My palette is off, but I don't know how off thoe!
G2F's color chooser:
Edited by _33, Sun Jun 24, 2007 1:57 PM.
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Posted Tue May 29, 2007 5:36 PM
Edited by _33, Sun Jun 24, 2007 1:57 PM.
Posted Tue May 29, 2007 5:58 PM
Posted Tue May 29, 2007 6:33 PM
Edited by _33, Tue May 29, 2007 6:40 PM.
Posted Tue May 29, 2007 8:01 PM
Posted Tue May 29, 2007 8:06 PM
The best method might be to reproduce that display on a real Atari then feed it to a video capture card.
But, the inherent problem with reproducing colours on a PC monitor is that typically a monitor will display any given RGB value at a lower brightness than a TV.
Then you have the additional problem that colour trimmers on different Ataris can fall out of adjustment and cause slight colour variations.
Not to mention the fact that PAL Ataris don't produce the same as NTSC. Colour 1 is the same as 15, and Colour 4 I believe is reddish on NTSC but more purple/violet on PAL.
Edited by _33, Tue May 29, 2007 11:38 PM.
Posted Tue May 29, 2007 8:29 PM
Posted Tue May 29, 2007 8:44 PM
If I have time later on, I'll get my real machines out and generate some captures. They're all PAL though - most emulations look best with NTSC colour representations.
Edited by _33, Tue May 29, 2007 8:45 PM.
Posted Tue May 29, 2007 10:25 PM
Posted Tue May 29, 2007 10:57 PM
Posted Tue May 29, 2007 11:33 PM
On the GTIA in 16 color modes, there is one mode with 16 shades (mode 9), and they are very distinct shades of one hue. Since there are 16 hues (mode 11), there are 256 colors to choose from. On the older CTIA, there are 128 colors to choose from, with several graphics modes less.
Posted Tue May 29, 2007 11:33 PM
Aside from possible differences in the way the color output is "tuned" on different Ataris, another issue when using a TV is the way the brightness, contrast, and tint are set-- especially with NTSC Ataris and TVs. Anyway, following is a video capture I made several years ago of a 256-color display. I believe I posted a short Atari BASIC program here a year or two back, to display the 256 colors as in this video capture, and there were a couple of people who posted their own video captures from it on their NTSC or PAL Ataris, so you might want to search this forum for it.
By the way, I've always thought that luminances 7 and 8 look virtually identical to each other, whereas the other luminances have a more noticeable "step" between them-- but when you display luminances 7 and 8 side-by-side (as in this video capture), you get a "dark line" where they meet.
Posted Wed May 30, 2007 1:05 AM
I think your hue 2 is off; it looks yellow, but it should be yellow-orange. Aside from that, it looks like your other hues are pretty close to my video capture, other than the saturations and luminances. And your hue 1 may be a tad too greenish. The literature says that hue 1 is the same as colorburst, and NTSC colorburst is mostly yellow with a definite hint of green.
See, this is what I came up with. And now it's more obvious that the real bugger is nailing down the reds and blues properly in the lower range, since the saturation is high but also the luminence is fairly high. So as the luminence increases, saturation decreases. But it's special in the reds and blues.
Posted Wed May 30, 2007 1:45 AM
Posted Wed May 30, 2007 11:30 AM
Posted Wed May 30, 2007 8:38 PM
I don't know, but if you're able to understand it (much of it is over my head), you could start with this page:
Is there is a formula to change a 24bit pixel BMP into 1byte APAC pixel color (1 nibble luminance+1 nibble hue)?
Posted Wed May 30, 2007 8:49 PM
Posted Wed May 30, 2007 9:18 PM
Posted Wed May 30, 2007 10:22 PM
Posted Thu May 31, 2007 8:44 AM
YIQ (YCbCr - Luminance/In phase/Quadrature phase)
A bandwidth optimized, matrixed, composite video signal format used by NTSC video systems employing separate luminance and two derived blue and red chroma components derived from the YUV format.
The modulated carriers (U) and (V) (phased 90 degrees apart) are what carry the color information in an NTSC-encoded composite color picture. This is called “quadrature”. We call the modulated carriers “I” and “Q” in NTSC ("In phase" and "Quadrature phase"). I and Q are bandwidth-limited differently so they’ll fit into the NTSC transmission spectrum.
