Variation in screen color for 8-bit Star Raiders

[Bryan]

High saturation gives you 'pure' colors (bright, solid red or green for example). Atari systems have a problem with low saturation when higher luminance values are used. This means as you crank the lum, the colors get more pale. The reason is simple: When TV's decode the color signal, the amplitude of the chroma color carrier should be proportional to the amplitude of the luminance. The Atari only has one chroma level, so darker colors are very saturated and lighter colors are unsaturated and pale. The darkest shade of each color (lum=0) is actually just the TV reacting to the chroma signal, as there is no luma. No real video equipment would ever produce funky signals like this.

 

The solution would be to use the luminance signal to control the gain of the chroma signal. Then you could get a nice bright red.

[Faicuai]

High saturation gives you 'pure' colors (bright, solid red or green for example). Atari systems have a problem with low saturation when higher luminance values are used. This means as you crank the lum, the colors get more pale. The reason is simple: When TV's decode the color signal, the amplitude of the chroma color carrier should be proportional to the amplitude of the luminance. The Atari only has one chroma level, so darker colors are very saturated and lighter colors are unsaturated and pale. The darkest shade of each color (lum=0) is actually just the TV reacting to the chroma signal, as there is no luma. No real video equipment would ever produce funky signals like this.

 

The solution would be to use the luminance signal to control the gain of the chroma signal. Then you could get a nice bright red.

 

Well, two key posts to sum two key issues: innate Atari's color reproduction under certain tonality range, and actual tonality range boundaries of analog signal itself (e.g. "blacker-than-black" o "whiter-than-white"). I have not yet seen the latter, but I I have witnessed the first case, clearly (when restoring and upgrading my 800XL and comparing to my JayMiner-800 native output, via composite and then s-Video).

 

Anyhow, attached are samples of what I am pulling out of the 800XL via minimalistic s-video upgrade (but ultra-high quality video cable).

 

F.

A800XL-sVideo-FRAME-256Colors.bmp

A800XL-sVideo-FRAME-Nautilus-1.bmp

[SeaGtGruff]

attached are samples of what I am pulling out of the 800XL via minimalistic s-video upgrade (but ultra-high quality video cable).

Thank you! I like to collect any 256-color screenshots that people post, as examples to compare and analyze.

 

Michael

[Faicuai]

attached are samples of what I am pulling out of the 800XL via minimalistic s-video upgrade (but ultra-high quality video cable).

Thank you! I like to collect any 256-color screenshots that people post, as examples to compare and analyze.

 

Michael

 

No probs.

 

Here are a couple more. One is a full gray-scale, prior to generating 256-color chart. This is good for checking/adjusting black and/or white levels. The second is the actual output of the SuperSalt diagnostic cart, running on the 800XL, after color-trimmer was checked/adjusted (last two bars need to be as close as possible for "ideal" color response).

 

Enjoy,

 

F.

A800XL-sVideo-FRAME-GrayScale.bmp

A800XL-sVideo-FRAME-SuperSalt.bmp

[Kr0tki]

Thanks, Faicuai. Could you also make a few screen captures while the colour pot in your 800XL is being de-adjusted a bit? I'd like to see the behaviour you described earlier, with my own eyes

[Faicuai]

Thanks, Faicuai. Could you also make a few screen captures while the colour pot in your 800XL is being de-adjusted a bit? I'd like to see the behaviour you described earlier, with my own eyes

 

You are welcome.

 

My comments:

 

 

1. The pot-adjustment is way elastic and hard to tune-in exactly. In other words, small movements make SIGNIFICANT changes on the screen. I spent quite a good deal of time adjusting it so you would see the above results (virtually IDENTICAL bottom-bars), and just the thought of messing with it, again, simply to show you how the hole bar-set gets screwed towards green or red, already feels painful.

 

2. External-adjustment to the pot turned to be problematic (in my case). I had to open the unit and adjust from the top left-side, instead (not from the back). I really prefer not to open the machine (if that is Ok. with you).

