I need your help guys

[versedmb]

This problem is something that I just can't explain.

I noticed that after I straighten an image there is an obvious loss of sharpness when viewed at 100%.

I first noticed this working on a jpeg image in Paint shop pro X2. So I tried straigtening a TIFF file - same thing. Then I tried it in Picasa - same thing - why should this be happening?

I'm no newbie to PP - I commonly blend multiple layers - no change in shaprness, but i simply rotate the file and there is an obvious loss of sharpness - why would this be? I'm really at a loss to understand this.

[conkeroo]

As far as I can gather, when you rotate an image, there is a need to resample the pixels so you end up losing finer detail as the pixel information needs to be changed. I normally just use unsharp mask to sharpen it up a bit but it's not 100% effective and you do lose some of the original detail.

[versedmb]

Originally Posted by conkeroo

As far as I can gather, when you rotate an image, there is a need to resample the pixels so you end up losing finer detail as the pixel information needs to be changed. I normally just use unsharp mask to sharpen it up a bit but it's not 100% effective and you do lose some of the original detail.

Wow; I had not idea that rotating an image could do this - I always thought is was a very bening manipulation.

I this true even for TIFF's? I commonly blend several images with no loss in sharpness and detail - its just hard for me to believe that simply rotating an image can result in loss of sharpness and detail.

[versedmb]

Here's an example. 110% crops from an image. Top is original, bottom is after straightening (only a few degrees)...

The straightened image (bottom) is softer and lacking some of the detial....

[versedmb]

I tried applying to a little USM to the rotated image and it does no good - the detail is lost. I am really surprised by this.

[bohdank]

When you think of an image as a row of pixels, arranged in columns... if you rotate it, slightly, the odds of the rotated pixels falling eaxctly on one of those (previous) row/columns is pretty low. The problem is worse when correcting for lens distortion since pixels might actually have to be created or deleted to fit the perspective. There is no way around it. You are going to lose image quality.

[versedmb]

Originally Posted by bohdank

When you think of an image as a row of pixels, arranged in columns... if you rotate it, slightly, the odds of the rotated pixels falling eaxctly on one of those (previous) row/columns is pretty low. The problem is worse when correcting for lens distortion since pixels might actually have to be created or deleted to fit the perspective. There is no way around it. You are going to lose image quality.

Well, this is a revelation to me. Thanks for the info. What you say definitely makes sense, but its still hard for me to accept.

In the past I've always tried to get my images resonably straight in camera and then just fix it in post, but this will change how I do things.

I'm into landscapes and when printing big this kind of lost detail really matters.

I can't believe that I've not heard of this before.

[tonybear007]

What a revelation! I will definitely pay attention to how I align my scenes while composing them.

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[versedmb]

Thanks again for the info, but I still can't believe that I've not heard of this before.

[adas]

I think it depends on software. I've never noticed an image degradation in Photoshop CS3 with arbitrary rotation (note that 90 degree and multiples rotation should not harm the image at all) so I believe it must be doing it to a lesser extent, probably a better algorithm.

[bohdank]

Don't panic....It is quite possible to do rotation without any degradation. It would not be hard to do. The software would have to limit the increments that you could rotate the image so that the pixels always fell on an image cel.

i.e. you can only rotate in 2 degree increments. I would think that PS does that, as would most software.

Lens correction is a different problem. It either fixes the perspective or it doesn't. If it does, then there will be degredation in the parts of the image that were stretched/compressed/skewed. I don't see a way around this. Maybe someone else can jump in.

[Halliday]

Shoot in RAW and rotate in Lightroom?