Instruction manual

Description of the data path
PIKE Technical Manual V4.0.0
157
High SNR mode (High Signal Noise Ratio)
To configure this feature in an advanced register: See Table 157: High Signal
Noise Ratio (HSNR) on page 306.
In this mode the camera grabs and averages a set number of images and out-
puts one image with the same bit depth and the same brightness. This means
that the camera will output an 8-bit averaged image when an 8-bit image
format is selected.
Because of the fact that normally uncorrelated (photon-, amplifier-) noise
dominates over correlated noise (fixed pattern noise), adding two images
will double (6 dB) the gray levels but only increase the noise levels by
(3 dB).
This enhances both the dynamic range as well as the signal-to-noise ratio.
Consequently adding 256 8-bit images will lead to a potential signal-to-noise
enhancement of 24 dB or a resulting bit depth of 16 bit.
Frame memory and deferred image transport
An image is normally captured and transported in consecutive steps. The
image is taken, read out from the sensor, digitized and sent over the 1394
bus.
Deferred image transport
As all PIKE cameras are equipped with built-in image memory, this order of
events can be paused or delayed by using the deferred image transport fea-
ture.
PIKE cameras are equipped with 64 MB of RAM. The table below shows how
many frames can be stored by each model. The memory operates according
to the FIFO (first in, first out) principle. This makes addressing for individual
images unnecessary.
Note
L
• The averaged image is output at a lower frame rate
being exactly the fraction: frame rate/number of
images.
• The camera must be in idle before turning this feature
on.
• The potential SNR enhancement may be lower when
using more than 8-bit original bit depth.
• Select 16-bit image format in order to take advantage
of the full potential SNR and DNR (DyNamic Range)
enhancements.
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