Calculating Exposure Quality Loss per IEEE CPIQ v2

Owned by Henry Koren
Jun 30, 2023
2 min read

CPIQ Auto exposure is in draft status. It will be added to the 2021 revision of the CPIQ Standard. You should use Imatest v2021.1 or later to perform this calculation.

Auto exposure error is based on deviation from a nominal luminance value for the neutral grey patch in an X-Rite Colorchecker SG. In a variant calculation, we can also calculate this metric from a 24-patch X-Rite Colorchecker.

 

A psychophysical study of the subjective quality based on luminance level was how the following model for exposure quality loss was developed:

 

CPIQ Auto exposure is measured with the Imatest Color/Tone module, which produces a Quality Loss (QL) score in units of Just Noticeable Differences (JND).

Results are available in display #4 2D a*b:

 

and display #7 B&W density & White Balance:

For more about Imatest’s CPIQ support click here