What does Lossless really mean?

Discussion in 'Digital Photography' started by Freedom55, Jun 19, 2005.

  1. Freedom55

    Freedom55 Guest

    I have lossless rotation for digital photos in PSP8. Does lossless
    really mean lossless? I mean there has to be some loss in a jpeg when
    you rotate it.

    Ron
    --
    And it really doesn't matter if
    I'm wrong I'm right
    Where I belong I'm right
    Where I belong.

    Lennon & McCartney
    Freedom55, Jun 19, 2005
    #1
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  2. Freedom55

    Scott W Guest

    Freedom55 wrote:
    > I have lossless rotation for digital photos in PSP8. Does lossless
    > really mean lossless? I mean there has to be some loss in a jpeg when
    > you rotate it.



    There does not have to be any loss if your rotate by 90 or 180 degrees.

    Scott
    Scott W, Jun 19, 2005
    #2
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  3. Scott W wrote:
    > Freedom55 wrote:
    >> I have lossless rotation for digital photos in PSP8. Does lossless
    >> really mean lossless? I mean there has to be some loss in a jpeg when
    >> you rotate it.

    >
    >
    > There does not have to be any loss if your rotate by 90 or 180
    > degrees.
    >
    > Scott


    ... and the image is a multiple of 8 (or sometime 16) in each dimension.

    David
    David J Taylor, Jun 19, 2005
    #3
  4. Freedom55

    Jim Townsend Guest

    Freedom55 wrote:

    > I have lossless rotation for digital photos in PSP8. Does lossless
    > really mean lossless? I mean there has to be some loss in a jpeg when
    > you rotate it.



    Yes, it's lossless.. Because the operation doesn't open
    the file first, it doesn't have to re-compress it.. It's
    the compression that causes the loss.

    There's a good explanation on just about everything you
    wanted to know about JPEG here:
    ``
    http://makeashorterlink.com/?Z1BB6294B

    Search the article for rotation and you'll find:


    "There are a few specialized operations that can be done on a JPEG file
    without decompressing it, and thus without incurring the generational loss
    that you'd normally get from loading and re-saving the image in a regular
    image editor. In particular it is possible to do 90-degree rotations and
    flips losslessly, if the image dimensions are a multiple of the file's
    block size (typically 16x16, 16x8, or 8x8 pixels for color JPEGs). This
    fact used to be just an academic curiosity, but it has assumed practical
    importance recently because many users of digital cameras would like to be
    able to rotate their images from landscape to portrait format without
    incurring loss --- and practically all digicams that produce JPEG files
    produce images of the right dimensions for these operations to work. So
    software that can do lossless JPEG transforms has started to pop up. But
    you do need special software; rotating the image in a regular image editor
    won't be lossless".
    Jim Townsend, Jun 19, 2005
    #4
  5. Lossless means identical to the uncompressed original.AFAIK jpeg is a
    lossless compression format, in contrast to MPEG which is lossy.That's why I
    bought a digital still camera, but I stick to the good ol' 8 mm analogue
    camcorder format.

    --
    Tzortzakakis Dimitrios
    major in electrical engineering, freelance electrician
    FH von Iraklion-Kreta, freiberuflicher Elektriker
    dimtzort AT otenet DOT gr
    ? "Freedom55" <"joinertake this out"@ns.sympatico.ca> ?????? ??? ??????
    news:Y8ete.49313$...
    > I have lossless rotation for digital photos in PSP8. Does lossless
    > really mean lossless? I mean there has to be some loss in a jpeg when
    > you rotate it.
    >
    > Ron
    > --
    > And it really doesn't matter if
    > I'm wrong I'm right
    > Where I belong I'm right
    > Where I belong.
    >
    > Lennon & McCartney
    Dimitrios Tzortzakakis, Jun 19, 2005
    #5
  6. Freedom55

    Ken Wright Guest

    jpeg isn't lossless, it's lossy, subject to the exceptions listed by the
    others.

    --
    Regards
    Ken.......................


