Artifacting on the A8...

[ijor]

Artifacts aren't much related to limitations of the TV or monitor, but to the limitations of the NTSC (and PAL and SECAM as well) encoding. At least "horizontal" artifacts. As such, they will appear in any kind of device, even with a high definition TV, monitor or capture device, as long as the same encoding is used. Of course that an older (or cheaper) TV would produce additional distorsion to the image.

 

There are two main types of artifacts. One is the "luma" artifacts, produced by the encoding of luma and chroma on the same signal. When luma and chroma signals are separate, as in s-video, they don't exist.

 

Color TV's have at their baseline 160 pixels of color resolution.

 

That's not accurate, that might be the resolution of the TV, but not of the TV signal. Despite what most people believe, the chroma resolution is much smaller, even when using s-video. And that's the source of the second type of artifacts. Quick changes on the chroma (or hue, if you prefer) might produce artifacts, even when done at a color clock boundary. The reason is simple. The bandwidth of the chroma signal is not enough to encode a different value on each different color clock. You would need video-component to reach this resolution.

 

Note that there isn't such a thing as a "fixed" resolution. The "resolution" depends on which hues are being used, or more precisely, on the hue transitions.

 

The ironic thing is that the GTIA generates perfect luma and chroma signals. The circuitry behind it makes the signal worse.

 

Not exactly. GTIA/CTIA produces an already encoded chroma signal (it doesn't have say, RGB output). It is then still limited by the chroma bandwidth issue I mentioned above.

 

Btw, all these issues were well known by the engineers that designed NTSC. It was by design to sacrifice chroma resolution for luma one. Because according to experts, the human eye is much more sensible to luma changes than to chroma ones.

Edited December 7, 2008 by ijor

[potatohead]

True enough about the lack of accuracy in the above post. Have to walk before you can run, you know

 

I left out a lot of stuff. Done on purpose.

 

As for the phase bit, I've never quite grokked that. I prefer to handle the idea as sub-pixels. If you've got 16 of those, you have 16 phase shifts possible around the color wheel for 16 hues. I know it's more complex, but who cares?

 

That works. And I've done it with micro-controllers to build color timing that reproduces what I see on early computers, so again, who cares?

 

If you want to factor in saturation and such, then it's a more complex beastie!

 

The information I provided is a sufficient working understanding of what artifacting is, and some idea of how it works, to grok what people may or may not be seeing on their tubes.

 

Technical commentary welcome. Maybe I will learn a few more things myself, and that's always good.

[Goochman]

I dont believe Ultima I used artifacting unless there are 2 versions. It uses a chunky colored char mode.

 

I must be thinking of III then. I'm positive II had it. Played the crap out of that one.

 

Yes, II, III and IV had it.

 

I kinda had it - when you entered a town there was some for limited coloring I believe. But the outside view was not.

[Bryan]

As for the phase bit, I've never quite grokked that. I prefer to handle the idea as sub-pixels.

Think of it this way:

 

Over in the left border of every color line is the colorburst. It's a dozen or so cycles of a 3.579Mhz signal (NTSC). The TV will synchronize it's color oscillator to that signal. During the line, the content at that frequency will be separated by a filter and its phase will be compared to the phase of the TV oscillator which was set by the colorburst. The difference is represented in degrees and becomes the hue. The amplitude of the color signal represents the saturation, which is similar to the action of the color control. Low saturation means the colors are pale and closer to shades of gray, while high saturation means vibrant, pure colors. The strong 3.579MHz content in a saturated image is what causes dot-crawl, or the ability to see the color carrier on the screen as a moving pattern of dots. Modern game systems often exhibit this phenomenon when used with a composite connection.

 

Anyway, the Atari cannot vary the level of its color signal so brighter shades tend to look washed out.

[atariksi]

Well,

this was a theme in the "Atari vs. Commodore" thread, but I think we should have it in a separate topic...

So please post all your info about A8 artifacting here. I will start with a simple (incomplete!) list of A8 titles that use artifacting - maybe someone can help me to complete this list... ?!?

 

NTSC artefacting programs on the A8:

 

- AE by Broderbund ***

- Choplifter by Broderbund (cart and disk; the cart by Atari uses 4-color Gr. 15)

- David`s Midnight Magic by Broderbund (disk) ***

- David`s Midnight Magic by Atari (cart.)

- Drol by Broderbund (disk) ***

- Head over Heels by Hitsquad/US-Gold

- Lode Runner by Broderbund (disk)

- Lode Runner by Atari (cart.)

- Pinball Construction Set by ECA (and all pinballs created with it!) ***

- (most) Sierra online Hi-Res Adventures, like The Dark Crystal and ...

- Threshold by ???

- Ultima 1 ? by Origin (not sure if it uses artifacting, since I have never seen it)

- Ultima 2 ? by Origin (not sure if it uses artifacting, since I have never seen it)

- Ultima 3 by Origin

- Ultima 4 by Origin

 

*** there are also cracked + patched versions of these programs in 4-color gr. 15 mode available...

 

 

PAL artefacting programs on the A8:

 

- Artifacting Character Editor by Joel Goodwin (Page 6, issue 52, pages 18-21)

- Runaround by Joel Goodwin (Page 6, issue 53 ?)

