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2023-03-01 11:11

NoiseEHC

Registered: Feb 2005
Posts: 51

dithering question

Hi!

I have been just looking at recently released MULTI graphics, and what I noticed is that the majority of images use horizontal line dithering. For example:
Always Look at the Bright Side of Life

While in the past most images used checkerboard dithering, for example Hein's graphics in Dutch Breeze. But current example:
Birdman

(Note both images contain both type of dithering, just one is much more dominant.)

And very few use diffuse (random) dithering for some reason.

So what is the reason of this difference? Is it only the preference of the artist, or is there an advantage of horizontal line dithering on a TV? I do not have a real C64 anymore, so I cannot check it unfortunately.

Another question: why are there so few diffuse dithering out there? Is this because this is much harder to do, or is there some visible disadvantage?

Thanks

... 21 posts hidden. Click here to view all posts....

2023-03-02 14:11

chatGPZ

Registered: Dec 2001
Posts: 11114

Color bleeding happens horizontally, while the PAL mixing happens vertically.

And yes, VICE (and every other emu) should emulate it - however, this is something to be implemented in shaders, its way too costly to do in software (if you want to do it correctly)

2023-03-02 15:28

Deev

Registered: Feb 2002
Posts: 206

Quote:

So what is the reason of this difference? Is it only the preference of the artist, or is there an advantage of horizontal line dithering on a TV? I do not have a real C64 anymore, so I cannot check it unfortunately.

Another question: why are there so few diffuse dithering out there? Is this because this is much harder to do, or is there some visible disadvantage?

I think horizontal versus checkerboard is mostly just a style preference. Obviously there are ways to blend colours using horizontal lines and I guess people are aware of those while pixelling, but I don't think that influences most of the choices on the examples you gave.

Personally I prefer checkerboard in most cases, I just think it looks better with my style. Some people's style might work better using lines.

As for diffuse dithering, I just think it looks kind of ugly. I prefer a neater, cleaner, more deliberate look. It's all about style preferences though.

Quote:

One thing worth mentioning is that checkerboard dithering in hires is a definite no-no*. It's very close to the colour carrier in both NTSC and PAL (a touch higher than NTSC, a touch lower than PAL). Either way, if you view it using a composite video or RF cable you get spurious colour banding.

* it's fine in multicolour

Again I'm very much aware this happens, but I don't think it makes it a no-no. Not supporting people using RF is no different than not supporting people loading from cassette.

And the reality is that most people judge an image based the screenshot anyway...

2023-03-02 16:36

ChristopherJam

Registered: Aug 2004
Posts: 1378

Quoting Deev

Not supporting people using RF is no different than not supporting people loading from cassette.

I mean, it's more like "only supporting people using s-video or buggy emulators" (admittedly at the moment the latter is most of them)

Quote:

And the reality is that most people judge an image based the screenshot anyway...

True - but again that does mean you're relying on shortcomings in the tools that make the screenshots. Golden Cow waiting to happen :)

NoiseEHC, Oswald - cheers for your interest in my video signal measurements article. As Groepaz pointed out, it'll probably take 'someone' writing a shader for emulating that properly to be performant. IIRC a few emulators do already emulate black-bleed to some extent at least.

2023-03-02 16:54

Deev

Registered: Feb 2002
Posts: 206

Quote:

I mean, it's more like "only supporting people using s-video or buggy emulators" (admittedly at the moment the latter is most of them)

Targetting a real C64 outputting s-video seems perfectly reasonable to me. Composite looks bad in lots of ways. Yes, some people might not have access to a better option (neither of the CRTs I own support s-video either), but again some people have nothing more to load from than a datasette.

And as for emulators, shouldn't these also recreate output through s-video?

2023-03-02 17:46

ChristopherJam

Registered: Aug 2004
Posts: 1378

Ok, fair points. Perhaps in the future it will just be like songs specifying which SID chip is preferred :)

After all, I prefer 8580 to 6581, 9-luma VIC to 5-luma VIC, and C64C (the original designers intent!) to C64, so in many ways I'm far from a traditionalist myself.

And at least s-video still exhibits black bleed* ;)

/me buys Deev a pint

* lighter pixels are a smidge narrower than darker pixels, as the luma rise time is longer than the fall!

