Rotating images

Swakoo · 26th April 2003

Will image quality image drop if I rotate in windows? for those vertical shots we take?

cos after discussing with my friend.. and after a test by him..

he tried to rotate a picutre continuously in winxp viewer, and true enough can see notable image quality drop..

then we are wondering.. is it because of the file being jpeg.. what abt raw?

How about if we use camera to rotate..? like the s45.. which automatically rotates pictures...

what abt g2.. can it rotate pictures?

gavinjung · 27th April 2003

using either photoshop or the camera, there should be absolutely no drop in quality as long as you rotate by exactly 90 degrees. at 90 degrees each pixel is simply remapped to another location. there is no interpolation or anything. might as well take your monitor and put it on its side. same thing. rotating an image at any angle that is NOT a multiple of 90 degrees, however, WILL result in image degradation. but as long as your image is sufficiently high res, just apply some unsharp mask, and it should be fine. just remember that sharpening should be the last thing you do to your image usually.

gavin

Swakoo · 27th April 2003

Quote:

Originally posted by gavinjung
using either photoshop or the camera, there should be absolutely no drop in quality as long as you rotate by exactly 90 degrees. at 90 degrees each pixel is simply remapped to another location. there is no interpolation or anything. might as well take your monitor and put it on its side. same thing. rotating an image at any angle that is NOT a multiple of 90 degrees, however, WILL result in image degradation. but as long as your image is sufficiently high res, just apply some unsharp mask, and it should be fine. just remember that sharpening should be the last thing you do to your image usually.

gavin

i see.. thanks!

but G2, can rotate the photo within?

I am using G2.. while my friend is using S45..

so far, am using zoombrowser (Canon's utilities) to rotate.. ok?

zod · 27th April 2003

Quote:

Originally posted by gavinjung
using either photoshop or the camera, there should be absolutely no drop in quality as long as you rotate by exactly 90 degrees. at 90 degrees each pixel is simply remapped to another location. there is no interpolation or anything. might as well take your monitor and put it on its side. same thing. rotating an image at any angle that is NOT a multiple of 90 degrees, however, WILL result in image degradation. but as long as your image is sufficiently high res, just apply some unsharp mask, and it should be fine. just remember that sharpening should be the last thing you do to your image usually.

gavin

i believe that is true when manipulating images saved in raw/tiff or any uncompressed format.
when you open a jpeg file, and rotate it 90 degrees, up till this point, no image quality has been lost. but when u save it as jpeg, even at the lowest compression/highest quality setting, there is a little quality lost.

can any expert confirm/deny this?

gavinjung · 27th April 2003

swakoo. any program should work. just rotate 90 degrees, no program should degrade image.

zodnm. in photoshop, rotation by 90 degrees, clone / heal tools and/or cropping will not affect quality. rotation by anything other than 90 degrees and/or resizing/scaling WILL affect quality (softens image). jpeg compression is a completely seperate issue. basically, whatever format you start with, if at the end photoshop prompts you to specify what jpeg compression to use, then you're losing some quality by saving. this always happens if you start with something other than jpeg, and sometimes happens with jpeg if you use certain tools/functions.

Good guideline: JPEG compression of 10 reduces files to approximately 1/10th the original size and the quality loss is virtually undetectable. Do a test yourself, on screen or by print, you may not be able to see a difference even with a magnifying glass. the difference, however, is when you want to edit your image again. apply levels to any great degree and you'll get a lot of noise and you won't be able to pull out much highlight or shadow detail from the image. so it's best to work on the raw or tiff image and do everything you want to it before saving to jpeg 10. cuz after that, editing is somewhat limited.

GJ

Azure · 27th April 2003

Quote:

Originally posted by Swakoo
but G2, can rotate the photo within?

I am using G2.. while my friend is using S45..

so far, am using zoombrowser (Canon's utilities) to rotate.. ok?

G2, S45, Zoombrowser, there should be no diff even when you rotate the image.

Gavinjung's explanation is a bit more technical, but it fits the bill.

zod · 29th April 2003

Hmmm, what i meant was that if we use zoom browser to rotate an image, when rotating the image, no quality is lost. but after the software rotates the image and saves it under a new filename, some quality is lost

gavinjung · 29th April 2003

nah, it shouldn't. photoshop doesn't do this and I dont' see why zoombrowser would either. if you think about the image as data and what software would do to manipulate it, there's no reason why there should be any loss in quality for this type of rotation. it's a simple remapping of pixel locations, as easy as turning your monitor on its side. there is no interpolation (for a 90 degree rotation) and there should be no changes in jpeg compression either (unless you specify it). pretty sure. like I said, not positive about zoombrowser, but pretty sure about photoshop.

