Editing Apple II (original) (section)

==Display and graphics==
{{Main|Apple II graphics}}

Color on the Apple II series uses a quirk of the [[NTSC]] television signal standard, which made color display relatively easy and inexpensive to implement. The original NTSC television signal specification was black and white. Color was added later by adding a 3.58-megahertz subcarrier signal that was partially ignored by black-and-white TV sets. Color is encoded based on the [[phase (waves)|phase]] of this signal in relation to a reference [[color burst]] signal. The result is that the position, size, and intensity of a series of pulses define color information. These pulses can translate into [[pixel]]s on the computer screen, with the possibility of exploiting [[composite artifact colors]].

The Apple II display provides two pixels per subcarrier cycle. When the color burst reference signal is turned on and the computer is attached to a color display, it can display green by showing one alternating pattern of pixels, magenta with an opposite pattern of alternating pixels, and white by placing two pixels next to each other. Blue and orange are available by tweaking the pixel offset by half a pixel-width in relation to the color-burst signal. The high-resolution display offers more colors by compressing more (and narrower) pixels into each subcarrier cycle.

The coarse, low-resolution graphics display mode works differently, as it can output a pattern of dots per pixel to offer more color options. These patterns are stored in the character generator ROM, and replace the text character bit patterns when the computer is switched to low-res graphics mode. The text mode and low-res graphics mode use the same memory region and the same circuitry is used for both.

A single HGR page occupied 8&nbsp;KiB of RAM; in practice this meant that the user had to have at least 12&nbsp;KiB of total RAM to use HGR mode and 20&nbsp;KiB to use two pages. Early Apple II games from the 1977–79 period often ran only in text or low-resolution mode in order to support users with small memory configurations; HGR not being near universally supported by games until 1980.