THORLABS DCC1 45 Series, Руководство пользователя

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372 DCx camera
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9.6 Gain and offset
Digital image sensors sum up electrical charge proportional to the amount of incident light. The
signal can be amplified directly on the sensor in order to increase the contrast of the image output
(hardware gain). An offset can be set in order to adjust the brightness of the image (blacklevel). The
results of the analogue signal processing are usually better than the results of digital post-
processing.
9.6.1
Hardware gain
Analogue amplification of read out pixels increases the overall image brightness and contrast.
Depending on the sensor type a global gain value for all pixels (master gain) or a separate gain value
for every color (RGB gain) can be set.
HINT
Using the sensor hardware gain also increases image noise.
It is not recommended to use high gain settings.
9.6.2 Offset (Black level)
Digital image sensors own light insensitive cells next to the active image area. These dark pixels are
used to measure a reference voltage (blacklevel) which is subtracted from the image signal. This
compensates thermally generated voltages which would otherwise falsify the signals. Normally the
sensor adjusts the blacklevel automatically, but the blacklevel value can also be manually adjusted.
9.7
Readout of relevant image areas
Each Camera sensor has a defined resolution determined by the number of horizontal and vertical
pixels (e.g. 1024 x 768 pixel). However for some applications it may be necessary to read out only a
certain subarea of the sensor. For this purpose DCU cameras offer different functions:
Area Of Interest (AOI)
Binning (combining) of pixel
Subsampling (skipping) of pixel
With these methods the volume of data to be transmitted is reduced. Therefore higher frame rates
can be achieved. Cameras with CCD sensors achieve higher frame rates with reduced image height.
Reducing image width has no effect on the possible frame rate.
9.7.1
Area Of Interest (AOI)
The sensor AOI function makes possible to specify the size and position of sensor area. Only the
data of this area will be read out and transferred to the PC. With a smaller image area higher
camera frame rates can be achieved. After specifying an AOI a new value for the exposure time can
be set.