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| p.7 #6 · Canon EF 24-70mm f/4L IS Resolution Tests! |
Fred Miranda wrote:
Fixing barrel distortion in post, reduces resolution even further and that is reason enough for some to upgrade.
It turns out that this concern is vastly over-rated, and that barrel distortion and other similar sorts of lens distortions can be corrected in post with typically no visible degradation of the image.
Well, this got me to wondering, so I decided to test it: http://www.lensrentals.com/blog/2013/01/you-can-correct-it-in-post-but
I guess it depends on what the definition of 'no visible' means. Resolution dropped to about 85% to 90% of original after correction, but that probably wouldn't be noticeable on a small print and certainly not an online jpg. But certainly in a large print the difference would be noticeable.
Did you have a chance to see my examples of the difference in crops from images that would be about five feet wide? There are links in my earlier post.
I regularly print pretty large from files that I have adjusted this way, and I'm completely confident that any deterioration of the image from typical adjustments to things like vignetting, barrel/pincushion (and related) distortion, and CA are not visible in very large prints.
As I wrote before, based on the logic of the claims that there is a degradation I used to assume that these sorts of corrections would create a problem. But testing (e.g. printing) has convinced me that this isn't the case in any but the most extreme adjustments.
I would not make the silly claim that there is "no degradation" of the image, but I am confident that this degradation is so tiny as to escape notice in prints, even with rather careful inspection. In many cases you cannot eve see it if you look for it in 100% crops, and in the cases where you can find it there, a) you have to look really closely and compare side-by-side examples, and b) it still won't be visible in prints, much less on the web.