Allied Vision Technologies Pike Manual de Instruções descarregar pdf (Página 157)

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

• 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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Allied Vision Technologies Pike Manual de Instruções Página 157