Does rotating a digital image reduce its quality?

Question

When rotating a large digital image Windows XP warns that the image quality may be reduced. Is that true? Why or why not?

I'd like to rotate images for viewing purposes, but don't want to reduce the quality for large prints.

Answer 1

Yes, it's true. There is no known algorithm to rotate a bitmap without losing quality; hence EVERY program that rotates an image does so at the expense of quality, whether it says so or not. The impact it makes, however, is generally very minor -- probably unnoticeable in a print.

Another possible reason could be that reapplication of the JPEG algorithm to an image can cause digital artifacts. Opening a JPEG image, changing it, and saving it as JPEG will eventually lead to serious quality loss.

In any event, rotate all you want for viewing, but don't save the picture when you're done.

Answer 2

Well, not, by default.
But if you rotate compressed JPG files, then the basic image for rotation would be the already-compromised compressed JPG, which - due to the changes of the image structure from the point of view of the compression algorithm - will encounter even more artifacts at the parts containing precise data.

For more details on this, check lossy compression algorithms details. If you are rather an end-user, you can find some informations here:
http://www.widearea.co.uk/designer/compress.html

By the way, these artifacts can be avoided by using some proper program for rotating your images and saving into JPG with custom compression factor. Such software is Paint Shop Pro or Photoshop, for instance.

After all, your (and some million other windows users') main question should be "What the hell does windows rotate the image on the disk instead of the one on the screen for??"

For this question, though, there is no answer, maybe if someone would regularly mail them with this, they would finally react something.

Answer 3

It relies upon on what software you employ to "rotate" them. In maximum photo editors, a special of ninety-stages rotation received't impression photo high quality in any respect. All it does is flow the starting place of the photo's coordinate equipment, not something more beneficial. even if, in Microsoft's "photo and Fax Viewer" software, it now and again rotates AND scales pictures mutually, which *will* impression photo high quality (in case then you shop the photo over the un-grew to develop into round unique). do exactly your rotation in a real photo-modifying software instead of abode windows' default viewer, and your photos will be unaffected except for orientation.

Answer 4

It depends what software you use to rotate it.
Irfanview supports lossless quality rotation.
http://www.irfanview.com

Answer 5

no