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Thread: Rotating images

  1. #1

    Question 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?

  2. #2

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    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

  3. #3

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    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?

  4. #4

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    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?

  5. #5

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    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

  6. #6
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    Default

    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.

  7. #7

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    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

  8. #8

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    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

  9. #9

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    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

  10. #10

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    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.

  11. #11

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

  12. #12

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    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.

  13. #13

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    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?

  14. #14

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    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.

  15. #15

    Default

    hmmmm

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

  16. #16
    vince123123
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    Does Nikon View fall under this category?

    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.

  17. #17

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    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.

  18. #18

    Default

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

    so.. if i rotate in the camera itself?

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