2023-03-02 18:20

Hein

Registered: Apr 2004
Posts: 933

Quoting NoiseEHC

The reason I ask these questions because I am working on an editor which is a plugin for GIMP. The plan is to draw pictures using my pen tablet, which are converted into 16 color dithered images in real-time. Controlling colors/sprites will be done using some extra layers in the source image. Obviously it will work only if the dithering is good in the first place.

I haven't experimented alot with different patterns, but I think it'd be nice if you'd let the user select the pattern to use while painting. I suppose the choice depends on what kind of effect or material needs to be created.

2023-03-02 18:59

chatGPZ

Registered: Dec 2001
Posts: 11114

Quote:

And at least s-video still exhibits black bleed

Until you replace the Modulator by one of the replacement circuits - then it is gone :)

2023-03-02 22:09

Deev

Registered: Feb 2002
Posts: 206

Quote:

Ok, fair points. Perhaps in the future it will just be like songs specifying which SID chip is preferred :)

I'm certainly in favour of exploiting these things for effect if possible. I'm not sure it's possible to do anything too interesting in composite, but I'd love to see someone prove me wrong! Seeing what people do with the 5 luma VIC is always interesting as well.

2023-03-03 03:26

NoiseEHC

Registered: Feb 2005
Posts: 51

Quoting Hein

I haven't experimented alot with different patterns, but I think it'd be nice if you'd let the user select the pattern to use while painting. I suppose the choice depends on what kind of effect or material needs to be created.

Yeah, that is the plan to have different dithering settings, most likely per layer, or per character. But for that it would be awesome if more graphicians would give their two cents about THEIR completely subjective opinion about how they like to dither, the way Deev already did. Because I am not an artist, I am a coder. I know only how to write code...

On the other hand, there are two objective differences I can see between checkerboard and horizontal line dithering:
1. Checkerboards have half the pixels on the second lines, where vertical PAL color mixing change their color, effectively creating 4 different colors from a 2 color checkerboard pattern. It does not happen with horizontal lines, they only have 2 colors.
2. Checkerboards have the horizontal color bleeding everywhere, which does not happen with horizontal lines, which are obviously homogenous horizontally.

Quoting Groepaz

Color bleeding happens horizontally, while the PAL mixing happens vertically. And yes, VICE (and every other emu) should emulate it - however, this is something to be implemented in shaders, its way too costly to do in software (if you want to do it correctly)

As far as I see, VICE (GtkVICE 3.6.1) already emulates something like that, it would be good to know from a VICE developer if that is the same thing we are talking about here:
https://i.ibb.co/pbrbzhk/pal-color-mix-4x.png
(I marked the color pairs with identical luma with rectangles.)

On the left side it is a screen capture with "CRT emulation" enabled, where "Double size" is not checked, magnified 4x so it is easier to pick colors in a photo editor. On the right "Double size" is checked, so it was magnified only 2x, and you can see VICE emulates the darker void between pixels, but the colors of the middle of the pixels seems to be the same both cases.

What I see interesting is that while the color of first lines seem to remain constant horizontally, it actually varies it just a little bit depending on the color pair. The color of the second lines varies a lot more obviously, because of the vertical color mixing. It would be good to know if the default "Pepto (PAL)" palette of VICE is actually representative of a real C64, because in the past the colors of emulation seemed much-much more brilliant than the real thing...

For the horizontal bleeding, there are a lot of transitional pixels, and it seems that the transition is 2 (or rarely 3) pixel wide, which seems to match the measured Luma change speed in the above shared webpage.

If somebody could run the test program on a real c64 and make a good quality photo of the monitor itself, that would be awesome. (I guess a frame grabber might not generate an image like a TV, but who knows?)
https://drive.google.com/file/d/17ZkQf4xm0rRyNWLNbAO1z4fr6gM67m..

2023-03-03 07:15

Hein

Registered: Apr 2004
Posts: 933

Quoting NoiseEHC

Yeah, that is the plan to have different dithering settings, most likely per layer, or per character.

How about selecting dithering (texture, hardness, opacity etc.) same as selecting a brush? Maybe also detect mouse direction and speed and change the dithering pattern based on that. This would feel more natural to me.

Then again, I'll leave the dithering to the pros, hope the other graphicians want to share their preference.

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