Image Processing To Reduce The Appearance of Lateral Chromatic Aberration
In some circumstances it is possible to correct some of the effects of chromatic aberration in digital post-processing. However in real-world circumstances, chromatic aberration results in permanent loss of some image detail. Detailed knowledge of the optical system used to produce the image can allow for some useful correction. In an ideal situation, post-processing to remove or correct lateral chromatic aberration would involve scaling the fringed color channels, or subtracting some of a scaled versions of the fringed channels, so that all channels spatially overlap each other correctly in the final image.
As chromatic aberration is complex (due to its relationship to focal length, etc.) some camera manufacturers employ lens-specific chromatic aberration appearance minimization techniques. All Nikon DSLRs with CMOS sensors and all Panasonic Lumix DSLRs, additionally some Nikon and Panasonic compact cameras, do such processing automatically in camera for JPEG images. Nikon DSLRs additionally store correction-data in RAW-files for use by Nikon Capture, View NX and some other RAW tools. Due to the Canon EF lens mount all-electronic lens communication and coupling system, the Canon's Digital Photo Professional software has one of the most advanced chromatic aberration appearance minimization (also vignetting and distortion handling) systems that uses lens model-specific focusing distance, focal length and aperture information stored in the Canon RAW (CR2) files. Third party software tools such as PTLens are also capable of performing complex chromatic aberration appearance minimization with their large database of cameras and lens.
In reality, even a theoretically perfect post-processing based chromatic aberration reduction-removal-correction systems do not increase image detail as a lens that is optically well corrected for chromatic aberration would for the following reasons:
- Rescaling is only applicable to lateral chromatic aberration but there is also longitudinal chromatic aberration
- Rescaling individual color channels result in a loss of resolution from the original image
- Most camera sensors only capture a few and discrete (e.g., RGB) color channels but chromatic aberration is not discreet and occurs across the light spectrum
- The dyes used in the digital camera sensors for capturing color are not very efficient so cross-channel color contamination is unavoidable and causes, for example, the chromatic aberration in the red channel to also be blended in to the green channel along with any green chromatic aberration.
The above are closely related to the specific scene that is captured so no amount of programming and knowledge of the capturing equipment (e.g., camera and lens data) can overcome these limitations.
Read more about this topic: Chromatic Aberration
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