Why Does My Photo Conversion Look Blocky?

A photo can hold millions of colors. A bead palette holds a few hundred at most, and a pattern uses perhaps twenty. Squeezing one into the other is where blockiness comes from: smooth gradients such as a sunset sky or a cheek in soft light turn into flat stripes, and edges turn into stair-steps. The good news is that blockiness usually has one or two clear causes, and each has a setting that addresses it.

Why it happens

• Too few colors. With a low Max Colors setting, a gradient that needs ten shades is forced into three, and you see bands where one shade jumps to the next.
• Too few beads across. Every bead is one square of color. At 40 beads wide a face has only a handful of beads for each eye, so curves become steps. This is a limit of size, not of settings.
• No dithering. Without it, each bead takes the single nearest color, and nothing softens the jump between shades.
• A hard-to-convert photo. Busy backgrounds, low contrast and soft focus all turn into noise or mush at bead scale.
• The palette itself. A bead brand may simply not have the in-between shade the photo needs.

Dithering: the main fix for banding

Dithering scatters beads of two nearby colors so that, from a normal viewing distance, your eye blends them into the shade in between. It is the same idea as a pointillist painting or the dots in a newspaper photo. In the Import Photo dialog it is the Dithering menu, and Floyd-Steinberg is the default.

The methods are all forms of error diffusion: when a bead cannot match the photo exactly, the leftover difference is passed on to neighboring beads, so the area as a whole comes out right. They differ in how widely they spread it. Floyd-Steinberg is a good all-round choice. Atkinson tends to keep flatter, cleaner areas and slightly more contrast. Stucki, Sierra and Burkes spread the difference over a wider neighborhood, which can look smoother. The effect is easy to judge on your own photo, so try two or three and compare the preview.

Secondary Dither lets you mix two methods, and a Blend slider then sets the balance between the first and the second. It is a fine-tuning control; most photos do not need it.

Set Dithering to None for flat artwork, logos and lettering. Scattering beads across a solid area just makes it look speckled.

Quantization: how colors are grouped

Before beads are matched, the photo’s colors are reduced to the number you set in Max Colors. The Quantization menu picks the method. Median Cut is quick. K-Means is slower and often groups colors better, which can help when a photo has a lot of subtle shading or a small but important color, such as a red flower on green. Neither one scatters beads the way dithering does; they decide which colors the pattern will use.

A worked example: a sunset

You import a sunset and the sky shows three hard orange stripes. Work through the settings one at a time, checking the preview after each:

1. Raise Max Colors from 20 to 30. If the stripes get narrower, color count was part of the problem.
2. Confirm Dithering is on (Floyd-Steinberg). Stripes that melt into a gradient mean banding was the cause.
3. Try K-Means under Quantization. If the sky is still coarse, compare Atkinson or Stucki.
4. If edges are still stair-stepped, raise Max Width. A wider pattern means more beads for the same picture, and the finished piece is larger or needs smaller beads.

Other things that help

• Adjust the photo first. Brightness, Contrast and Saturation sliders change the picture before conversion. A little extra contrast often rescues a dull photo.
• Try Auto-Optimize Settings. It analyzes the photo and suggests Max Colors and dithering; you can still change them.
• Use Grayscale Mode for a black-and-white look. Working with only gray beads removes color noise and can look more refined for portraits.
• Run Cleanup afterwards. Dithering can leave single stray beads, and Cleanup replaces isolated beads with the color around them.
• Crop to the subject. Every bead spent on background is a bead not spent on the face.

When blocky is the honest answer

Some blockiness is part of the medium. A bead pattern is a grid of colored squares, and a pattern 60 beads wide cannot hold the detail of one 150 beads wide. If a conversion looks coarse at every setting, check the width and the bead size before blaming the settings. Choosing the Right Bead Size shows how width, bead size and finished dimensions fit together, and How to Turn a Photo into a Bead Pattern walks through the whole import. For choosing colors by hand, see Color Theory for Bead Patterns. For the technical background on dithering, see the Glossary.