Digital Capture Resolution Measurements

This page describes standards developed by ISO/TC 42, applicable to measuring the resolution of digital capture devices, including digital still cameras, camera phones, print scanners, and film scanners. ISO 12233:2014, Photography -- Electronic still picture imaging -- Resolution and spatial frequency responses, is available now. (Click to go to the US ANSI website to purchase ISO 12233.)

Background information and links to the standards and source code available to perform the measurements are provided below.


Index

  1. What is digital capture resolution?
  2. Camera resolution measurements
  3. Scanner resolution measurements
  4. Measurement software
  5. Sources for printed test charts
  6. Related IS&T papers

 

1. What is digital capture resolution? Digital capture resolution is the ability of an imaging device, such as a digital camera or scanner, to optically capture finely spaced detail.  This resolution is typically measured using a resolution test chart, taking into account the complete optical and digital system of the device. Note that resolution cannot be understood or evaluated according to just the number of addressable photo elements, or pixels, used to encode the images produced by the imaging device.  

Camera resolution test chart from ISO 12233:2000

2. Camera resolution measurements: ISO/TC 42 has revised ISO 12233, now ISO 12233:2014, Photography -- Electronic still picture imaging -- Resolution and spatial frequency responses, with methods for measuring the resolution and the Spatial Frequency Response (SFR) of digital cameras.

The first edition, issued in 2000, provided a scientifically sound and easily accomplished standard way to measure the true optical resolution performance of any digital camera image of the test target shown above. The protocols in this standard debunk the use of pixel count (megapixels) as a representation of camera resolution.

Spatial frequency response (SFR) refers to the use of a slanted-edge gradient technique for capturing a super-resolution edge profile and transforming this into a spatial frequency signature. This approach greatly enhances imaging performance diagnostics to measure lens blur, sharpening and potential aliasing.

Hyperbolic wedge refers to features on the resolution test chart for quickly and more reliably assessing the limiting optical resolution visually. Rather than using a traditional radial grating feature (for example a starburst pattern) in which line spacing increases linearly with distance, the line spacing of a hyperbolic wedge increases linearly with spatial frequency. This effectively stretches high-frequency regions, to enable more precise resolution assessment.

ISO 12233 has been revised by ISO TC 42/WG 18. Notable enhancements in the second edition include:

  • Methods for Measuring SFR and Resolution – Selection Rationale and Guidance
  • Low-contrast edge features for more stable slanted-edge SFR results
  • A sine wave-based Siemens star SFR approach
  • Objective measurement software tools for measuring visual resolution using the hyperbolic wedge feature.

low contrast edge SFR chart in revised ISO 12233

 

sinusoidal Siemens star SFR chart in revised ISO 12233



visual resolution chart in revised ISO 12233

3. Scanner resolution measurements: ISO/TC 42 develops standards for measuring the resolution of reflection print scanners and film scanners. The available standards are:

ISO 16067-1:2003 Photography -- Spatial resolution measurements of electronic scanners for photographic images -- Part 1: Scanners for reflective media,which specifies methods for measuring and reporting the spatial resolution of electronic scanners for continuous tone photographic prints. This standard is applicable to both monochrome and color reflection print scanners.

ISO 16067-2:2004 Photography - Electronic scanners for photographic images - Spatial resolution measurements -- Part 2: Film scanners, which specifies methods for measuring and reporting the spatial resolution of electronic scanners for continuous tone photographic negatives and reversal (e.g. slide) films. This standard is applicable to both monochrome and color film scanners.


Scanner resolution test chart from ISO 16067-1: 2003

 

4. Measurement software: Experts from ISO/TC 42 have also developed software for performing the measurements specified in these resolution measurement standards.

Click to go to analysis software for the Siemens Star.

To run the executable you will also need the Matlab Compiler Runtime (MCR) which can be found here:
Matlab Compiler Runtime (MCR) Win 32
Matlab Compiler Runtime (MCR) Win 64

Click to go to analysis software for the SFR measurements.  

5. Sources for printed test charts

Applied Image Inc.
Image Engineering
Image Science Associates
Imatest LLC

6. Related papers published by IS&T: The following are links to IS&T papers which describe the development or use of these resolution measurement standards:

  1. FISCHER, T. A. and HOLM, J., Electronic still-picture camera spatial frequency response measurement, IS&T's 47th Annual Conference / ICPS 1994, vol. II, pp. 626-630.  
  2. OKANO, Y., MTF Analysis and its Measurements for Digital Still Camera, IS&T's 50th Annual Conference, pp. 383-387.  
  3. WILLIAMS, D., Benchmarking of the ISO 12233 Slanted-edge Spatial Frequency Response Plug-in, PICS 1998, pp 133-136.  
  4. Williams, D., Debunking of Specsmanship:  Progress on ISO/TC42 Standards for Digital Imaging Performance, PICS 2003 pp. 77-81, 2003. 
  5. Williams, D., et. al., A Pilot Study of Digital Camera Resolution Metrology Protocols Proposed under ISO 12233, Edition 2, IS&T/SPIE Electronic Imaging 2008.  
  6. Burns, P. and Williams, D., Sampling Efficiency in Digital Camera Performance Standards, Proc. IS&T/SPIE Electronic Imaging 2008.  
  7. Loebich, C., Wueller, D., Klingen, B. and Jaeger, A., Digital Camera Resolution Measurement Using Sinusoidal Siemens Stars, IS&T/SPIE Electronic Imaging 2007.
  8. Burns, P. and Williams, D., "Using Slanted Edge Analysis for Color Registration Measurement", IS&T/PICS, Final Program and Proceedings, pp. 51-53, 1999. 
  9. Okano, Y., "Influence of Image Enhancement Processing on SFR of Digital Cameras", IS&T/PICS Final Program and Proceedings, pp. 74-78, 1998. 
  10. Williams, D., "Benchmarking of the ISO 12233 Slanted Edge Spatial Frequency Response Plug-in", IS&T/PICS, Final Program and Proceedings, pp. 133-136, 1998.