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 | Normalization methods | Light 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.
Overview
| Standard | Description | Normalization | Note(s) | References |
| Imatest Recommended: New User | These settings are intended to help a new user get some results quickly. | None | Results may not be comparable from sensor to sensor due to the lack of normalization. | |
| Imatest Recommended: Advanced User | These settings are what Imatest recommends for camera-to-camera comparable stray light flare measurement. | Direct Reference Image | In some literature, this is referred to as “Point Source Rejection Ratio (PSRR)”. | |
| IEEE Std 2020-2024: Flare Intensity | Lambertian Reference Image | This has heritage to the Flare Attenuation metric from the IEEE P2020 Pre-Release [2]. | [1] §2.8.1 | |
| IEEE Std 2020-2024: Normalized Flare | Direct Reference Image | This is inspired by “Imatest Recommended Advanced User”. | [1] §2.8.3 |
Syntax
Items in fixed-width font indicate settings that are determined from the test setup.
Calculation Settings
Core Calculation
| Setting | Standard/Recommendation | Notes | |||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Calculation Type | Transmission | Transmission | Transmission | Note: the prerelease version of IEEE-2020 [2] used Attenuation for the flare attenuation metric. | |
| Data Transform | Linear (None) | Linear (None) | dB (Voltage) | Linear (None) | |
| Dark Level | 0 | Set based on camera noise | 0 | 0 | IEEE Std 2020-2024 [1] does not specify subtracting off a dark level. |
| Clip To One | Disable | Disable | Enable | Disable | Clip To One performs IEEE Std 2020-2024 [1] eq 2-6. |
Saturation
Manually setting the saturation level is the most reliable way to get saturation values.
| Setting | Standard/Recommendation | Notes | |||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Measurement Type | IEEE Std 2020-2024 [1] does not specify saturation calculations. | ||||
| Value | N/A | If needed, set based on camera properties | N/A | N/A | |
| Bit Depth | N/A | If needed, set based on camera properties | N/A | N/A | |
Analysis Channel
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Analysis Channel(s) | Automatic | Each Channel | Luminance | Luminance | |
| Luminance Type | N/A | N/A | Set per [1] §1.7.6 | Set per [1] §1.7.6 | IEEE Std 2020-2024 [1] §2.7.1 does not specify which luminance weights to use. [1] §1.7.6 recommends using the weights of the color space, if given, otherwise to use ITU-R BT.709-6 (sRGB) weights. |
| Custom RGB Weights | N/A | N/A | Set if needed per [1] §1.7.6 | Set if needed per [1] §1.7.6 | |
| RGB Order | N/A | N/A |
Set based on data type |
Set based on data type |
|
| Statistics | N/A | N/A |
N/A |
N/A |
|
Normalization
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Normalization Type | None | Direct Reference Image | Lambertian Reference Image | Direct Reference Image | Normalization types other than none require other settings. |
Normalization: Direct Image
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Reference Image FIle(s) | N/A | Select the reference image(s) | N/A | Select the reference image | IEEE Std 2020-2024 [1] does not specify that more than one image can be combined |
| Normalization Aggregation | N/A | Median | N/A | Mean | IEEE Std 2020-2024 [1] §2.8.3.1 specifies the use of “the average linearized per-pixel gray level signal”. |
Normalization: Direct Image: Source Compensation
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Light Level Ratio | N/A | Set based on the test setup | N/A | Set based on the test setup | |
Normalization: Direct Image: Source Compensation: Neutral Density
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| ND Measurement Type | N/A | Set based on the test setup |
N/A |
Set based on the test setup |
|
| ND Density Value | N/A | Set based on the test setup | N/A | Set based on the test setup | |
| ND Transmission Value | N/A | Set based on the test setup | N/A | Set based on the test setup | |
Normalization: Direct Image: Camera Compensation
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Integration Time Ratio | N/A | Set based on the test setup |
N/A |
Set based on the test setup |
|
| Gain Ratio | N/A | Set based on the test setup | N/A | Set based on the test setup | |
Normalization: Lambertian Image
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Refrence Image FIle(s) | N/A | N/A | Select the reference image | N/A | IEEE Std 2020-2024 [1] does not specify that more than one image can be combined |
| Normalization Aggregation | N/A | N/A | Mean | N/A | IEEE Std 2020-2024 [1] Eq. 2-5 specifies the use of the average in the symbols |
