clickety

I would like objective, quantifiable, or 'sound' theoretical responses if possible.

Using horizon or perspective alignments as an example. When an image is straightened in PP it requires cropping because of the slices created by the image realignment. This demonstrates that the pixels have been disassembled and reassembled to achieve the correction. Is there demonstrable evidence of the extent of image deterioration as a result?

Does this effect apply equally to rotating an image 90 or even 180 degrees in PP, how about flipping side to side? It's so easy to manipulate images with the computer, done so routinely with great results that we may never know the diffence.

For the purist, I suspect there's benefit to "getting it right in camera". But will anyone notice.........?

Rongnongno Loc: FL

Any sort of post processing that changes pixels will create artifacts. Searcher, a long lost UHH member demonstrated it in one his tutorial posts.

What it really comes down to is not if does modify anything but what one deems acceptable.

Flipping or reversing an image will not change anything, as far as I know. 90 degrees will not change either unless you modify the ratio at the same time.

artBob Loc: Near Chicago

Unless radical (vague, but determinable through experimentation and pixel-peeping), such distortions do not noticeably affect the image in my experience. I have to be rather picky, as I submit portfolios to galleries and museums.

Bill_de Loc: US

These 2 articles from Adobe should spell it all out.

https://helpx.adobe.com/photoshop/using/crop-straighten-photos.html

https://helpx.adobe.com/photoshop/kb/advanced-cropping-resizing-resampling-photoshop.html

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selmslie Loc: Fernandina Beach, FL, USA

Your instinct is correct. Any time you take an image apart geometrically and reassemble it, it will lose some fidelity. The exception would be if you rotate in 90 degree increments or flip it.

It is difficult to demonstrate because the original image has to be very sharp overall. The degradation will not show up in a soft image.

Blenheim Orange Loc: Michigan

Here are some 500x500 pixel crops from an image at 100%, rotated 0,1,2,3,4 and 5 degrees.

Mike

CHG_CANON Loc: the Windy City

Who would be able to tell anything from a thumbnail ....
unless that's the point?

Blenheim Orange Loc: Michigan

Those aren't thumbnails.

Mike

Linda From Maine Loc: Yakima, Washington

When you post a jpg less than 600 px wide on UHH, no download is generated. I don't know if right-clicking a UHH "thumbnail" off the web page and saving to computer is going to provide the same quality of image as the original. Maybe someone can test that too?

Blenheim Orange Loc: Michigan

Of course.

I said "500x500 pixel crops from an image at 100%, rotated 0,1,2,3,4 and 5 degrees."

Nothing to do with "thumbnails" or store original or downloads.



Mike

CHG_CANON Loc: the Windy City

Clearly proves the point ...

selmslie Loc: Fernandina Beach, FL, USA

It only proves that it's hard to demonstrate if the original is not sharp enough.

You need to be able to download and view it at 400% or more to see the degradation.

Blenheim Orange Loc: Michigan

So, save it to your local machine and blow it up 400%.

"The original is not sharp enough?" What do you mean by that? The same image is being compared with 6 different amount of rotation, from 0-5 degrees. They are all at 100% and then cropped to 500x500 pixels. I don't know what going to 400% would tell you, but there is nothing stopping you from doing that.

With your permission, I will execute the same demonstration with one of your images of your choice.

Mike

selmslie Loc: Fernandina Beach, FL, USA

I guess there is no point in letting logic and reason cloud your mind.

A digital image is captured as a discrete number of pixels, for example, 4000x6000 to give you a 24 MP image. Those original pixels are arranged in parallel horizontal and vertical rows and columns of pixels.

What happens when you level it? Some of the information is discarded (you can see that happen in your editor) and the image gets smaller. The same thing happens when you apply a keystone correction or a correction for barrel or pincushion distortion.

But what happened to the original regularly arranged pixels? They are also moved from their original location. Clearly, they cannot occupy the same relative positions where they were originally recorded. The information that they each contained have to be used to create four new pixels that will be arranged in parallel horizontal and vertical rows and columns of pixels.

Since it will be almost impossible for any of the new pixels to be created from a single old pixel, the image will necessarily be degraded - whether you can see it with your own eyes or not.

Blenheim Orange Loc: Michigan

How is any of that relevant to what I said, and why be so rude? You are refuting things I didn't say. You did not respond to the things I did say.

In the visual arts, how something looks is all there is. I worked years ago in a company that did custom paint color matches. Periodically a customer would say about a match "sure it looks the same, but is it really the same?" That was always good for a chuckle.

Of course when you rotate an image and then crop it you have fewer pixels. Of course when you re-align the pixels you introduce changes. No one claimed otherwise that I am aware of. I simply posted an example.

The OP asked "is there demonstrable evidence of the extent of image deterioration as a result? " I created a demonstration. How else would you judge or measure how much an image has been degraded other than by looking at it?

Mike