How Apple II NTSC video works
I am working on a Windows application that will take a graphics file and convert it to Apple II graphics format.
Right now I'm just trying to understand how a certain pixel pattern will look in color NTSC. The Apple II reference manual tries to explain this, but it seems like it is missing out on many details.
The basic idea is simple. The Apple II generates two pixels per colorburst cycle, so one can change the color by selecting which pixels are on and which are off. E.g. an alternating pattern of 010101... will give a certain color, while 101010... gives another color.
If displaying only one row with this pattern, every other pixel will be black. However if displaying TWO adjacent rows with this pattern, NO pixels are black. This is one thing the reference manual says nothing about.
Also, if the first pattern (010101...) is used on one row, and the other pattern (101010...) is used on the next row, every other pixel will be black and every other will be white.
So it seems like the appearance of every pixel depends on ALL adjacent pixels (up, down, left, right)... or?
Can someone explain how this works? How can I determine what color a pixel will have?