Create a shading-reference (PRNU)

  • Updated on Jun 17, 2024
  • Published on Jan 25, 2023
  • 1 minute(s) read
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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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