Correct colors for Atom emulator

discussion of games, software, hardware & emulators relating to the Acorn Atom
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flohofwoe
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Correct colors for Atom emulator

Postby flohofwoe » Wed Feb 01, 2017 7:27 pm

Hi, I'm having some trouble finding out what colors a real Atom produces on a TV / CRT monitor, I would appreciate some guidance on what a real Atom looks like :)

Question 1: what are the correct background colors in text mode?

For instance in text mode, this JS emulator has a nearly black background:

http://phils-place.co.uk/HTeMuLator/atom/

In MESS the back is a fairly bright green:
Image

The MC6847 datasheet says (on page 18): "Characters may be either green on a dark green background or orange on a dark orange background".

The background color in MESS strikes me as too bright, so I went with darker colors:

Image

Image

Which of those is closest to the real thing?

Question 2: what's the correct border color in text mode?

The MC6847 datasheet says for the text mode (also on page 18): "The area outside the display window is black".

Is it a pure black or more light a dark grey on a TV set? On my emulator I went for a dark grey, is this about right?

Image

Question 3: graphic mode colors

I took those from the discussion here, which made it then into MAME/MESS: http://forums.bannister.org/ubbthreads. ... mber=64986

On my emulator, the graphics mode colors (first half of palette) look like this:

Image

And with the CSS bit set:

Image

Are these about right? Not too bright and 'pure'?

And finally, Question 4: quick moment of junk on display when switching the Atom on?

When initializing the Atom system, I'm filling the RAM with random values, this leads to a very short time of junk on the display (some other systems have this effect too). Is this effect visible on a real Atom when switching it on?

Image

Thanks a lot!
-Floh.

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roland
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Re: Correct colors for Atom emulator

Postby roland » Thu Feb 02, 2017 8:29 am

The normal Atom produces a green background with brighter green characters, something like the first two pictures. The exact colours are depending on the brightness and contrast settings of the monitor. Also the colour of the phosphor layer of the monitor matters ;) On an amber monitor you won't see green colours. Other Atom emulators like Atomulator have a real good approach to a real Atom, including timing of the screen display.

The garbage at power on is also visible on many Atoms but that will disappear when break is pressed.
256K + 6502 Inside
MAN WOMAN :shock:

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oss003
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Re: Correct colors for Atom emulator

Postby oss003 » Thu Feb 02, 2017 6:38 pm

Hi Floh,

IIRC there are only 2 official colourboards for the Atom but the colours weren't that great.
That's why some modern boards were developed like Phill's Colourboard and hoglets Godil.

These are from my original Atom with Phill's colourboard on a CRT monitor:

col-txt1.png
col-txt2.png

col-grp1.png
col-grp2.png


These are from Rolands Atom 2015 with Godil video board on a VGA monitor:

col-txt3.png
col-txt4.png


Greetings
Kees

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flohofwoe
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Re: Correct colors for Atom emulator

Postby flohofwoe » Thu Feb 02, 2017 9:48 pm

Wonderful! These photos are excellent, I'll see if I can match those colors as closely as possible :)


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