Stray light (flare) documentation pages
Introduction: Intro to stray light testing and normalized stray light | Outputs from Imatest stray light analysis | History
Background: Examples of stray light | Root Causes | Test overview | Test factors | Test Considerations | Glossary
Calculations: Metric image calculations | Normalization methods | Light source mask methods | Summary Metrics | Analysis Channels
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
- Calculation Settings
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 |
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