    "Dimitrios Tzortzakakis" <> wrote in message
    news:d94ieg$e2f$...
    > Lossless means identical to the uncompressed original.AFAIK jpeg is a
    > lossless compression format, in contrast to MPEG which is lossy.That's why

    I
    > bought a digital still camera, but I stick to the good ol' 8 mm analogue
    > camcorder format.
    >
    > --
    > Tzortzakakis Dimitrios
    > major in electrical engineering, freelance electrician
    > FH von Iraklion-Kreta, freiberuflicher Elektriker
    > dimtzort AT otenet DOT gr
    > ? "Freedom55" <"joinertake this out"@ns.sympatico.ca> ?????? ??? ??????
    > news:Y8ete.49313$...
    > > I have lossless rotation for digital photos in PSP8. Does lossless
    > > really mean lossless? I mean there has to be some loss in a jpeg when
    > > you rotate it.
    > >
    > > Ron
    > > --
    > > And it really doesn't matter if
    > > I'm wrong I'm right
    > > Where I belong I'm right
    > > Where I belong.
    > >
    > > Lennon & McCartney

    >
    >
    Ken Wright, Jun 19, 2005
    #6
  7. Freedom55

    Ralf Schmode Guest

    Dimitrios Tzortzakakis wrote:

    > Lossless means identical to the uncompressed original.AFAIK jpeg is a
    > lossless compression format, in contrast to MPEG which is lossy.


    Hi, Dimitrios,

    sorry, that is not true. JPEG compression, as offered by consumer image
    editing software on the market, is lossy even at 100% quality setting.
    However, there are operations - such as rotation by a multiple of 90
    degrees - that can be carried out without *further* loss in comparision
    to the JPEG input file.

    Greets - Ralf

    --
    My animal photo page on the WWW: http://schmode.net (currently offline)
    "Best of" portfolio: http://www2.fotocommunity.de/pc/pc.php4?mypics=254
    My "adventure" of learning to ride: http://schmode.net/riding.htm
    Mein "Abenteuer", Reiten zu lernen: http://schmode.net/reiten.htm
    Ralf Schmode, Jun 19, 2005
    #7
  8. Freedom55

    Paul Mitchum Guest

    David J Taylor
    <-this-bit.nor-this-part.uk.invalid>
    wrote:

    > Scott W wrote:
    > > Freedom55 wrote:
    > >> I have lossless rotation for digital photos in PSP8. Does lossless
    > >> really mean lossless? I mean there has to be some loss in a jpeg when
    > >> you rotate it.

    > >
    > > There does not have to be any loss if your rotate by 90 or 180
    > > degrees.

    >
    > .. and the image is a multiple of 8 (or sometime 16) in each dimension.


    Just to expand on that: You can lose data along the edges, and this is
    likely to get clipped by rotation software, except under some
    circumstances like the one above.
    Paul Mitchum, Jun 19, 2005
    #8
  9. Freedom55

    Paul Mitchum Guest

    Ralf Schmode <> wrote:

    > Dimitrios Tzortzakakis wrote:
    >
    > > Lossless means identical to the uncompressed original.AFAIK jpeg is a
    > > lossless compression format, in contrast to MPEG which is lossy.

    >
    > Hi, Dimitrios,
    >
    > sorry, that is not true. JPEG compression, as offered by consumer image
    > editing software on the market, is lossy even at 100% quality setting.


    This isn't strictly true any more. There's a newish format called
    JPEG2000 which has a lossless setting. Unfortunately, not much software
    supports JPEG2000 at the moment, especially the software in your camera.
    Paul Mitchum, Jun 19, 2005
    #9
  10. Freedom55

    Ralf Schmode Guest

    Paul Mitchum wrote:

    > Ralf Schmode <> wrote:
    >
    >> Dimitrios Tzortzakakis wrote:
    >>
    >> > Lossless means identical to the uncompressed original.AFAIK jpeg is a
    >> > lossless compression format, in contrast to MPEG which is lossy.

    >>
    >> Hi, Dimitrios,
    >>
    >> sorry, that is not true. JPEG compression, as offered by consumer image
    >> editing software on the market, is lossy even at 100% quality setting.

    >
    > This isn't strictly true any more. There's a newish format called
    > JPEG2000 which has a lossless setting. Unfortunately, not much software
    > supports JPEG2000 at the moment, especially the software in your camera.


    Hi, Paul,

    exactly that was I referring to when talking about "consumer software".
    In other words: I don't see any contradiction between your words and
    mine ;-)

    Greets - Ralf

    --
    My animal photo page on the WWW: http://schmode.net (currently offline)
    "Best of" portfolio: http://www2.fotocommunity.de/pc/pc.php4?mypics=254
    My "adventure" of learning to ride: http://schmode.net/riding.htm
    Mein "Abenteuer", Reiten zu lernen: http://schmode.net/reiten.htm
    Ralf Schmode, Jun 19, 2005
    #10
  11. Jim Townsend wrote:
    > it is possible to do 90-degree rotations and flips losslessly,
    > if the image dimensions are a multiple of the file's block size
    > (typically 16x16, 16x8, or 8x8 pixels for color JPEGs).


