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Does arbitrary rotation affect sharpness?

Nill Toulme

New member
Does arbitrary (i.e., something other than 90 or 180 degrees) rotation of an image affect its sharpness? In general, but also more specifically at the RAW conversion stage, and more specifically still with Capture One? If so, how much?

Nill
 

Mike Shimwell

New member
Anything other than 90 degreee intervals will lead to interpolation at some point in the image. This may be expected lead to to degradation that may become visible if the operation is repeated or the image printed very large.

Having said that, I don't seem to have problems when I print images and make the effort to correct the horizon by my stadard error of 1.26 degrees.

Mike
 

Ken Tanaka

pro member
Simple rotation without resizing will not affect absolute sharpness of an image, regardless of the degree of rotation. But it might appear to do so on your screen, since your monitor's resolution is only 72-96 dpi.

Nevertheless, I always save postpone final sharpening until the last post-production step and RAW pre-sharpening until after rotation/straightening.
 

Daniel Buck

New member
rotation other than 90, 180, or 270 degree increments will result in interpolation of the pixels. Theoretically, yes you'll loose a bit of definition. And I would not do arbitrary rotations after you have done your sharpening, since you would be interpolating the sharpened image, possibly causing some oddities.
 

Cem_Usakligil

Well-known member
Simple rotation without resizing will not affect absolute sharpness of an image, regardless of the degree of rotation. But it might appear to do so on your screen, since your monitor's resolution is only 72-96 dpi.

Nevertheless, I always save postpone final sharpening until the last post-production step and RAW pre-sharpening until after rotation/straightening.

rotation other than 90, 180, or 270 degree increments will result in interpolation of the pixels. Theoretically, yes you'll loose a bit of definition. And I would not do arbitrary rotations after you have done your sharpening, since you would be interpolating the sharpened image, possibly causing some oddities.
I think these statements may look contradictory to the casual reader. Let me try and explain a little bit (and hope that I won't confuse matters even more).

I assume what Ken is mentioning is the undestructive rotation of a file in an application such as LR. In that case, the sharpness won't change since the relative positions of the pixels with respect to each other do not change either. But when you "render" the rotated image to be displayed on the screen or to be printed, the pixels will be remapped into their new positions. Just like Daniel says, this will cause interpolation of the position and introduce jitter, unsharpness or maybe even jaggies.

So to summarize, if one outputs the rotated image onto a finite raster (such as the monitor or a printer), interpolation is inevitable. It may not be immediately visible though.

Hope I did not confuse matters ;-)

Cheers,
 

J.T. Shaver

New member
Just a tip for anyone who cares, as I always notice a difference when rotating arbitrarily...make sure you convert anything you'll be rotating in Photoshop to a Smart Object before rotating, it will allow you to continue trying different angles without degrading the quality with each rotation.
 

Asher Kelman

OPF Owner/Editor-in-Chief
Simple rotation without resizing will not affect absolute sharpness of an image, regardless of the degree of rotation. But it might appear to do so on your screen, since your monitor's resolution is only 72-96 dpi.

Nevertheless, I always save postpone final sharpening until the last post-production step and RAW pre-sharpening until after rotation/straightening.
It used to be that any rotation would degrade the image for non exact multiples of 90 degrees. However, the software today, I believe is much more sophisticated. In CS extended one can rotate the canvas at will to any angle more convenient for handiwork. Still, I think that all such changes should be made in 16 BIT mode to minimize odd interval posterization in the shading.

Asher
 

JohanElzenga

New member
Simple rotation without resizing will not affect absolute sharpness of an image, regardless of the degree of rotation. But it might appear to do so on your screen, since your monitor's resolution is only 72-96 dpi.

I disagree. Simple rotation does affect absolute sharpness, because interpolation takes place. The resolution doesn't matter, but the effect obviously becomes clearer when you view the image at a low resolution. In print it may not be visible to the naked eye, but that doesn't mean it didn't happen.
 
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