Nokia 6620 サービスマニュアル
NHL-12
Nokia Customer Care
6 - Baseband
142
COMPANY CONFIDENTIAL
Issue 3 05/2005
Copyright © 2005 Nokia. All Rights Reserved.
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Image quality analysis
Possible faults in image quality
When checking possible errors in the 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 (in order of appearance probability):
significantly helps 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
Testing for dust
For detecting this kind of problem, take an image of a uniform white surface and analyse it in
full resolution; search carefully – finding these defects is not always easy. Figure 13, “Effects
of dust in optical path,” is an example of an image containing easily detectable dust problems.
full resolution; search carefully – finding these defects is not always easy. Figure 13, “Effects
of dust in optical path,” is an example of an image containing easily detectable dust problems.
Black spots in the 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 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 disappears 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.
visible and sharp edged black dots in image are typically dust particles on 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 disappears 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 are out of focus, and appear in image as large, greyish and fading-edge
'blobs'. Sometimes they are very hard to find, and thus the user probably does 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.
to locate because they are out of focus, and appear in image as large, greyish and fading-edge
'blobs'. Sometimes they are very hard to find, and thus the user probably does 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.
Figure 13:Effects of dust in optical path
If large dust particles get trapped on top of the lens surface in the cavity between camera win-
dow and lens, they may cause image blurring and poor contrast (see also item 'sharpness').
The seal between the window and lens should prevent any particles from getting into the cavity
after the manufacturing phase.
dow and lens, they may cause image blurring and poor contrast (see also item 'sharpness').
The seal between the window and lens should prevent any particles from getting into the cavity
after the manufacturing phase.
If dust particles are found on sensor or are suspected to be inside the camera module, this is
classified as a manufacturing error of the module and thus the camera should be replaced. The
particles inside the cavity between the window and the lens are most probably been trapped
there in the assembly phase at a Nokia factory. It is of course also possible that the user has
classified as a manufacturing error of the module and thus the camera should be replaced. The
particles inside the cavity between the window and the lens are most probably been trapped
there in the assembly phase at a Nokia factory. It is of course also possible that the user has