Image Quality Analysis; Possible Faults In Image Quality; Testing For Dust In Camera Module - Nokia RM-42 Service Manual

RM-42
Camera Module Troubleshooting Nokia Customer Care
Figure 87 Good image taken outdoors

Image quality analysis

Possible faults in image quality

When checking for possible errors in 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:
• 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 the probability of their appearance is going to be minimized by
production testing.

Testing for dust in camera module

Context
For detecting these kinds of problems, take an image of a uniform white surface and analyse it in full resolution.
A good quality PC monitor is preferred for analysis. Search carefully, since finding these defects is not always
easy. Figure "Effects of dust on optical path" is an example image containing easily detectable dust problems.
When taking a white image, use uniformly lightened white paper or white wall. One possibility is to use uniform
light but in this case make sure that the camera image is not flickering when taking the test image. In case
flickering happens, try to reduce illumination level. Use JPEG image format for analysing, and set the image
quality parameter to 'High Quality'.
Black spots in an image are caused by dirt particles trapped inside the optical system. Clearly visible and sharp
edged black dots in an image are typically dust particles on the image sensor. These spots are searched for in
the manufacturing phase, but it is possible that the camera body cavity contains a particle, which may move
onto the image sensor active surface, for example, 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.
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