 

3. Instead, I will suggest you two (2) possible aternatives, so you can experience this on your own, and come back here marvelled with your (and same) results (this is exactly what I did, BTW):

 

a. First and foremost, find some good cash (a small pile of it).

b. Go to Best-Electronics and purcase your own copy of SuperSalt Service cart.

c. Get yourself a NTSC 800XL, as well as a NTSC-capable TV displaty (either CRT or LCD, it will not matter) set.

d. Get yourself an AtariMax Flasher + 8Mb cart. Dump the SuperSalt cart into your PC.

e. At this point you have two (2) options:

i. Plug your brand-new SuperSalt cart in 800L, light-it-up, turn the pot (from the back or inside), and watch the effect.

ii. AND/OR simply boot Altirra with the SuperSalt cart, go to Video, set to NTSC, and change HUE START to any other value.

iii. What you will see should pretty much reproduce what happens in my 800XL and my JayMiner-800.

 

When turning the pot, the ENTIRE scale from the second-bar up-top (after the thin gray bar), to the last color-bar (right BEFOER hitting the bottom-gray thin bar) gets screwed up, either to the RED or to the GREEN side. The very-bottom color bar DOES NOT change with the POT, which is nice, as it seems the only real, visible reference left by Atari folks that I have been able to find, in other to adjust the machines colors to "given" criteria.

 

Enjoy,

 

F.

(P.S.: I am attaching, however, a high-quality video capture of StarRaiders Shields-On display, so anyone wondering can see how it should really look, with NTSC 800XL via s-Video and after proper color calibration).

A800XL-sVideo-FRAME-SRaiders-2.bmp

[Faicuai]

Thanks, Faicuai. Could you also make a few screen captures while the colour pot in your 800XL is being de-adjusted a bit? I'd like to see the behaviour you described earlier, with my own eyes

 

UPDATE:

 

Loaded (again) my SuperSalt dump on Altirra v2.0_T3, and went straight to the Tests Menu, and chose Color Bars. Once there, I opened the Video/Color adjustment panel in Altirra, and proceeded to adjust HUE-Start and HUE-Step. It turns out that Hue-Start changes everything from the top second-bar (right below the first, thin gray bar) all the way to the last colored-bar, INCLUDING the reference bar (!)... While HUE-Step, on the other hand, does change everything from the second-bar to the last color bar EXCEPT the reference one (which is what it should and what exactly happens when you mess with the HW color-trimmer/pot).

 

So it turns out that (as you suggested) that the HW control is mimicking the HUE-Step, not just because of what is being altered, but HOW it is altered: I remember that, when performing extreme adjustments on the HW pot, eventually I got a solid wash of green or red accross most of the screen, which is what also happens when you play with HUE-Step in Altirra.

 

So it seems that your association of the HW-trimmer with HUE-Step is CORRECT. Now, the actual behavior on real HW remains exactly as I described it, though (it is what it is: it either goes to red-side or green-side, from the second top bar, all the way to the last color bar on top of the bottom thin gray-bar).

 

Regards,

 

F.

Edited May 27, 2011 by Faicuai

[Kr0tki]

1. The pot-adjustment is way elastic and hard to tune-in exactly. In other words, small movements make SIGNIFICANT changes on the screen.

That's indication of a worn-out potentiometer. I understand why you'd not want to tinker with it further.

 

3. Instead, I will suggest you two (2) possible aternatives, so you can experience this on your own, and come back here marvelled with your (and same) results (this is exactly what I did, BTW): (...)

Wow, what a disturbingly polite way of saying "f* off". Was that all necessary? Was it not enough to answer "No, too much burden"? Was my question somehow impolite to you or what?

 

Seriously, I was asking for your help only in order to further verify your account, since it contradicted with what was already known about the GTIA. But, since now your account has been expanded with a new, crucial bit of information, I can say with confidence that in reality, no contradiction exists, and you were in fact wrong.

 

You say:

The very-bottom color bar DOES NOT change with the POT,

and that confirms the established knowledge about hue 1 always being equal to the colorburst (the bottommost colour bar is hue 1). Since that bar does not change with the pot, it is wrong to claim that "This trimmer seems to be the equivalent of Altirra's HUE-START parameter". The reason is, Altirra's Hue Start also affects the bottommost colour bar, together with all other colours. The setting in Altirra that matches the pot's behaviour and changes all colours apart of the bottommost, is "Hue Step", as I claimed earlier.

