Quick way to get rid of blue tones on white background/shadows?

Started 5 months ago | Discussions thread
Mark Scott Abeln
Mark Scott Abeln Forum Pro • Posts: 15,513
Chromatic aberration or...

doubledye wrote:

I use photoshop (not Lightroom) and the PS Raw editor. What setting in the RAW editor will remove this fringing/aberration? I have tried everything.

Thanks again! I will continue reading all of the great info above

As already mentioned, go the Lens Correction setting in Adobe Camera Raw and select the "Remove Chromatic Aberration" checkbox. If you still see some, go to the "Manual" tab and adjust the Defringe settings. However, this may not completely work.

I would go around the image looking at all high contrast edges, and if you always see a color fringe of one color on the outside edge—away from the image center—and always see a different color on the inside edge towards the image center, and if you have no fringing at the image center, and fringing increases in size towards the corners, then that is classic transverse (or lateral) chromatic aberration, and that is what's corrected. This isn't fully corrected and it does leave the image slightly softer than if it didn't exist in the first place.

However, if you see fringes of one color before the point of focus, and fringes of another color after the point of focus, anywhere in the image, but with the fringes getting more prominent the more out-of-focus the area is, then that is axial or longitudinal chromatic aberration, and there is no really suitable fix for this. I'd suggest either stopping down more or getting a different lens that does not have this aberration.


But there is a kind of fringing that is not related to optical aberrations, but rather is due to processing problems. In some older raw converters (and presumably some older cameras) mistakes in processing can cause fringing all around high contrast edges, such as tree twigs against the sky turning blue, despite chromatic aberration being removed. This can be due to the order of calculations during processing. I've seen this in software and cameras from the early 2000s, and I fixed problematic raw files simply by using newer and better raw processors.

We can expect errors in the finest level of details, which is called aliasing, which sometimes can be seen as colored fringes. Raw processors deal with this aliasing in different ways, but it can't be completely eliminated without drastic measures. The problem is due to the mechanism of color detection in cameras:


This aliasing is most seen when using the combination of very sharp optics and low megapixel cameras, and is less of a problem with high megapixel cameras and lousy optics. Low megapixel cameras typically use antialias filters, and cinematographers use diffusion filters to blur the image enough to eliminate aliasing altogether.

Color aliasing artifacts are reduced in Adobe Raw Converter in the Detail settings, under Noise Reduction: by default, some Color noise reduction is done partly to reduce this problem, and in effect the color information in an image is blurred.

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