Why doesn't the NES show artifact colors like, for example, the Apple II? The NES has 256 pixels and the Apple II has 280 pixels, yet only the latter shows artifacts with alternating pixel/no pixel graphics. From what I have read here and elsewhere, I can come up with the following factors that tend to eliminate most visible artifacting.
1. 5.37MHz Pixel Clock
The NTSC Color Carrier is 3.58MHz, which gives 160 pure horizontal pixels per line. The 5.37MHz pixel clock gives us 256 pixels per line, but because the dot clock exceed the color clock, the pixels are not quite as pure as we would like. The Apple II uses a 7.16MHz pixel clock, which would ordinarily give us 320 pixels per line. Apple blanks out the first 40 pixels for each line, and did this either to save memory or ensure that all graphics would be within the visible area of the monitor. The IBM CGA card also uses a 7.16MHz pixel clock and gives a true 320 pixels per line. We do not have that nice 2:1 ratio that really bring out the artifacts, but still artifacts can exist at 256 pixels, just look at the Sega Master System's Shinobi in Stages 2-1 and 2-3. The background warehouses show something really like artifact color, especially when the screen scrolls.
2. 1/3 Pixel Shift Every Scanline
The NES does not put out an integer number of pixels, the last pixel is a fractional pixel. From the first displayed line, this causes the graphics to shift to the left on the second displayed line. Then the graphics are further shifted on the third line in relation to the second. This is easy to see on a column of colored pixels next to black, the classic example are the Inventory boxes in the Legend of Zelda. This pixel shift helps break up the solid wall of color that artifact colors work best with. However, with those games that do use alternating vertical lines of color like Spy vs. Spy, you can still get something like diagonal artifacting going on.
3. Missing Pixel Every Other Frame
Here is what really kicks the artifact colors to the curb. The NES shifts its its drawing by one pixel back and forth every frame. I think this is what they call the dot crawl effect, but it has the effect of further eliminating the artifact color since to the eye because it is never in the same place long enough to notice. However, many composite capture devices do not seem to get this part right, because instead of showing slightly crooked alternating lines, they give a sort of diagonal artifacting effect, as seen in this video of Spy vs. Spy : https://www.youtube.com/watch?v=LJC7DIP5JIw Is this an issue with capturing itself, whereas the properties of a CRT tend to show something different?
So, did I miss anything here?
1. 5.37MHz Pixel Clock
The NTSC Color Carrier is 3.58MHz, which gives 160 pure horizontal pixels per line. The 5.37MHz pixel clock gives us 256 pixels per line, but because the dot clock exceed the color clock, the pixels are not quite as pure as we would like. The Apple II uses a 7.16MHz pixel clock, which would ordinarily give us 320 pixels per line. Apple blanks out the first 40 pixels for each line, and did this either to save memory or ensure that all graphics would be within the visible area of the monitor. The IBM CGA card also uses a 7.16MHz pixel clock and gives a true 320 pixels per line. We do not have that nice 2:1 ratio that really bring out the artifacts, but still artifacts can exist at 256 pixels, just look at the Sega Master System's Shinobi in Stages 2-1 and 2-3. The background warehouses show something really like artifact color, especially when the screen scrolls.
2. 1/3 Pixel Shift Every Scanline
The NES does not put out an integer number of pixels, the last pixel is a fractional pixel. From the first displayed line, this causes the graphics to shift to the left on the second displayed line. Then the graphics are further shifted on the third line in relation to the second. This is easy to see on a column of colored pixels next to black, the classic example are the Inventory boxes in the Legend of Zelda. This pixel shift helps break up the solid wall of color that artifact colors work best with. However, with those games that do use alternating vertical lines of color like Spy vs. Spy, you can still get something like diagonal artifacting going on.
3. Missing Pixel Every Other Frame
Here is what really kicks the artifact colors to the curb. The NES shifts its its drawing by one pixel back and forth every frame. I think this is what they call the dot crawl effect, but it has the effect of further eliminating the artifact color since to the eye because it is never in the same place long enough to notice. However, many composite capture devices do not seem to get this part right, because instead of showing slightly crooked alternating lines, they give a sort of diagonal artifacting effect, as seen in this video of Spy vs. Spy : https://www.youtube.com/watch?v=LJC7DIP5JIw Is this an issue with capturing itself, whereas the properties of a CRT tend to show something different?
So, did I miss anything here?