Overview
The ISO 18844:2017 standard specifies the measurement method for flare in digital cameras.

Applicable Standard:

ISO 18844:2017
Photography — Digital cameras — Image flare measurement

Technical Committee:
ISO/TC 42 Photography

Principle
The standard for camera flare measurement in photography is ISO 18844:2017. Its core logic involves placing multiple circular black areas with low reflectance/transmittance (i.e., a diagonal array of high-density light traps or black dots, as shown in the figure below) on a uniformly illuminated or uniformly luminous white background. The severity of flare is quantitatively evaluated by calculating the flare index F, which is the ratio of the luminance of the black areas to that of the white background in the image. A smaller F value indicates a lesser impact of flare on image quality.

The formula for calculating the flare index F is:

$$F=\frac{S_{Black}}{S_{White}}\times 100\%$$ where $S_{Black}$ represents the average luminance of the black area, and $S_{White}$ represents the average luminance of the four white areas surrounding the black area.

How to Measure?
Environment Setup
The test chart can be either reflective or transmissive, and the environment setups are as follows:

Reflective chart environment setup	Transmissive chart environment setup

Test Conditions:

• Reflective test chart: The illuminance on the chart surface shall be 1000 lx to 2000 lx;
  
• Transmissive test light box: The luminance of the surface source shall be 318 cd/m² to 637 cd/m²;
  
• Illuminance uniformity: The illuminance deviation at each measurement point shall not exceed 5%, satisfying: $\frac{|E_\mathrm{max}-E_\mathrm{avg}|}{E_\mathrm{avg}}<0.05,\quad \frac{|E_\mathrm{min}-E_\mathrm{avg}|}{E_\mathrm{avg}}<0.05$;
  
• Light source color temperature: CIE average daylight illuminant shall be used, with a correlated color temperature of $\mathrm{CCT}=5700\ \mathrm{K}\pm1000\ \mathrm{K}$;
  
• Precautions: During testing, ambient stray light around the test chart must be shielded to prevent inflated flare index results; the camera should be set to a low ISO sensitivity to minimize the impact of image noise on the measurement data.
  

Test Targets
The test targets are divided into two structures: single-point measurement and multi-point measurement. Target 1 (white background with black areas) and Target 2 (black background with white frame) are interchangeable. The overall horizontal and vertical dimensions of the chart must exceed the camera's effective imaging field of view by (41±2)%.

• Target 1 (white background with black areas) (see Figure a below): Uses a white substrate, with a black frame whose line width is 1/500 of the vertical dimension of the field of view to delineate the $H×V$ effective field of view. The total area of the black dots inside the frame shall not exceed 5% of the area inside the frame. For the multi-point version, the black dots are arranged diagonally; for the single-point version, an $H/10×V/10$ black block is placed at the center.
  
• Target 2 (black background with white frame) (see Figure b below): Uses a black substrate, with an outer white frame whose line width is also 1/500 of the vertical dimension of the field of view, delineating the $H×V$ effective field of view. A closed loop of white line is placed at the center of the board. The line width of the white line and the distance from the white line to the center of the board are both 1/100 of the vertical dimension of the field of view. The perimeter of the loop is consistent with the outer contour perimeter of the central black block in Target 1. For the single-point version, an $H/10×V/10$ hollow square hole is opened at the center of the white line.
  
• Optical specification requirements: The reflectance of the white areas in the reflective target shall be ≥80% and approach Lambertian diffuse reflection, and the transmittance of the white areas in the transmissive target shall be ≥80%; the reflectance parameters (for reflective targets) or transmittance parameters (for transmissive targets) of the black areas in both targets shall be uniform; specular reflection is not allowed in the two critical sampling black areas: the black area inside the central loop of the black-background target and the central black block of the white-background target. For reflective targets, light traps can be added to these two areas to eliminate reflection interference. The black-and-white contrast of the targets is divided into two categories: 40:1 to 3000:1 and ≥3000:1; selection should be based on actual testing requirements.
  

Test Equipment
(Taking flare measurement with a reflective chart as an example)

Equipment Name	Yanding Multi-CCT LED Vertical Fill Light Source	Reflective Flare Test Chart	RIQA - Camera Module
Test Equipment
Equipment Function	Provides uniform and stable standard light source	Flare test target	Analyzes test images and calculates flare-related metrics

(Taking flare measurement with a transmissive chart as an example)

Equipment Name	Yanding TLB Series Transmissive Light Box	Transmissive Flare Test Chart	RIQA - Camera Module
Test Equipment
Equipment Function	Provides uniform and stable standard light source	Flare test target	Analyzes test images and calculates flare-related metrics

Result Interpretation
RIQA is an image analysis software independently developed by Yanding. Its Camera module supports flare measurement according to the ISO 18844:2017 standard, capable of calculating the flare index F from a diagonal array of 17 high-density light traps (black dots), objectively quantifying the camera's flare performance.

A smaller F value indicates a lesser impact of flare on image quality; a larger F value indicates severe camera flare.