Introduction to camera module troubleshooting
Background, tools and terminology
Faults or complaints in camera operation can be roughly categorised into three subgroups:
1 Camera is not functional at all; no image can be taken.
2 Images can be taken but there is nothing recognizable in them.
3 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, or is there anything wrong at all.
It is easy for the user to take bad images in bad conditions. Therefore the camera operation has to be checked
always in constant conditions (lighting, temperature) or by using a second, known-to-be good device as
reference. Experience helps significantly in analysing image quality.
Terms
Autofocus Camera module contains lens movement mechanics for focus adjustment.
Autofocus enables camera to take sharp images of objects positioned
between 10cm to infinity. During AF the viewfinder image will be
momentarily blurred as the camera searches for the right focus setting.
Digital zoom Digital zoom is done by first cropping the image by the zoom ratio and
then upscaling it to the output resolution. This will decrease the image
quality especially with high zoom ratios.
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.
Flicker Phenomenon, which is caused by pulsating in scene lighting, typically
appearing as wide horizontal stripes in an image.
ND-filter Neutral density filter is a filter which is used in very bright conditions to
reduce the amount of light hitting the sensor. The filter is built into the
camera module and applied automatically when needed.
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.
RM-824; RM-825; RM-826
Camera Module Troubleshooting
Issue 2 NOKIA INTERNAL USE ONLY Page 5 – 5
Copyright © 2012 Nokia. All rights reserved.
To Next Page
Loading...
Need help?
General
