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IMAGE DATA FLOW A4.2.3
The sCMOS image sensors provide an extremely high frame rate
compared to other scientific image sensors. The high frame rate,
along with the high dynamic, creates a large amount of data that
must be handled and stored. The maximum data rate of the sCMOS
image sensor is given by:
pco.edge 5.5 Camera Link:
[2560 * 2160 (pixel in 1 frame) * 2 Byte (= 16bit dynamic)] * 100
[frames/s] = 1.1 GB/s (pco.edge 5.5, Camera Link)
To handle this considerable amount of data, there are two options
available:
Option 1: Real-time Recording to Computer
The pco.edge sCMOS camera series uses this option. For this
purpose, the interface must be capable of transmitting data at the
required speed. Interfaces such as GigE, USB 3.0 and Camera Link
are not fast enough to transmit this data, which is delivered by the
largest sCMOS image sensor. Nevertheless, there is a sophisticated
solution that uses the Camera Link interface, which is integrated into
the pco.edge camera. It is a fact of nature that light, itself, has its
own noise component called photon or shot noise, which increases
with light signal. In this approach, no compression is made in small
signals, while for large signals a suitable compression is applied.
Since the introduced compression error is always smaller than the
photon noise induced error, it is not seen and a so called visual
lossless compression has been performed.
It can be shown that this is possible without any significant loss of
information. Therefore, the calculation for the pco.edge camera at
full speed and full frame has to be re-written:
[2560 * 2160 (pixel in 1 frame) * 1.5 Byte (= 12bit dynamic)] * 100
[frames/s] = 0.829 GB/s
The Camera Link interface can transmit this in real-time. In the future,
recently introduced machine vision interfaces including CoaXPress
and Camera Link HS are capable of transmitting sCMOS image data
without any compression. A network type interface, 10GigE, is similar
with respect to hardware to Camera Link HS, but incorporates all of
the known GigE advantages and disadvantages. Here, the usual
protocols are not favorable for image data transmission, and any
network traffic can dramatically reduce available transmission speed.
The real-time data transmission into the computer allows for a
variety of applications, since it is free from camera memory
limitations. Image data can be stored directly in the computer’s
random access memory (RAM) up to more than 64 gigabyte. With an
appropriate RAID system, the data can be stored directly to hard
disks and there is no delay involved.
Option 2: Recording in the Camera (not available for pco.edge)
For high-speed imaging applications where data transfer rates are in
the range of several GB/s it is accepted that the primary image
memory (camRAM) must be located in the camera. Two examples of
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