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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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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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Oswald
Registered: Apr 2002
Posts: 5086 |
scanlines are too strong imho |
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chatGPZ
Registered: Dec 2001
Posts: 11350 |
delay line only for U is interesting. i think 1701 does the same....
perhaps that finally explains why so many ppl complain about scanlines being too strong - they are used to displays that have delay line for U and V? |
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ChristopherJam
Registered: Aug 2004
Posts: 1408 |
Quote: 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.
Not only is the rise slower than the fall (even without using the RF modulator), but luma changes overshoot then continue to oscillate for around four pixels. More later this week; Pepto's most excellent posts here have reminded me I've a post of my own I've been meaning to write for a while now.
And yes, sadly the chroma phase is random every power cycle :( |
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