| Posted By
Degauss
on 2005-11-14
02:04:53
|  Expierince with Interlaced Modi
Hi There!
I came across this issue while playing around with interlaced graphics: Although the Video-Display-Emulation in YAPE is fabulous, i am having a big trouble getting the display-settings configured in a way that the YAPE display is mostly exact (or at least comparable) to my CRT displays. it gets even more complicated when i (as mentioned) play around with interlaced graphic-modes.
I don't have any knowledge about the behaviour of the PAL-coding, i just will give you an example: I've watched an interlaced graphic on a quite modern 16:9 television. I noticed that $72 is a really problematic (or shall i say "polymorphic") color  the interlacing behaved very strange aswell: the distinct pixel-rows of the odd and even planes of the interlaced picture weren't on top of each other (in other words: as if i had 400 instead of 200 pixel-rows)
BTW: The interlacing was done very straight. I only flipped between two multicolor bitmaps each frame. one of the plane was scrolled by 1 pixel in the x-direction.
My question is: Does anyone (Gaia?) have expierince with this? I don't want to say that somethings missing in YAPE, i only want to bring the REAL and the EMULATED displays in their results closer together.
I think answers could probably be:
- You're using the wrong CRT! Use a Commodore-Monitor!
- Don't use the R/F-Connector, use the Luma/Chroma-Connectors!
- Use the calculated palette instead of the digitised palette!
asf.
At least one thing i found out myself: To simulate the interlace-flickering of my CRT it was more appropriate to hold the PageDown-Key instead of letting YAPE do this. I don't know why, probably my CRT just flickers more than others do.
I thank you in advance for your feedback!
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Posted By
Degauss
on 2005-11-14
02:09:09
| Re: Expierince with Interlaced Modi
Addition:
I found out two more things:
- The TFT where i ran YAPE is shit. The displaysettings of YAPE show more effect on a different PC-Monitor.
- That 400-Rows-Where-Normally-200-Rows-Are-Thing is (weirdly) only visible of dark colors like $01. (!??!!?)
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Posted By
Gaia
on 2005-11-14
04:32:13
| Re: Expierince with Interlaced Modi
Just one thing about the screen settings of Yape: you can as well adjust them on the driver level among the settings of the overlay of your graphic card (at least on NVidia, but it should exist for the Ati, too)
I admittedly used my old card's video-in port to compare the colours, but I was never 100% happy with the results. Although both screens were shown on the same TFT, the monitor itself is having a somewhat weird gamma I think. I have read somewhere TFT's have different gamma than CRT's, so what one should actually should do, take the original luma voltages and calculate Y' (here comes the gamma of the ORIGINAL C= monitor in the picture) but adjust to the gamma of the ACTUAL display on which the emulator runs. Does anyone know about the gamma value of the C= monitor? We should use that as reference, but I could only guess back then.
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Posted By
Crown
on 2005-11-14
05:38:09
| Re: Expierince with Interlaced Modi
About your CRT television issue. In color CRT televisions there are three separate electron guns drived individually for each primary color. They are driven separately, and it is very much possible that they are not aligned together. (They can get out of alignment with time I believe).
The easiest to check for this is to go to a Teletext screen and look at the picture closely. you should check a white text very closely. You might see red green and blue dots separately, fallen away from each other. The effect might be strongest in the corners. If this is the case than you probably need a service repairman to tune it properly.
If you know the service remote code for your TV you might try to tweak it yourself, but obviously you can end up ruining your TV altogether.
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Posted By
Degauss
on 2005-11-14
06:41:34
| Re: Expierince with Interlaced Modi
Thank you for your suggestions.
@Crown: My TV is alright i think
@Gaia: For what i wanted to do it's probably no good idea to compare with something that went through a video-in-port. But your suggestion to touch the driver-level-configuration seems to be very practical. For some reason, i managed to get the display quite similar to my TV. What is your expierience with the palettes? My impression was, that the digitized palette "looks nice" but the calculated palette is more correct (or more flexible if you want to "tune" your driver-config for similarity)
Whats still a hard task is getting a proper config to test interlaced screenmodes. I think i would have to set the refresh-rate of my monitor to 50hz or 100hz to get at least a chance of CRT-Like display...
