Is it true that image is degrade after rotation?

Discussion in 'Digital Photography' started by Editor www.nutritionsoftware.org, Dec 1, 2003.

  1. If so why?
    I remember seeing this warning when rotating a horizontal image to vertical
    in Windows viewer.
    Thanks for any explanation.

    --
    Editor, Internet's Convenient and Unbiased Directory of Nutrition Software
    http://nutritionsoftware.org
    Editor www.nutritionsoftware.org, Dec 1, 2003
    #1
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  2. Editor www.nutritionsoftware.org wrote:
    > If so why?
    > I remember seeing this warning when rotating a horizontal image to vertical
    > in Windows viewer.


    It depends on the application doing the rotation. The "normal" reason
    why there might be degradation is that when you rotate a .JPG image it
    has to be resaved which caused the compression to be done again,
    creating more compression artifacts.

    However, there are programs that can rotate the JPG image without
    recompressing it and those programs cause absolutely no deradation of
    the image. I use PIE (Picture Information Extractor) myself. I allows
    for lossless JPG rotation.

    Other programs will do it as well, I think the freeware IrfanView does it.
    Andrew McDonald, Dec 1, 2003
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  3. Editor  www.nutritionsoftware.org

    Mxsmanic Guest

    "Editor www.nutritionsoftware.org" <nseditor2002 >
    writes:

    > If so why?


    The image is not degraded if it is rotated a multiple of 90 degrees.
    Otherwise degradation is possible and probable (but not certain).

    The problem is that there are rounding and other errors in interpolating
    the old pixels to the new pixels that almost inevitably sacrifice image
    information during the rotation. There are a few specific types of
    rotation that fully avoid this (rotating in multiples of 90 degrees is
    one example), but in most cases there is some loss, however small.

    --
    Transpose hotmail and mxsmanic in my e-mail address to reach me directly.
    Mxsmanic, Dec 1, 2003
    #3
  4. Editor  www.nutritionsoftware.org

    Mark Johnson Guest

    "Editor www.nutritionsoftware.org" <nseditor2002 >
    wrote:

    >If so why?
    >I remember seeing this warning when rotating a horizontal image to vertical
    >in Windows viewer.
    >Thanks for any explanation.


    As someone else just mentioned, I think it's just the jpg format
    that's at issue. Even a 100% 'uncompressed' jpg still attempts some
    compression, and loss of info. And that can accumulate if you use a
    lot of filtering and sharpening and so on, to where the photo might be
    a lesser quality for repeatedly loading and saving in jpg. So if you
    start with a jpg, always save it in uncompressed png, for example,
    before doing anything else. Only go back to jpg for the final print -
    say if the photo shop only takes jpg.
    Mark Johnson, Dec 1, 2003
    #4
  5. Editor  www.nutritionsoftware.org

    IMKen Guest

    I use Photoshop 7 or Nikon View 6 and both alter the image making it
    unsuitable. Both alter the photo so that people or other objects become
    noticeably thinner when rotated from horizontal to vertical. If there is
    a solution please pass it along. I hate making my chubby friends look lean
    and mean.

    Ken



    "Mark Johnson" <> wrote in message
    news:...
    > "Editor www.nutritionsoftware.org" <nseditor2002 >
    > wrote:
    >
    > >If so why?
    > >I remember seeing this warning when rotating a horizontal image to

    vertical
    > >in Windows viewer.
    > >Thanks for any explanation.

    >
    > As someone else just mentioned, I think it's just the jpg format
    > that's at issue. Even a 100% 'uncompressed' jpg still attempts some
    > compression, and loss of info. And that can accumulate if you use a
    > lot of filtering and sharpening and so on, to where the photo might be
    > a lesser quality for repeatedly loading and saving in jpg. So if you
    > start with a jpg, always save it in uncompressed png, for example,
    > before doing anything else. Only go back to jpg for the final print -
    > say if the photo shop only takes jpg.
    IMKen, Dec 1, 2003
    #5
  6. "IMKen" <> wrote in message
    news:AQAyb.60549$...
    > I use Photoshop 7 or Nikon View 6 and both alter the image making it
    > unsuitable. Both alter the photo so that people or other objects become
    > noticeably thinner when rotated from horizontal to vertical. If there

    is
    > a solution please pass it along. I hate making my chubby friends look

    lean
    > and mean.


