Joey Z Posted October 10, 2014 Share Posted October 10, 2014 In 1987 in USA standard NTSC was changed from NTSC(1953) to SMPTE "C". They changed colorimetry values for prime colors (RGB) and white point. Is this the answer I'm looking for? Here you have what I found on internet. This is vectorograph of SMPTE "C" NTSC standard. Atari color 1 is at 180° of phase. I found original SMPTE document with tables of phase values for NTSC color bars. And vector diagram from Texas Instrument document. Pinpointing phase angles of prime colors. All of this might be very useful for Altirra. Interesting fact is that prime colors are not spaced 120° from each other. All phase angles are like in Atari CGIA document(page 50-51) I don't think so. Colorimetric values determine the actual color that they call 'red' as perceived by humans. They are mapping 'red' as defined by NTSC to a color in the xyY system as defined by CIE 1931, and doing similar for blue green and red. But colors should not change all that much. However, the actual chroma phase angles that consitute 'red' and the other primaries do not change, and a chroma amplitude of 0 is still 'white' chrominance. Quote Link to comment Share on other sites More sharing options...
firestorm Posted October 10, 2014 Author Share Posted October 10, 2014 This is just picture I found on internet better look at this: I calculated angles of phase rotation between RGB colors for all 3 attached documents and hope it might be significant in getting colors in Altirra right. Red to Blue is 115.5° for Atari document(page50-51), 116° for Texas instrument and 116.4° for SMPTE. Blue to Green is 107,9° for Atari document, 106° for Texas one and 106.4 for SMPTE Green to RED is 136.6° for Atari document, 138° for Texas one and 137.2° for SMPTE Difference between Texas and SMPTE might come from SMPTE being precise one. Difference between Atari and SMPTE comes possibly from difference between NTSC(1953)standard and NTSC(1987). As you noticed primary colors are not spaced 120° from each other. I believe that by having this data is possible to create precise model for creating Atari NTSC colors. cgia.pdf Texas Instruments.pdf SMPTE tables.pdf Quote Link to comment Share on other sites More sharing options...
firestorm Posted October 20, 2014 Author Share Posted October 20, 2014 Back from holiday You can compare my screenshot with the one from Analog page 3 Pages from analog_no_30.pdf Quote Link to comment Share on other sites More sharing options...
thorfdbg Posted October 21, 2014 Share Posted October 21, 2014 I calculated angles of phase rotation between RGB colors for all 3 attached documents and hope it might be significant in getting colors in Altirra right. Red to Blue is 115.5° for Atari document(page50-51), 116° for Texas instrument and 116.4° for SMPTE. Blue to Green is 107,9° for Atari document, 106° for Texas one and 106.4 for SMPTE Green to RED is 136.6° for Atari document, 138° for Texas one and 137.2° for SMPTE Difference between Texas and SMPTE might come from SMPTE being precise one. Difference between Atari and SMPTE comes possibly from difference between NTSC(1953)standard and NTSC(1987). As you noticed primary colors are not spaced 120° from each other. I believe that by having this data is possible to create precise model for creating Atari NTSC colors. This is pretty much it, and exactly what I said before already. The color space definitions changed slightly over time, and so did the implementation in the TVs. The old hardware still implements the old NTSC standard, and expects the user to correct the (usually unstable) color phase of NTSC with the tint control. Newer TVs implement the new norm, TV is broadcasted digitally, so no need for a tint control, and hence colors from old systems appear partially off. There's no miracle here - the Atari circuit just has a different understanding on how the color should be coded compared to how the TV understands how it should be decoded. If you want to fix that, well, you can try to work around by adjusting the Atari color circuit to fit approximately to the HDTV color encoding (only if even approximately) or you can try to persuade your TV to use the legacy NTSC encoding, either by the tint control or some menu settings somewhere hidden in the dialogs. 2 Quote Link to comment Share on other sites More sharing options...
firestorm Posted October 21, 2014 Author Share Posted October 21, 2014 This is pretty much it, and exactly what I said before already. The color space definitions changed slightly over time, and so did the implementation in the TVs. The old hardware still implements the old NTSC standard, and expects the user to correct the (usually unstable) color phase of NTSC with the tint control. Newer TVs implement the new norm, TV is broadcasted digitally, so no need for a tint control, and hence colors from old systems appear partially off. There's no miracle here - the Atari circuit just has a different understanding on how the color should be coded compared to how the TV understands how it should be decoded. If you want to fix that, well, you can try to work around by adjusting the Atari color circuit to fit approximately to the HDTV color encoding (only if even approximately) or you can try to persuade your TV to use the legacy NTSC encoding, either by the tint control or some menu settings somewhere hidden in the dialogs. Thank you for understanding the problem Now I'm looking for the way to implement it on Altirra emulator. Quote Link to comment Share on other sites More sharing options...