    Oh Oh.
    I always use the Irfanview lossless rotation plugin on Windows to
    rotate photos of my kids at 90 degrees, 180 degrees, and 270 degrees.

    QUESTION #1:
    Does this mean the 180 and 270 degree rotations are actually lossy
    (but not the 90 degree rotations)?

    I also often crop my photos of the kids in many cases, to non-standard
    sizes.
    QUESTION #2:
    Does cropping destroy the 8x8 pixel multiplication such that a
    subsequent Irvanview lossless rotation suddenly becomes lossy even at
    90 degrees?

    Scared,
    Susan Henderson




    > Yes, it's lossless.. Because the operation doesn't open
    > the file first, it doesn't have to re-compress it.. It's
    > the compression that causes the loss.
    >
    > There's a good explanation on just about everything you
    > wanted to know about JPEG here:
    > ``
    > http://makeashorterlink.com/?Z1BB6294B
    >
    > Search the article for rotation and you'll find:
    >
    >
    > "There are a few specialized operations that can be done on a JPEG file
    > without decompressing it, and thus without incurring the generational loss
    > that you'd normally get from loading and re-saving the image in a regular
    > image editor. In particular it is possible to do 90-degree rotations and
    > flips losslessly, if the image dimensions are a multiple of the file's
    > block size (typically 16x16, 16x8, or 8x8 pixels for color JPEGs). This
    > fact used to be just an academic curiosity, but it has assumed practical
    > importance recently because many users of digital cameras would like to be
    > able to rotate their images from landscape to portrait format without
    > incurring loss --- and practically all digicams that produce JPEG files
    > produce images of the right dimensions for these operations to work. So
    > software that can do lossless JPEG transforms has started to pop up. But
    > you do need special software; rotating the image in a regular image editor
    > won't be lossless".
    Susan (Graphic Artist), Jun 20, 2005
    #11
  12. Freedom55

    MikeZ Guest

    On Sun, 19 Jun 2005 13:34:31 -0700, 0m (Paul Mitchum)
    wrote:

    ->Ralf Schmode <> wrote:
    ->
    ->> Dimitrios Tzortzakakis wrote:
    ->>
    ->> > Lossless means identical to the uncompressed original.AFAIK jpeg
    is a
    ->> > lossless compression format, in contrast to MPEG which is lossy.
    ->>
    ->> Hi, Dimitrios,
    ->>
    ->> sorry, that is not true. JPEG compression, as offered by consumer
    image
    ->> editing software on the market, is lossy even at 100% quality
    setting.
    ->
    ->This isn't strictly true any more. There's a newish format called
    ->JPEG2000 which has a lossless setting. Unfortunately, not much
    software
    ->supports JPEG2000 at the moment, especially the software in your
    camera.


    Actually JPEG2000 isn't lossless either. But with the new compression
    algorithms used it is much less lossy than JPEG or any other lossy
    formats. It's advertised as lossless because it is visually lossless to
    some pretty high level of compression. But if the developers are really
    pushed on it they will admit that it is technically still a lossy
    format. So for most general photographic purposes I guess it could be
    said to be lossless. I suspect that there is still some number of
    manipulations and resaves which would eventually render it visually
    lossy as well.
    MikeZ
    MikeZ, Jun 20, 2005
    #12
  13. MikeZ wrote:
    []
    > Actually JPEG2000 isn't lossless either. But with the new compression
    > algorithms used it is much less lossy than JPEG or any other lossy
    > formats. It's advertised as lossless because it is visually lossless
    > to some pretty high level of compression. But if the developers are
    > really pushed on it they will admit that it is technically still a
    > lossy format. So for most general photographic purposes I guess it
    > could be said to be lossless. I suspect that there is still some
    > number of manipulations and resaves which would eventually render it
    > visually lossy as well.
    > MikeZ


    Both standard JPEG and JPEG 2000 do offer a truly lossless compression
    option with zero data loss, but this option is rarely implemented in
    consumer software, and (obviously) does not produce such small files.

