Image Quality Analysis; Possible Faults In Image Quality; Testing For Dust - Nokia NHL-10 Baseband Troubleshooting And Manual Tuning Manual

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NHL-10

Baseband Troubleshooting

Image quality analysis

When checking for possible errors in camera functionality, knowing what error is suspected 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 appearance is going to

be minimized by production testing.

For detecting this kind of problems, take an image of uniform white surface and analyse it in

full resolution; search carefully – finding these defects is not always easy.

Effects of dust in optical path are an example of image containing easily detectable dust prob-

lems.

Black spots in image are caused by dirt particles trapped into the optical system: clearly visible

and sharp edged black dots in the image are typically dust particles on the image sensor.

These spots are searched for in the 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 it has been in some phase verified that

the problem has been present.

If dust particles are located on the infrared filter surface on either side, they are much harder

to locate because they will be out of focus, and appear in the image as large, greyish and fad-

ing-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 the need for service.

ISSUE 2 01/2004

COMPANY CONFIDENTIAL

CCS Technical Documentation

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