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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 |
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NoiseEHC
Registered: Feb 2005
Posts: 51 |
Quoting Groepaz
Quote:
On my setup (new C64/1701 monitor) eg the odd/even lines difference is even more visible than in default VICE settings, eg in solid violet areas.
Today I finally got an analog TV (Panasonic TX-29S95Z) which has an S-Video port - that is why I choose this one, getting a Commodore monitor here is night impossible. I have created a Luma/Chroma cable, and the results with a C64C are below (unfiltered is when my cheapo phone camera focused on the TV pixels):
https://i.ibb.co/Thf4hqy/c64-filtered.jpg
https://i.ibb.co/dt7n7k2/c64-unfiltered.jpg
There is absolutely no difference between even/odd lines. How can it be? Does it happen only through composite connection? I do not think so, as your 1701 should be connected with a Luma/Chroma cable... |
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NoiseEHC
Registered: Feb 2005
Posts: 51 |
What is even more interesting is that if I connect with RF, then there is still no even/odd line difference, but there is a very visible dot crawl (https://en.wikipedia.org/wiki/Dot_crawl).
https://i.ibb.co/G2Vb8Gs/c64-rf-filtered.jpg
This dot crawl was one of the reasons that I did not use my big LCD TV. (The other is that it lost the sync of the C64 repeatedly, so I thought that the problem is with the C64 signal and LCD TV DSP compatibility.)
So now I think that the dot crawl might be simply that the DSP ICs in modern TVs interpret the wrong Chroma phase as a pixel shift every even line? Can it be? If so then how could I check this? |
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chatGPZ
Registered: Dec 2001
Posts: 11510 |
This TV seems to be quite modern and probably does more image processing than what a plain old PAL TV does... one interesting feature is that you can apparently independently select the color system (and it has both "old" and "new" NTSC) and the audio carrier frequency (this is usually tied to the color system in a certain region). My guess would be that it simply evens out the difference between two adjacent lines completely, perhaps by mixing 3 instead of 2 lines, or something like that. You could play with the "sharpness" parameter and see if that makes it visible in one of the extremes. There is also a "channel colour set" parameter which is not really explained in detail. |
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NoiseEHC
Registered: Feb 2005
Posts: 51 |
Can you please post a photo how your image looks like? (It can be uploaded to imgbb.com without creating an account there...)
The image is just inverse (Control+9 RVS ON) SPACE characters with the colors changes by Control+1..8 then Commodore+1..8
When I was young, we were poor so I never had a color monitor, coded on a mono one so unfortunately have no idea how it should look like. Two pictures with and without visible TV pixels would be the best. Thanks!!! |
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chatGPZ
Registered: Dec 2001
Posts: 11510 |
I'll do... but cant now, there is a bit of chaos around me and the setup is out of order right now :) Perhaps someone else can help out? :) |
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NoiseEHC
Registered: Feb 2005
Posts: 51 |
After paying a ridiculous amount of money to buy it, then driving 16 hours to fetch it, I am a proud owner of an original Commodore 1802 monitor.
Still no even/odd lines, LOL:
https://i.ibb.co/QcMQZBf/commodore-1802.jpg
I will borrow another C64 and will test with that, maybe I have a special unit, who knows? |
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