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The Apple II's somewhat exotic "hires" mode didn't even HAVE an indexed palette. Instead you just wrote 1s and 0s for pixels directly to the display memory, and

The Apple II's somewhat exotic "hires" mode didn't even HAVE an indexed palette. Instead you just wrote 1s and 0s for pixels directly to the display memory, and their arrangement on the screen determined their color. This all owing to the fact that the Apple II only had color at all due to some crazy phase-based hacking of the NTSC color standard. EDIT: Oops I partially messed up this description. The MSB in each byte of the display memory did set the "palette" (phase, actually, according to Wikpedia) for each set of 6 pixels. So you could either have blue/orange or green/purple in that set with the exact color depending on whether or not you had one alternating pattern of bits or another.

function_seven 8y ago
You have any links for this? It sounds both terrifying and clever as hell. Similar to the Amiga's HAM mode[1], where you could get 4,096 simultaneous colors, but the restriction was that the succeeding pixel could only differ from the preceding in just one of the R, G, or B values. [1] https://en.wikipedia.org/wiki/Hold-And-Modify https://en.wikipedia.org/wiki/Hold-And-Modify
- jdblair 8y ago
  The bit patterns are described in Wikipedia: https://en.wikipedia.org/wiki/Apple_II_graphics#High-Resolution_(Hi-Res)_graphics https://en.wikipedia.org/wiki/Apple_II_graphics#High-Resolut...
  - nategri 8y ago
    Yes and the 64:1 interleave pattern on the display is also another "fun" feature to code around.
- jdblair 8y ago
  and this goes into detail about how the bit patterns worked: https://www.xtof.info/blog/?p=768 https://www.xtof.info/blog/?p=768
  - function_seven 8y ago
    Thank you. I just had an epiphany. In elementary school computer lab, we'd all fight for the color machines. There were two of those and like 25 of the green screens. I remember wondering how the game "knew" what kind of screen it was on. How did it change from a solid color (for the lucky kids) to a pattern (for the rest of us)?? I just shrugged it off as the computer knowing the display type from the connection. Those two images in your link made it all just click right now, 30 years later.
- dbcurtis 8y ago
  "terrifying and clever" describes a lot of the Woz's work... So I am a little fuzzy on the NTSC standard, because it has been a while since I looked at it... but the hack goes something like this: Monochrome TV puts video on an upper vestigial sideband with the carrier at (IIRC) 1.25 MHz up from the lower edge of the 6 MHz channel. (The high frequency parts of the lower sideband of the video signal are whacked off with a filter.) The FM sound subcarrier is up closer to the top edge, I forget what the offset is exactly. Then color came along... so they added a color subcarrier just below the sound subcarrier. This reduced the bandwidth available for luminance, but got you color in return. The color subcarrier IIRC is kind of a flavor of independent sideband, but is really two double sideband signals on the same carrier, 90 degrees out of phase with each other, one skinny, and the other fat but with a notch filter applied to allow the skinny signal to ride in the middle. Or something like that. Anyway... if you send a monochrome signal with high-frequency components (high frequency == high dot rate) that fall in the range of the color sub-carrier, you will get color artifacts. This is because the color decoder simply responds to the rf it is getting, whether on a proper subcarrier or not. Another thing I used to know but am fuzzy about is I am pretty sure you need to put out the standard color burst on the back porch of the horizontal sync. Otherwise, the TV receiver will not sync to the "color subcarrier" that you are faking with artifacts.
  - ddingus 8y ago
    You are correct. Something like a colorburst must be there. Turns out you can abuse that very considerably. And still get stable, useful displays.
CharlesW 8y ago
The TRS-80 Color Computer had a similar trick used by lots of commercial games, but you couldn't predict when the effect might result in red or blue. You'd have to reset your CoCo until an example graphic was the right color before proceeding. http://vdgtricks.blogspot.com/ http://vdgtricks.blogspot.com/
- cr0sh 8y ago
  On the CoCo 3 you didn't have to hit reset; there was a way to switch it in software. Also on the CoCo 3, there was the 640 x 192 4-color "hires" mode. Way, way back - I believe published in Hot CoCo - someone figured out that using a television, and setting those 4 colors to the grayscale in the 64 color palette (black, dark grey, light grey, and white) - and with proper 4-bit pixel settings, you could get a virtual 128x192 image with colors. Basically the same technique (called artifact colors, or artifacting) - but applied to the high-res screen of the CoCo 3. Unfortunately - he sent it to Hot CoCo! Had he sent it to the Rainbow instead...things might have been different. You see, by sending it to that magazine, it didn't reach a large audience, so only a few people saw it, nobody much played with it, and it faded into history. On the Rainbow side of things, there were a couple of articles about using patterns of color to create "virtual colors" - but it was geared toward the RGB monitor (CM-8), and not really the TV - and using colors, not the gray scales... So - what am rambling about then? Well - long story short - this: http://richg42.blogspot.com/2014/02/the-little-known-color-computer-3s-256.html http://richg42.blogspot.com/2014/02/the-little-known-color-c... A virtually unknown "256 color" mode on the Color Computer 3 that was lost to history. Now - this isn't the mystery 256 color mode that has been described elsewhere hiding in the GIME chip (and most people believe that it is a false rumor; but the Microware CoCo 3 prototype holds out hope) - but it is a working "hi color" mode available on the CoCo 3. Unfortunately, today, it is only a curiosity more than anything, and it is unknown whether it could have been used back then; from what I recall, they had to use a PC to figure out the proper bit patterns for each of the colors, and that kind of processing would have been difficult at best back then. EDIT: This really shows off what is possible with the mode: http://atariage.com/forums/blog/105/entry-6693-color-computer-3-artifact-art/ http://atariage.com/forums/blog/105/entry-6693-color-compute...
  - 8y ago
mrec 8y ago
Interesting! Sounds a bit like ClearType in reverse - there, the color determines the (perceived) position on the screen.
sp332 8y ago
I only know of one way to output accurate color from Apple II's to HDMI. This is new as of last year. You have to email the developer and he'll add you to the waiting list. http://atariage.com/forums/topic/285010-vidhd-hdmi-board-update/ http://atariage.com/forums/topic/285010-vidhd-hdmi-board-upd...
cr0sh 8y ago
For a little bit of completeness sake - it was also possible on the PC CGA card to gain artifact colors in certain modes, using a composite monitor. This led to some interesting possibilities, which were later exploited: https://int10h.org/blog/2015/04/cga-in-1024-colors-new-mode-illustrated/ https://int10h.org/blog/2015/04/cga-in-1024-colors-new-mode-...

