Introduction To Camera Module Troubleshooting - Nokia RM-42 Service Manual

RM-42
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, 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
Dynamic range
Exposure time
Flicker
Noise
Resolution
Sensitivity
9241872 (Issue 1)
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.
Camera's ability to capture details in dark and bright areas of the scene
simultaneously. See "Image taken against light (Page
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.
See "Noisy image (Page
Usually the amount of pixels in the camera sensor; for example, RM-42 has
a 1600 x 1200 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.
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