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How many colors a chart needs

The slider goes up to thirty. That is not a recommendation: past a certain point every extra color adds another skein to buy and another thread to switch, and almost nothing to the likeness.

Updated

Color count is the one builder setting that changes both how the chart looks and how long the piece takes. Every color in the legend is a skein to buy and another thread to switch to mid-row. So the question is not which count is most accurate — the maximum is. The question is where accuracy stops being worth the work.

What actually disappears

Below is one picture put through the builder four times. Only the color slider changed; width, fabric and everything else are identical. These are not mock-ups: the charts are built by the same code that processes your photo, and they were generated while this page was being assembled.

Source image: a flower drawn by formula, with smooth tonal transitions

Source image

Chart with a palette of 4

Colors requested4

Chart with a palette of 8

Colors requested8

Chart with a palette of 11

Colors requested12Palette after quantization: 11

Chart with a palette of 19

Colors requested20Palette after quantization: 19

One source, four palettes. A 40 × 40 chart, which on Aida 14 works out at roughly 7 × 7 cm.

At four colors the flower is still recognizable, but the center is gone entirely — the gold ring and the dark middle have merged into the petals, because no separate shade was left for them. The background has split into two flat blocks with a visible seam: where the original has a smooth gradient, the chart has to pick one or the other.

At eight the dark center comes back, though the gold around it does not. At twelve both the gold ring and the soft shading on the petals return. Between twelve and twenty, though, you have to hunt for the difference: a slightly smoother background, a slightly softer shadow on one petal. Eight more skeins for that.

This threshold moves with size. The larger the chart, the more cells fall across each transition, and the more the extra shades earn their place. On a chart 200 stitches wide twenty colors make sense; on the 40 stitches shown here they simply vanish.

So how many

A practical way to choose: set the slider to 10, then add two at a time and watch the chart. The moment two more colors change nothing you can see is your ceiling. It differs for every picture, which is exactly why there is no single right number.

Why you sometimes get fewer than you asked for

The builder is not obliged to return exactly the number on the slider. It looks for groups of similar shades inside the picture itself, and if the picture is simpler than the request, there is nothing to fill the extra groups with. On a flat logo there will be no difference at all between ten and twenty. That is fine: the legend always shows the real number of threads, not the one you asked for.

The reverse happens too. If you placed a color by hand and then reduced the palette, that thread stays in the legend as its own row — you chose it deliberately, and the builder has no business removing it.

In short

How many thread colors should a cross stitch chart have?
For a first project, 8 to 12: enough for a recognizable image without much to buy or switch between. A portrait with soft shading wants 12 to 18. More than 20 only pays off on a piece from 150 stitches wide — on anything smaller the extra shades are invisible.
Why does the legend show fewer colors than I set on the slider?
The slider sets an upper limit, not an exact count. The builder looks for groups of similar shades within the picture, and if it is simpler than the request there is nothing to fill the extra groups with. The legend always shows the real number of threads to buy.

The numbers and charts on this page are computed by the same code as the builder.

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