Mathworks

esfr

Starting with the 2017b release, MATLAB’s esfrChart class offers an analysis of most of the features of Imatest’s Extended eSFR-ISO test chart.

You can purchase a print of this test chart from the Imatest Store.

 

It is important to note that camera system measurements from test chart images require careful consideration of the real-world setup, not just the analysis code. What follows is a brief introduction to some of these points- please note that in general it is easy to misinterpret image quality results if such guidelines are ignored.

 

Getting the Right Chart

Measuring a camera system from a test chart is fundamentally about what engineers call system identification: You put in a known input (the chart) to your camera (the system) and you observe the output (the image). 

Measuring the output tells you about your camera system. But as the old adage goes: Garbage in, garbage out.  The office inkjet or laser printer is probably not going to cut it when producing a test chart.

The following are a few of the necessary considerations when making measurements from a test chart:

  • Printer and print media resolution limit : Sharpness results are affected by being able to resolve on the order of the points of the print itself. Choosing an appropriate print size (allowing increased camera-to-chart distance) and print medium helps this.
  • Print media texture : Resolvable texture from the paper or ink will affect noise measurements
  • Color-managed printing : Color measurements made from a poorly color-managed print will be unreliable

To ensure that your measurements tell you about the camera and not the chart, Imatest offers expertise and test charts (beyond the eSFR-ISO chart, each tailored to a specific use) produced in a wide variety of forms, ranging over:

  • Print media: Inkjet paper, transmissive film, photographic paper
  • Print size: from 132 x 235 mm to 800 x 1460mm, depending on substrate

For more information on the different characteristics of the available sizes and media (substrates), see the Test Chart Substrate and Sizing Guide.

If you have questions about what form of chart is right for your system, please contact charts@imatest.com.

 

Photographing a Test Chart

It is also important to note that artifacts of your photography itself can affect results.

For example, a poorly lit glossy chart, as seen here, will not tell you very much useful about your camera. The chart texture visible and uneven lighting here will be misinterpreted as meaningful by the esfrChart analysis.

For further tips about correctly photographing a test chart for image quality testing, see here.