    David
    David J Taylor, Jun 20, 2005
    #13
  14. thx for all the answers, anyway, lossy or not, I like my digital camera very
    much, while I think that it will be a long time when I 'll replace my 8mm
    camcorder.

    --
    Tzortzakakis Dimitrios
    major in electrical engineering, freelance electrician
    FH von Iraklion-Kreta, freiberuflicher Elektriker
    dimtzort AT otenet DOT gr
    Ï "David J Taylor"
    <-this-bit.nor-this-part.uk.invalid> Ýãñáøå
    óôï ìÞíõìá news:KOtte.53131$...
    > MikeZ wrote:
    > []
    > > Actually JPEG2000 isn't lossless either. But with the new compression
    > > algorithms used it is much less lossy than JPEG or any other lossy
    > > formats. It's advertised as lossless because it is visually lossless
    > > to some pretty high level of compression. But if the developers are
    > > really pushed on it they will admit that it is technically still a
    > > lossy format. So for most general photographic purposes I guess it
    > > could be said to be lossless. I suspect that there is still some
    > > number of manipulations and resaves which would eventually render it
    > > visually lossy as well.
    > > MikeZ

    >
    > Both standard JPEG and JPEG 2000 do offer a truly lossless compression
    > option with zero data loss, but this option is rarely implemented in
    > consumer software, and (obviously) does not produce such small files.
    >
    > David
    >
    >
    Dimitrios Tzortzakakis, Jun 20, 2005
    #14
  15. Susan (Graphic Artist) wrote:
    > Jim Townsend wrote:
    >
    >>it is possible to do 90-degree rotations and flips losslessly,
    >>if the image dimensions are a multiple of the file's block size
    >>(typically 16x16, 16x8, or 8x8 pixels for color JPEGs).


    > Oh Oh.
    > I always use the Irfanview lossless rotation plugin on Windows to
    > rotate photos of my kids at 90 degrees, 180 degrees, and 270 degrees.
    >
    > QUESTION #1:
    > Does this mean the 180 and 270 degree rotations are actually lossy
    > (but not the 90 degree rotations)?


    No. Lossless rotation is possible with any multiple of 90 degrees.

    > I also often crop my photos of the kids in many cases, to non-standard
    > sizes.
    > QUESTION #2:
    > Does cropping destroy the 8x8 pixel multiplication such that a
    > subsequent Irvanview lossless rotation suddenly becomes lossy even at
    > 90 degrees?


    Multiple questions here.

    A crop that is not a multiple of 8 (or sometimes 16) will become a
    multiple of 8 (or 16) when losslessly rotated. There is no loss of
    quality, but you might lose a few pixels around the edges. This is
    not what most people mean by "lossy".

    Lossless cropping is possible, but it is constrained by the same
    8 (or 16) pixel boundary issue as lossless rotation. A lossless
    crop will always be a multiple of 8 (or 16) pixels in each dimension.

    Cropping in an image editor is lossy if the software has to decompress
    the JPEG in order to show it to you and then re-compress the result of
    the crop. Irfanview doesn't run on my OS, so I don't know anything
    about it. I use jpegtran for lossless cropping and rotation under
    Linux.

    Paul Allen
    Paul L. Allen, Jun 21, 2005
    #15
  16. Freedom55

    Paul H. Guest

    "Freedom55" <"joinertake this out"@ns.sympatico.ca> wrote in message
    news:Y8ete.49313$...
    > I have lossless rotation for digital photos in PSP8. Does lossless
    > really mean lossless? I mean there has to be some loss in a jpeg when
    > you rotate it.


    Display a jpeg on your monitor, then pick up the monitor and physically
    rotate it by 90 degrees. How much data have you lost by doing this?
    Rotating a jpeg by 90 degrees is a rows-and-columns book-keeping issue which
    does not require the existing data in the file to be re-compressed, only
    rearranged. Some restrictions apply, as the travel ads say:

    " Lossless Rotation: The rotation of an image without the loss of image
    quality. This works best on images with dimensions that are a multiple of 8
    or 16. ACDSee digital photo software includes a lossless rotation function.
    "

    --From the ACDSee glossary, obtained using the Google search expression '
    define: "lossless rotation" '. Include the double quotes, but not the
    singles.


    But always remember that even data in a normal jpeg rotation are never truly
    lost--they're just waiting for you in jpeg heaven. Or so it is written.
    Paul H., Jul 1, 2005
    #16
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