At the time, I had no idea what they meant, but as I worked on the tablet I began to understand the color anomalies. Any pixel on the screen can be black or white, but only pixels with odd X-coordinates could be green or orange. Likewise, only even X-coordinates can be purple or blue. There were small companies that were building circuit boards to add more colors to the Apple Il’s hardware, but I wanted to see what I could come up with using the tool for creating different “brushes” defining pixel by pixel. I started experimenting and found that by manipulating each pixel I could create patterns that looked like more colors. This is similar to what happens when we look at a painting by Georges Seurat, who lived in the late 1800s and developed a very scientific way of painting known as Pointillism. He used tiny dots of pure color, side by side, to build the people and landscapes in his paintings. Seen from a distance, these tiny dots of paint appear to blend. Using a pointillist approach, I was able to create patterns that optically blended to create other colors. (Of course, television using only red, green and blue dots, creates color television.)
Woz was a master of getting the most out of computer memory. The first Apple II had 4 kilobytes memory, then 16 , and when I got my Apple II+ it had 48 kilobytes. (One megabyte is equivalent to 1024 kilobytes.) Now most computers have so much memory that users rarely think about it. But in 1979 memory was very expensive and the goal was to get the most out of it. The way Woz managed to create High Resolution graphics is no less than brilliant, but using less memory had trade offs.
In the manual on the Graphics Tablet there is a section called “Unusual Color Effects” that gives a description of the Apple II colors.
“You may have already noticed that a few strange things happen when you try to use certain combinations of colors with the Graphics Tablet. Don’t worry: these are normal, predictable phenomena which are caused not by the Tablet, but by the Apple itself.
The Graphics Tablet displays its picture using the Apple’s high resolution graphics mode. In this mode, there are 53,760 individual dots on the screen, and six colors (black, white, orange , blue, green and violet). The Apple should therefore need several hundred thousand individual “bits” of information to form a picture. But the Apple uses only 65,536 bits of information (organized into 8,192 eight bit “bytes” to form a picture! ...”
©Lucia Grossberger Morales 2015