Spyder 3 Camera User's Manual GigE Dual Line - Frame Grabbers
Spyder 3 Camera User's Manual GigE Dual Line - Frame Grabbers Spyder 3 Camera User's Manual GigE Dual Line - Frame Grabbers
70 Spyder 3 GigE User Manual Calibrating the Camera to Remove Non-Uniformity (Flat Field Correction) Flat Field Correction Overview Note: The QuickCam software that ships with the Spyder 3 GigE camera has a flat field correction wizard. For easy flat field correction, use the wizard located on the Calibration tab. This camera has the ability to calculate correction coefficients in order to remove nonuniformity in the image. This video correction operates on a pixel-by-pixel basis and implements a two point correction for each pixel. This correction can reduce or eliminate image distortion caused by the following factors: • Fixed Pattern Noise (FPN) • Photo Response Non Uniformity (PRNU) • Lens and light source non-uniformity Correction is implemented such that for each pixel: V output =[(V input - FPN( pixel ) - digital offset) * PRNU(pixel) – Background Subtract] x System Gain where V output = digital output pixel value V input = digital input pixel value from the CCD PRNU( pixel) = PRNU correction coefficient for this pixel FPN( pixel ) = FPN correction coefficient for this pixel Background Subtract = background subtract value System Gain = digital gain value The algorithm is performed in two steps. The fixed offset (FPN) is determined first by performing a calibration without any light. This calibration determines exactly how much offset to subtract per pixel in order to obtain flat output when the CCD is not exposed. The white light calibration is performed next to determine the multiplication factors required to bring each pixel to the required value (target) for flat, white output. Video output is set slightly above the brightest pixel (depending on offset subtracted). Flat Field Correction Restrictions Note: If your illumination or white reference does not extend the full field of view of the camera, the camera will send a warning. It is important to do the FPN correction first. Results of the FPN correction are used in the PRNU procedure. We recommend that you repeat the correction when a temperature change greater than 10°C occurs or if you change the analog gain, integration time, or line rate. PRNU correction requires a clean, white reference. The quality of this reference is important for proper calibration. White paper is often not sufficient because the grain in the white paper will distort the correction. White plastic or white ceramic will lead to better balancing. 03-032-10158-06 DALSA
Spyder 3 GigE User’s Manual 71 For best results, ensure that: • 50 or 60 Hz ambient light flicker is sufficiently low not to affect camera performance and calibration results. • For best results, the analog gain should be adjusted for the expected operating conditions and the ratio of the brightest to darkest pixel in a tap should be less than 3 to 1 where: 3> Brightest Pixel (per tap) Darkest Pixel (per tap) • The camera is capable of operating under a range of 8 to 1, but will clip values larger than this ratio. • The brightest pixel should be slightly below the target output. • When 6.25% of pixels from a single row within the region of interest are clipped, flat field correction results may be inaccurate. • Correction results are valid only for the current analog gain and offset values. If you change these values, it is recommended that you recalculate your coefficients. DALSA 03-032-10158-06
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<strong>Spyder</strong> 3 <strong>GigE</strong> User’s <strong>Manual</strong><br />
71<br />
For best results, ensure that:<br />
• 50 or 60 Hz ambient light flicker is sufficiently low not to affect camera performance<br />
and calibration results.<br />
• For best results, the analog gain should be adjusted for the expected operating<br />
conditions and the ratio of the brightest to darkest pixel in a tap should be less than 3<br />
to 1 where:<br />
3><br />
Brightest Pixel (per tap)<br />
Darkest Pixel (per tap)<br />
• The camera is capable of operating under a range of 8 to 1, but will clip values larger<br />
than this ratio.<br />
• The brightest pixel should be slightly below the target output.<br />
• When 6.25% of pixels from a single row within the region of interest are clipped, flat<br />
field correction results may be inaccurate.<br />
• Correction results are valid only for the current analog gain and offset values. If you<br />
change these values, it is recommended that you recalculate your coefficients.<br />
DALSA 03-032-10158-06
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