Why are the colours in the XL self-test different between PAL & NTSC?

[ldelsarte]

Does anyone know why the memory test colours are different between the PAL and NTSC versions of the Atari XL?

• In PAL, the background is green.
• In NTSC, the background is blue.

What is really strange is that the rest of the colours do not change:

• Titles (GR.1), white text.
• RAM/ROM, green (ok), red (bad)
• Text (GR.0), text using the background colour.

Is the source code of the self-test different in the PAL and NTSC ROMs or is there another reason?

[marauder666]

I suspect the code is the same and doesnt take into account the different palettes between NTSC and PAL.

[José Pereira]

It's more or less this:

-> colour 0 (black/grays/white) the same on the two;

-> then on other colours PAL increments +1 from NTSC. On your example: blue colour 9 turma green colour 10 but the green stays green but is another one (10 is +1 so is colour 11).

Edited August 15, 2022 by José Pereira

[José Pereira]

29 minutes ago, marauder666 said:

I suspect the code is the same and doesnt take into account the different palettes between NTSC and PAL.

Yes, is true then follow the rule +1 value on my previous post.

 

[Rybags]

Code is the same - the XL/later OS differs from 400/800 in that it's universal and caters for both systems.  But there's no colour adjustment.

 

There's key colour differences between the two systems.  Colour 4 on NTSC is red but more of a violet/purple on PAL - Star Raiders red alert is a glaring example of wrong colour being used there.

Colour 10 in NTSC is a greenish blue but in PAL it's a bluish green.  Again, Star Raiders with shields on shows the annoying green colour where it should be blue.

 

I suppose we shouldn't complain too much - the 2600 PAL has a bunch of repeated colours so gets nowhere near the claimed 128.  Secam is even worse.

[José Pereira]

2 hours ago, José Pereira said:

It's more or less this:

-> colour 0 (black/grays/white) the same on the two;

-> then on other colours PAL increments +1 from NTSC. On your example: blue colour 9 turma green colour 10 but the green stays green but is another one (10 is +1 so is colour 11).

 

2 hours ago, José Pereira said:

Yes, is true then follow the rule +1 value on my previous post.

 

Ler me explain better and as @Rybags said values are the same but result / what shows is if +1/'a colour ahead' was added (NTSC to PAL) on most of the colours. 

Example(s) NTSC/PAL:

colour 01: (in doubt)/brown (same as 15 on PAL and why people say it doesn't really have 128/256colours);

     "      02: brown/red orange;

     "      03: red orange/red pink;

     "      04: red pink/pink violet;

     "      05: pink violet/purple;

     "      06: purple/lilac;

     "      07: lilac/blue1;

     "      08: blue1/blue2; 

     "      09: blue2/blue marine (cyan);

     "      10: blue marine (cyan)/green marine;

     "      11: green marine/green1;

     "     12: green1/green2;

     "     13: green2/green3;

     "     14: green3/green4 (pale green);

     "     15: green4 (pale green)/brown;

 

 

 

 

Edited August 15, 2022 by José Pereira

[ldelsarte]

Colour palette picture source: MrFish
Altirra screenshots source: myself

 

If I try to summarise what I have understood:

• The colour palettes (256 or 128 colours) are slightly different in NTSC and PAL. In particular, some colours are shifted by 1 between the two. In particular, colour number 10 "blue" in NTSC is actually "green" in PAL
• The Self-Test source code remains the same in both PAL & NTSC OS

 

Are my conclusions correct?

• Atari was careless in the choice of colours for the Self-Test. In particular, the visual consistency between PAL & NTSC versions was not tested. Atari did not take extra steps to ensure that the colours remained the same in both versions.
• Atari did not test whether the machine is PAL or NTSC to run the Self-Test. So, Atari does not choose different colours according to the PAL or NTSC OS and its specific colour palette. It's one and only one set of colours.

 

Hence my further question: How do the game developers do it to ensure visual consistency? Do they test PAL vs. NTSC and choose colours accordingly? Do they choose colours that remain more or less the same between PAL & NTSC versions of the OS?

