08-07-2011, 09:29 AM
[quote name='Tiz' timestamp='1312649666' post='10434']
I agree. Not twice. I just wanted to emphasize that also the center is affected. If you just cut the corners, the image size will be reduced from 4000*3000 to maybe 3850*2900 (4:3 12MP example). If you now save the image, you will not have a 12 MP image. But the cameras and also Adobe Lightroom do not do that. They save a full 12 MP (4000*3000) image. Therefore, it is necessary to extrapolate the entire, cropped image. I am wondering about the impact on IQ (depending on the extrapolation algorithm). In any case, I do not like the idea.
[/quote]
No, you do not really have to affect the center.
The edges are what needs "correcting" by stretching them, basically. This leaves the center more or less unaffected. You end up with a larger image, pixel resolution wise. Then you crop this to original pixel resolution.
You can (some software applications do that, and I think PS does that too in its lens correction module)) also shrink the center. and leave the edges relatively resolution unaffected, and end up with a smaller image... but that is not what is the smart thing to do usually.
I agree. Not twice. I just wanted to emphasize that also the center is affected. If you just cut the corners, the image size will be reduced from 4000*3000 to maybe 3850*2900 (4:3 12MP example). If you now save the image, you will not have a 12 MP image. But the cameras and also Adobe Lightroom do not do that. They save a full 12 MP (4000*3000) image. Therefore, it is necessary to extrapolate the entire, cropped image. I am wondering about the impact on IQ (depending on the extrapolation algorithm). In any case, I do not like the idea.
[/quote]
No, you do not really have to affect the center.
The edges are what needs "correcting" by stretching them, basically. This leaves the center more or less unaffected. You end up with a larger image, pixel resolution wise. Then you crop this to original pixel resolution.
You can (some software applications do that, and I think PS does that too in its lens correction module)) also shrink the center. and leave the edges relatively resolution unaffected, and end up with a smaller image... but that is not what is the smart thing to do usually.