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      Create a shading-reference (PRNU)
      • 17 Jun 2024
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      Contents

      Create a shading-reference (PRNU)

      • Updated on 17 Jun 2024
      • 1 Minute to read
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      Article summary

      Calculation of PRNU 

      The following equation describes the calculation of the PRNU 

      CalibratedImage = (RawImage - DSNU) / PRNU

      PRNU = (PRNUImage-DSNU)/TargetValue

      CalibratedImage = Camera output with applied DSNU and PRNU

      RawImage = Camera output image without any correction

      TargetValue =  Target Value of PRNU, default value is 255

      PRNUImage =  Acquired image of the white-reference 

      PRNU = Photo response non-uniformity

      DSNU = Dark signal non-uniformity


      Standard PRNU reference generating

      Create a shading-reference with PRNU.

      1. Place a moving white target.
        If using a stationary target, place it slightly out of focus.
      Acquire an image:
      1. In the toolbar click Acquire a single frame 
        or 
        click Start grabbing, wait until an image ist displayed,
        click Stop grabbing.

      1. In the menu bar navigate to Tools → Calibration. 
      2. Click Generate PRNU Reference.


      The Generate PRNU Reference wizard opens.

      1. Click Acquire image to generate the PRNU directly from the camera
        or
        click Load from Disk to load an image from the hard drive.
        NOTE: Load from Disk
        Make sure that the image has been taken with active image calibration mode by using the wizard.

      The raw image and the line plot of the image is displayed. 

      1. Click Start 2-Click-Selection. 
      2. Click on the image to select the ROI.
      Send the calculated PRNU to the camera: 
      1. Select LUT 1 or LUT 2.
      2. Click Send data to camera.
      Activate brightness and contrast:
      1. Select the Activate Brightness and contrast checkbox.
      2. Set the contrast to 0.9.

      Extrapolation function

      If the white reference does not cover the entire FOV, the extrapolation function can be used to generate it. In this case, a straight line is fitted to the gradient. Therefore follow the description below.

      On the right side, you can see the raw image and the Applied PRNU reference without the extrapolation function.
      In the area with low image content, the Applied PRNU reference shows some artifacts.

      		shading_1shading_2
      1. Select the ROI, by using the Start-2-Click-Selection.
      2. Press the button with the three dots on the bottom.
      3. Enable your option, in this example the left extrapolation.
      4. Select the start position of your extrapolation. The width defines the area where the extrapolation is created. From the start position to column 0, the extrapolation is applied.
      		shading3
      1. Check the applied PRNU in the Applied PRNU reference tab.
      		sahding_4

      Target Value 

      The Target Value limits the maximum intensity of your CalibratedImage.

      Note
      Make sure that the Values of your PRNUImage are smaller than your TargetValue
      1. Press the button with the three dots on the bottom.image-1718193423609
      2. Change the Target Value.

      3. Check the applied PRNU in the Applied PRNU reference tab.


      		image-1718193458389
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