By Ranga Burada
Autofocus plays a major role in many camera system applications with variable focus, including consumer electronic devices. Camera systems must be able to focus at a variety of distances. Optical systems on cameras only allow a certain range of distances from the camera to be in focus at once (this is often known as the depth of field, or depth of focus). The distance from the camera where objects will be most in focus, effectively the center of this range, is the focus distance—the role of the autofocus system in a camera is to set this point accurately every time.
We refer to autofocus consistency as the ability of a camera to focus on a given point correctly, repeatedly. To determine if a point is in focus, we measure the sharpness of an object (specifically, a test chart) at that distance. By taking many images of the chart—and letting the autofocus system reset each time and try to focus on the chart anew—we can tell if the camera system is focusing consistently or not. By examining the MTF50 values calculated from these images—a common objective image quality metric which correlates well with perceived sharpness—we can tell if sharpness varied between captures, and thus if focus accuracy on the chart varied.
Imatest Autofocus Consistency Module
The Imatest Autofocus Consistency module analyzes the sharpness (specifically MTF50) results from a set of images captured at a fixed distance from an Imatest sharpness chart, such as SFRplus chart, eSFR-ISO chart, or the new AutoFocus chart. The user can then generate MTF50 values from these images using the SFR, SFRplus, or eSFR-ISO modules in Imatest. The Autofocus Consistency module is a post-processor that runs on the outputs of these analyses and consolidates them into a more useful form. You can find a more detailed description of the test procedure here.
In the above plot, each x-axis position indicates the distance from chart to camera. The colored data marks spread vertically at each position indicate the MTF50 values calculated from the images captured at that chart distance. The consistency of the autofocus system at a given distance is indicated by the tightness of the spread of MTF50 values for images taken at that distance. The narrower this spread, the more consistent the autofocus system is. In order to determine if the system’s consistency depends on distance (perhaps it has an easy time focusing on nearby points, but tends to fail for faraway ones), this analysis is repeated at many test distances, as in the plot above.
To learn more about maintaining consistency while measuring sharpness with MTF values, visit Increasing the Repeatability of Your Sharpness Tests.
Over the last few years, the automotive industry has taken great strides to incorporate camera systems into vehicles. From ADAS to rear-view cameras, there are many applications for camera systems in vehicles.
With this integration of camera systems in the automotive industry, companies now have a variety of image quality factors to verify and standards to adhere to.
Imatest is a leader in image quality testing solutions for the automotive industry. Join us for this free webinar to learn more about image quality testing in the automotive industry.
During this webinar, you can expect to learn:
- An introduction to image quality factors and industry standards
- What image quality factors matter most to the automotive industry
- An overview of tests to deploy for automotive camera systems
- How to begin testing your camera systems
For many engineers tasked with designing camera systems for a product, image quality testing is a complicated endeavour given the variety of test charts and measurements available.
Understanding which image quality factors to measure in your product and how to interpret results will ensure your product is equipped with quality imaging systems.
Join us on October 12, 2016 for a free webinar, Fundamentals of Image Quality Testing, presented by Imatest’s Director of Engineering, Henry Koren.
Imatest 4.5 is the most powerful version of the platform yet with enhancements and additions for a variety of industries, including automotive, medical, consumer electronics, security, and more. The newest features give users increased flexibility in the range of target distances and light levels to improve your high-speed, automated testing.
To learn more, please visit imatest.com/4.5.