firestorm Posted October 25, 2014 Author Share Posted October 25, 2014 (edited) Super Breakout Below is manual from this game, look at the pointing system. "defined by color..." hmm This one? Or that one? Edited October 25, 2014 by firestorm Quote Link to comment Share on other sites More sharing options...
firestorm Posted October 30, 2014 Author Share Posted October 30, 2014 Atari Qix 1982, in manual boxes drawn at slow speed(fire pressed) are described as RED, boxes drawn at slow speed are described as BLUE. http://www.atarimania.com/game-atari-400-800-xl-xe-qix_4207.html So here are screenshots: Quote Link to comment Share on other sites More sharing options...
foft Posted October 31, 2014 Share Posted October 31, 2014 Interesting discussion. I've still got the wrong palette for the FPGA stuff (just the PAL one for both), so am looking to use a better one. Before I get round to doing the phase stuff properly in gtia... I found this related thread on the 5200: http://atariage.com/forums/topic/218439-pam-finally-gets-some-clothes/ http://atariage.com/forums/topic/216590-stella-gets-some-new-clothes/page-4?do=findComment&comment=2845568 1 Quote Link to comment Share on other sites More sharing options...
firestorm Posted October 31, 2014 Author Share Posted October 31, 2014 Interesting discussion. I've still got the wrong palette for the FPGA stuff (just the PAL one for both), so am looking to use a better one. Before I get round to doing the phase stuff properly in gtia... I found this related thread on the 5200: http://atariage.com/forums/topic/218439-pam-finally-gets-some-clothes/ http://atariage.com/forums/topic/216590-stella-gets-some-new-clothes/page-4?do=findComment&comment=2845568 Foft, thank you very much for your input. So it looks like is not just only me against whole world After long research I found that proper color pot adjusted Atari 800/XL/XE should be as described in Atari 800 Field Service Manual. That was confirmed by Bruce from Atari Sales. The problem is that Atari hardware needs at least 15 minutes to warm up what might be the reason wrongly adjusted computers during production process, specially XL/XE produced abroad. Tomorrow I show you a pictures of colorbars from SALT test on cold machine and warmed up. Phase shift from above pictures of Qix is done by monitor Phase/Hue/Color Balance setting to get color 1 Gold. Now you can get proper shields color on Star Riders as described by Doug Neubauer! Quote Link to comment Share on other sites More sharing options...
foft Posted November 1, 2014 Share Posted November 1, 2014 From your research do you have suggested adjustments to the Altirra palette settings for those doing emulation? Earlier you mentioned two colour schemes in use - with your current settings did you find a middle ground that works? It strikes me that different developers would just test on their own tv each with different tint settings so the settings may differ per developer. 1 Quote Link to comment Share on other sites More sharing options...
firestorm Posted November 1, 2014 Author Share Posted November 1, 2014 Yes you right that is very important to get proper colors, specially when you making new game. We need color standard for NTSC and PAL. Take example of new RGB game with color off for PAL machines just because it was developed using Altirra default PAL palette. Altirra have problem with colors because is using RGB model with prime colors spaced by 120°. Proper for NTSC prime color phase angles you can find few posts above. Anyway my Altirra settings for now is hue start -35° and hue step 25.6°. and you can check few first Atari games like Star Riders(shields) or Basketball(skin tone of player brown not green) or Super Breakout(first row of bricks gold not green)... Quote Link to comment Share on other sites More sharing options...
firestorm Posted November 1, 2014 Author Share Posted November 1, 2014 (edited) First picture shows SALT colorbars on Atari 800XL NTSC just switched on. Second picture of the same computer after 15 minutes, please notice changes of color of bar 15. So it was possible that in production process computers where color adjusted wrongly because there was not time to wait for 15 minutes... Edited November 1, 2014 by firestorm Quote Link to comment Share on other sites More sharing options...
