Nokia NHL-2NA Series, Инструкции по устранению неисправностей, Страница: 131 / 148

CCS Technical Documentation
NHL-2NA
Issue 1 06/02 ¤ Nokia Corporation Page 1
Camera Troubleshooting Instructions
Background, tools and terminology
A fault or complaint associated to camera operation can be roughly categorized to three
subgroups:
1 Camera is not functional at all, no image can be obtained
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
Type 1 and 2 faults are most often similar to what traditionally has been found in any
electronic devices. Type 3 faults are new to NMP and maybe the most challenging to find
and verify.
Image quality is very hard to measure quantitatively, and even comparative measure-
ments are difficult (comparing two images) if the difference is small. Especially if the
user is not satisfied with his/her devices' image quality, and tells e.g. that the images are
not sharp, it is fairly difficult to accurately test the device and get an exact figure which
then would tell if the device is OK or not.
Most 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 ref-
erence device may be needed in order to detect what actually is wrong, or is there any-
thing wrong at all. It is easy for the user to take bad looking images in bad conditions;
thus the camera operation has to be checked always in constant conditions (lighting,
temperature) or by using a second, known to be good device as a reference. Experience
significantly helps in analyzing image quality.
Terms
Dynamic range:
camera's ability to capture details in dark and bright areas of the scene
simultaneously. See Image which has been taken "against light". The actual object is
dark. for example.
Exposure time:
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.
Flicker:
Phenomena, which is caused by pulsating in scene lighting, typically appearing
as wide horizontal stripes in image.
Noise:
Variation of response between pixels with same level of input illumination. See
e.g. Noisy image taken in +70 degrees celsius for example of noisy image.