Apple II Hi Res Resolution Calculator

Apple II HiRes graphics

The Apple II HiRes mode (1977) gives you a 280×192 bitmap with 6 colors: black, white, green, violet, orange and blue. Those colors aren't stored anywhere; they come out of NTSC chroma artifacting. Pairs of adjacent pixels in even and odd columns get read as a color signal, so even a single isolated pixel turns green or violet (page 1, high bit = 0), or orange or blue if the high bit is 1. The framebuffer takes 8 KB per page, with page 1 at $2000–$3FFF and page 2 at $4000–$5FFF. The row layout is famously non-linear, interleaved in groups of 8 and 64 rows, which means you need some clever bit twiddling to draw fast. Each byte carries 7 pixels plus 1 high bit that picks the palette pair. HCOLOR= in Applesoft BASIC maps onto these 6 colors plus 2 blacks/whites.

Applications

Retrocomputing on the Apple II/IIe/IIc/IIgs, Applesoft BASIC and 6502 assembly tutorials, vintage emulators like AppleWin, MAME and Virtual ][, homebrew game development with cc65 or Merlin32, pixel-art conversion into .HGR / .BIN formats, and demoscene work that runs on real hardware through SD-card adapters such as the CFFA3000 or Floppy Emu.

FAQ

Why is the row order so weird? Steve Wozniak interleaved the rows so that the same 1-bit DRAM refresh logic could handle both video scanning and CPU memory access, which cut down the chip count. The formula: address = $2000 + (row & 7)*$400 + (row >> 3 & 7)*$80 + (row >> 6)*$28.

Why only 6 colors? They fall out of NTSC composite encoding as a side effect; there's no real color RAM behind them. Hook the machine to a green monochrome monitor and everything stays monochrome. On a color TV the chroma subcarrier reads pixel pairs as hue.

Double Hi-Res? The Apple IIe (1983, with the 80-column card) doubled the resolution to 560×192 with 16 colors by bank-switching auxiliary memory. Later commercial games leaned on it a lot.