 

Thanks for your cooperation, I'm glad that we've sorted the initial confusion out (I hope). I'm also asking for less attitude-driven comments the next time.

 

EDIT: Ah well, didn't notice your last post since I started writing. I guess all of the above isn't necessary anymore.

 

EDIT 2: BTW. Faicuai, does your CPS SuperSalt dump happen to be an original? The only dump available on the net has a hacked title screen (says (E) 1900 IRATA,INC. instead of ATARI).

Edited May 27, 2011 by Kr0tki

[Faicuai]

 

Thanks for your cooperation, I'm glad that we've sorted the initial confusion out (I hope). I'm also asking for less attitude-driven comments the next time.

 

EDIT: Ah well, didn't notice your last post since I started writing. I guess all of the above isn't necessary anymore.

 

EDIT 2: BTW. Faicuai, does your CPS SuperSalt dump happen to be an original? The only dump available on the net has a hacked title screen (says (E) 1900 IRATA,INC. instead of ATARI).

 

 

No probs, Kr0tki. For good or bad, attitude is plentiful and abundant, on this side. I did try to help to the best of my abilities, though...

 

Attached is a screen-shot (digital-to-digital, from Altirra), of what shows up two or three seconds after you fire-up the cart. I actually bought this cart from Best Electronics, because I believe that having some basic/formal diagnostics tools (aligned or mentioned in Service Manuals) will help on the long run. I am still missing the actual fixture to complete advanced testing (also supported in the SuperSalt Cart).

 

Let me know if you have any other questions on this matter. I will try to answer/illustrate them to the best of my resources.

 

Regards,

 

F.

[Keatah]

(P.S.: I am attaching, however, a high-quality video capture of StarRaiders Shields-On display, so anyone wondering can see how it should really look, with NTSC 800XL via s-Video and after proper color calibration).

 

As best as I can tell, those colors are spot-on! Can you show us a picture of the Galactic Chart using that correctly tuned machine?

Edited May 27, 2011 by Keatah

[Kr0tki]

No probs, Kr0tki. For good or bad, attitude is plentiful and abundant, on this side. I did try to help to the best of my abilities, though...

Actually you did help. We now have a solid confirmation that hue 1 is constant.

 

Attached is a screen-shot (digital-to-digital, from Altirra), of what shows up two or three seconds after you fire-up the cart.

Thank you. Yup, that's the one that is not hacked. The unhacked SuperSalt is not available on the Web. Would you consider publishing your dump? (You paid for it, anyway.)

[SeaGtGruff]

Thank you. Yup, that's the one that is not hacked. The unhacked SuperSalt is not available on the Web. Would you consider publishing your dump? (You paid for it, anyway.)

I know *I* would like to have a dump of it! How much does it cost to buy the actual cartridge? Regarding the hacked dump, couldn't someone hack it again to change it back to the correct title screen? On the other hand, do we know if they hacked anything else besides the title screen? It *would* be nice to have a pristine dump.

 

Michael

[Keatah]

Playing Star Raiders for the 8-bit computers, is it normal for the viewer screen with shields on to be pea-soup green on the Atari 800 and blue on the Atari 800XL?

The author addresses this question on his blog, with pictures:

 

http://dougneubauer.com/starraiders/

 

I originally wanted the color of the shields to be a dark blue/greenish color (Like the picture on the Left), but depending on the color settings of your television, the shields will appear as green (Right).

 

- KS

 

That website, after some slid research, is totally all wrong.

[Faicuai]

(P.S.: I am attaching, however, a high-quality video capture of StarRaiders Shields-On display, so anyone wondering can see how it should really look, with NTSC 800XL via s-Video and after proper color calibration).

 

As best as I can tell, those colors are spot-on! Can you show us a picture of the Galactic Chart using that correctly tuned machine?

 

Sure, attached is the Galactic Map high-quality Analog-to-Digital conversion, direct from my Atari 800XL via s-Video.

