High Snr Mode (High Signal Noise Ratio) - AVT Pike Technical Manual

Description of the data path

High SNR mode (High Signal Noise Ratio)

Note Configuration
To configure this feature in an advanced register: See
145: Advanced register: High Signal Noise Ratio (HSNR)
page 291.
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.
Note
• The averaged image is output at a lower frame rate
roughly equivalent to fps_old/N, where N is the number
of images averaged. In fact, due to camera internal
conditions, and according to which format and mode
settings are in use, it can vary slightly to be closer
sometimes to 1/ ((N/fps_old) + T_shutter). It's imprac-
tical to express in a formula or tables, across all camera
models and modes. But these notes should be sufficient
to help each user determine that the camera behaves as
described.
• 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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