Introduction To Camera Module Troubleshooting - Nokia 6680 RM-36 Service Manual

RM-36
Camera Module Troubleshooting

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.
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 operation has 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. The following types of image quality problems may
be expected to appear:
• Dust (black spots)
• Lack of sharpness
• Bit errors
Terms
Dynamic range
Exposure time
Flicker
Noise
Resolution
Sensitivity
Issue 1
Camera's ability to capture details in dark and bright areas of the scene
simultaneously.
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.
Phenomenon, which is caused by pulsating in scene lighting, typically
appearing as wide horizontal stripes in an image.
Variation of response between pixels with same level of input illumination.
Usually the amount of pixels in the camera sensor; for example, RM-1 has a
1280 x 960 pixel sensor resolution. In some occasions the term resolution is
used for describing the sharpness of the images.
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.
Company Confidential
Copyright ©2005 Nokia. All Rights Reserved.
Nokia Customer Care
Page 8–5