firestorm Posted November 4, 2014 Author Share Posted November 4, 2014 (edited) Color Palette I found this program in Antic magazine 6/1985. Please notice color description in this program: 0-Gray 1-Gold 2-Orange 3-Red 4-Pink 5-Violet 6-Purple 7-Blue 8-Cyan 9-Lt Blue 10-Turquoise 11-Blue-Grn 12-Green 13-Yllw-Grn 14-Orng-Grn 15-Lt Orange Load program with Basic. Antic Vol 4-02 1985-06 S2 Computer Arts.atr Pages from Antic Vol 4-02 1985-06 Computer Arts.pdf Edited November 4, 2014 by firestorm 1 Quote Link to comment Share on other sites More sharing options...
phaeron Posted December 17, 2014 Share Posted December 17, 2014 Altirra have problem with colors because is using RGB model with prime colors spaced by 120°. Proper for NTSC prime color phase angles you can find few posts above. Sorry, I have to correct this. Altirra has never used 120 degree spacing for the primary colors. It uses a regular YIQ decoding matrix, which puts the primaries at 77, 299, and 193 degrees in I-Q space. Quote Link to comment Share on other sites More sharing options...
firestorm Posted January 7, 2015 Author Share Posted January 7, 2015 Phaeron, I had pm you with question about it before your post... It is not changing fact that by default Altirra gets NTSC colors wrong. Quote Link to comment Share on other sites More sharing options...
firestorm Posted January 7, 2015 Author Share Posted January 7, 2015 Now Star Raiders from ATARI 800 NTSC Look at RED ALERT Quote Link to comment Share on other sites More sharing options...
firestorm Posted January 7, 2015 Author Share Posted January 7, 2015 I'm waiting for CTIA chip to see Star Riders as it looked in 1979 Quote Link to comment Share on other sites More sharing options...
phaeron Posted January 7, 2015 Share Posted January 7, 2015 Phaeron, I had pm you with question about it before your post... It is not changing fact that by default Altirra gets NTSC colors wrong. I'm always open to changing the defaults, and have been tweaking it for 2.60. However, the statement about Altirra using 120d spaced primaries is still wrong, and I'd appreciate it if you didn't make up such "facts" about my emulator. Quote Link to comment Share on other sites More sharing options...
firestorm Posted January 7, 2015 Author Share Posted January 7, 2015 Phaeron are you sure, that it is not RGB space? Altirra NTSC Hue Step 25.6 Hue Start 70 gives you red color on self test screen Hue Start 70+120(190) gives blue color Hue Start 190+120(310) gives you green color Quote Link to comment Share on other sites More sharing options...
phaeron Posted January 8, 2015 Share Posted January 8, 2015 You can't eyeball the colors like that to get 120 degrees. The angles are determined by the vectors in the conversion matrix. Here's the dump from Scilab: -->A = inv([1 0.956 0.620; 1 -0.272 -0.647; 1 -1.108 1.705]); atand(A(2,, -A(3,) - 33 + [0 360 360] ans = 76.567359 299.27007 192.89553 These are the values in Atari's CGIA document, to within one degree. TI's document also uses the same matrix, aside from rounding differences that make less than 0.1 degree of difference. 3 Quote Link to comment Share on other sites More sharing options...
firestorm Posted August 24, 2016 Author Share Posted August 24, 2016 (edited) Hi everybody, in July I managed to connect my Atari 800 NTSC to my parents old Sony TV from end of 80's. This is European multi system version, it can display NTSC monitor AV signal using SCART. TV setings were set to defaults which is visible on one of the pictures as small icon in left down corner of TV screen. And what big surprise! NTSC ATARI 800 on old 1980's TV !!! Edited August 24, 2016 by firestorm 1 Quote Link to comment Share on other sites More sharing options...
invisible kid Posted November 28, 2019 Share Posted November 28, 2019 (edited) On 10/3/2014 at 6:17 PM, firestorm said: Based on Atari 400/800 Field Service Manual, there is simple way to adjust color pot on NTSC Atari computer without using SALT cartridge. Before you try this please keep your Atari switched on to warm up for 15 minutes. SETCOLOR 2,1,8 REM CHANGES BACKGROUND COLOR TO 1, PRESS RETURN SETCOLOR 4,15,8 REM CHANGES FRAME COLOR TO 15, PRESS RETURN Then adjust Atari color pot to make background and frame around the screen of the same color as possible. Necroing this thread just to say I adjusted my NTSC 800xl color pot using this method and it worked great. Maybe it can help someone else. Thanks! Edited November 28, 2019 by invisible kid 1 Quote Link to comment Share on other sites More sharing options...
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