    I do not even know how such a problem could arise. Rotating an image 90
    degrees (an exact right angle) is merely a matter of swapping the vertical
    and horizontal coordinates.

    QUESTION: Is there something wrong with your monitor? You may be using a
    video mode that doesn't suit it. Use Photoshop to create something that is
    perfectly square (e.g., a canvas 300 x 300 pixels) and measure it on your
    screen. Is it rectangular?

    If so, the problem is with screen adjustments.
    Michael A. Covington, Dec 1, 2003
    #6
  7. Editor  www.nutritionsoftware.org

    Don Stauffer Guest

    Only when rotation is 90 degrees is compression the only source of
    degradation. If rotation is anything other than 90 or 180, then
    resampling MUST be done, and resampling itself can cause degradation
    regardless of compression or what format the file is stored in.

    This degradation is likely to be minor, so do not hesitate to rotate if
    the image really calls for it, but be aware that shooting so that
    rotation is not required is best.

    Mark Johnson wrote:
    >
    > "Editor www.nutritionsoftware.org" <nseditor2002 >
    > wrote:
    >
    > >If so why?
    > >I remember seeing this warning when rotating a horizontal image to vertical
    > >in Windows viewer.
    > >Thanks for any explanation.

    >
    > As someone else just mentioned, I think it's just the jpg format
    > that's at issue. Even a 100% 'uncompressed' jpg still attempts some
    > compression, and loss of info. And that can accumulate if you use a
    > lot of filtering and sharpening and so on, to where the photo might be
    > a lesser quality for repeatedly loading and saving in jpg. So if you
    > start with a jpg, always save it in uncompressed png, for example,
    > before doing anything else. Only go back to jpg for the final print -
    > say if the photo shop only takes jpg.


    --
    Don Stauffer in Minnesota

    webpage- http://www.usfamily.net/web/stauffer
    Don Stauffer, Dec 1, 2003
    #7
  8. Editor  www.nutritionsoftware.org

    Ray Murphy Guest

    ----------
    In article <>, Mark Johnson
    <> wrote:


    >"Editor www.nutritionsoftware.org" <nseditor2002 >
    >wrote:
    >
    >>If so why?
    >>I remember seeing this warning when rotating a horizontal image to vertical
    >>in Windows viewer.
    >>Thanks for any explanation.

    >
    >As someone else just mentioned, I think it's just the jpg format
    >that's at issue.


    RM: There are other "lossy" formats, but JPEG is the main one to be
    concerned about.

    >Even a 100% 'uncompressed' jpg still attempts some
    >compression, and loss of info. And that can accumulate if you use a
    >lot of filtering and sharpening and so on, to where the photo might be
    >a lesser quality for repeatedly loading and saving in jpg.


    RM: I have experimented with this and found that if the highest
    quality is used the image is not degraded further.

    > So if you
    >start with a jpg, always save it in uncompressed png, for example,
    >before doing anything else. Only go back to jpg for the final print -
    >say if the photo shop only takes jpg.


    RM: That's a good idea if you don't want anything to go wrong.

    Here's how to avoid loss of quality when working with JPEGS:

    PHOTOSHOP
    * Do not "SAVE" the job, but "SAVE AS" (with the same name). This will
    automatically throw up the page in Photoshop where you can control the
    compression.
    When you get there, place the slider at the highest quality and the
    JPEG quality will remain identical.

    PAINTSHOP PRO
    If you are using Paintshop Pro you need to select "Options" after
    selecting "Save" or "Save As" and this will allow saving at the best
    compression without any degradation of the image.

    This can be proven by doing it and measuring the precise colour of
    pixels from an original and a "Saved As" copy in Photoshop or the
    "Saved" copy in Paintshop Pro.

