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372 DCx camera

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.

THORLABS DCU22 Series User Manual

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