Why does the iMac display show non-zero values for blue and green pixels for a .png image whose blue and green color planes are zero? I used the digital color meter to show the non-zero values for the blue and green pixels and I confirmed that the .png file has zero values in the blue and green color planes by using python scripts to inspect the array values.

1 Answer 1


You might check the iMac's monitor calibration settings.

System Preferences > Displays > Color > Calibrate...

or choose one of the other Display profiles. Which Digital Colour Meter are you using? It probably must be also calibrated in sync with the above setting...

  • Thank you for responding to my question. I used the Digital Color Meter utility that came with osx 10.10.1. I did look at the different color maps and switching maps changes the values reported by the DCM but the BG pixels are still active. I calibrated my display and I also changed my displays map to RGB to match the .png file but the GB pixels remain active. I confirm that these pixels are active using a magnifying optical system to view the pixel visually.
    – slk
    Commented Feb 27, 2015 at 22:22

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