25 replies to this topic

[Tempest]

Do any 2600 or 7800 games use artifacting? The reason I ask is that I'm thinking about doing an S-video mod to my 7800, and that prevents artifacting. I'd hate to do a mod like this and have my games not look right.

Tempest

[EricBall]

What do you mean by artifacting?

The 2600 & 7800 graphics are based around pixel clock = colorburst or half colorburst with (on the 2600 at least) the color provided by a delay tapped colorburst signal.

Everything I've read about video mods for the 2600 & 7800 haven't indicated any color problems. (I haven't worked up the courage to do my own mod. I also have some ideas using some VLSI video amplifiers.)

[DanBoris]

I don't believe either of them has color artifacts like the high-res mode on the 5200/8-bits.

Dan

[Tempest]

Quote

I don't believe either of them has color artifacts like the high-res mode on the 5200/8-bits

That's what I thought, but I wasn't sure about the 7800. Thanks.

Tempest

[Bryan]

Tempest said:

Do any 2600 or 7800 games use artifacting?  The reason I ask is that I'm thinking about doing an S-video mod to my 7800, and that prevents artifacting.  I'd hate to do a mod like this and have my games not look right.

Tempest

The artifacting is only produced when using the high-rez 320 mode on the 8-bit. The 2600 has no such mode, and although it should be possible on the 7800, I've never seen anything that attempts it (you don't really need to with the 7800's color capabilities).

-Bry

[jindroush]

I think that 7800 does artifacting. I was reported that Tower Toppler is 'colored' whereas in MESS it's stipped b&w, which suggests artifacting.

Maybe also second screen of Jinks is artifacted?

[EricBall]

jindroush said:

I think that 7800 does artifacting. I was reported that Tower Toppler is 'colored' whereas in MESS it's stipped b&w, which suggests artifacting.

Maybe also second screen of Jinks is artifacted?

There were a couple of bugs in the MESS a7800 video driver which should be corrected in the next release. I'll give Tower Toppler a try.

[EricBall]

jindroush said:

I think that 7800 does artifacting. I was reported that Tower Toppler is 'colored' whereas in MESS it's stipped b&w, which suggests artifacting.

Maybe also second screen of Jinks is artifacted?

There were a couple of bugs in the MESS a7800 video driver which should be corrected in the next release. I'll give Tower Toppler a try.

[DanBoris]

jindroush said:

I think that 7800 does artifacting. I was reported that Tower Toppler is 'colored' whereas in MESS it's stipped b&w, which suggests artifacting.

Maybe also second screen of Jinks is artifacted?

When I was working on the MESS 7800 driver someone suggested this to me, but I really don't think problem is caused by a lack of artifacting, I think there is something else causing it.

Dan

[Bryan]

Can somebody post a screen capture of Tower Toppler in MESS?

-Bry

[jindroush]

You can compare to actual screenshots here.

http://www.atari7800...pplerscreen.htm

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[EricBall]

Well, it's getting better. The ball sprites don't blend in with the tower quite as much. Don't know about the colors though. Hmm.

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[EricBall]

Ahh-ha! I think I understand what is happening. Because the 7800 MARIA has a 2*colorburst pixel clock, the alternating on/off pixels of the tower creates a waveform at colorburst frequency. So rather than producing the stripes shown by MESS, it gives the solid color shown in the screenshots.

This reminds me of hi-res mode on the Color Computer. Although it was a 256x192 two color mode, single pixels would be either red or green/blue depending on whether it was odd or even.

So Tempest, I was wrong. The 320 modes may have color artifacts (especially Tower Toppler). Whether these artifacts will occur with an S-Video mod is an interesting question. Because S-Video doesn't have a colorburst filter (notch or comb) I suspect the output will look more like MESS.

I'm not sure if this effect can be easily reproduced in MESS. I suspect the programmers did a lot of trial and error development to determine what each color / stripe combination did.

This also calls into question the value of 320 modes. I wonder why GCC included them.

[Bryan]

EricBall said:

Ahh-ha!  I think I understand what is happening.  Because the 7800 MARIA has a 2*colorburst pixel clock, the alternating on/off pixels of the tower creates a waveform at colorburst frequency.  So rather than producing the stripes shown by MESS, it gives the solid color shown in the screenshots.

Exactly... The reason you can't see the light-dark luma pattern is because

1. TV's try to filter out that frequency so you don't see the color carrier as a dot pattern and

2. The TV detects the high-rez luma pixels as a strong color signal with a high saturation value, so it adds brightness to the overall signal masking the dark pixels.

The vertical high-rez bars in the picture lead me to believe there's at least one 7800 game that uses artifact (luma-as-chroma) colors.

My question is: If the 7800 supports colored objects in the 320 mode, why use artifacting at all?

-Bry

[Tempest]

Hmm... Which other games use this mode? If it's just Tower Toppler I'm willing to put up with it for that crisp S-Video picture. I wonder if I wouldn't be better off just doing composite? Can you really tell the difference between the two with such low resolutions?

Tempest

[Bryan]

I think it's worth it. A composite signal won't be as sharp. A TV allows more high frequency content from the S-Video Luma input than from the Video input.

-Bry

[cwilkson]

Tempest said:

Can you really tell the difference between the two with such low resolutions?

Yes! Yes you can! It shows up more if you have a monochrome only image. The best way to see the difference is to look at the s-video image for a while, then suddenly switch to composite. Or vice versa. I was _AMAZED_ the first time I saw this on a 2600.

-Chris

[jindroush]

EricBall said:

Well, it's getting better.  The ball sprites don't blend in with the tower quite as much.  Don't know about the colors though.  Hmm.

Please explain.

thanks,

[jindroush]

EricBall said:

This also calls into question the value of 320 modes.  I wonder why GCC included them.

There's a option to turn off the color burst for hi-res modes. Then it should display as pure 320 b&w picture without any artifacting. (At least I understand the docs that way).

[Mitch]

Tempest said:

Hmm... Which other games use this mode?  If it's just Tower Toppler I'm willing to put up with it for that crisp S-Video picture.  I wonder if I wouldn't be better off just doing composite?  Can you really tell the difference between the two with such low resolutions?

Tempest

You should ask Lee, he has his 7800 modded for S-Video.

Mitch

[cschell]

I have one of Lee's S-video modified 7800's and I get the lines in the bricks like the screen shots above.

Chad

[Tempest]

Ok so other than Tower Toppler, what 7800 games used artifacting?

Tempest

[Bryan]

Anything that shows vertical high-rez bars in the emulator will produce a color. I don't know of any others, but I didn't know of Tower Toppler.

-Bry

[EricBall]

The two screenshots show the impact of the forthcoming changes to MESS on Tower Toppler. As you can see with the old version the player shows through the top of the space ship and the tower shows through the bottom of the space ship too. Neither occurs with the new version.

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[EricBall]

EricBall said:

This also calls into question the value of 320 modes.  I wonder why GCC included them.

jindroush said:

There's a option to turn off the color burst for hi-res modes. Then it should display as pure 320 b&w picture without any artifacting. (At least I understand the docs that way).

bryede said:

My question is: If the 7800 supports colored objects in the 320 mode, why use artifacting at all?

Bry, you answered your own question. The color isn't important, it's the repeating on/off pixels which cause the artifacts. The artifacts may allow colors to be shown which aren't in the 7800 palette, or display more colors than the given 320 mode is capable of.

Jindroush, I suspect even in B&W 320 mode alternating on/off pixels could cause artifacts.