The human visual system has less spatial acuity for magenta-green transitions than it does for red-cyan. Thus, if signals I and Q are formed from a 123 degree rotation of U and V respectively, the “Q” signal can be more severely filtered than “I” without being perceptible to a viewer at typical TV viewing distance. YIQ is equivalent to YUV with a 33 degree rotation and an axis flip in the UV plane. The first edition of W.K. Pratt “Digital Image Processing”, and presumably other authors that follow that bible, has a matrix that erroneously omits the axis flip; the second edition corrects the error.
Since an analog NTSC decoder has no way of knowing whether the encoder was encoding YUV or YIQ, it cannot detect whether the encoder was running at 0 degree or 33 degree phase. In analog usage the terms YUV and YIQ are often used somewhat interchangeably. YIQ was important in the early days of NTSC but most broadcasting equipment now encodes equiband U and V.
The D-2 composite digital DVTR (and the associated interface standard) conveys NTSC modulated on the YIQ axes in the 525-line version and PAL modulated on the YUV axes in the 625-line version. (See YUV)
Function yiq_rgb(y#,i#,q#, r%, g%, b%) ;Y = range [0.,1.] ;I = range [-.6,.6] ;Q = range [-.52,.52] red% = ((1.00309 * y) + (0.95485 * i) + (0.61786 * q)) * r green% = ((0.99678 * y) + (-0.27071 * i) + (-0.64479 * q)) * g blue% = ((1.00850 * y) + (-1.11049 * i) + (1.69957 * q)) * b If red < 0 Then red = 0 ElseIf red > 255 Then red = 255 If green < 0 Then green = 0 ElseIf green > 255 Then green = 255 If blue < 0 Then blue = 0 ElseIf blue > 255 Then blue = 255 Return ((red And $FF) Shl 16) Or ((green And $FF) Shl 8) Or (blue And $FF) End Function
Edited by _33, Thu May 31, 2007 12:41 PM.
Posted Thu May 31, 2007 10:18 PM
Posted Fri Jun 1, 2007 3:57 AM
Edited by Rybags, Fri Jun 1, 2007 4:01 AM.
Posted Fri Jun 1, 2007 5:31 AM
Edited by Rybags, Fri Jun 1, 2007 5:32 AM.
Posted Fri Jun 1, 2007 6:12 AM
If I remember correctly, my capture was made a few years back by connecting my NTSC 8-bit to a VCR, and then connecting the VCR to my computer via a Snappy video capture device. (At the time, the only way I could connect my Atari to video was via the antenna connectors on the RF switch box!) Anyway, I played with the brightness and contrast settings in the Snappy software to get a good picture, from a nice dark black to a reasonably bright white. I kept the tint adjusted "in the middle" so it would be as "pure" as possible, rather than trying to adjust it more toward red or green to get a nice yellow for hue 1. (I'm not sure if I knew it at the time, but hue 1 on an NTSC Atari is said to be equal to "colorburst," which is sort of greenish yellow, but closer to yellow, so it's a good thing I didn't try to adjust the tint to make hue 1 equal a nice-looking yellow!)
Interesting comparing that cap to mine.
I've got them both loaded up in Photoshop and checking the colours with the eyedropper and RGB and HSB sliders.
Despite being somewhat grainy, the cap from SeGtGruff seems to have perfectly consistent whites, ie - the R,G,B values for each sampled pixel are always the same.
Mine seems to have a misbalance - don't know if that's a PAL thing or just the settings on my capture card (I have them at default, other than adjusting interlace compensation and sharpness for a better looking display).
Posted Fri Jun 1, 2007 6:18 AM
Posted Fri Jun 1, 2007 1:23 PM
Here's a captured screen from my PAL 130XE via it's S-Video output.
I wrote my own program to generate it - it leaves space between the colours and also uses 3 black-coloured Players to help delineate the changes at the borders and between luminence levels 0 and 1.
Here is the program I used - Zipped ATR - mount it after loading DOS with BASIC, then ENTER "D:COLORBAR.BAS" and RUN it.
Colorbar.zip 1.2KB 221 downloads
Edited by _33, Fri Jun 1, 2007 1:25 PM.
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