Application Notes By Camera Model; Dcc1240X / Dcc3240X Application Notes - THORLABS DCU223x Operation Manual And Sdk

3.3 Application Notes by Camera Model

Cameras with CMOS sensors

DCC1240x / DCC3240x Application Notes

DCC1545M Application Note
DCC1645C Application Notes
Cameras with CCD sensors
DC223x Application Notes
DC224x Application Notes
3.3.1 DCC1240x / DCC3240x Application Notes
For the technical specifications of this model go to: Camera and sensor data >
Shutter modes
The following table displays the four shutter modes and their advantages and disadvantages in different situations:
Black level constancy
Capturing of moving
objects
Hotpixels
Image quality with high gain
The rolling shutter mode offers a better signal/noise ratio and a more consistent black level compared to the
global shutter mode.
If the sensor is used in global shutter mode at a low pixel clock frequency and a high gain, the bottom pixel rows
might become brighter for technical reasons. Color distortion will occur for the color sensor with active white
balance. In this case, use a higher pixel clock frequency, less gain or the rolling shutter mode.
The "Global shutter (alternative timing)"
shutter mode. This mode should not be used with a frame rate below 2 fps. This mode is also not suitable for
bright, moving image contents in combination with long exposure times.
The rolling shutter mode with global start is suitable for capturing moving objects with flash.
When using flash in rolling shutter mode make sure to set the flash duration accordingly ((1/maxFramerate) +
exposure) or that the global time window is available by a long exposure time (2 * (1/MaxFramerate) +
FlashDuration). For flashing into this time window use the flash delay (1/MaxFramerate).
The hardware sensor gamma curve is piecewise linear with three sections. This allows evaluating four times
more details per pixel for lower gray level values and in 8 bit per pixel mode in dark image areas.
In global shutter mode the shutter efficiency of 1:3000 have a negative impact with bright conditions and the
usage of exposure times under 100 µs. In this case, set the pixel clock to the maximum possible value and close
the aperture a little bit. Also enabling the Log mode with low values achieve huge improvements.
Black level
The black level can also be set to negative values. Therefore, the factory setting of the offset control is nearly in
the middle of the range.
Use of the gain functions can lead to slight fluctuations of the black level. In global shutter mode the black level
can also vary slightly.
In global shutter mode the black level can also vary slightly between two image captures.
When enabling the rolling or global shutter mode the black level is set to a fixed factory-provided value.
Therefore, the black level can individually adjusted after switching the shutter mode.
Depending on the internal black level and shutter mode the offset control shows no additional cumulative effect
at the top.
The factory setting of the offset control are so selected that the black level is always slightly increased to avoid
losing image information by cutting underneath the origin. For linearity measurements the black level must be
© 2013 Thorlabs GmbH
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Global shutter Global shutter
(default) (alternative timing)
-
++
-
-
mode offers a more consistent black level compared to the global
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DCC1240x / DCC3240x
Rolling shutter
+ ++
+ -
- +
+ ++
3 Operation
.
461
Rolling shutter
(global start)
++
+
+
+
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