Retro Graphics Viewer & Converter — C64 (.KOA, .ART) & ZX Spectrum (.SCR)

This utility operates 100% inside your browser using HTML5 Canvas and typed JavaScript ArrayBuffer views. Whether you are inspecting raw binary dumps from a vintage floppy disk or encoding modern artwork into native 8-bit video RAM formats, no files are ever uploaded to a server.

Hardware Limits & Binary Memory Maps

• Commodore 64 Multicolor KoalaPaint (.KOA — 160×200 Double-Wide Pixels, 10,003 Bytes): Driven by the MOS 6567/6569 VIC-II. Bytes $0000–$0001 store the $6000 load address; $0002–$1F41 (8,000 B) store the 2-bit-per-pixel bitmap; $1F42–$2329 (1,000 B) store Screen Matrix RAM; $232A–$2711 (1,000 B) store 2114 Colour SRAM nybbles; and $2712 (1 B) stores the global background colour ($D021). Each 4×8 multicolor cell can display at most 3 unique cell colours plus the shared global background colour.
• Commodore 64 Art Studio Hi-Res (.ART — 320×200 Pixels, 9,002 Bytes): Uses a $2000 load address header (2 B), an 8,000-byte 1-bit high-resolution bitmap, and 1,000 bytes of Screen RAM allowing 2 unique colours (1 foreground, 1 background) per 8×8 character cell.
• Sinclair ZX Spectrum Screen Dump (.SCR — 256×192 Pixels, 6,912 Bytes): Addressed by the ZX Spectrum ULA. Bytes $0000–$17FF (6,144 B) store the non-linear interleaved 1-bit pixel bitmap, followed by $1800–$1AFF (768 B) for the 32×24 colour attribute grid. Each 8×8 cell supports 2 colours (INK bits 0–2 and PAPER bits 3–5) sharing a single BRIGHT bit (bit 6) and FLASH bit (bit 7).

Pro Tips for Best 8-Bit Conversion Results

• Boost Contrast Before Dithering: 8-bit palettes like the VIC-II Pepto/Colodore LUT have muted mid-tones. Adding +10 to +20 contrast separates foreground subjects from background cells and reduces colour clash.
• When to Use Floyd-Steinberg Dithering: Enable Floyd-Steinberg dithering (around 75%–90% strength) for photographic portraits, gradients, and painted artwork. Disable dithering (0%) for pixel art, logos, or text where crisp solid colour cells are preferred.
• Locking C64 Background Register ($D021): Because every 4×8 Koala cell shares colour 00 ($D021), locking the background dropdown to $00 Black or $0B Dark Grey often preserves dark outlines across the entire 40×25 screen matrix.