Introduction To Camera Module Troubleshooting - Nokia RM-701 Service Manual

RM-701
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
Digital zoom
Dynamic range
Exposure time
Flicker
Noise
Resolution
Sensitivity
Issue 1
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.
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. 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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