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pepto
Account closed
Registered: Nov 2004
Posts: 35 |
colodore is the new pepto
Hey guys, I remeasured the video-signals of my VIC-II's and slightly updated my 15 year old attempt at calculating an rgb-clone. While at it, I also measured VIC & TED and made a little website about it, that allows you to adjust brightness, contrast and saturation as you like and then save your own custom palette to a png-file.
http://www.colodore.com
I took extra care to make sure, that the brightness, contrast and saturation sliders behave the same way as my 1084s.
While closely comparing my LCD to the 1084s, I found that making the transparency of scanlines dependent on YUV's Y (so they are less visible for brighter colors) looked a lot more like the real thing. I also noticed that the phase-shift on odd-lines happens for YUV's V only and there's even a name for it in video-lingua: hanover bars.
After implementing this, I'm happy to say that the images on my LCD and 1084s are remarkably close.
I will write a more detailed article about it in January, but seriously need a christmas-break first...
Cheers,
pepto |
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Kabuto
Account closed
Registered: Sep 2004
Posts: 58 |
Great work!
There is another effect that was mentioned in an old demo, I think it was made by Crest when they introduced NUFLI or something similar:
The video chip is slower at changing the voltage level from black to white than the other way round. This means that a sequence of for example black and white pixels appears darker than one would expect (even when considering gamma level effects on a slightly blurred output). This effect also is less prominent on later video chips, probably because their internal transistors work faster.
I didn't find this being mentioned in this thread before, so I just thought I'd mention it.
Also, is the phase of the chroma carrier fixed? If I remember correctly it's chosen randomly on every power cycle. But I totally understand that this one would be a bit nasty to emulate, but I still wonder how much this affects the appearance of pictures. |
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chatGPZ
Registered: Dec 2001
Posts: 11350 |
the so called black bleeding is NOT caused by the VIC as suggested in that crest demo - it completely disappears when removing the modulator, so its basically the result of the shitty video circuit. |
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pepto
Account closed
Registered: Nov 2004
Posts: 35 |
Quoting peptoYou are correct, a delay-line would be the weapon of choice to suppress hanover bars, but they are a clearly visible artefact, along with delay-line style vertically blended chroma.
Oh snap, the 1084s seems to have a delay-line for YUV's U only. This explains a lot of things, especially why the phase-offset for YUV's V still is perfectly visible on screen after passing the delay-line and why more modern TVs manage to hide the hanover bars so much better, as they delay-line both YUV's U & V...
Quoting peptoI have a first idea on how to get "play with colors" to blend right. I have a feeling it's something simple. I will try to find some time this weekend to investigate.
The solution is simple indeed. I have an internal version of colodore.com now, that renders every single field of "play with colors 2" precisely like the real VIC II and solid single-colored fields still look identical to the original version... \o/
I will try to find time tomorrow to tidy up my code, update the website and tell you how it appears to work tomorrow. |
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pepto
Account closed
Registered: Nov 2004
Posts: 35 |
Considering how important it is, that a color ends up on an even or odd line, for this effect to work: Is the first line of the 200 line high main-field (without borders) considered an even or odd line, if you start counting at 1? |
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chatGPZ
Registered: Dec 2001
Posts: 11350 |
you can scroll it.... so... :) i think you should start counting from the actual first scanline |
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pepto
Account closed
Registered: Nov 2004
Posts: 35 |
Quoting Groepazyou can scroll it.... so... :) i think you should start counting from the actual first scanline
Yeah well... unscrolled, freshly booted C64... Vice shows 35 pixels of upper-border for me. But as far as I understand, the first line in Vice isn't the first scanline, right? Isn't Vice's view masked to a sane value to hide overscan? |
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chatGPZ
Registered: Dec 2001
Posts: 11350 |
to bei honest.... not sure how exactly VICE determines that... alankila write those renderers, i just improved some bits here and there.
but isnt it just a matter of trying both options and check against a real monitor which one is correct? :) |
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pepto
Account closed
Registered: Nov 2004
Posts: 35 |
Quoting Groepazbut isnt it just a matter of trying both options and check against a real monitor which one is correct? :)
Yes, it's easy to check with a test-image like "play with colors 2", there are just two ways to do it... I just wanted to use correct terminology for variables, that's all... :) |
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chatGPZ
Registered: Dec 2001
Posts: 11350 |
as said, count from the first actual scanline, then its obvious what is odd and what is even :) |
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pepto
Account closed
Registered: Nov 2004
Posts: 35 |
I updated http://www.colodore.com
Changes:
- do hanover-bars before delay-line
- added option to delay-line YUV's U only -- 1084s style (default for now)
- added Ed's "Play With Colors 2" at bottom of image-list
None of the changes affect the palettes.
In order for hanover-bars to work correct, there's a phase-shift (hue-rotation) needed for both U & V of 22.5 degrees on even lines, and -22.5 degrees on odd lines, before going into the delay-line.
To check if you have the even/odd stuff in the right order, make sure that the two fields in "Play With Colors 2", look like this (greyish on left, greenish on right)...
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