Apple II Hi Res Resolution Calculator
Computes pixels and bytes occupied by Apple II hi res 280x192 screen with 6 active bits per byte and color bytes per line.
—
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.
Related Tools
Pixel Resolution Image Size Calculator
Computes megapixels and estimates raw file size in megabytes from image width, height and bits per pixel color depth value.
ADC Resolution
Compute the resolution of an analog-to-digital converter (ADC), R = FSR/2ⁿ, dividing the full-scale range (FSR, in volts) by the number of levels (2 to the power of the number of bits). It is the smallest voltage step the converter distinguishes — the more bits, the finer the resolution: a 12-bit ADC divides the range into 4096 levels. Fundamental in data-acquisition and digital-instrumentation design. Enter the full-scale range and the number of bits.
Maya Mental Ray Render Time by Resolution
Estimates Maya Mental Ray render time from resolution and frames.
Blender Eevee Render Time by Resolution
Estimates total Blender Eevee render time from resolution and frames.
Spectrum Attribute Clash Calculator
Computes how many 8x8 attribute clash regions exist on a 256x192 pixel ZX Spectrum screen used by the famous color hardware issue.
Stepper Motor Resolution
Compute the angular resolution of a stepper motor, R = 360°/(steps per revolution · microsteps), the smallest angle the shaft can position. A common 200-step motor (1.8°/step) with 16 microstepping reaches 0.1125° per microstep — 3200 positions per revolution. Microstepping smooths motion and raises resolution, though it lowers the holding torque per microstep. Enter the steps per revolution and the microstepping factor.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.