 

greetings, Andreas Koch.

 

I also used artifacting in the multimedia Gita CDROM, but I never tried on PAL systems. I guess the white colors would still show up as white. How well does the Ultima or some of the other games look on PAL (what happens to the colors) or did they make a separate PAL version?

[Bryan]

I also used artifacting in the multimedia Gita CDROM, but I never tried on PAL systems. I guess the white colors would still show up as white. How well does the Ultima or some of the other games look on PAL (what happens to the colors) or did they make a separate PAL version?

It's pretty much black & white on PAL systems.

[Fröhn]

Anyway, the Atari cannot vary the level of its color signal so brighter shades tend to look washed out.

That's a result of amplitude not being saturation completely. The amplitude alone tells nothing about saturation because you have to know the luminance aswell -> lighter colors need more amplitude for the same saturation. A8/C64 etc use the same amplitude for all colors, so lighter colors are less saturated.

[Ross PK]

Thanks for answering guys.

 

So the artifacting still shows up on LCD HD TV's?

Edited December 8, 2008 by Ross PK

[potatohead]

Yes it does.

 

I hooked my 400 up to the new telly and it was all there. RF sucks though Gonna have to do a mod. BTW: The wider DMA does mostly fill the frame, like I thought it would too.

[Bryan]

Anyway, the Atari cannot vary the level of its color signal so brighter shades tend to look washed out.

That's a result of amplitude not being saturation completely. The amplitude alone tells nothing about saturation because you have to know the luminance aswell -> lighter colors need more amplitude for the same saturation. A8/C64 etc use the same amplitude for all colors, so lighter colors are less saturated.

I thought including that info would just be confusing.

 

Because of the fixed carrier level, dark shades are oversaturated which causes blooming. Example: If you pick a color with no luminance and any hue ($10-$F0) you get a color with fair amount of brightness even though all the LUM pins are off. The edges of the colored area are very poorly defined (slow fade in and out) because the strong carrier is actually causing the rise in lightness. The slower chroma response causes shadows to appear around the darker colors. This is result of there being one chroma amplitude just like the unsaturated bright colors are. Only mid-bright colors have the correct lum/chroma ratio.

 

The fix would be to level control the chroma using the luminance. A quad-CMOS switch would do the job, or since the chroma comes from a digital line, it could be mixed with luma using a quad AND gate and then a resistor ladder. The palette would be noticeably different after that, though.

Edited December 8, 2008 by Bryan

[www.atarimania.com]

Does anybody have Shoot'em Up by CS Software mentioned here? This is supposed to be the only commercial game using artifacting developed in a PAL country...

 

Please don't direct us to the program by Rino Marketing, this is another Shoot'em Up

 

--

Atari Frog

http://www.atarimania.com

[Thorsten Günther]

Thanks for answering guys.

 

So the artifacting still shows up on LCD HD TV's?

 

LCD TVs tend to create vertical scaling artifacts instead. At least my 1024x768 Toshiba 15" does, and believe me: the b/w default screen of an Atari ST

or games like Lode Runner on the XL look pretty ugly this way.

 

Thorsten

[potatohead]

True that.

 

Wish they would offer a 1:1 mode, or a simple 2:1 mode, where simple scaling happens. On my tube, I see not only scaling and vertical artifacts, but lots of stuff going on with the pixels themselves. Twiddling with the TV can reduce a lot of it, but clearly the CRT is the way to go

[Allas]

Thanks for answering guys.

 

So the artifacting still shows up on LCD HD TV's?

 

LCD TVs tend to create vertical scaling artifacts instead. At least my 1024x768 Toshiba 15" does, and believe me: the b/w default screen of an Atari ST

or games like Lode Runner on the XL look pretty ugly this way.

 

Thorsten

 

Using the composite connection, I see the screen as the same on CRT TVs. The unique difference, games with flickering method (Space Harrier, Gem Drop, fe) and TIP pictures, doesn't show the flickering in anyway. It seems LCD mix 2 frames.

[+remowilliams]

Twiddling with the TV can reduce a lot of it, but clearly the CRT is the way to go

Yes, sadly even the best new sets don't handle the old equipment well. One reason why I now have two of these as my new primary classic gaming displays.

 

I haven't found an LCD that doesn't look hideous in some way with s-video/composite from the old hardware. My plasma does seem to do a pretty good job though.

[potatohead]

I'm with you there.

 

My classic rig is a SONY WEGA. It's heavy, but it just rocks picture wise.

[Mclaneinc]

Sorry to rehash an old thread but it's better than just polluting with a new thread about the same subject.

 

Could anyone explain why emulation authors have to guess as to the look of an Gr8 artifacted screen on an NTSC, I've noticed that they use in Atari800win Plus at least 3 versions. Does the screen display vary from US TV to TV colour wise?

