Amiga OCS Palette Calculator
Computes simultaneous colors and required bitplanes for Amiga Original Chip Set video modes per chosen horizontal width.
—
Amiga OCS color palette
The Amiga OCS (Original Chip Set, 1985) pushes video through the Denise chip, which carries a master palette of 4096 colors stored as 12-bit RGB (4 bits per channel, $RGB nibbles). How many of those you actually see in a single frame comes down to the bitplane count: 1 bitplane gives 2 colors, 2 gives 4, 3 gives 8, 4 gives 16, and 5 bitplanes = 32 colors in lowres (320×256 PAL / 320×200 NTSC). The famous HAM6 mode (Hold-And-Modify, 6 bitplanes) gets all 4096 colors on screen by holding two channels and modifying one per pixel, and the price you pay is color fringing. EHB (Extra HalfBrite) spends its 6 bitplanes on 64 colors instead: 32 base plus 32 darkened versions. The 32 palette registers live at $DFF180–$DFF1BE.
Applications
Retrocomputing and Amiga homebrew (vasm, vbcc, AmigaOS 1.3), Amiga demoscene productions like Eurocharts and Breakpoint, moving IFF ILBM images to and from PNG, pixel-art workflows on vintage hardware, and writing emulators such as FS-UAE and WinUAE.
FAQ
Why 12-bit RGB and not 24-bit? The 1985 Denise chip had a modest DAC. Four bits per channel fit the silicon budget of the day and still gave you 4096 distinct colors, which was plenty back then.
Is HAM6 truecolor? Almost. It does show all 4096 palette entries at once, but each pixel can only change one channel relative to its left neighbor, which is why you get color bleed on sharp transitions.
OCS vs ECS vs AGA? OCS is the original from 1985, with its 4096 colors. ECS arrived in 1990 as the enhanced version: same 4096, but higher resolutions. AGA (1992, A1200/A4000) is the big leap, with a 24-bit / 16.7M palette, 256 on-screen colors and HAM8.
Related Tools
C41 Color Development Time by Temperature
Estimates C41 color film development time by bath temperature.
RGB Color Temperature
Estimate the correlated color temperature (Kelvin) of an RGB color via McCamy approximation.
Star Color Temperature Calculator
Estimates effective star temperature in Kelvin from the B-V color index using Ballesteros approximation.
Beer SRM Calculator
Calculates beer SRM from malt color and amount.
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.
Peak Flow Rate (PHF)
Calculate the peak flow rate of a roadway, q = V ÷ PHF, dividing the hourly volume V (vehicles/h) by the peak hour factor PHF (between 0 and 1, the ratio of the hour's volume to four times the busiest 15-minute volume). The result, in vehicles/h, is the equivalent flow rate of the busiest 15-minute period — always greater than or equal to the hourly volume, since traffic does not arrive uniformly. It is the design flow used in capacity and level-of-service analysis by the HCM, since sizing by the hourly average would underestimate the peaks. Enter the hourly volume and the peak hour 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.