Normalization: Lambertian Image: Light Source Measurements
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Light Measurement Type | N/A | N/A | Set based on the test setup | N/A | |
| Radiance From Lambertian Diffuser | N/A | N/A | Set based on the test setup | N/A | |
| Irradiance at the Camera Location | N/A | N/A | Set based on the test setup | N/A | |
| Luminance From Lambertian Diffuser | N/A | N/A | Set based on the test setup | N/A | |
| Illuminance at the Camera Location | N/A | N/A | Set based on the test setup | N/A | |
Normalization: Lambertian Image: Camera Compensation
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Integration Time Ratio | N/A | N/A |
Set based on the test setup |
N/A | |
| Gain Ratio | N/A | N/A | Set based on the test setup | N/A | |
Normalization: Reference Image Source Detection
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Reference Image Mask Options | N/A | Image Processing | IEEE Std 2020-2024 [1] does not specify separate settings for reference and test images. Use the test image masking settings. | ||
Normalization: Reference Image Source Detection: Image Processing
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Reference Image Level Threshold Type | N/A | Percent of Max | IEEE Std 2020-2024 [1] does not specify separate settings for reference and test images. Use the test image masking settings. | ||
| Level Threshold (Value) | N/A | N/A | IEEE Std 2020-2024 [1] does not specify separate settings for reference and test images. Use the test image masking settings. | ||
| Level Threshold (Percent) | N/A | 50% | IEEE Std 2020-2024 [1] does not specify separate settings for reference and test images. Use the test image masking settings. | ||
| Image Close Radius | N/A | 5 | IEEE Std 2020-2024 [1] does not specify separate settings for reference and test images. Use the test image masking settings. | ||
| Multiple Connected Component Strategy | N/A | Pick Biggest | IEEE Std 2020-2024 [1] does not specify separate settings for reference and test images. Use the test image masking settings. | ||
| Reference Image Mask Area Threshold | N/A | 1 | IEEE Std 2020-2024 [1] does not specify separate settings for reference and test images. Use the test image masking settings. | ||
Analysis Image Mask
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Test Image Mask Type | None | Image Processing + Circle |
Image Processing or Geometric Camera Model + Circle |
Image Processing or Geometric Camera Model + Circle |
IEEE Std 2020-2024 [1] provides three methods for creating the mask:
Test Image Masking requires additional settings for types other than None. |
Analysis Image Mask: Image Processing
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity |
Normalized Flare |
||
| Level Threshold Type | N/A | Percent Of Max | Percent Of Max | Percent Of Max | |
| Level Threshold (Value) | N/A | N/A | N/A | N/A | |
| Level Threshold (Percent) | N/A | 95 | 95 | 95 | See IEEE Std 2020-2024 [1] §2.7.2.1. The 95% threshold is allowed to be tuned. |
| Minimum Source Level | N/A | Set to a value slightly less than the level of the direct image of the source in the image. | Set to a value slightly less than the level of the direct image of the source in the image. | Set to a value slightly less than the level of the direct image of the source in the image. | Although not explicitly part of IEEE Std 2020-2024 [1] §2.7.2.1, the first paragraph of that clause assumes the source’s image is in the FOV. Setting this value helps validate that assumption. |
| Image Close Radius |
N/A | 5 | Set as needed to fill in holes in the mask. | Set as needed to fill in holes in the mask. | In IEEE Std 2020-2024 [1] §2.7.2.1, it says to perform a closing, but does not specify a radius. |
| Multiple Connected Component Strategy | N/A | Pick Biggest | |||
| Mask Area Threshold | N/A | Set to a value slightly larger than the pixel area of the well-exposed source. | 0 | 0 |
This helps filter out saturated ghost images or hot pixels/noise smaller than the direct image. IEEE Std 2020-2024 [1] §2.7.2.1 does not specify a mask area threshold. |
Analysis Image Mask: Geometric Camera Model + Circle
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity |
Normalized Flare |
||
| Negate Field Angle | N/A | N/A | Set as needed. | Set as needed. | |
| Negate Azimuth Angle | N/A | N/A | Set as needed. | Set as needed. | |
Analysis Image Mask: Geometric Camera Model + Circle: Camera Model
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity |
Normalized Flare |
||
| Model Type | N/A | N/A | Set as needed. | Set as needed. | |
Analysis Image Mask: Geometric Camera Model + Circle: Camera Model: Image Coordinate System
