Method of stitching overlapping printhead segments

Summary

Pagewide inkjet printers use multiple heads with overlap zones where both heads can lay down ink on the same region. The overlap is necessary — it gives the heads flexibility in sharing responsibility for the join — but it also creates an ambiguity. Which head should print which pixel inside the overlap? Pick wrong, and slight head misalignment turns a clean image into a streaky one.

The standard answers are either a hard line (one head handles left, the other handles right — fast, but the line is visible on photographs) or a soft fade across the entire overlap (better on photos but vulnerable to moiré when heads are misaligned, and impossible to tune without test-printing every job).

This patent claims the stitching algorithm itself: a content-aware seam that threads through the overlap zone pixel by pixel, preferring low-ink and high-luminance regions and routing around high-density content. The cost function can be weighted by human visual sensitivity to different colors, so the seam hides where the eye is least likely to spot it. Because the path adapts to each image, the same algorithm works on text, photos, and mixed content without per-job tuning, and stays robust as printheads drift out of perfect alignment in normal operation.