PAL blurring and artifacts

[phaeron]

You can probably get a bit better result by using dithering to achieve the desired phase rather than thresholding. This needs to operate on vector sums since phases don't add. Each luma pixel contributes to the chroma signal with a vector that is negated depending on whether the pixel is on or off, and then you can do dithering based on which pixel polarity reduces error in UV space.

 

Clamping is going to be a bigger issue as it introduces hue shifts that are hard to control. Vector math will tell you approximately where a group of pixels lands in UV space, but that hue isn't necessarily what you get because of clamping in RGB space: it isn't possible for the display to produce negative color. Artifacting tends to produce excessive chroma that causes clamping far more strongly than the standard color generation.

[R0ger]

You can probably get a bit better result by using dithering to achieve the desired phase rather than thresholding. This needs to operate on vector sums since phases don't add. Each luma pixel contributes to the chroma signal with a vector that is negated depending on whether the pixel is on or off, and then you can do dithering based on which pixel polarity reduces error in UV space.

 

Clamping is going to be a bigger issue as it introduces hue shifts that are hard to control. Vector math will tell you approximately where a group of pixels lands in UV space, but that hue isn't necessarily what you get because of clamping in RGB space: it isn't possible for the display to produce negative color. Artifacting tends to produce excessive chroma that causes clamping far more strongly than the standard color generation.

 

Hmmmm ! I'm actually quite deep in the image convertor. I went for Floyd-Steinberg dithering, which is centered around error correction. I can easily say in some places 'no, you can't put bright pixel here', or 'only this or this hue can be used here' and the FS dithering will handle it just fine.

At the moment I think in HSV, but YUV sounds as better idea indeed.

 

Damn you artifacts, I want to play Dark Souls Remastered, but how can I ?

[+Adam+]

So here is the "Artifact Character Editor" by Joel Goodwin (Page 6, issue 52)... it is on diskside A under the name Artifact.BAS...

 

Now, I also found a PCS pinball in Gr. 8 that displays colours on my PAL-only tv (and PAL A8). I can see there red, green, violet and brown. Violet is a mix of red+blue, but brown (is it a mix of red+green) ?!?

(...)

PCS pinball ("Das U-Boot") looks like it was prepared purposely for NTSC artifacting and PAL artifacts effects seem accidental.

 

"Artifact Character Editor" shows many patterns one can use for PAL artifacting:

[+CharlieChaplin]

 

PCS pinball ("Das U-Boot") looks like it was prepared purposely for NTSC artifacting and PAL artifacts effects seem accidental.

 

"Artifact Character Editor" shows many patterns one can use for PAL artifacting:

 

Errm yes, Artifact Char. Editor was published in Page 6 magazine in GB/UK - a PAL country. And the article (+ program) was specifically made for PAL artifacting, as well as his follow-up program Runaround II...

 

Regarding the PCS pinball "Das U-Boot", I also guess it was made for NTSC but the few artifact colours look really good on PAL, in my opinion.

 

Now someone make 100 more A8 games that use PAL artifacting and only b/w on NTSC (and if NTSC users want colour, they do have to convert into Gr. 15). Because thats what we PAL Atarians have to do with all those games using NTSC artifacting...

[R0ger]

I'm still far from the image convertor. I keep experimenting with the stuff, some things still don't feel intuitive enough. Anyway, I was trying to make as many distinct hues as possible. 6 are everywhere, 8 are in my last demo, now I managed to do 16. The extra hues are made on the even lines. I can either use correctly reflected V coordinate, or I can also shift one step. That way even and odd line create 1 step different color, and they are mixed by PAL. I can't make more colors like this though, because if you differ the vectors too much on odd lines, you will simply loose saturation and go to white.

Artifact3.xex

Edited May 27, 2018 by R0ger

[R0ger]

Huh .. just got an idea right before going to bed .. and I had to test it .. what if we don't use white, but some actual color ? Would the hue shift be strong enough to be seen ? To create some completely new hues ?

Well here is the answer, just on the red ($20/$2f). Other colors looks nice too, but on red the change is the strongest IMHO. Nobody can laugh at ATARI reds anymore !

Artifact4.xex

Edited May 27, 2018 by R0ger

[R0ger]

So I have image converter working. But it's all very clunky. You have to fine tune it to the picture a lot. If the image is too bright or too dark, it wont result in about 50% pattern which you need for color encoding. Then you have to balance focus on detail and focus on color. You can't have both. And you have poor resolution in hue anyway.

Photos in general are pretty bad. What works lot better is anime. Like Pokemon. Big shapes, bright colors, but only few of them in the image. Like this:

 

 

And source image:

 

Here is the XEX, please note that it does not have any phase calibration, so the colors might be completely off on you computer. There should be some colors though.

Pikachu.xex

Edited May 27, 2018 by R0ger

[antrykot]

I've got four different color arrangements from the same computer and the same tv set. Just different runs of Artifact.xex.

 

Edited May 28, 2018 by antrykot

[R0ger]

I've got four different color arrangements from the same computer and the same tv set. Just different runs of Artifact.xex.

 

 

Very nice ! Thanks for testing !

[R0ger]

Finally got to test on real HW .. and indeed I can also get different setups every reboot. I get one setup in like 80%, but not always.

Also I'm starting to noticing more differences between real HW and Altirra. It's nothing which would allow this technique to be any better though. Will report later.

[R0ger]

Here is the case of difference between Altirra and real hardware. Here there is the most simple pattern. 1 pixel per each byte. On left half of the screen only even rows are used, on right half only odd rows are used. The pattern is changing set pixel location from top to bottom.

 

You can see how every pixel position corresponds to different hue phase, and how the even and odd fields (left and right half) have mirrored hue phase.

 

Now here's the catch. On real hardware every pixel position creates false color, and to about same extent. Which is as expected.

Altirra shows correct hues, but only on pixel horizontal offset 0,2,4,6. On offset 1,3,5,7 there is simply no color, pure white. IMHO it's no principal issue of how Altirra does it, most likely it's just simplification, or even speed optimization. In my experience it has pretty low effect on more complex images. But still .. maybe it's really simple fix ? Pretty please, dearest Phaeron

 

 

Real hardware (XE, CRT TV)

 

Altirra:

Edited May 28, 2018 by R0ger

[R0ger]

Oh I forgot to include the XEX ..

Artifact-1pixel.xex

[Mclaneinc]

Hi Roger,

 

Sure its not in the preset palette you are using for the Pal settings inside Altirra? (View / Adjust colours)

 

Or an adjusted Palette?

 

And hopefully on one of the latest beta's too...So many changes in the beta's over a few months let alone full releases..

 

If none of these then nicely done sir....Something for Avery to look at

 

Paul..

[R0ger]

Hi Roger,

 

Sure its not in the preset palette you are using for the Pal settings inside Altirra? (View / Adjust colours)

 

Or an adjusted Palette?

 

And hopefully on one of the latest beta's too...So many changes in the beta's over a few months let alone full releases..

 

If none of these then nicely done sir....Something for Avery to look at

 

Paul..

 

I came to the same conclusion over night. That the white pixels might have exactly opposite phase on up edge and down edge, and they cancel out. Which would be perfectly correct, just unlikely on real hardware.

Color adjustment in Altirra even has artifact phase and saturation, which should be the solution. But it does nothing. No artifact slider changes anything for me.

[Mclaneinc]

Yup, same here...

 

Overall saturation makes a difference but obviously wrongly impacts standard visuals..