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity |
Normalized Flare |
||
| Type | N/A | N/A | Set as needed. | Set as needed. | |
Analysis Image Mask: Geometric Camera Model + Circle: Camera Model: Geometric Camera Model Intrinsics
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity |
Normalized Flare |
||
| Focal Length | N/A | N/A | Set as needed. | Set as needed. | |
| Principal Point Type | N/A | N/A | Set as needed. | Set as needed. | |
| Principal Point | N/A | N/A | Set as needed. | Set as needed. | |
| Alpha | N/A | N/A | Set as needed. | Set as needed. | |
| Skew | N/A | N/A | Set as needed. | Set as needed. | |
Analysis Image Mask: Geometric Camera Model + Circle: Camera Model: Geometric Camera Model OpenCV Distortion
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity |
Normalized Flare |
||
| Radial Coefficients | N/A | N/A | Set as needed. | Set as needed. | |
| Tangential Coefficients | N/A | N/A | Set as needed. | Set as needed. | |
| Thin-Prism Coefficients | N/A | N/A | Set as needed. | Set as needed. | |
| Tilt Coefficients | N/A | N/A | Set as needed. | Set as needed. | |
Analysis Image Mask: Radius
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity |
Normalized Flare |
||
| Radius Type | N/A |
User-Specified |
Focal Length Ratio |
Focal Length Ratio | |
| Mask Radius | N/A | Set via measurement of the on-axis image. |
N/A |
N/A | |
| Camera Pixel Pitch |
N/A | N/A | Set to the pixel pitch in μm of the device under test. | Set to the pixel pitch in μm of the device under test. | This is part of IEEE Std 2020-2024 [1] eq 2-4. |
| Camera Focal Length | N/A | N/A | Set to the focal length in mm of the device under test. | Set to the focal length in mm of the device under test. | This is part of IEEE Std 2020-2024 [1] eq 2-4. |
| Source Focal Length | N/A | N/A | Set to the focal length in mm of the light source. | Set to the focal length in mm of the light source. | This is part of IEEE Std 2020-2024 [1] eq 2-4. |
| Source Diameter | N/A | N/A | Set to the diameter of the light source in mm. | Set to the diameter of the light source in mm. | This is part of IEEE Std 2020-2024 [1] eq 2-4. |
Crop
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| 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 Std 2020-2024 [1] does not mention the cropping of non-imaging pixels; however, this is recommended. |
Downsample
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Size Measurement | Full Resolution | Full Resolution | Full Resolution | Full Resolution | IEEE Std 2020-2024 [1] does not mention the downsampling of analysis images. |
| Factor | N/A | N/A | N/A | N/A | |
| Output Image Size | N/A | N/A | N/A | N/A | |
| Row Count | N/A | N/A | N/A | N/A | |
| Column Count | N/A | N/A | N/A | N/A | |
Metadata
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Filename Regular Expression Method | None | Set if needed to correlate images to capture information. | Set if needed to correlate images to capture information. | Set if needed to correlate images to capture information. | |
| Filename Regular Expression | N/A | Set if needed to correlate images to capture information. | Set if needed to correlate images to capture information. | Set if needed to correlate images to capture information. | |
| Decimal Point | N/A | Set if needed to correlate images to capture information. | Set if needed to correlate images to capture information. | Set if needed to correlate images to capture information. | |
Extra Calculation
| Standard/Recommendation | Notes | ||||
|
Imatest Recommended New User |
Imatest Recommended Advanced User |
Flare Intensity ([1] §2.8.1) |
Normalized Flare ([1] §2.8.3) |
||
| Percentile Ranks | use default | Set values as desired | Set values as desired | Set values as desired | IEEE Std 2020-2024 [1] 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 Std 2020-2024 [1] does not mention count-based summary metrics. |
| Level Count Calculation | % Of Pixels | % Of Pixels | % Of Pixels | % Of Pixels | IEEE Std 2020-2024 [1] does not mention count-based summary metrics. |
Unsupported Parts of Standards
IEEE Std 2020-2024 [1]
The analysis software does not support:
- Mask creation from well-exposed reference images (§2.7.2.3). Note that this requires two exposures for each capture position.
- Changing the source light level when the source is in vs. out of the FOV (§2.6.4). Note this can be done via two analysis runs.
References
[1] IEEE Std 2020:2024 “IEEE Standard for Automotive System Image Quality” https://standards.ieee.org/ieee/2020/6765/
[2] IEEE P2020/D3 – “IEEE Draft Standard for Automotive System Image Quality” https://ieeexplore.ieee.org/document/9969530