Radiometric Correction Specifications

To be able to perform radiometric corrections, the Pix4D software requires at a minimum the following tags

 

  • Exif.Photo.ExposureTime
  • Exif.Photo.FNumber
  • Exif.Photo.ISOSpeedRatings

 

Vignetting

The information for the vignetting correction can be provided either as a 2D polynomial or as a radial polynomial.

Radial Polynomial

The polynomial is of the form

 equation.svg

with (Cx, Cy) read from Xmp.Camera.VignettingCenter and the coefficients ci read from Xmp.Camera.VignettingPolynomial.

2D polynomial

The polynomial is of the form

equation__1_.svg

The tag Xmp.Camera.VignettingPolynomial2DName contains the i and j values of c{i,j} and the value of c{i,j} is stored in Xmp.Camera.VignettingPolynomial2D. For example, Xmp.Camera.VignettingPolynomial2DName={"0,0,1,0, ..., 2,2,3,1"} and Xmp.Camera.VignettingPolynomial2D={0.633287676149, 1.47936368033, ..., -1.58329242609, 0.130259802058} means c_{0,0}=0.633287676149, c_{1,0}=1.47936368033, etc...

Dark current

Xmp.Camera.BlackCurrent indicates the dark current. There is one value per band, and the dark current is assumed uniform for all pixels on this band. 

It is also possible to use the standard tags Exif.Image.BlackLevel and Exif.Image.BlackLevelRepeatDim. 

 

 

Normalized images

If the image was already radiometrically corrected and contains absolute irradiance or temperature, the following tag should be set to 1:

  • Xmp.Camera.IsNormalized
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