Any further expieriences?
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Posted By
Gaia
on 2005-11-14
07:31:19
| Re: Expierince with Interlaced Modi
Yes, the digitized palette is only in because many people found it to be nicer than the calculated one, altough I never use that myself either. It isn't even specific to Yape, that palette was first featured in M.E.S.S. then later utilized in the WinEMU and Artifex emulators and was considered as a very good approximation in its time (around 1999 I think). A little less known is the fact that this palette was made by the (then) maintainer of the CBM drivers of M.E.S.S. (Peter Trauner) who had never owned a real 264 and therefore used RGB values extracted from a screenshot made with a TV card via the composite line (and publicly available at C64.rulez.org). Yape versions before 0.31 had this palette built in, too. It is now however converted to YUV internally when selected, so that it can be used with video display emulation, either.
The calculated palette uses chroma angles and luma voltages (just like VICE does). Voltages are based on actual oscilloscope measurements done by TLC, although we still have the gamma to worry about. And gamma DOES matter a lot more than hue, when perceiving colours! Chroma (hue) angles are from the TED preliminary manual with some appropriate manual adjustments where the colours seemed to be off a bit. As far as I recall from a conversation with John Selck (aka Graham) VICE xplus4 admittedly has 10 of the C64 chroma values which is not really case in my opinion (and anyone who converted C64 pictures back then, could prove it I guess ).
Last time I heard Larry/WLS experimented a lot with interlaced palettes and found the calculated palette much better, too.
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Posted By
Gaia
on 2005-11-14
07:43:02
| Re: Expierince with Interlaced Modi
One more thing: setting the monitor to a refresh rate of a multiple of 50Hz does help a lot against flicker, especially in DirectX modes (thus: either 'Use GDI' off, or VD emulation on) where the screen refresh is synced to the vertical retrace signal. If you are looking at a still picture, you can select the 'Vblank' sync option in the 'Speed' settings of Yape and there will be no flickering at all (but the emulator will run faster when in PAL mode), actually even a lot less than on the real TV but this can't be helped of I'm afraid (unless you find a monitor that can do real 50 Hz... )
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Posted By
Degauss
on 2005-11-17
01:45:03
| Re: Expierince with Interlaced Modi
Again: Thanks for the hints/suggestions. They helped a lot.
I've widened my expirience aswell. I tested my interlaced-graphics with a modern 100 hz TV and an original commodore monitor. result: YAPE looks closest to the commodore monitor, everything is roses! The 100hz TV is (for some reason) inappropriate for testing.
i figured out that $72 is still an "untrustable" color. further more, i found out that when using this (fake) 320x200-multicolor-interlaced mode, tuning the palette is a secondary issue. my feeling is that a proper dithering is the real challenge.
so i will now "renew" my question: does anyone have good suggestions about how to dither a picture thats supposed to be converted in this 320x200-multicolor-interlaced mode !?
(BTW: my current approach seems to be inferior: when converting a picture, i am currently dithering the whole picture with an unordered error-diffusion-algorithm (photoshop). then i build the odd and even planes from the odd and even pixel-columns. )
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Posted By
Csabo
on 2005-11-17
09:26:53
| Re: Expierince with Interlaced Modi
You're breaking new ground with this stuff. I know Gaia, Crown, TLC probably know and understand a lot about the colors and hardware, their research work is probably the most advanced. I also know Larry (Drea-M-time series, P4PC FLI Converter) has done quite a bit of research, and if I recall correctly, he stopped at exactly at the same place: proper display/conversion of interlaced colors. We haven't heard from him in quite a while and he has no email listed - too bad, you should try to get in touch with him.
I for one could not be happier to know that there are some people out there who are still pushing the limits of the hardware.
Go forth boldly to where no Plus/4er has gone before 
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