Mosaicus

The C64 graphics tool I always wanted

Every other C64 tool I used did just enough for whoever wrote it, and I always ran into its limits before I ran into the C64’s. Mosaicus is a converter and a pixel editor built around the Commodore 64’s own rules, for a modern computer: drag a slider or paint a stroke and the result keeps up with you.

  • Measured, not guessed. Each cell’s colors are chosen for what the dither will actually mix, judged by how a C64 screen looks to the eye. Every method was tuned with care.
  • You steer every step. Framing, tone, palette, dither and each format’s colors.
  • A pixel editor that knows the rules. A pixel-perfect pencil, live gradients, 26 generated patterns (mazes, 10 PRINT, tartan, starfields), fills, shapes and selections, all kept within the format’s color limits.
  • Logos for demos and games. Charset logos fitted into 64 or 256 characters, and multicolor sprite sheets.
  • Many C64 formats. From the basic hires and multicolor bitmaps to FLI with sprites. Extreme formats for the Commodore 64 Ultimate, too.
Download 0.1.0 Read the help

For Windows, macOS and Linux. Free software under the MIT license; its source will be published in the future.

The Mosaicus window in its CRT view: an alien ambassador's portrait converted to Multicolor FLI + sprites, shown as a PAL TV would, with the tools on the left and the frame, preset, adjustment and color panels on the right

What it does

A converter that thinks about how a C64 screen looks to the eye, and a pixel editor that knows each format's limits.

  • The Frame tool on Bierstadt's Among the Sierra Nevada in Multicolor FLI + sprites: the source around the frame, the conversion inside it, and the Format and Frame panels
    The Frame tool: Bierstadt’s Among the Sierra Nevada scaled and placed, in Multicolor FLI + sprites.

    Converts any picture

    Photos, paintings, pixel art and transparent PNGs, framed by crop or fit, with brightness, contrast, gamma, saturation and more. Pictures already drawn in a C64 format open exactly as they are.

  • Hokusai's Red Fuji as a multicolor bitmap with a 4 by 4 ordered dither, at 2x, with the Colors and dither panel
    Hokusai’s Red Fuji in Koala with the ordered 4 × 4 dither, at 2×.

    Dithers your way

    Error diffusion (Floyd–Steinberg, Atkinson, Sierra and more), ordered patterns, blue noise and two-color pair mixes, with hard outlines kept clean.

  • A yellow pencil stroke over Friedrich's Wanderer above the Sea of Fog in hires, the cells it gave too many colors outlined in red
    A pencil stroke with clashes allowed: each hires cell it gave a third color is outlined, and the status bar counts them.

    Paints within the rules

    A pixel-perfect pencil, fills, 26 generated fills, a Gradient tool, shapes, text and stamps. Painting recolors the cell, refuses the pixel or marks the clash, as you choose, and exports always keep the format's rules.

  • A live radial gradient from blue through purple and pink to yellow, its two handles on the picture, and the gradient settings open: the ramp's colors, dither, angle, repeat, bias and offset
    A radial gradient while it’s live, with its settings: the ramp of colors, the dither, the angle and how the ramp repeats.

    Live gradients

    Linear, radial, diamond or conical, through any run of C64 colors, dithered or in bands. A gradient stays live until you apply it: drag its ends, change its colors, dither or ramp, and it follows at once.

  • The generated fills pop-up: a large preview of Iso cubes and the 26 generators as thumbnails, beside a blank multicolor picture filled with cubes
    The generated fills, each shown in the paint colors: Iso cubes filling a blank multicolor picture.

    Generated fills

    26 fills made for logo backgrounds and filler: mazes, 10 PRINT, bricks, tilings, tartan, plasma, starfields and more, each with its own settings, laid in the format’s own pixels.

  • A floating piece of the Earthrise photograph, scaled up and turned 25 degrees, with its handles
    A pasted piece of Earthrise, scaled up and turned 25° with RotSprite.

    Selections and transforms

    Rectangle, lasso and magic wand, saved selections, and floating pieces you can move, flip, scale, outline and turn at any angle with RotSprite.

  • Compare view: the Mona Lisa, the source left of the line and the multicolor FLI result right of it
    Compare: the source left of the line, the Multicolor FLI result right of it. The Mona Lisa.

    Checks your work

    Compare with the source, see brightness only, find stray pixels and jaggies, trace over the source, and sketch construction lines that are never exported.

  • Vermeer's Girl with a Pearl Earring in the CRT view, as a PAL TV over composite shows it, with the Screen, Signal and Tube panels
    Vermeer’s Girl with a Pearl Earring on a PAL TV over composite, with the Screen, Signal and Tube panels.

    Shows it on a CRT

    A model of a PAL or NTSC TV from the video signal up: composite or S-Video, the delay line, the phosphor mask, the beam and the glow.

  • Chooses the best pixels

    Each cell's colors are chosen for what the dither will actually mix, judged by how a C64 screen looks. A fast conversion while you adjust, refined to best quality when you pause.

  • Exports what fits

    Classic C64 paint program files, raw data, assembly for KickAssembler, ACME or 64tass, PNGs, and a .prg that shows the picture, with its viewer as source you can build.

  • Runs it on a C64

    One key runs the picture in VICE, or on a C64 Ultimate or Ultimate 64 over the network.

Every C64 picture format worth having

From the classic hires and Koala bitmaps every C64 shows, through FLI and sprite overlays, to formats that only a C64 Ultimate at 48 or 64 MHz or a SuperCPU can show. Each conversion keeps to the format's rules exactly, so what you see is what the C64 shows.

Van Gogh's The Starry Night as a multicolor bitmap
Multicolor bitmap (Koala)A background plus three colors in each 4 × 8 cell. Any C64. The Starry Night, more saturation and contrast.
Dürer's Rhinoceros woodcut as a hires bitmap
Hires bitmap320 × 200, two colors in each 8 × 8 cell. Any C64. Dürer's Rhinoceros, no dither: line art suits hires.
Hokusai's The Great Wave as hires FLI
Hires FLI (AFLI)Two colors in each 8 × 1 cell: new colors on every line. The Great Wave.
The Mona Lisa as multicolor FLI
Multicolor FLITwo colors of each 4 × 1 cell's own, new on every line. The Mona Lisa, framed on her face.
An alien ambassador's portrait as multicolor with sprites
Multicolor + spritesUp to 64 multiplexed sprites over a Koala picture, for more color and detail. An alien ambassador.
Buzz Aldrin on the Moon as hires with sprites
Hires + spritesA hires bitmap with up to 64 multiplexed sprites behind it for more color. Any C64. Aldrin on the Moon, 1969.
The Pillars of Creation in hires with 16 colors per pixel
Hires, 16 colors per pixelAny color on every hires pixel, raced at 64 MHz on a C64 Ultimate. The Pillars of Creation.
The Earth from Apollo 17 as chunky 160 by 200
Chunky 160 × 200Any of the 16 colors on every wide pixel, on a C64 Ultimate. The Blue Marble, fitted inside.
A chrome logo over an inferno, as multicolor with a background per 4 by 1
Multicolor, background per 4 × 1A Koala picture with a background of each 4 × 1 cell's own. Needs a SuperCPU. A chrome logo over an inferno.

Each picture chosen for its format and converted by Mosaicus with settings tuned for it, the tone too (why tone matters); no hand edits. Apart from the alien ambassador and the chrome logo, the pictures are public domain (credits). All the formats

Learn it

The help explains every format, tool and option, from your first picture to the viewer source.

Your first picture All the help