User Guide

Xenon flash troubleshooting
Introduction to camera module troubleshooting
Background, tools and terminology
Faults or complaints in camera operation can be roughly categorised into two subgroups:
1 Flash is not functional at all; no image can be taken.
2 Images can be taken and they are recognizable but for some reason the quality of images is seriously
degraded, or customer complains about image quality
Image quality is very hard to measure quantitatively, and even comparative measurements are difficult
(comparing two images) to do, if the difference is small. Especially if the user is not satisfied with his/her
device's image quality, and tells, for example, that the images are not sharp, it is fairly difficult to accurately
test the device and get an exact figure which would tell whether the device is functioning properly.
Often subjective evaluation has to be used for finding out if a certain property of the camera is acceptable
or not. Some training or experience of a correctly operating reference device may be needed in order to
detect what actually is wrong.
It is easy for the user to take bad images in bad conditions. Therefore the camera and the flash operation
have to be checked always in constant conditions (lighting, temperature) or by using a second, known-to-
be good device as reference.
When checking for possible errors in camera functionality, knowing what error is suspected significantly
helps the testing by narrowing down the amount of test cases.
Terms
Dynamic range Camera's ability to capture details in dark and bright areas of the scene
simultaneously.
Exposure time Camera modules use silicon sensor to collect light and for forming an
image. The imaging process roughly corresponds to traditional film
photography, in which exposure time means the time during which the
film is exposed to light coming through optics. Increasing the time will
allow for more light hitting the film and thus results in brighter image. The
operation principle is exactly the same with silicon sensor, but the shutter
functionality is handled electronically i.e. there is no mechanical moving
parts like in film cameras.
Noise Variation of response between pixels with same level of input illumination.
Resolution Usually the amount of pixels in the camera sensor. In some occasions the
term resolution is used for describing the sharpness of the images.
Sensitivity Camera module's sensitivity to light. In equivalent illumination conditions,
a less sensitive camera needs a longer exposure time to gather enough
light in forming a good image. Analogous to ISO speed in photographic
film.
Sharpness Good quality images are 'sharp' or 'crisp', meaning that image details are
well visible in the picture. However, certain issues, such as non-idealities
in optics, cause image blurring, making objects in picture to appear 'soft'.
Each camera type typically has its own level of performance.
RM-313
Camera Module Troubleshooting
Issue 1 COMPANY CONFIDENTIAL Page 5 –13
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