Summary of findings and fix (by Copilot):

• Root cause: On macOS/Retina (devicePixelRatio=2), we set the canvas backing store to width2/height2 and then divided by dpr when computing fit/center. Panzoom computed transforms from the doubled backing size, causing the image to appear 4x larger with black padding.

• Fix applied (packages/tiffviewer/src/ui-manager.ts): Draw at 1:1 logical pixels and stop dpr math in fit/center. Specifically:

  • Set canvas.width/height to the TIFF logical width/height (no dpr multiplier) and keep CSS width/height the same.
  • Removed context.scale(dpr, dpr) and dpr-based division when calculating sizes in fitImageToScreen and centerImageInContainer (use canvas.width/height directly).
  • This keeps Panzoom and layout in agreement across devices (Retina vs non-Retina).