Hamamatsu ORCA-Flash4.0 LT3, Инструкция по эксплуатации

Страница: 38 / 47

ORCA-Flash4.0 LT3 Digital CMOS camera C11440-42U40 Instruction manual_Ver.1.1
36
10. PRECAUTION WHEN USING THE CMOS
IMAGE SENSOR
This camera uses the scientific CMOS image sensor. Careful attention must be paid to the
following points when using the CMOS image sensor:
(1) White spot
CMOS image sensor has some high dark current pixels caused by the defect of silicon
wafer. Those high dark current pixels appear as higher intensity and brighter pixels than
around pixels when the exposure time is set long. Those pixels are called as “White spot”
(“hot pixel”).
This camera has real time defect pixel correction function which can replace the defect
pixels registered in advance with the data of surrounding pixels.
Hitting of cosmic ray or radiation ray (X-ray, gamma ray, UV light, etc.) on the sensor
generates many electrons and they may appear as a white spot, but this white spot is
temporary and disappear in the next frame.
In addition, although the probability is very low, the impact of cosmic rays and radiation (X-
rays, gamma rays, ultraviolet rays, etc.) is large, and it may cause permanent defects in
silicon wafers and defective pixels with large dark current. In current technology, there is no
way to avoid generating high dark current defect pixels. It means there is a possibility to
generate new white spots after the factory shipment.
Even if the white spot occurs, dark offset subtraction* with software can reduce the effect
of white spots because intensities of white spots are proportional to the exposure time and
have reproducibility with a constant sensor temperature.
*
After acquiring an image using a certain exposure time is loaded, the CMOS image sensor is exposed to darkness for
the same amount of time, and another image is obtained. After this, the difference between the images is determined,
and the data for the dark portion of the original image is nullified.
(2) Folding distortion
A rough-edged flicker may be visible when imaging striped patterns, lines, and similar
subject matter.
(3) Over light
•
Be careful not to input too strong light such as high-energy laser
into the CMOS image sensor because the CMOS image sensor
may be damaged by over light.