[+mytek]

That looks too green for a PAL system in my opinion.

Seems like either your color adjustment pot is slightly off, or your capture device is not accurately showing the color.

 

[vitoco]

16 minutes ago, ldelsarte said:

Hence my further question: How do the game developers do it to ensure visual consistency? Do they test PAL vs. NTSC and choose colours accordingly? Do they choose colours that remain more or less the same between PAL & NTSC versions of the OS?

If the game is intended to be run on both systems, you can check which one is the current one and select it's palette if the colours have a meaning. But sometimes that could be hard as an intensive use of DLI could end on a duplication of code, and then finish with two different executables.

 

In the other hand, when colours are meaningless, just pick the ones that are not similar. Default colours for playfield are good ones.

 

[Rybags]

Generally they either didn't care or weren't aware of the differences.

Self Test - and Audio-visual in particular - there is no mention or requirement of any specific arrangement of colours.

 

Games - there are plenty that just look wrong on one system or the other.  Then again look at a lot of the early Apple II conversions, plenty of them have poor colour choices regardless of what they're running on.

[pseudografx]

1 hour ago, mytek said:

That looks too green for a PAL system in my opinion.

Seems like either your color adjustment pot is slightly off, or your capture device is not accurately showing the color.

 

It is Altirra, as was stated in ldelsarte's post.

[+mytek]

9 minutes ago, pseudografx said:

It is Altirra, as was stated in ldelsarte's post.

Thanks for the explanation

 

Not enough time in my day to read topics in their entirety, so I sometimes miss those details.

[pseudografx]

This is what it looks like on my PAL Atari.

[+mytek]

This is the variation I'm used to seeing with PAL hardware or emulation.

 

 

Your example looks far too green.

[Ricky Spanish]

3 hours ago, ldelsarte said:

Altirra screenshots source: myself

Is it set to DX9 or DX11 ? I have my real hardware hooked up to a CRT TV (NTSC) & it looks much different to the Altirra screenshot.

[ClausB]

Does the color adjustment pot work the same way for PAL as for NTSC? There is a lot of variability in how those are set, sadly.

[pseudografx]

3 hours ago, mytek said:

This is the variation I'm used to seeing with PAL hardware or emulation.

 

 

Your example looks far too green.

Did you miss the command that was executed before the screenshot was taken? 🙂

[+mytek]

4 hours ago, pseudografx said:

Did you miss the command that was executed before the screenshot was taken? 🙂

LOL so you're playing tricks on me 

 

Obviously I missed it. I think I'll go listen to some music and keep thoughts to myself 

[phaeron]

5 hours ago, ClausB said:

Does the color adjustment pot work the same way for PAL as for NTSC? There is a lot of variability in how those are set, sadly.

 

No, it doesn't. The general principle is the same, but due to quirks in the way that the PAL GTIA works, there are specific bands that appear in the hues that the color adjustment pot cannot cross as easily. This is why almost any picture of the full 256 color palette on a real-world PAL machine shows uneven hue steps on specific boundaries. You can see some examples from these captures:

 

 

[pseudografx]

4 hours ago, mytek said:

LOL so you're playing tricks on me 

 

Obviously I missed it. I think I'll go listen to some music and keep thoughts to myself 

I just copied what ldelsarte did.

[+mytek]

1 minute ago, pseudografx said:

I just copied what ldelsarte did.

And I totally get that now. The problem was my mind was focused elsewhere, but I kept jumping into this discussion without really understanding what was being done at the time. So I should have just kept my mouth shut, or better yet, my hands off the keyboard and let everyone else carry on. No hard feelings on my part

[ldelsarte]

17 hours ago, mytek said:

Seems like either your color adjustment pot is slightly off, or your capture device is not accurately showing the color.

It is a screenshot from Altirra, not from an actual/physical Atari machine.

I should have kept the Windows border to make it obvious (although it's stated at the beginning of the message)