Dalsa Spyder3 Bedienungsanleitung PDF herunterladen (Seite 46)

46 Spyder3 GigE Vision SG-14 Monochrome Cameras User’s Manual

03-032-20123-01 Teledyne DALSA

Analog Processing

Optimizing offset performance and gain in the analog domain lets you achieve a better signal-to-noise

ratio and dynamic range than you would achieve by trying to optimize the offset in the digital domain

only. Therefore, you should perform all analog adjustments prior to any digital adjustments.

1. Analog gain (the Gain (dB) or Calibrate Gain Target parameters in the Analog Controls set) is

multiplied by the analog signal to increase the signal strength before the A/ D conversion. It is used

to take advantage of the full dynamic range of the A/ D converter. For example, in a low light

situation the brightest part of the image may be consistently coming in at only 50% of the DN. An

analog gain of 6 dB (2x) will ensure full use of the dynamic range of the A/ D converter. Of course

the noise is also increased.

2. The analog offset or black level (Black Level (DN) command) is an ―artificial‖ offset introduced into

the video path to ensure that the A/ D is functioning properly. The analog offset should be set so that

it is at least 3 times the rms noise value at the current gain.

Digital Processing

To optimize camera performance, digital signal processing should be completed after any analog

adjustments.

1. Fixed pattern noise (FPN) calibration (calculated using the Calibrate FPN parameter) is used to

subtract away individual pixel dark current.

2. The digital offset (Digital Offset (DN) parameter) enables the subtraction of the ―artificial‖ A/ D

offset (the analog offset) so that application of the PRNU coefficient does not result in artifacts at low

light levels due to the offset value. You may want to set the Digital Offset (DN) value if you are not

using FPN correction but want to perform PRNU correction.

3. Photo-Response Non-Uniformity (PRNU) coefficients (calculated using the PRNU Target and

Calibrate PRNU, or PRNU Calibration Algorithm Selector parameters in the Data Processing

family) are used to correct the difference in responsivity of individual pixels (i.e. given the same

amount of light different pixels will charge up at different rates) and the change in light intensity

across the image either because of the light source or due to optical aberrations (e.g. there may be

more light in the center of the image). PRNU coefficients are multipliers and are defined to be of a

value greater than or equal to 1. This ensures that all pixels will saturate together.

4. Background subtract (Background Subtract (DN) parameter) and system (digital) gain (Digital

Gain (DN) parameter) are used to increase image contrast after FPN and PRNU calibration. It is

useful for systems that process 8-bit data but want to take advantage of the camera’s 12 bit digital

processing chain. For example, if you find that your image is consistently between 128 and 255DN (8

bit), you can subtract off 128 (Background Subtract (DN) 2048) and then multiply by 2 (Digital Gain

(DN) 8192) to get an output range from 0 to 255.

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Dalsa Spyder3 Bedienungsanleitung Seite 46