Secret colours of the Commodore 64
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Secret colours of the Commodore 64
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Re: Secret colours of the Commodore 64
#2This overlooks a key detail, namely interlacing. The C64 wasn't producing 60 frames per second, but rather 60 fields: sets of odd or even scanlines. So on the CRT TVs of the time, you'd get one colour on the odd scanlines, and another on the even scanlines. Scanline striping, essentially.
Re: Secret colours of the Commodore 64
#3Near the bottom, I wonder if high-speed img flipping in js could be done by absolute-positioning the two images and toggling display:none/display:block (or flip the z-index above/below) on the upper layer on every animation frame?
Re: Secret colours of the Commodore 64
#4This overlooks a key detail, namely interlacing. The C64 wasn't producing 60 frames per second, but rather 60 fields : sets of odd or even scanlines. So on the CRT TVs of the time, you'd get one colour on the odd scanlines, and another on the even scanlines. Scanline striping, essentially.
Great point.
I wonder how much better the modern version of this effect (as seen in the article) would be if they implemented this.
Re: Secret colours of the Commodore 64
#5The page http://vik.cc/dvik-joyrex/download/105Colors.ppt has an algorithm to convert a 24-bit RGB to interlaced 8-bit on the MSX palette.
Re: Secret colours of the Commodore 64
#6This overlooks a key detail, namely interlacing. The C64 wasn't producing 60 frames per second, but rather 60 fields : sets of odd or even scanlines. So on the CRT TVs of the time, you'd get one colour on the odd scanlines, and another on the even scanlines. Scanline striping, essentially.
I was under the impression that there must have been some additional signaling to make interlacing happen. If for no other reason than the display would need to know which frame was the upper scanline and which was the lower.
Apart from the fact that they would have advertised the increased resolution (albeit flickery). On the Amiga, which did do interlaced modes. you could tell on a screen showing a single colour whether it was interlaced or not.
Re: Secret colours of the Commodore 64
#7Brilliant talk on using these techniques to draw hires color pix on c64. The NUFLI technique is based on combining hires mono images with color sprites underneath AND color flashing.
Re: Secret colours of the Commodore 64
#8This overlooks a key detail, namely interlacing. The C64 wasn't producing 60 frames per second, but rather 60 fields : sets of odd or even scanlines. So on the CRT TVs of the time, you'd get one colour on the odd scanlines, and another on the even scanlines. Scanline striping, essentially.
If the TV displays N fields per second, and the C64 produces N fields per second, then you'll see one at a time. The only effect of the interlace is to shift alternate frames down by 0.5 scanlines. TV phosphor decay is too rapid for anything else to happen. By the time the next field starts the previous one is already gone. (I took some short-exposure shots with my camera and it looks like the phosphor decays from white to black in less than 1/6th of a frame.)
(Well... it's been a long time since I've seen a C64 plugged into a TV, but I don't see how anything else could happen! You definitely don't get an alternating effect from a BBC Micro.)
Re: Secret colours of the Commodore 64
#9I once toyed with Temporal dithering on VGA ModeX.
While the bullet point listed resolution for standard VGA was 320x200. Hitting the hardware registers and paying the price of a rather peculiar addressing mechanism for pixels you could get a lot more(and double buffering to boot).
320x240 was the most common tweaked mode, because it gave you square pixels and page flipping.
At the edge of what momitors could handle there was a 400x300 mode which ran at 87Hz Flipping two images with this mechanism give you a 43Hz shimmer, which is amost impossible to pick on colours if the two components are similar luminance.
I never saw this get used for anything, but it would have made an excellent paint program for standert VGA.
Re: Secret colours of the Commodore 64
#10This overlooks a key detail, namely interlacing. The C64 wasn't producing 60 frames per second, but rather 60 fields : sets of odd or even scanlines. So on the CRT TVs of the time, you'd get one colour on the odd scanlines, and another on the even scanlines. Scanline striping, essentially.
That isn't quite correct. The C64 outputs a progressive-scan image, which is a hack on top of NTSC or PAL. In this configuration, there are only even or odd fields, which double-strike the same area. Thusly, it is 60 fields per second, and since only one field forms the full frame, it's 60 frames per second as well.
There is no scanline striping; that is strictly an artifact of poor NTSC capture devices (like most HDVTs) that naively assume the incoming signal is a 480i image with odd and even fields.