GJ

zod · 29th April 2003

Quote:

Originally posted by gavinjung
nah, it shouldn't. photoshop doesn't do this and I dont' see why zoombrowser would either. if you think about the image as data and what software would do to manipulate it, there's no reason why there should be any loss in quality for this type of rotation. it's a simple remapping of pixel locations, as easy as turning your monitor on its side. there is no interpolation (for a 90 degree rotation) and there should be no changes in jpeg compression either (unless you specify it). pretty sure. like I said, not positive about zoombrowser, but pretty sure about photoshop.

GJ

what i meant is the quality is lost when the image is saved under a new name, not when rotating

darkness · 29th April 2003

The quality loss is due to the file being resaved in jpg format again. You will get this loss even in Photoshop.

To do a lossless rotation u need to do an exif rotation. Breezebrowser and irfanview allows you to do that.

Swakoo · 30th April 2003

hmm so how? will lose quality when re-save?

Zerstorer · 30th April 2003

Quote:

Originally posted by Swakoo
hmm so how? will lose quality when re-save?

If you resave as Jpeg, resaving as TIFF or any other lossless format will be ok.

Anyway I think some programs do degrade image quality when rotating, those that do not usually specifically state "Lossless rotation" as one of their attributes.

Swakoo · 30th April 2003

Quote:

Originally posted by Zerstorer
If you resave as Jpeg, resaving as TIFF or any other lossless format will be ok.

what you mean?

got comma at jpeg there.. makes the sentence diff from what I think you are trying to say?

Zerstorer · 30th April 2003

Quote:

Originally posted by Swakoo
what you mean?

got comma at jpeg there.. makes the sentence diff from what I think you are trying to say?

That's what I meant, perhaps a semicolon( ; ) would be more appropriate.

Saving as jpeg will always result in a quality loss.

Swakoo · 30th April 2003

hmmmm

so your POV is that saving jpeg (again) will definitely loss quality.. even if it is just a 90deg shift?

vince123123 · 2nd May 2003

Does Nikon View fall under this category?

Quote:

Originally posted by darkness
The quality loss is due to the file being resaved in jpg format again. You will get this loss even in Photoshop.

To do a lossless rotation u need to do an exif rotation. Breezebrowser and irfanview allows you to do that.

Zerstorer · 2nd May 2003

Quote:

Originally posted by Swakoo
hmmmm

so your POV is that saving jpeg (again) will definitely loss quality.. even if it is just a 90deg shift?

Yes. Even if you don't do anything, resaving as a jpeg will result in a quality loss as the jpeg algorithm will recalculate and recompress the image.

Swakoo · 3rd May 2003

interesting, something all digital pic takers should be wary off..

so.. if i rotate in the camera itself?

26th April 2003	#1
Swakoo Member Join Date: Jul 2002 Posts: 197	Rotating images Will image quality image drop if I rotate in windows? for those vertical shots we take? cos after discussing with my friend.. and after a test by him.. he tried to rotate a picutre continuously in winxp viewer, and true enough can see notable image quality drop.. then we are wondering.. is it because of the file being jpeg.. what abt raw? How about if we use camera to rotate..? like the s45.. which automatically rotates pictures... what abt g2.. can it rotate pictures?

27th April 2003	#2
gavinjung New Member Join Date: Mar 2003 Posts: 16	using either photoshop or the camera, there should be absolutely no drop in quality as long as you rotate by exactly 90 degrees. at 90 degrees each pixel is simply remapped to another location. there is no interpolation or anything. might as well take your monitor and put it on its side. same thing. rotating an image at any angle that is NOT a multiple of 90 degrees, however, WILL result in image degradation. but as long as your image is sufficiently high res, just apply some unsharp mask, and it should be fine. just remember that sharpening should be the last thing you do to your image usually. gavin

29th April 2003	#7
zod Member Join Date: Mar 2003 Posts: 1,295	Hmmm, what i meant was that if we use zoom browser to rotate an image, when rotating the image, no quality is lost. but after the software rotates the image and saves it under a new filename, some quality is lost

29th April 2003	#10
darkness Member Join Date: Aug 2002 Posts: 757	The quality loss is due to the file being resaved in jpg format again. You will get this loss even in Photoshop. To do a lossless rotation u need to do an exif rotation. Breezebrowser and irfanview allows you to do that.

30th April 2003	#11
Swakoo Member Join Date: Jul 2002 Posts: 197	hmm so how? will lose quality when re-save?

3rd May 2003	#18
Swakoo Member Join Date: Jul 2002 Posts: 197	interesting, something all digital pic takers should be wary off.. so.. if i rotate in the camera itself?