Stray Light (Flare)

Stray Light Calculations

Background Testing Calculation Testing With Imatest Inputs Outputs

 

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At a high level, the measurement of stray light is very simple: normalize the digital numbers (DNs) of an image, while (optionally) masking out the image of the light source.

Metric Image Calculations

Normal

The “normal” stray light metric image calculation is to take the test image and divide it by a normalization factor.

\(\text{stray light} = \frac{\text{image [DN]}}{\text{normalization factor [DN]}} \)

With appropriate normalization factors, this is used to compute the Point Source Transmission (PST) [1] and Point Source Rejection Ratio (PSRR) [2] metrics.

For a “normal” calculation, no stray light is indicated with a value of 0 and the worst possible stray light is indicated with a value of 1.

Reciprocal

The “reciprocal” stray light metric image calculation is to take a normalization factor and divide it by the test image.

\(\text{stray light} = \frac{\text{normalization factor [DN]}}{\text{image [DN]}}\) 

With appropriate normalization factors, this is used to compute the flare attenuation metric proposed within IEEE-P2020 [3].

For a “reciprocal” calculation, no stray light is indicated with a value of infinity and the worst possible stray light is indicated with a value of 1.

References

[1] E. Fest. 2013. “Stray Light Analysis and Control”. SPIE Press. ISBN: 9780819493255. DOI: https://doi.org/10.1117/3.1000980.

[2] B. Bouce, et. al, 1974. “GUERAP II – USER’S GUIDE”. Perkin-Elmer Corporation. AD-784 874.

[3] IEEE-P2020 Automotive Image Quality Working Group. https://site.ieee.org/sagroups-2020/