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 inputStray light (flare) documentation pages
Page Contents
This page describes the analysis channel options.
Channel Groups
Channel groups describe which groups of channels to analyze.
| Name | # Input Channels | Description | |
|---|---|---|---|
| Automatic | Any | Automatically choose what analysis channels to use based on the provided image(s).
| 0 |
| Each Channel | Any | Analyze each input channel | 1 |
| RGB | 3 | Analyze each of the three provided channels as red, green, blue. | 2 |
| Monochrome | 1 | Analyze the single provided channel as monochrome. | 3 |
| Mean | Any | Analyze the mean of all provided channels. | 4 |
| Luminance | 3 | Analyze the luminance channel. Data are assumed to be 3 channel in (red, green, blue) order. | 5 |
| RGB + Luminance | 3 | Analyze the three (red, green, blue) channels and the computed luminance channel. | 6 |
Luminance Channels
The luminance channel is calculated by applying weights to each of the red, green, and blue channels:
\(\text{Luminance} = w_{red}\cdot \text{Red} + w_{green} \cdot \text{Green} + w_{blue} \cdot \text{Blue} \)
The following weights are available for computing a luminance channel:
| Name | Red | Green | Blue | INI Value | Notes |
|---|---|---|---|---|---|
| IEC 61966-2-1 | 0.2126 | 0.7152 | 0.0722 | 1 | The weights are the same as IEC ITU-R BT.709-6. |
| ITU-R BT.601-7 | 0.299 | 0.587 | 0.114 | 2 | |
| ITU-R BT.709-6 | 0.2126 | 0.7152 | 0.0722 | 3 | The weights are the same as IEC 61966-2-1. |
| ITU-R BT.2020-2 | 0.2627 | 0.6780 | 0.0593 | 4 | |
| MATLAB | 6 | This uses the MATLAB rgb2gray function. |
Notes
Coloring and Data Labeling
The choice of analysis channels controls how the data are labeled and colored in plots and results.
Image/Settings Mismatches
Imatest will not run if there is a mismatch between the selected settings and the provided image (e.g., trying to analyze a monochrome image as RGB or Luminance, each of which requires three input channels).
Module Specific Notes
Stray Light Notes
Normalization Factor Analysis Channel
For Direct Reference Image and Lambertian Reference Image normalization, if the Channel Group is Luminance or RGB + Luminance, then the Luminance channel of the reference image is used. Otherwise, the Mean of the reference image is used.
Masking Analysis Channel
When producing a mask, if the Channel Group is Luminance or RGB + Luminance, then the Luminance channel of the image is used. Otherwise, the Mean of the image is used. This mask is then applied to each of the analysis channels.