LINES & EDGES · NOVEMBER 9, 2026
Coloring Page Maker: Can Similar-Brightness Colors Still Create an Outline?
Yes. In one controlled test, a red-green boundary with nearly equal calculated brightness still produced a line in Clean Outline. A grayscale control with no boundary produced no seam. This was one synthetic image pair and one Chrome run, not a result that predicts every photo or style.
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What we compared
We made two 640 × 480 PNGs with the same white background and centered rectangle. The color version split the rectangle into RGB (200, 0, 0) red and RGB (0, 102, 0) green. Using the weighted brightness formula 0.299R + 0.587G + 0.114B, the two regions measure about 59.8 and 59.9 on a 0–255 scale. The control used RGB (60, 60, 60) on both halves, so it had no center boundary.
Both inputs were opened in the production Maker snapshot in Chrome 156.0.8078.80 with Clean Outline and A4 selected. We saved the actual PNG downloads; each measured 3508 × 2480 pixels. In a two-percent-wide band around the center seam, across the middle half of each output, we counted pixels with all RGB channels below 150. The color test had 12,400 dark seam pixels. The grayscale control had zero.
The current edge calculation combines brightness gradients with a scaled color-channel gradient. That explains why this particular color edge can remain visible even when the weighted brightness is nearly equal. The pixel count is a simple thresholded measurement, not a perceptual score or a measure of edge quality.
How to use this finding
When two neighboring objects in a photo have different colors but similar brightness, inspect their shared edge in the generated page. Zoom in before saving. If an edge is faint, try a detail-preserving line style or improve the photo's lighting and contrast, then generate a fresh result.
This test used one hand-coded color pair, one gray control, Clean Outline, A4, and Chrome 156.0.8078.80. It did not test photographs, other hues, other styles, other browsers, PDFs, physical printing, or every combination of colors. See the test method and measurements. For practical controls, read the faint-edge guide or how photo edge tracing works.
Read or watch the similar-color outline video, try the Coloring Page Maker, or browse Maker Help & Guides.