely correct, because YIQ to RGB transformation as well as the band-limiting is even in theory meant to apply to electrical signals, not to light. I'm not convinced about that - it's a linear transformation of voltage but ideally it would be linear transformation of light. Consider a …

---

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-19, 04:02

by

by reenigne

in DOSBox Patches

in DOSBox Patches

The "non-linearity" merely refers to what the electrical (or digital) RGB signals actually represent. A linear signal directly represents light, because double the voltage means double the light, whereas a "non-linear" signal doesn't directly represent light, because it's "distorted", if you will, …

---

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-18, 22:00

by

by reenigne

in DOSBox Patches

in DOSBox Patches

As for the hard part (refactoring the proposed code to work with DOSBox's palette precalculation), here's what I was thinking: derive the 16 pixel patterns corresponding to each nybble for the current mode/color register, and feed them to reenigne's code (upsampled as necessary - the algorithm …

---

Re: CGA Composite Mode under DOSBOX?

Posted on 2012-04-18, 21:31

by

by reenigne

in DOSBox Patches

in DOSBox Patches

Most CRT television sets don't convert to linear RGB, as that is difficult with analogue electronics, but just apply the conversion matrix to the non-linear voltages from the YIQ decoder. Ah, here's where the confusion lies then - my understanding is that the voltages (composite, Y, I, Q and the R, …

---