The remaining failures showed up across four images and they shared a shape. A phantom sky-blue snuck into the dragon-fruit palette from a tiny pocket of cool shadow pixels. Brown was unwelcome in the telephone palette. The bicycle returned three reds and two warm-tinted grays when the image is a near-grayscale scene. The Pantone deck returned two light gray swatches instead of one. Three small structural changes addressed what more merge-distance tuning could not.

First, before any forced collapse, any cluster whose pixel weight is below 2.5% and whose centroid chroma is below 0.05 was dropped. Population alone can't separate phantoms from real small accents, fruit's phantom blue is at 2.31% and bicycle's red bell is at 1.04%. Dropping the cluster outright was cleaner than merging the phantom and hoping it wasn’t promoted in the next pass.

Second, allocate slots by mass by counting how much of the image is achromatic versus chromatic. The bicycle image is 97% achromatic, lion is 100%, fruit is 0%. Achromatic slots are reserved in proportion to that mass, while saving room for chromatic accents. Achromatic clusters are bucketed into dark, mid, and light. Two clusters that fall in the same bucket read as the same role even when they're mathematically distinct. Collapsing same-bucket pairs gives the Pantone image one slot for paper instead of two, and the freed slot moves to the chromatic side. An exception keeps lion's grayscale ramp intact when there are no chromatic clusters to fall back to.

Third, swatches are chosen depending on whether the cluster is essentially chromatic or essentially gray. Previously, the highest-chroma pixel within the cluster's typical radius of the centroid became the swatch. But, when the centroid sits in mostly-gray territory, the highest-chroma pixel is a warm-tinted outlier from the cluster's edge, and the swatch reads as sepia or mauve or sage green even though the cluster is essentially gray. Now, when the centroid's chroma is below 0.03, the pixel closest to the centroid is chosen instead, whereas the original highest-chroma rule still applies for any cluster whose centroid is clearly chromatic.

If I tackle another round, I'll thin same-family ramps so the lightbulb image returns one or two pinks instead of four, collapse cross-side near-duplicates so the ink image doesn't return both a warm dark and a near-black, and sort same-family swatches by lightness so the wood image reads as a smooth ramp.

This iteration does enough to make the palette feel more human-selected, without hard-coding edge cases or optimizing for any specific test scenario. In the Spectrimage app, the user can adjust any of the swatches before saving the palette.