Photography. Digital cameras. Image flare measurement
1Key Takeaways
This document specifies the definition, test patterns, measurement conditions and methods for digital camera image flare to enable comparison of measurement results. The measurement method is intended to evaluate the performance of a digital camera by using the image data output by the digital camera. This document doe…
2Expert Interpretation
This in-depth analysis of the ISO 18844:2017 standard's technical requirements for glare measurement in digital cameras includes test chart specifications, measurement condition settings, a comparison of three measurement methods, and implementation recommendations, providing a standardized solution for camera performance evaluation.
Standard Core Content Interpretation
ISO 18844:2017 defines a quantitative measurement method for image glare in digital camera systems, covering the full impact of the lens, camera body, image sensor, and image processing. Unlike ISO 9358, which only measures lens stray light, this standard focuses on the glare effect of the final output image.
Key Measurement Elements
| Elements | Technical Requirements | Allowable Deviation |
|---|---|---|
| Test Chart Contrast | ≥40:1 (Class A/B) ≥3000:1 (Class C) | ±5% |
| Illumination Uniformity | Reflective 1000-2000lx Transmissive 318-637cd/m² | |Max-Ave|/Ave＜0.05 |
| Color Temperature | 5700K | ±1000K |
Comparison of Measurement Methods
Type A: Achieves high-precision measurement of 0.005% through 8x exposure compensation. Manual exposure control is required, suitable for professional camera evaluation.
Type B: Basic solution in automatic exposure mode, with a quantization error of approximately 0.04%-0.168%. It is recommended to maintain a Y′luma of 225±25.
Type C: A simplified solution for ultra-high contrast (≥3000:1). Be aware of the 0.033% baseline error caused by reflection interference from the test chart.
Key Points for Implementation
- The use of the lens hood must be recorded, as it can affect the measured value by over 30%.
- The sRGB color space conversion formula is recommended: Y=0.2126R+0.7152G+0.0722B.
- The measurement area should be ≥D/70 from the edge (D is the diagonal dimension of the image).
- When processing RAW format, the conversion software version and parameters must be indicated.
Technology Evolution Analysis
This standard incorporates image processing algorithms into the glare assessment system for the first time, resolving the disconnect between traditional optical measurement and the final image quality. Compared to ISO 3664:2000, the 2017 version removes the old definition of "image flare" and more accurately distinguishes the impact of the PSF (point spread function).