Image crop displaying LCA

 

Chromatic aberration in digital images refers to the incorrect correlations in intensity variation of the colour planes in the image. It results from the wavelength dependent transmission properties of lens optics, specifically the refractive index of the lens elements. Different wavelengths of light see different refractive indices and thus are refracted by different amounts as the light passes through the lens. Consequently light at each frequency is focused at different locations.

 

 

There are two types of chromatic aberration: lateral (or transverse) chromatic aberration (LCA) and axial chromatic aberration (ACA). See here for more detail on ACA. LCA is a common problem in images and is manifested as a variation in image magnification with wavelength, resulting in misalignments between colour planes in a digital image. The magnitudes of the misalignments vary across the image and are typically largest towards the image periphery. The figure on the right shows a crop from the upper left portion of an image, in which green and purple colour fringing due to LCA is visible.

 

LCA is generally modelled as having both radial and tangential components, although the majority of LCA is captured in the radial part of the model.

 

Removal Solution

LCA varies with lens aperture for prime lenses, and additionally varies with focal length for zoom lenses. We have developed a method to calibrate any lens for LCA, requiring the user to simply image a structured target at several different zoom and aperture settings. Our fully automatic feature registration process is applied to these calibration images in order to determine the LCA model parameters. The variation in these parameters across changes in lens settings is captured in our model, thus allowing any images from any calibrated lens to be corrected for LCA.

 

Key Advantages

  • Model uses images of a specific target
  • Particularly suited to RAW image data correction

 

Examples of our calibrated LCA removal solution applied to images from varies cameras/lenses are shown below.


LCA images

Nikon D200, 18-200mm lens: Image crop exhibiting LCA, and corrected image crop after LCA removal.
Mouse over the image to see correction.



Olympus point-and-shoot: Original image exhibiting LCA, and corrected image with LCA removed.
Mouse over the image to see correction.

 


Nikon D200, 18-200mm lens: Original image exhibiting LCA, and corrected image with LCA removed.
Mouse over the image to see correction.

 


 
Nikon D200, 55-200mm lens: Crop of above image before and after correction for LCA.
Mouse over the image to see correction.

 

 

Nikon D200, 55-200mm lens: Crop of above image before and after correction for LCA.
Mouse over the image to see correction.

 


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