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Yellows are greenish on Atari 2600 (S-Video modded)

Atari 2600 picture

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#1 skooter OFFLINE  


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Posted Fri Mar 3, 2017 12:48 PM

I have an Atari 2600 with Longhorn S-Video/Composite mod.


The yellows are kind of greenish on it. See picture below:




This is using Composite output on CRT TV. Things get worse when I use S-Video output on Framemeister and LCD TV:




And this is from another Atari 2600 I have, with RF:




It looks better, but also not quite right.


I already adjusted the tint trimpot on both of them, but it won't help.


Is there anything else I can do to make them better?


#2 save2600 OFFLINE  



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Posted Fri Mar 10, 2017 5:59 PM

Does adjusting the tint on your TV help? :grin:

#3 skooter OFFLINE  


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Posted Fri Mar 10, 2017 6:18 PM

No, it doesn't.

#4 skooter OFFLINE  


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Posted Fri Mar 10, 2017 6:27 PM

Here is some video footage I made after trying new cables. Notice the rainbow on the Activision logo. It has a greenish tone where it should be yellow.



#5 Trebor OFFLINE  


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Posted Sat Mar 11, 2017 6:43 AM

There can be a very strong lean towards green for the Atari consoles under a modern display, unfortunately.  The adjustment for "more red/less green" on the display may need to be quite significant to obtain a palette closer to a CRT; a comparison example has been posted.


The pot inside the 2600 is not a tint/hue control; rather, it adjusts the number of degrees separating the various hues and is highly sensitive.  If you own a Harmony cart, the easiest way to set this pot (if misaligned) is to utilize the Color Bar Generation from VideoSoft.  The ROM image is attached to this post.  Within the first minute or two of powering on a cold (Powered off for at least 45 minutes) console, ensure the bottom border color matches the top border color.


Attached File  Color Bar Generator.bin   4KB   36 downloads


When the border match is achieved, the degrees of separation is ~25.7, and the Hue 1 range (very closely) matches the Hue 15 range.  In turn, the console then is displaying a palette of 120 colors.  


Some additional console warm-up will occur thereafter*, resulting in a degrees shift that is slightly greater.  Ideally, a setting between ~25.7 and ~27.7 degrees. That setting places Hue 15 between the hues of 1 (Gold) and 2 (Orange), as described in the Stella Programmer's Guide, a 'Light Orange', ultimately providing a 128 colors palette for the console.


*NOTE: This can be observed by continuing to run the Color Bar Generator image, the bottom border will become a darker/richer brown color than the top portion automatically.

#6 alex_79 OFFLINE  



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Posted Sat Mar 11, 2017 8:41 AM

Would it be possible to adjust the color pot in a PAL 2600 following the same principle? That is, are there 2 hues in the PAL palette that behave in a similar manner so that an hack of the "Color Bar Generator" could be used for the same purpose?

#7 Trebor OFFLINE  


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Posted Sat Mar 11, 2017 10:29 AM

At no time for a PAL console is there an instance where two entire hue ranges are (near) exact and should match.  


Although there is a warm-up and shifting of colors that does occur for both regions, the hue order and number of colors is substantially different between an NTSC and PAL Atari 2600 console.  There is not an equivocal NTSC Hue 15 for PAL.  There is an additional 3 'rows' of grayscale values, for a total of 4 'rows' under PAL, as opposed to just 1 'row' under NTSC. 


The color test program from Eckhard Stolberg (attached) displays the color palette for either the PAL or NTSC system.


Attached File  Color Test (26-09-2002) (Eckhard Stolberg).bin   2KB   31 downloads

#8 skooter OFFLINE  


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Posted Sat Mar 11, 2017 7:13 PM

Thanks, Trebor.


I've applied your method on my S-Video modded Atari 2600, which is on the LCD TV.


Then I left the console off for about an hour and tried the Color Bar Generator again to see if it was right.


I don't think I got it right yet because it took around a minute until the borders matched, and then the bottom one started getting brown. Also, the red looks a little too magenta. I got all this on a video I'll upload later.


Now I'll wait until the console gets cold and try to adjust it again. It's difficult to get it right because it has to be done in only half a minute.


Also, I'll try the same with the unmodded console on the CRT TV tomorrow. I didn't mention it before, but the unmodded one is PAL-M. Perhaps the palette isn't the same?

#9 skooter OFFLINE  


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Posted Mon Mar 13, 2017 5:33 AM

Now I think I got it right.




The other console has more problems. The top bar on the Color Bar Generator is brown instead of green, no matter what I do on the trimpot.

#10 Reality Studio OFFLINE  

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Posted Thu Mar 16, 2017 11:37 PM

Be curious to see if you can fix this. My modded 2600 has the same issue, I can never get the yellow to look quite right using the adjustment pot and the controls on the mod board. Sorta gave up on it, been wondering if a modded Colecovision 2600 adapter has the same issue.

#11 skooter OFFLINE  


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Posted Fri Mar 17, 2017 7:59 AM

I'm giving up on this. While my modded NTSC Atari is too green, both my PAL-M Atari are too brown and the pot won't help either.


I guess the RGB Mod is the only way I can get a proper palette, but I don't have the skills to install one myself.

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