Published on: November 3, 2017
Traditionally, the purpose of image quality testing is to act as a quality gate by catching imaging related bugs and problems before product launch. By applying several image quality testing rounds during the product development, problems and issues can be found earlier and there is clear metrics showing how the image quality improves during the image quality tuning work. Image quality engineers will get meaningful feedback on how the tuning updates are affecting the image quality. The current test asset includes still image, video, auto focus, auto exposure, image stabilization, latency, flash and field image tests.
In still image testing, test images are taken in Image Quality Chart Laboratory from Image Engineering Test Charts with different illuminations and illumination levels. After capturing images, the key image quality parameters like colours, shading, noise, resolution/sharpening, and tones can be calculated from the images.
Video tests are carried out in Image Engineering moving light studio. In addition to traditional light studio, video studio includes moving objects specially tailored for video testing. Some of the key parameters for video is the MTF and AWB/AE convergence times.
Indoor field test images taken in five predefined conditions in photo space laboratory which corresponds the clusters where most of the images are taken by end user.
In flash testing, 46 images are taken in a mixed light condition with flash. Background is lit with Philips Hue lights changing the CCT from 2000 to 6500 K with 100 K increments. At each step the flash illuminates the dark front scene. Both the front and the rear scene have grey charts which are then used to calculate the R/G and B/G.
Specially designed photo space laboratory is used for AF testing. Altogether 500 images are captured automatically from macro (10cm), 70cm, 150cm, 200cm and “infinity”. Testing can be done in different illumination levels (e.g. 10 lux, 100 lux, 1000 lux) and illuminates (halogen, warm fluorescent, cold fluorescent, warm LED and cold LED). Images are analysed later automatically, and blurry images are detected. As a result, pass/fail % in each test case is reported.
LB-800 light box is used for AE testing. Maximum 171 images can be taken with different illumination levels. Based on the test results AE curve (gain & exposure time) in function of lux level can be plotted.
For image stabilization testing, camera is shaken with a shaker device and images are captured in different illumination levels. Normally used shake profile represents natural hand movements, when people are capturing images.
The latency, i.e. Shutter Lag and Shot-To-Shot delay measurements are done by using Image Engineering’s LED-Panel V4 inside Image Engineering AF Test box.
In addition to test results from each test, comparison to the reference product is made by viewing images with calibrated Eizo displays. Our Image Quality Specialist will highlight the problem areas in each test and proposes how to improve the situation.
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