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View topic - Notes & Measures: Nonlinear Blue on Sega Master System 1 & Other Findings by bfbiii

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Notes & Measures: Nonlinear Blue on Sega Master System 1 & Other Findings by bfbiii
Post Posted: Sat Dec 19, 2020 8:36 pm
In the form of a Google document, attached here for posterity.

https://docs.google.com/document/d/1MrPrSDpp6PmHPx45LzxTVJt2uCfl0MajA8GVtpWcois/...

(Google's PDF export seems to be broken currently)

Highlights:

- Red, green, blue levels measured using a video capture card, and checked for any odd biases produced by the card and the slightly funny video signals
- Red and green levels are pretty much linear
- On an SMS1, blue isn't, in particular the lowest intensity blue is 22-23% above where it ought to be
- Confirmed with an oscilloscope
- On an SMS2, the blue is more "normal" and the overall intensity is a bit higher (higher range) than SMS1/JSMS
- On a Genesis with PBC the colours are non-linear in a different way
SMS.zip (2.14 MB)
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Post Posted: Mon Dec 21, 2020 5:30 pm
I was wondering if all SMS 1 have the same Sony video encoder chip...
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Post Posted: Tue Dec 22, 2020 12:55 am
I believe not. I guess it may be VDP related, perhaps unbalanced voltages at the encoder are the root cause. The doc does not list VDP or encoder versions.
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Post Posted: Tue Dec 22, 2020 11:49 am
so if we have both first revision SMS and second revision SMS using the same video encoder chip we could rule out that...
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Hi there
Post Posted: Tue Dec 22, 2020 9:17 pm
That's my Google Doc which I do hope to update over time. I didn't even know we were going to find this, so slowly I am getting more details about the captures others submitted. It seems quite clear at this time that this is the VDP, the 315-5124 and not the encoder as it shows in various encoders with that VDP as well as RGB bypasses with that VDP. And it also seems the 315-5246 is always linear.
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Post Posted: Wed Dec 23, 2020 12:04 am
If you’re going into this rabbit hole, I guess you can scope the voltages from the VDP? How do the RGB out voltages correspond to perceived brightness on a typical TV of the era, compared to a typical PC screen now, especially regarding gamma? Does the progressive scan change that (as the electron beam double-scans the same rows)?
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Post Posted: Wed Dec 23, 2020 12:39 pm
Those are all great ideas. I've written them down for when I magically find time :-) Many thanks.
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Post Posted: Wed Dec 30, 2020 7:41 am
I did some measurements myself a while back (https://www.smspower.org/forums/15700-SMSVideoOutputLevels), somehow I didn't notice this blue difference you did. This is cool info none the less ~
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Post Posted: Sat Jan 02, 2021 3:16 pm
That is INTERESTING, TimEE, and god knows I am happy to be wrong somehow. I hope more people test and maybe we all learn something. From personal measures and submissions it appears that consoles that have the 315-5124 have this blue push.

It is fascinating to see a more or less linear result with yours.

Always willing to learn more!
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