    Both Photoshop and Paintshop Pro have default saving modes which are
    of fairly low quality but as indicated above, they can be altered.

    Ray
    Ray Murphy, Dec 1, 2003
    #8
  9. Editor  www.nutritionsoftware.org

    zbzbzb Guest

    >RM: Yes, if you rotate any image at any angle other than 90, 180 or
    >270 degrees it is degraded because it has to be re-constructed.



    Thing is though if you start off with a very large file to begin with it is
    hard if not impossible to see any degradation. In my case rotating 60 meg files
    from 4000dpi negative scans. I can't see any obvious effect on them after
    rotating. If I work with a much smaller file then the effects are very
    noticeable.




    This
    >can be very easily checked by making a solid box (without any fuzzy
    >edges) and then rotating it.
    >The fuzzy edges in the original can be removed by the eraser (as if
    >that was not obvious to everyone).
    >
    >Incidentally, talking about rotating images. We cannot rotate B+W
    >bitmap images in the Bitmap mode. We have to convert any such images
    >to grayscale first and then rotate and go back to bitmap.
    >
    >Ray
    >
    zbzbzb, Dec 1, 2003
    #9
  10. Editor  www.nutritionsoftware.org

    Ray Murphy Guest

    ----------
    In article <UAwyb.28348$>, "Editor
    www.nutritionsoftware.org" <nseditor2002 > wrote:

    [Is it true that image is degrade after rotation?]

    >If so why?
    >I remember seeing this warning when rotating a horizontal image to vertical
    >in Windows viewer.
    >Thanks for any explanation.
    >
    >--
    >Editor, Internet's Convenient and Unbiased Directory of Nutrition Software


    RM: Yes, if you rotate any image at any angle other than 90, 180 or
    270 degrees it is degraded because it has to be re-constructed. This
    can be very easily checked by making a solid box (without any fuzzy
    edges) and then rotating it.
    The fuzzy edges in the original can be removed by the eraser (as if
    that was not obvious to everyone).

    Incidentally, talking about rotating images. We cannot rotate B+W
    bitmap images in the Bitmap mode. We have to convert any such images
    to grayscale first and then rotate and go back to bitmap.

    Ray
    Ray Murphy, Dec 1, 2003
    #10
  11. Editor  www.nutritionsoftware.org

    Bob Niland Guest

    > zbzbzb <> wrote:

    > ... start off with a very large file to begin with ...


    When possible, start with at least twice
    the resolution (4x the pixels) you need to
    end up with.

    Also, rotate only ONCE. If you need to
    experiment to get the exact rotation, UNDO
    each rotation except the last.

    Also, if your image editor supports
    combined transforms, do your geometry
    corrections (e.g. rotation, keystone,
    barrel/pincushion) as a single operation.

    --
    Regards, PO Box 248
    Bob Niland Enterprise
    mailto: Kansas USA
    which, due to spam, is: 67441-0248
    email4rjn AT yahoo DOT com
    http://www.access-one.com/rjn

    Unless otherwise specifically stated, expressing
    personal opinions and NOT speaking for any
    employer, client or Internet Service Provider.
    Bob Niland, Dec 1, 2003
    #11
  12. Editor  www.nutritionsoftware.org

    Ray Murphy Guest

    ----------
    In article <>,
    bzbzb (zbzbzb) wrote:


    >>RM: Yes, if you rotate any image at any angle other than 90, 180 or
    >>270 degrees it is degraded because it has to be re-constructed.

    >
    >
    >Thing is though if you start off with a very large file to begin with it is
    >hard if not impossible to see any degradation. In my case rotating 60 meg
    >files
    >from 4000dpi negative scans. I can't see any obvious effect on them after
    >rotating. If I work with a much smaller file then the effects are very
    >noticeable.
    >

    RM: Yes that sounds right.
    I would imagine that the difference would be miniscule and not worth
    considering.

    Ray
    Ray Murphy, Dec 2, 2003
    #12
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