Image Quality Analysis; Possible Faults In Image Quality; Testing For Dust - Nokia NHL-2NA Series Troubleshooting Instructions

CCS Technical Documentation

Image quality analysis

Possible faults in image quality

When checking for possible errors in camera functionality, knowing what error is sus-
pected will significantly help the testing by narrowing down the amount of test cases.
The following types of image quality problems may be expected to appear (in order of
appearance probability):
• Dust (black spots)
• Lack of sharpness
• Bit errors
In addition, there are many other kinds of possibilities for getting bad image quality, but
those are ruled out from the scope of this document since probability of their appear-
ance is going to be minimized by production testing.

Testing for dust

For detecting this kind of problems, take an image of uniform white surface and analyze
it in full resolution; search carefully – finding these defects is not always easy. Effects of
dust in optical path is an example of image containing easily detectable dust problems.
For taking an uniform white image: The best results are obtained using the docking sta-
tion adapter MJF-7. Care should be taken that the diffuser (white) surface of the adapter
is clean.
If adapter is not available, uniform white target such as a clean, straight white sheet of
paper, may be used, but extreme care should be taken to arrange illumination conditions
so that the target is uniformly illuminated.
Black spots in image are caused by dirt particles trapped into the optical system: clearly
visible and sharp edged black dots in image are typically dust particles on image sensor.
These spots are searched for in manufacturing phase, but it is possible that the lens
holder cavity contains a particle, which may move onto the image sensor active surface,
e.g. when the phone is dropped. Thus it is also possible that the problem will disappear
before the phone is brought to service. The camera should be replaced if the problem is
present when the service technician analyses the phone.
If dust particles are located on infrared filter surface on either side, they are much harder
to locate because they will be out of focus, and appear in image as large, grayish and
fading-edge 'blobs'. Sometimes they will be very hard to find, and thus the user probably
will not notice them at all since they do no harm. But it is possible that a larger particle
disturbs the user, causing need for service.
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