measured colour output levels?

Discussion of development of software for any "obsolete" computer or video game system.
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vdpcolor
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measured colour output levels?

Post by vdpcolor » Wed Feb 06, 2019 10:49 am

Hello there. There's documents written about voltages for systems like nes (kevtris), megadrive (TmEE), master system (TmEE), SC-3000 (TmEE). I haven't been able to find measurements for other systems like snes (byuu says non-linear ramp with notably darker greys), psx (no$cash mentions a non-linear ramp, largely brighter than normal greys), pc engine, n64. Mostly interested for "purist" sake. Thanks.

tepples
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Re: measured colour output levels?

Post by tepples » Wed Feb 06, 2019 7:44 pm

I'd like to see voltages for Super NES and GameCube in order to display IRE levels in Super Game Boy and Game Boy Player software.

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TmEE
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Re: measured colour output levels?

Post by TmEE » Wed Feb 06, 2019 11:31 pm

If someone can make a test ROM that shows a greyscale ramp I'll be able to take measurements on SNES and PCE/TG16 aswell. The ramp needs to show a solid white bar on left edge, then go to black and progressively higher until it reaches white and then to black again. White on left allows to me to know exactly where the useful image begins.
End result is a bunch of vertical bars of all available shades.

PCE is going to be fun because it has two types of outputs, RGB and Y with modulated chroma components and latter uses a LUT to create a different result. I'm not sure how one will go about measuring the chroma components, one will have to know the phase difference compared to color subcarrier to get anywhere. My equipment is not able to report such info and doing it manually is very error prone.

Hardware with a very fine ramp would need it to be split up into multiple ramps, separated by a button press or such. One quarter on one screen, other quarter on the next etc. Otherwise it will be too difficult to tell individual levels apart.

lidnariq
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Re: measured colour output levels?

Post by lidnariq » Thu Feb 07, 2019 12:54 am

Here's something I quickly whipped together for measuring the SNES DACs. Displays grey ramp on every scanline, starting with white on both leftmost and rightmost pixels, black bars to separate things, and then 224 pixels going from <0,0,0> black to <31,31,31> white. Additionally uses HDMA to adjust the reportedly-analog dimming factor, 7 scanlines for each value.
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TmEE
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Re: measured colour output levels?

Post by TmEE » Thu Feb 07, 2019 1:01 am

That analog dimming should be under a button press or such if I were to measure it. My scope lacks video line triggers (DRM option no less lol) and it has not enough memory to do a full frame capture. I can only work with a stable frame with solid vertical bars per one test, once all bars are measured I can go onto the next.

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Re: measured colour output levels?

Post by lidnariq » Thu Feb 07, 2019 11:21 am

.... lulz.

Up (brighter) and down (dimmer) change analog dimming level, wrapping around.


(edit: this was apparently my 8086th post)
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ccovell
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Re: measured colour output levels?

Post by ccovell » Thu Feb 07, 2019 6:52 pm

Here's a similar simple PCE ROM that I whipped up.

You can cycle through some basic RGB etc palettes by pressing any button or pad direction (except for RUN or I to account for flashcart menu buttons).


[edit] ROM updated to guarantee SPR palette & screen border are black.
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turboxray
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Re: measured colour output levels?

Post by turboxray » Thu Oct 31, 2019 3:34 am

TmEE wrote: PCE is going to be fun because it has two types of outputs, RGB and Y with modulated chroma components and latter uses a LUT to create a different result. I'm not sure how one will go about measuring the chroma components,
I have a VCE patent doc somewhere, where it has the first few and last entries of the LUT. It's 5bits for each channel of U, U, V. So the RGB to LUT translation is kinda unique (certain colors blend better on the composite out). RGB out was never official on the system, even if the back port had it.
luma_scale_capture.png
You can see the coarse luma stepping here. This is ccovell's 512 color demo. Do the same on an emulator and remove the color, and it'll look much different.

It's been known for like 10 years and no one's figured it out haha.

FYI, composite is made by mixing Y+C before the amp, but C is actually Q and I simply added. So VCE actually outputs Y, Q, and I separately and it's mixed before the amp.

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Re: measured colour output levels?

Post by lidnariq » Thu Oct 31, 2019 9:57 am

turboxray wrote:but C is actually Q and I simply added. So VCE actually outputs Y, Q, and I separately and it's mixed before the amp.
It emits modulated U and V components? Or is there something (like the CoCo's MC1372 IC) that multiplexes U,V,-U,-V in sequence?

turboxray
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Re: measured colour output levels?

Post by turboxray » Thu Oct 31, 2019 12:51 pm

lidnariq wrote:
turboxray wrote:but C is actually Q and I simply added. So VCE actually outputs Y, Q, and I separately and it's mixed before the amp.
It emits modulated U and V components?
Yeah. If you can demodulate U and V outputs, you can do a component setup. I cut the traces to U and V amp circuit and fed just Y+sync (well, color burst too haha) to component Y on my TV and it was the most incredibly sharp image. I'm not an EE so I didn't have the ability to build a component converter myself.

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