Can you please explain what threshold means? #155

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1. mourner

   added

   question

   on May 19, 2025
2. jhned commented on Aug 18, 2025

   

   jhned

   on Aug 18, 2025

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   I checked the source and it looks like threshold is the amount that one pixel can be different from another pixel. If it's over the threshold, it's a different pixel and added to the number of different pixels.

   If you want to stay within a certain ratio, take the number of different pixels and compare it against the total pixel area, kind of like this:

   const numDiffPixels = pixelmatch(
       img1.data,
       img2.data,
       diff.data,
       img1.width,
       img1.height,
       { threshold: 0.4 } // Adjust sensitivity here
   );
   
   const pixelArea = img1.width * img1.height;
   const maxDiffPixelsByRatio = pixelArea * 0.4;
   
   if (numDiffPixels > maxDiffPixelsByRatio) {
     yellAboutIt();
   }
3. mourner commented on Oct 6, 2026

   

   mourner

   on Oct 6, 2026

   Member

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   Clarified this in the readme:

   How different two colors must be for a pixel to count as mismatched, from 0 to 1. It's a per-pixel perceptual color difference, where 1 is the difference between black and white, not a share of the image; to allow some percentage of the image to differ, compare the returned count against width * height instead. Smaller values make the comparison more sensitive. 0.1 by default.
4. mourner

   closed this as completedon Oct 6, 2026