Stray Light Standards and Recommendations

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	Notes
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	Notes
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

where

: pixel pitch of the camera in μm

: focal length of the camera in mm

: focal length of the collimator in mm

: radius of the pinhole in the collimator in mm