Chromatic aberration correction
Automatically remove color fringing due to lateral chromatic aberration
Photo Ninja includes a highly effective solution for removing color fringing due to lateral chromatic aberration (LCA). In most cases, Photo Ninja can accurately measure and correct LCA without user intervention and with excellent results. Significantly, for RAW images, Photo Ninja corrects LCA prior to demosaicing, before the aberration is smeared across channels by demosaicing, color correction, and other processing. The resulting improvement is striking compared to post-demosaicing correction. The technology is powerful enough to remove complex, nonlinear LCA that is exhibited by some modern lenses.
Note that LCA is only one cause of color fringing in digital images. Longitudinal CA and so-called “purple-fringing“ have different causes. Photo Ninja includes a general-purpose "Defringe" tool in the noise reduction filter that can help with these types of fringing. Also, stopping down the lens or avoiding high-contrast lighting can reduce the problem at exposure time.
Example 1
Canon 24-105/4.0L on 5D Mark II body, crop from edge of image. Left: Original image. Right: With automatic correction in Photo Ninja. Note how the color channels have been almost perfectly realigned, resulting in clean edges and detail.
Example 2
Photo courtesy of Pete Myers
Illustration of complex chromatic aberration, from a Nikon 28mm f/2.8 AI-S wide-angle lens on Nikon D3x body. These crops are from the same image, at varying distances from the center. Top row is uncorrected, bottom row after correction in Photo Ninja. Left: Halfway from center, fringing is mostly red/cyan, indicating a misalignment of the red channel. Center: Near the corner, fringing is green-magenta, resulting from misalignment of both the red and blue channels relative to green. Right: In the extreme corner, fringing becomes blue/yellow, indicating misalignment of the blue channel. Conventional linear scaling corrections are inadquate for this kind of chromatic aberration. Also, notice how Photo Ninja's pre-demosaicing correction of LCA removes zipper artifacts in the left image, because the color channels are properly realigned before demosaicing.
Example 3
Extreme corner of Canon 24-105/4L at 105mm on full-frame body. Left: Original image. Right: With automatic correction in Photo Ninja.
Example 4
From extreme corner of Canon 24-105/4L at 24mm on full-frame body. Left: Original image. Right: With automatic correction in Photo Ninja. Note how the diagonal line in the upper right quadrant is not only realigned but also smoother in the corrected version.
