User`s manual

Piranha HN RoHS User Manual

03-032-20135-01 Teledyne DALSA

PRNU Correction

The PRNU correction is more involved since the key requirement is that the camera be exposed to a

uniform illumination with no pattern in the image. The light level should be at the same level over the

whole width of the sensor. Then the cpa command is issued. As well, the highest pixel value must not

exceed the target value. (The cpa command generates 2 outputs. The first is the per pixel coefficient

where all pixels are gained to match the highest pixel. The second is the sensor gain equal to the targ et

divided by the highest pixel value.) Note: Before the micro executes the cpa command all gains are set to

0 dB.

 Calibration is performed using a white reference where your object is normally located.

o Use a white material that has no texture, such as a non glossy plastic.

o If you must use white paper, make sure it is moving during the calibration process. If

you do not do this, your image will have vertical stripes.

There are two input parameters for the cpa com mand, the first is the algorithm type and ―2‖ is u sed to

select all 8192 pixels from the CCD. The second parameter is the target light level value which must be

entered as a 14 bit number since the ADC is a 14 bit device. If the camera is oper ating in 8-bit mode (clm

21), and then if the target level is 200 DN 8-bit, then the entered parameter converted to 14-bit is 64x

bigger or 200 x 64 = 12800. Enter the command: cpa 2 12800. If the camera is operating with 12-bit data

(clm 16), then multiply the target value by 4.

The method then is to adjust the uniform white light level before the calibration is applied to

approximately the level desired, for example, set so that the average output is 200 DN 8-bit. Then apply

the command cpa 2 12800. The successful result is that the data level across the whole sensor should

become 200 DN 8-bit.

When using the camera on a solar cell PL inspection system, the challenge is that the light source used for

the PL imaging is not seen by the camera. Therefore, a separate light source will need to be applied and

ideally it would be near the operating wavelength (> 1000 nm). To keep the process simple, it might be

good enough to instead apply a broad band white light source.

To help remove any pattern in the image, the lens should be de-focused. Since the lens will already be

focused for 1000 nm, then with white light (shorter wavelengths) the image will be de -focused. The

target needs to be a uniform white surface with a mat or diffusing surface. It is going to require some

experimenting to discover how to achieve the best uniform light.

Note that the ccf and cpa need to be applied to both scan directions if you are using both scan directions.

 On completion of the ‗cp a‘ com mand , you should see an image from the camera with very little

PRNU at the target level you set.

You are now ready to evaluate the image quality of the camera under your operating conditions.