| Author | Thread |
|
|
09/06/2006 04:08:49 PM · #1 |
I've heard that if you change the orientation of an image (rotate a photo 90 degrees either direction), you will lose some data (pixels, thus quality) unless both dimensions are an even multiple of 8.
If the image's dimensions are not evenly divisible by 8, then what methods do the various editing software use? I have heard that some software will crop first (to meet the "8" requirement), rotate, then fill in the missing pixels with pixels of their own making.
Also, does PS support the EXIF Orientation setting (page 29 of the official specification)?
|
|
|
|
09/06/2006 04:21:28 PM · #2 |
I've never heard of this problem before, and it makes no sense with a 90-degree rotation; maybe a problem at odd angles.
If you rotate a JPEG file and re-save it as JPEG, you can lose some quality due to repetitive lossy compression. |
|
|
|
09/06/2006 04:31:55 PM · #3 |
| It's a fact, rotation and also cropping and flipping are not necessarily lossless. Here is more information than you probably want, LOL. The bottom line is that at least up to CS, Photoshop apparently does not support lossless rotation for digital comaera files. The good news is that the loss incurred is very minor, and is usually less than one generation of editing "entropy" though that of course depends on the amount of compression at the time of saving. |
|
|
|
09/06/2006 04:32:25 PM · #4 |
Edited: Kirbic answered the point I was making while I was making it. :)
Message edited by author 2006-09-06 16:33:19. |
|
|
|
09/06/2006 04:39:40 PM · #5 |
Originally posted by kirbic:
It's a fact, rotation and also cropping and flipping are not necessarily lossless. Here is more information than you probably want . . . |
Nice article on the explanation of losing quality when rotating. Even Photoshop CS can't rotate an image from a digital camera without compromising quality. I did not know that.
However, if my image dimensions are multiples of the MCU, does PS still lose data?
I guess I just need to test using the article on how to test for lossless rotation in your own software.
My edit: The good news is that it appears that the lossy results of rotation are relatively and practically invisible to the naked eye. :-)
Message edited by author 2006-09-06 16:45:26. |
|
|
|
09/06/2006 04:48:24 PM · #6 |
| IrfanView has a lossless JPEG rotation function in one of the menus. I tested it and it is lossless. iView MediaPro also has lossless rotation that can be batch performed. |
|
|
|
09/06/2006 05:05:47 PM · #7 |
Originally posted by kirbic:
It's a fact, rotation and also cropping and flipping are not necessarily lossless. Here is more information than you probably want, LOL. |
But this all seems only to do with decoding/re-encoding JPEG data and converting color spaces -- the actual rotation in RGB-space doesn't alter or degrade the image.
I open my original (JPEG) image, rotate, and save a .PSD -- there shouldn't be any more "loss" than there was from the original decompression from JPEG to RGB. Open, rotate, flip, SaveAs in .PSD or TIFF -- still should be no further degradation. |
|
|
|
09/06/2006 05:09:15 PM · #8 |
Originally posted by GeneralE:
Originally posted by kirbic:
It's a fact, rotation and also cropping and flipping are not necessarily lossless. Here is more information than you probably want, LOL. |
But this all seems only to do with decoding/re-encoding JPEG data and converting color spaces -- the actual rotation in RGB-space doesn't alter or degrade the image.
I open my original (JPEG) image, rotate, and save a .PSD -- there shouldn't be any more "loss" than there was from the original decompression from JPEG to RGB. Open, rotate, flip, SaveAs in .PSD or TIFF -- still should be no further degradation. |
Rotate by 90 degrees doesn't discard any data, it's saving to JPEG that discards data. The program that do lossless JPEG rotation do it without recompressing the image. |
|
|
|
09/06/2006 06:12:33 PM · #9 |
Using ACDSee, I first made a copy of an image (a jpeg). Then I rotated it left. Then rotated it right. Then compared the final image with the one I had saved. It appeared that the only difference within the file was in the EXIF data. The picture data remained constant.
|
|
|
|
09/06/2006 06:33:02 PM · #10 |
Originally posted by dwterry:
Using ACDSee, I first made a copy of an image (a jpeg). Then I rotated it left. Then rotated it right. Then compared the final image with the one I had saved. It appeared that the only difference within the file was in the EXIF data. The picture data remained constant. |
Are the dimensions of said photo multiples of 8? If so, then you shouldn't have any lossness.
|
|
|
|
09/06/2006 06:39:56 PM · #11 |
Originally posted by lesgainous:
Are the dimensions of said photo multiples of 8? If so, then you shouldn't have any lossness. |
The one I had tried in my earlier post, yes, even multiples of 8.
So I just tried it again. This time on an image that was 3632x3007. Same results. For what it's worth, ACDSee advertises their rotation as being lossless. I only investigated it today out of concern from the OP's comments.
|
|
Home -
Challenges -
Community -
League -
Photos -
Cameras -
Lenses -
Learn -
Help -
Terms of Use -
Privacy -
Top ^
DPChallenge, and website content and design, Copyright © 2001-2026 Challenging Technologies, LLC.
All digital photo copyrights belong to the photographers and may not be used without permission.
Current Server Time: 01/03/2026 10:10:49 AM EST.