 

A few words for those tuning Altirra, for maximum color fidelity in NTSC:

 

1. You NEED to consider your display's native response (whether CRT or LCD, it does have its bias). In my case, here is MY data:

-Main screen is Sony Bravia KDL-52W3000 LCD (WIDER gamut than NTSC!)

-Input port is HDMI, and video signal comes from Dell Studio 1440z + NVidia 9300/9400 chipset.

-Black-level is 0.15 cd/m2, approx.

-White-level is 120-125 cd/m2, approx.

-White-Point is calibrated set to illuminant D75 (close to 7500K, which gives best neutrality in Grays, better than D65).

-Calibration performed with Monaco Optix DTP94 colorimeter, in separate computer.

-Gamma left to Sony's default (and lowest) setting, as it seems already.

-Color Saturation and "hue" fine-tuned for SMPTE NTSC 75% chart (directly in RGB mode). You NEED a BLUE filter, as a minimum.

-White-point and Illuminant re-checked after SMPTE adjustment.

 

Once you consider the above, I then capture MULTIPLE samples of JayMiner-800 and 800XL output, of not only a 256-color chart key, but many key games/intros (where there are challenging color renditions, such as Zaxxon's playfield, StarRaiders environment, Frogger I and II, Stealth, Fractalus, Blue Max I&II, River Raid, DigDug and Joust, which test about about all key primaries, many gradients and hues, as well as different degrees of CHROMA RESOLUTION/finer-detail). Here is the summary of my resulting settings:

 

=> Palette: My 800-series (via s-video, SuperSalt adjusted)

=> Hue Start: (-57 for 800XL; -51 for "JayMiner" Atari800)

=> HUe Step: (25.1 for 800XL; 25.5 for Atari800)

=> Brightness: -1%

=> Contrast: 83%-85%

=> Saturation: (19%-21% for 800XL; 22%-23% for Atari800)

=> Art. Phase: 180 (Artifacts BLUE and RED, as seen with RF modulator)

=> Art. Sat.: 100% (and when C56 was still present on 800XL board)

=> Art. Bright: -15%

 

There WILL NOT be an absolute single-value recipe (it will be a range), because YOUR DISPLAY's own settings (and calibration or LACK of it) will completely bias your initial rendering. As an example, if your LCD offers a native WIDE gamut, you will notice that LESS saturation will be needed. Conversely, if your LCD's chroma response is more limited, you need a bit higher saturation. You will adjust SATURATION (above) to your taste (real colors are not TOO pale nor TOO rich). Contrast (above) is adjusted as high as your display can show COMPLETE TONAL/CHROMA separation on the 256-color chart, on the brightest areas.

 

It is very important to understand first how ACCURATE your CRT/LCD is overall, and, for this reason, I DO NOT recomment using CRTs (as unorthodox as it sounds) with Altirra, or emulation of old equipment in general. The reason for this lies on the fact that it is MUCH easier to adjust/calibrate a modern, high-quality LCD set (like Sony's Bravias, or even computer LCDs lie ViewSonic's) than an older, typical CRT/TV sets. In the LCD you can adjust almost ANYTHING, except brightness-uniformity on-surface and possibly Gamma (for which I would need my EIZO CG241W wide-gamut, which I am really using for more demanding work... :-)

 

In the near future, I am sure Altirra will incorporate texture-overlay via Direct3D (as done in MameUI-64), and when that happens, it will emulate ANY MONITOR's micro-cell structure, look and scanline spacing, to the T, right at the convenience of your calibrated LCD.

 

Enjoy,

 

F.

A800XL-sVideo-FRAME-SRaiders-3.bmp

A800XL-sVideo-FRAME-CartMenu.bmp

Edited May 28, 2011 by Faicuai

[Keatah]

And yes, again, those are correct Star Raiders colors as best as I can tell, based on historic photos and vcr recordings, promotional materials, real hardware of course, and what I remember. But best of all, those screenshots feel correct right from the start!

 

http://atari800.sourceforge.net/ -- seems to be an emulator that gets the colors almost right, right out of the box.