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Testing CRT Screen Size

Thomas Jentzsch

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The programming guidelines of Atari suggest a visible screen area of just 192 lines (NTSC). But CRTs can display a lot more lines. To find out the safe areas (and improve future games), I would like to run tests on as many CRTs as possible.

Therefore I have created a little test program, which allows you to determine the borders of the visible area of your CRT. The controls are:

  • Color = NTSC, B.W = PAL display
  • Joystick up and down: move top border
  • Fire + Joystick up and down: move bottom border

Please test when the console and CRT are cold and (more relevant) after some time when they have warmed up. Analog devices tend to change a bit with temperature. Move the two borders to the most top or bottom position where you still can see the complete white top and bottom lines (without any color artifacts). And then please report the TV format (NTSC or PAL) and the three displayed values here. If your TV supports both formats, then please report both.

My results (PAL Sony 15" Trinitron):

  • NTSC: 22, 222, 18
  • PAL: 30, 264, 18

Thanks in advance!

Results (warm) so far:

NTSC:    100%, 28 tests    | 60%, 21 tests
Average: 26.7, 217.8, 17.9 | 23.3, 224.2, 14.5
Min:     19  , 190  ,  8   | 16  , 215  ,  6
Max:     41  , 234  , 31   | 30  , 239  , 22 
PAL:     100%, 19 tests    | 60%, 14 tests
Average: 31.4, 263.1, 18.1 | 29.1, 269.1, 14.5
Min:     24  , 234  ,  7   | 21  , 255,    7 
Max:     37  , 280  , 42   | 36  , 283,   24

Screenshot from Stella with default settings (you can't see the border on the white background of AA icon_smile.gif).

Edit: New version, previously bottom was calculated 2 too low and resulting kernel size too large by 2 too. No need for to post again (I can adjust manually), but please start using v1.1 from now on.

ScreenSize v1.1.bin


Edited by Thomas Jentzsch
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Commodore 1084S cold:

  • NTSC: 26, 226, 10
  • PAL: 50, 229, 33

The monitor doesn't auto-adjust the screen size for PAL, if I run it after adjusting vertical size for Bobby is Going Home the values are:

  • NTSC: 13, 246, 3*
  • PAL: 35, 259, 18

I'll check it again this evening after work when I've let the console and monitor warm up while I work on the bus stuffing.


* Adjusted for PAL, the NTSC 3 could go even lower though that appears to be your lower limit.

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Overall your 1084 might be centered a bit low.

That's possible - I typically adjust it to PAL sizes when I play the Amiga CD32, as most games I have for it are from Europe, then back to NTSC sizes when I play the 2600.



When I finished the prior test I adjusted the screen so the NTSC and PAL values matched initial results (ie: not adjusted for Bobby)


Warmed up:

  • NTSC: 27, 224, 11
  • PAL: 52, 226, 34
Adjusted for Bobby:
  • NTSC: 13, 246, 3 (no change)
  • PAL: 36, 259, 17
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I didn't see the updated binary until after I tested the TVs, so the following results are for v1.0 of the rom:

Roadstar 32" 16/9
NTSC 20/232/10
PAL 27/277/08
Sony Trinitron 28"
NTSC 25/221/16
PAL 32/266/14
Philips 14"
NTSC 21/234/07
PAL 24/282/06
Mivar 10" B&W
NTSC not supported
PAL 30/264/18

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Many thanks for the test. Interesting that the picture either shrinks or grows when the devices are warmed up.


The frame shows the maximum width of the screen the Atari 2600 is using. Unlike the height, this one is fixed and cannot be influenced by the developer.


To everyone reading this, who has a chance to run the really simple test: Please help!

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The frame shows the maximum width of the screen the Atari 2600 is using. Unlike the height, this one is fixed and cannot be influenced by the developer.



"but I could make it wider to still get an acceptable picture"


I guess this is related to my post, actually I meant "higher" or "taller", not wider sorry.

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Probably your TV's picture is a bit more round, right? So by further extending the height, you would loose the corners, but still can see the line in the middle, correct?


With this test, I try to find (and define) safe parameters for future development (and emulator setup). Then a developer knows, that he can e.g. for NTSC display 210 scanlines (and knows the minimum required top and bottom border sizes) without risking that some people have any problems with visibility.


And he know he can utilize the full width of the screen. So he can do 210 scanlines and still display a score e.g. in the top left and right corners (like Boulder Dash). Therefore the test cares for full visibility of the whole horizontal lines including the corner. And last not least, most more modern CRTs have an almost square picture.

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Yes this is correct :)


It's this tv :

Wow, that one looks quite old. And fits pretty well to the ancient 2600. :)


To everyone reading this: PLEASE test! This will improve future homebrews (more space for the display, more vertical arcade like screen layouts...).

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I remember in 2002-3 I was testing the VGA to 15 kHz RGB connection in Advance MAME and the TVs were not able to display 240p at 60 Hz. So I came to conclusion that for many arcade games that use 240p 60 Hz I would need an arcade monitor (or at least the board) designed for 240p. Looking at the results so far it kinda proves my "theory".

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Yes, the nominal output was 240p, but all TVs have a quite large overscan. Testing the size of this overscan is exactly what I am doing here.


By now I found 215..232 visible scanlines, which results into 3..10% overscan.


Note: Most TVs have a hidden system menu, where the overscan can be changed. But those have to be used with great caution.

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In fact, I used the service menu to increase the visible area of the Sony TV (after testing with your rom, so the results in my previous post are for the TV with its original settings) and to reduce some of the geometry issues it has near the borders. (quite common with large "flat" CRTs. The "rounded" ones usually have less issues)

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