function_seven 8y ago

You have any links for this? It sounds both terrifying and clever as hell. Similar to the Amiga's HAM mode[1], where you could get 4,096 simultaneous colors, but the restriction was that the succeeding pixel could only differ from the preceding in just one of the R, G, or B values. [1] https://en.wikipedia.org/wiki/Hold-And-Modify https://en.wikipedia.org/wiki/Hold-And-Modify

jdblair 8y ago
The bit patterns are described in Wikipedia: https://en.wikipedia.org/wiki/Apple_II_graphics#High-Resolution_(Hi-Res)_graphics https://en.wikipedia.org/wiki/Apple_II_graphics#High-Resolut...
- nategri 8y ago
  Yes and the 64:1 interleave pattern on the display is also another "fun" feature to code around.
jdblair 8y ago
and this goes into detail about how the bit patterns worked: https://www.xtof.info/blog/?p=768 https://www.xtof.info/blog/?p=768
- function_seven 8y ago
  Thank you. I just had an epiphany. In elementary school computer lab, we'd all fight for the color machines. There were two of those and like 25 of the green screens. I remember wondering how the game "knew" what kind of screen it was on. How did it change from a solid color (for the lucky kids) to a pattern (for the rest of us)?? I just shrugged it off as the computer knowing the display type from the connection. Those two images in your link made it all just click right now, 30 years later.
dbcurtis 8y ago
"terrifying and clever" describes a lot of the Woz's work... So I am a little fuzzy on the NTSC standard, because it has been a while since I looked at it... but the hack goes something like this: Monochrome TV puts video on an upper vestigial sideband with the carrier at (IIRC) 1.25 MHz up from the lower edge of the 6 MHz channel. (The high frequency parts of the lower sideband of the video signal are whacked off with a filter.) The FM sound subcarrier is up closer to the top edge, I forget what the offset is exactly. Then color came along... so they added a color subcarrier just below the sound subcarrier. This reduced the bandwidth available for luminance, but got you color in return. The color subcarrier IIRC is kind of a flavor of independent sideband, but is really two double sideband signals on the same carrier, 90 degrees out of phase with each other, one skinny, and the other fat but with a notch filter applied to allow the skinny signal to ride in the middle. Or something like that. Anyway... if you send a monochrome signal with high-frequency components (high frequency == high dot rate) that fall in the range of the color sub-carrier, you will get color artifacts. This is because the color decoder simply responds to the rf it is getting, whether on a proper subcarrier or not. Another thing I used to know but am fuzzy about is I am pretty sure you need to put out the standard color burst on the back porch of the horizontal sync. Otherwise, the TV receiver will not sync to the "color subcarrier" that you are faking with artifacts.
- ddingus 8y ago
  You are correct. Something like a colorburst must be there. Turns out you can abuse that very considerably. And still get stable, useful displays.

