Readout mode
Single Read
The entire frame is read once before a reset period.
The particularity of C-RED 3 readout mode allows to adjust the integration time (Tint) independently of
the frame rate.
Depending of these two parameters, the camera will run in ITR or IWR mode, please refer to Fig. 10 :
and Fig. 11 : for further information.
By default, in single read readout, the images are acquired in correlated double sampling (CDS) mode.
An internal CDS is done directly on the sensor.
By default, the pixels sent by the camera are 16-bits signed values. The firmware 1.3.0 offers the
possibility to force the camera to send unsigned 16 bits values instead of 16-bits signed values. This
may be useful on environments that do not support signed pixels.
To request transmission of unsigned pixels, use the command “set unsigned on”. To use signed
pixels, use the command “set unsigned off”.
Note: The default behavior remains to send 16 bits signed values.
High Dynamic Range mode
Note: Please note that this feature is an option for cameras built before 2021, and requires a specific
license file into the camera. For more information, please contact us: contact@first-light.fr
HDR mode is a readout mode that provides high dynamic range images by combining successive images
acquired using high and low conversion gain of the sensor. Since the high and low gain images are used
two times, the framerate of the composite output image is the same, even if the scene sampling is
performed at half the speed.
Three different options are available:
- HDR mode standard: output dynamic is 83.2 dB, pixels are sent in 16 bits signed format
- HDR mode extended: output dynamic is 89.2 dB, pixels are sent in 16 bits unsigned format
- Raw HDR mode: introduced in firmware version 1.3.0
The HDR standard mode exists to maintain the compatibility with CDS mode where pixels are output as
signed 16 bits numbers.
In raw HDR mode, the camera sends the images acquired using high conversion and low conversion
gain of the sensor instead of sending the resulting composite image. The conversion gain
corresponding to each image can be determined using image tags.
For more information about HDR: theory of operation, system gain, restrictions and limitations, please
read the specific technical note dedicated to HDR mode:
C-RED 2-3 TN1 HDR Mode.
To operate properly, the HDR mode needs a proper bias correction.
If the HDR mode is enabled without bias correction, or with invalid bias correction (for example bias
correction file made at different temperature, different integration time ...) the resulting combined
image will not be correct. Flat correction improves even more the images but remains optional.
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