 

It would just be nice to get the correct colour scheme for all the emulators so it matches the box and what a peron playing the game saw in the 80's, surely there was a reasonable constant in the colours seen?

 

Anyone care to make a correct colour screen shot or colour table for the authors if it's possible?

Edited August 23, 2009 by Mclaneinc

[Rybags]

I think artifacting in emulation is a bit of a kludge. You'll also notice it seems to affect all pixels. I never use it, looks ugly, doesn't work properly, and PAL TVs don't do very "attractive" artifacting anyway so I find the entire concept to be more a hinderance than anything.

 

I guess it could be emulated more properly, but would no doubt slow things down somewhat. And so far as improving emulation accuracy of the machine, I'd put it kinda low on the priority list so far as things that aren't covered right now.

[ClausB]

It would just be nice to get the correct colour scheme for all the emulators so it matches the box and what a peron playing the game saw in the 80's, surely there was a reasonable constant in the colours seen?

According to various web sources, the real artifact colors depend on the type of Atari computer and whether it has a GTIA or CTIA, making it complicated to emulate.

 

IMO, Atari++ artifact emulation is disappointing. Haven't seen the others.

 

Perhaps the Atari emulator authors could take a lesson here from Apple ][ emulators. The Apple's hi-res colors are generated by artifacting, and their emulator screen shots on the web look good.

[Kr0tki]

I think artifacting in emulation is a bit of a kludge.

 

(...)

 

I guess it could be emulated more properly, but would no doubt slow things down somewhat. And so far as improving emulation accuracy of the machine, I'd put it kinda low on the priority list so far as things that aren't covered right now.

 

 

IMO, Atari++ artifact emulation is disappointing. Haven't seen the others.

 

Perhaps the Atari emulator authors could take a lesson here from Apple ][ emulators. The Apple's hi-res colors are generated by artifacting, and their emulator screen shots on the web look good.

 

Seems you haven't played with Atari800 and its "NTSC filter" effect, have you?

[bfollett]

I always thought the atari800win emulator would look better if they just included a simpler 2 color artifacting option. Instead it tries to show extra color combinations, that from my recollection weren't all that visible (if visible at all).

 

Bob

[Mclaneinc]

@Krotki

 

I maybe doing something wrong but I do not get the same colours you do with the same games, mine seem to select green as the dominant colour. I'm using the latest Windows SDL port from Soundforge, setting the display to NTSC, and setting the NTSC filter on?

 

Have I missed something, I tried both Drol and Choplifter in their original Gr.8 format ie not the Gr.15 hacks.

[Kr0tki]

Try repeatedly pressing Left Alt+9 or Left Alt+0.

 

As you know, artifact colours are different between different Atari models. Currently it is emulated by having a variable parameter called "burst phase", which can be changed using the above keys. I've actually cheated a little and set the "burst phase" differently for each screenshot.

 

Also, see DOC/USAGE, section "SDL keyboard, joystick and other controllers", for other key combinations.

Edited August 24, 2009 by Kr0tki

[a8isa1]

Well,

this was a theme in the "Atari vs. Commodore" thread, but I think we should have it in a separate topic...

So please post all your info about A8 artifacting here. I will start with a simple (incomplete!) list of A8 titles that use artifacting - maybe someone can help me to complete this list... ?!?

 

NTSC artefacting programs on the A8:

 

- AE by Broderbund ***

- Choplifter by Broderbund (cart and disk; the cart by Atari uses 4-color Gr. 15)

- David`s Midnight Magic by Broderbund (disk) ***

- David`s Midnight Magic by Atari (cart.)

- Drol by Broderbund (disk) ***

- Head over Heels by Hitsquad/US-Gold

- Lode Runner by Broderbund (disk)

- Lode Runner by Atari (cart.)

- Pinball Construction Set by ECA (and all pinballs created with it!) ***

- (most) Sierra online Hi-Res Adventures, like The Dark Crystal and ...

- Threshold by ???

- Ultima 1 ? by Origin (not sure if it uses artifacting, since I have never seen it)

- Ultima 2 ? by Origin (not sure if it uses artifacting, since I have never seen it)

- Ultima 3 by Origin

- Ultima 4 by Origin

 

*** there are also cracked + patched versions of these programs in 4-color gr. 15 mode available...

 

 

PAL artefacting programs on the A8:

 

- Artifacting Character Editor by Joel Goodwin (Page 6, issue 52, pages 18-21)

- Runaround by Joel Goodwin (Page 6, issue 53 ?)

 

greetings, Andreas Koch.

 

I had a list at one time but to your list I would add the following NTSC games

 

The Wizard and the Princess - Sierra

Diamond Mine - ???

Pensate - ???

 

Also, I've always wondered if the artificting in Crush, Crumble and Chomp was intentional or incidental.

 

- Steve Sheppard

Edited August 24, 2009 by a8isa1

[Goochman]

Ulysses and the Golden Fleece graphic/text adventure

 

Mission Pinball (the one with the Plane)

 

The Marc Benioff adventures

Edited August 24, 2009 by Goochman