Stray Light (Flare) Documentation

Stray Light Standards and Recommendations

 

Current Documentation

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Stray light (flare) documentation pages

Introduction: Intro to stray light testing and normalized stray lightOutputs from Imatest stray light analysis | History

Background: Examples of stray lightRoot Causes | Test overview | Test factors | Test ConsiderationsGlossary

Calculations: Metric image | Normalization methodsLight source mask methods | Summary Metrics | Analysis Channels | Saturation

Instructions: High-level Imatest analysis instructions (Master and IT) | Computing normalized stray light with Imatest | Motorized Gimbal instructions

Settings: Settings list and INI keys/values | Standards and Recommendations | Configuration file input

Page Contents

This page enumerates the settings required to obtain metrics named in standards and Imatest’s recommendations.

Syntax

Items in fixed-width font indicate settings that are determined from the test setup.

Items with a TBD (To Be Determined) indicate that the value has yet to be determined.

Items with a TBR (To Be Revised) indicate the current best practice, but this value has yet to be finalized.

 

Calculation Settings

  Standard/Recommendation Notes

Imatest Recommended

New User

Imatest Recommended

Advanced User

IEEE P2020

Flare Attenuation

IEEE P2020

Normalized Flare

Standard/Recommendation Notes These settings are intended to help a new user get some results quickly. Results may not be comparable from sensor to sensor due to the lack of normalization. These settings are what Imatest recommends for camera-to-camera comparable stray light flare measurement.   This is inspired by “Imatest Recommended Advanced User”.  
Calculation Type Transmission Transmission Attenuation Transmission  
Data Transform Linear (None) Linear (None) dB (Power) Linear (None)  
Dark Level 0 Set based on camera noise 0 0 IEEE-P2020 does not specify subtracting off a dark level.
Clip To One Disable Disable Enable Disable The clip-to-one control is hidden in the settings GUI if the calculation type is transmission and the data transform is linear.
Analysis Channel(s) Automatic Each Channel Each Channel Each Channel IEEE-P2020 does not specify which channel(s) to analyze.
Normalization Type None Direct Reference Image Lambertian Reference Image Direct Reference Image Normalization types other than none require other settings. See the additional settings for Direct Reference Image and Lambertian Reference Image below. 
Test Image Mask Type None Image Processing + Circle (Radius) Image Processing + Circle (Radius) Image Processing + Circle (Radius)

IEEE-P2020 provides a method for computing the size of the source mask but does not provide a method for localizing the mask. 

Test Image Masking requires additional settings for types other than None. See below.

Crop LRTB 0, 0, 0, 0 Set to exclude any non-imaging rows/columns Set to exclude any non-imaging rows/columns Set to exclude any non-imaging rows/columns IEEE-P2020 does not mention the cropping of non-imaging pixels, however, this is recommended.
Percentile Ranks use default Set values as desired Set values as desired Set values as desired IEEE-P2020 does not mention percentiles as summary metrics.
Level Count Thresholds use default Set values as desired Set values as desired Set values as desired IEEE-P2020 does not mention count-based summary metrics.
Level Count Calculation % Of Pixels % Of Pixels % Of Pixels % Of Pixels IEEE-P2020 does not mention count-based summary metrics.

 

Normalization Settings

Direct Reference Image Normalization Settings

  Standard/Recommendation Notes
 

Imatest Recommended

Advanced User

IEEE P2020

Normalized Flare

 
Image Filename Select the reference image Select the reference image  
Normalization Aggregation Median Median  
Integration Time Ratio Set based on the test setup Set based on the test setup  
Gain Ratio Set based on the test setup Set based on the test setup  
Light Level Ratio Set based on the test setup Set based on the test setup  
ND Measurement Type Set based on the test setup Set based on the test setup  
ND Density Value Set based on the test setup Set based on the test setup This setting is displayed in the GUI when the ND Measurement Type is Density.
ND Transmission Value Set based on the test setup Set based on the test setup This setting is displayed in the GUI when the ND Measurement Type is Transmission.
Reference Image Mask Options Image Processing Image Processing  
Reference Image Level Threshold Type Otsu’s Method Otsu’s Method  
Reference Image Mask Area Threshold 4 [TBR] 4 [TBR]  

Lambertian Reference Image Normalization Settings

  Standard/Recommendation Notes
 

IEEE P2020

Flare Attenuation

 
Image Filename Select the reference image  
Normalization Aggregation Mean  
Integration Time Ratio Set based on the test setup  
Gain Ratio Set based on the test setup  
Light Measurement Type Set based on the test setup  
Radiance From Lambertian Diffuser Set based on the test setup This setting is displayed in the GUI when the Light Measurement Type is Radiometric.
Irradiance at the Camera Location Set based on the test setup This setting is displayed in the GUI when the Light Measurement Type is Radiometric.
Luminance From Lambertian Diffuser Set based on the test setup This setting is displayed in the GUI when the Light Measurement Type is Photometric.
Illuminance at the Camera Location Set based on the test setup This setting is displayed in the GUI when the Light Measurement Type is Photometric.
Reference Image Mask Options Image Processing  
Reference Image Level Threshold Type Otsu’s Method  
Reference Image Mask Area Threshold 4 [TBR]  

Test Image Mask Settings

  Standard/Recommendation Notes

Imatest Recommended

New User

Imatest Recommended

Advanced User

IEEE P2020

Flare Attenuation

IEEE P2020

Normalized Flare

Mask Radius N/A Set via measurement of the on-axis image

TBD

TBD  
Level Threshold Type N/A Percent Of Max TBD TBD  
Level Threshold % N/A 95 TBD TBD  
Minimum Source Level N/A Set to a value slightly less than the level of the direct image of the source in the image TBD TBD  
Mask Area Threshold N/A 4 [TBR] TBD TBD  

 

IEEE-P2020 flare is still under development regarding instructions on how to mask. The latest working group drafts have methods that use a pinhole geometric camera model to place the mask, however, this fails if the camera has any distortion. Additionally, it provides for a geometric optics-based calculation of the size of the circular mask in pixels

\(\frac{1000 \cdot f_{cam} \cdot r_{col} }{pp \cdot f_{col}} \)

where

\( pp \): pixel pitch of the camera in μm

\( f_{cam} \): focal length of the camera in mm

\( f_{col} \): focal length of the collimator in mm

\( r_{col}\): radius of the pinhole in the collimator in mm