What the slider controls

Before any outline is drawn, the tracer chooses a small set of flat colors for your image. It looks only at the solid insides of shapes, not at their soft edges, groups those pixels into colors, merges colors that are practically the same, and adds back small but clearly different colors such as a thin outline or an accent dot while the slider allows. The slider is the most it may use: "Colors, up to 8" means eight at most, and a logo with five colors comes back with five.

Every pixel then gets one of those colors. A pixel on an edge is decided between the two colors on either side of that edge, so the blend between a black letter and a white background never becomes a gray color of its own. Each connected area of one color becomes a <path> with that color as its fill: the SVG is grouped by object (the background first), and inside each object the shapes are nested by what encloses what, each shape its own path.

So the slider is really "how many distinct fills may the result have". It is not a sharpness or detail slider.

The presets' starting points

  • Standard: 8
  • Cricut / Vinyl: 4 (and Remove background switches on)
  • Line art / Stencil: always 2, black ink and white paper; the slider is switched off while this preset is selected
  • Detailed artwork: 16

With Standard, Cricut / Vinyl and Detailed artwork you can move the slider after choosing the preset; the range is 2 to 24.

A method that works

  1. Name the colors. Look at the image and list the distinct fills you can see. Ignore anti-aliased edges and JPEG noise — those are not colors you want.
  2. Add one for the background if it is opaque and you are not removing it.
  3. Set that number and convert. Previews are free.
  4. Read the palette strip in the result. If two fills you listed came out as one, go one higher. If a fill you did not list shows up as a near-copy of another (two slightly different reds), go one lower.
  5. Read the palette, not the path count. The result is grouped by object with every shape its own path, so an image usually has more paths than colors. Set Layers to By color in Settings if you want exactly one path per color.

What happens at the extremes

Too low. Neighboring fills merge: a dark blue and a black become one black shape, and a light gray highlight vanishes into white. On a photo, 2–4 colors produces the poster look — sometimes exactly what you want for a stencil.

Too high. On flat artwork, usually nothing: the palette stops at the colors the image has, so 8 and 16 give the same result. On a noisy JPEG, a large fill can occasionally split into two very close shades. On shaded artwork and photographs every extra color is one more band, so the file gets bigger and the bands get narrower.

Six flat icons traced at 2, 4, 8 and 16 colors: at 2 the coral is gone and the paper has turned pink; at 4, 8 and 16 the results are the same

Six of our guide icons, which have four flat colors (blue, navy, coral and white paper), traced at 2, 4, 8 and 16 colors (left to right, top to bottom). At 2, coral merges away and tints the paper; at 8 and 16 the palette stops at the 4 colors the image has, and all three give the same 29 paths.

Special cases

  • Two-tone logos on transparent backgrounds: 2. Transparent pixels never count as a color.
  • Illustrations with shading: the Detailed preset's 16 is a reasonable start, but expect visible bands where a gradient was. Use the SVG editor to recolor bands afterwards if the banding is acceptable but the tones are off.
  • Screenshots or UI mock-ups: often 8–12 works, because they are already flat; text will trace as shapes, not editable type.
  • Photographs: see the guide on why photos posterize; the color count changes how many bands you get, not whether banding happens.

Holes and overlaps

A hole — the inside of a ring or of a letter "O" — stays open under either SVG fill rule, including in programs that ignore the file's fill rule. You do not need to raise the color count to "see" a hole.

Colors are stacked largest area first. Where a small fill sits completely inside a larger one — a white star on a blue badge — the larger color is drawn solid underneath and the small fill sits on top of it, and every color continues a little way under the colors drawn over it, so no background shows through along the seams. That is why a two-color badge on white can be traced with 3 colors and still look right.