JAI CV-L108CL User Manual

Contents

JAI CV-L108CL User Manual Manual pdf 12 page image

CV-L108CL116.2. Pixel Gain (flat-field) correction (PRNU correction)Pixel Response Non-Uniformity is, as the name expresses, a non-uniformity of the response of eachindividual pixel. This means that for a fixed light level each pixel will have a slightly differentoutput level (response).To correct for PRNU, the camera‟s internal correction circuit captures one or several lines of dataunder non-saturated illuminated conditions (not more than 80% of maximum - recommend level ishalf of maximum), and the average across the line is calculated. Based on this average, coefficientsare then generated for each individual pixel. The coefficient has the function of multiplying thepixel output with factor greater or less than 1. These coefficients are stored in a non-volatilememory, and are therefore maintained after power down.6.3. Pixel black level correction (DSNU / FPN correction)Dark Signal Non-Uniformity or Fixed Pattern Noise is, as the name expresses, fixed pattern on thesensor output, which is not dependent on the incoming light.To correct for DSNU/FPN, the camera-internal correction circuit captures one or several lines ofdata under dark conditions (the lens must be covered by a lens cap), and the average across the lineis calculated. Based on the average, coefficients are then generated for each individual pixel. Thecoefficient has the function of adding or subtracting a value to the pixel output. These coefficientsare stored in a non-volatile memory, and are therefore maintained after power down.As the dark signal is highly dependent on the exposure time, this correction must be performedunder the operating conditions (exposure time and line rate) that will be used by the application.MaxMinMultiply byFactor > 1Multiply byFactor < 1Before correction: Non-uniform response from pixel to pixelAverageAfter correction: flat response from pixel to pixelAverageMaxBefore correction: dark signal non-uniformity from pixel to pixelSubtract factorAdd factorMinAverage