CharlesW 8y ago

The TRS-80 Color Computer had a similar trick used by lots of commercial games, but you couldn't predict when the effect might result in red or blue. You'd have to reset your CoCo until an example graphic was the right color before proceeding. http://vdgtricks.blogspot.com/ http://vdgtricks.blogspot.com/

cr0sh 8y ago
On the CoCo 3 you didn't have to hit reset; there was a way to switch it in software. Also on the CoCo 3, there was the 640 x 192 4-color "hires" mode. Way, way back - I believe published in Hot CoCo - someone figured out that using a television, and setting those 4 colors to the grayscale in the 64 color palette (black, dark grey, light grey, and white) - and with proper 4-bit pixel settings, you could get a virtual 128x192 image with colors. Basically the same technique (called artifact colors, or artifacting) - but applied to the high-res screen of the CoCo 3. Unfortunately - he sent it to Hot CoCo! Had he sent it to the Rainbow instead...things might have been different. You see, by sending it to that magazine, it didn't reach a large audience, so only a few people saw it, nobody much played with it, and it faded into history. On the Rainbow side of things, there were a couple of articles about using patterns of color to create "virtual colors" - but it was geared toward the RGB monitor (CM-8), and not really the TV - and using colors, not the gray scales... So - what am rambling about then? Well - long story short - this: http://richg42.blogspot.com/2014/02/the-little-known-color-computer-3s-256.html http://richg42.blogspot.com/2014/02/the-little-known-color-c... A virtually unknown "256 color" mode on the Color Computer 3 that was lost to history. Now - this isn't the mystery 256 color mode that has been described elsewhere hiding in the GIME chip (and most people believe that it is a false rumor; but the Microware CoCo 3 prototype holds out hope) - but it is a working "hi color" mode available on the CoCo 3. Unfortunately, today, it is only a curiosity more than anything, and it is unknown whether it could have been used back then; from what I recall, they had to use a PC to figure out the proper bit patterns for each of the colors, and that kind of processing would have been difficult at best back then. EDIT: This really shows off what is possible with the mode: http://atariage.com/forums/blog/105/entry-6693-color-computer-3-artifact-art/ http://atariage.com/forums/blog/105/entry-6693-color-compute...
- 8y ago

mrec 8y ago

Interesting! Sounds a bit like ClearType in reverse - there, the color determines the (perceived) position on the screen.

sp332 8y ago

I only know of one way to output accurate color from Apple II's to HDMI. This is new as of last year. You have to email the developer and he'll add you to the waiting list. http://atariage.com/forums/topic/285010-vidhd-hdmi-board-update/ http://atariage.com/forums/topic/285010-vidhd-hdmi-board-upd...

cr0sh 8y ago

For a little bit of completeness sake - it was also possible on the PC CGA card to gain artifact colors in certain modes, using a composite monitor. This led to some interesting possibilities, which were later exploited: https://int10h.org/blog/2015/04/cga-in-1024-colors-new-mode-illustrated/ https://int10h.org/blog/2015/04/cga-in-1024-colors-new-mode-...