Image size question

Discussion in 'Digital Photography' started by cnavazio, Jan 5, 2004.

  1. cnavazio

    cnavazio Guest

    I have a question regarding image size of digital pictures from my
    Nikon Coolpix 3100. I set the camera to take pictures in the highest
    resolution. When I download them to my PC they are typically about
    4MB in size. Now within the software that Nikon provides, there is an
    editing option that let's me change picture size. It will let me
    select different sizes such as 1024 x 768 or 800 x 600, which really
    reduces the file size (typically down to less than 1MB).

    Correct me if I'm wrong, but that basically means that if my picture
    is origally approximately 2400 x 1200 and I reduce it to 1024 x 768,
    that means that the width was 2400 pixels and now it's 1024 pixels
    (and same thing for the height). So basically what the software is
    doing is compressing the file, and shouldn't the software call that
    "picture compression" instead of "picture size". I just think that
    calling it "picture size" can be confusing to people who are not too
    familiar with digital photography.

    My second question is about printing these pictures. If I'm going to
    email them to someone, it's probably better to drop the size down to
    1024 x 768, to get a reasonable file size to email. But if I'm going
    to upload them to a site and print them, it's better to upload the
    full 4 MB file, right??

    Just wondering, because I don't want to print pictures and get them
    back and find out they're blurry when they looked fine on my monitor.
     
    cnavazio, Jan 5, 2004
    #1
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  2. cnavazio

    Pete Guest

    On 5 Jan 2004 07:58:21 -0800, cnavazio wrote:

    > Correct me if I'm wrong, but that basically means that if my picture
    > is origally approximately 2400 x 1200 and I reduce it to 1024 x 768,
    > that means that the width was 2400 pixels and now it's 1024 pixels
    > (and same thing for the height).


    Correct

    > So basically what the software is
    > doing is compressing the file, and shouldn't the software call that
    > "picture compression" instead of "picture size".


    I disagree. When you change the width from 2400 to 1024, you really are
    changing the size of the displayed image (in the absence of any scaling by
    the displaying application). Compression is a term reserved for processes
    that reduce the byte-size of an image file without changing the number of
    pixels in the image. JPEG compression is the best example.

    > My second question is about printing these pictures. If I'm going to
    > email them to someone, it's probably better to drop the size down to
    > 1024 x 768, to get a reasonable file size to email. But if I'm going
    > to upload them to a site and print them, it's better to upload the
    > full 4 MB file, right??


    If you're emailing an image, you really need to do TWO things:

    1. Resize the image (pixel size) so that it will display in a reasonable
    size if the recipient's displaying application doesn't scale to fit the
    screen. That is, you want it small enough to fit on any monitor, and large
    enough to see it. Constraining width and height to 400 pixels is a good
    start.

    2. Adjust the JPEG compression level (sometimes quality setting) to achieve
    a reasonable file size, so that your images download quickly on a dial-up
    connection. A file size of 30-60K bytes is often a good compromise between
    file size and image quality.

    If you want to store high-quality images on a web site, you can use larger
    image sizes (pixels) and larger file sizes, but they will take
    proportionately longer to download. It should rarely be necessary to upload
    the original hi-res file, which as you say can be several MBytes. A file
    size of 300K bytes is hard to distinguish from the original unless you are
    doing very high quality printing.

    If you want some free software that does all this for you in one step,
    check out

    http://www.seanet.com/~pgm/jpepgsizer.htm

    HTH

    Pete
     
    Pete, Jan 5, 2004
    #2
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  3. cnavazio

    Pete Guest

    Pete, Jan 5, 2004
    #3
  4. cnavazio

    Pete Guest

    Pete, Jan 5, 2004
    #4
  5. There are three ways to reduce the file size of an image.
    1) Reduce the number of pixels.
    2) Compress the data.
    3) Both of the above

    #1 Reduces the size of the image seen on a monitor. It actually discards
    pixels which can never be retrieved
    #2 Leaves the image size, seen on a monitor, the same as before
    compression but slightly degrades the image quality.
    Compression also requires fewer bytes of data to transmit the image.
    #3 Reduces the size of the image seen on a monitor AND slightly degrades
    the image quality.

    Both reducing the number of pixels in an image and compressing the data
    are irreversible processes.
    That is why it is best to capture and archive images in the LARGEST size
    and with the LEAST compression.
    You can always resample an image to make it smaller (Ex. 1200 x
    1600>>>>600 x 800 pixels), and you can always reduce the file size by
    increasing the compression. But once this is done there is no way to
    reconstruct the information in the image file to its original condition

    Since most viewers still set their monitors to view 800 x 600 pixels, and
    e-mail windows are smaller than that, it is probably best to send pictures
    at 640 x 480 pixels or less, to avoid having to scroll to see the entire
    picture.
    Bob Williams



    cnavazio wrote:

    > I have a question regarding image size of digital pictures from my
    > Nikon Coolpix 3100. I set the camera to take pictures in the highest
    > resolution. When I download them to my PC they are typically about
    > 4MB in size. Now within the software that Nikon provides, there is an
    > editing option that let's me change picture size. It will let me
    > select different sizes such as 1024 x 768 or 800 x 600, which really
    > reduces the file size (typically down to less than 1MB).
    >
    > Correct me if I'm wrong, but that basically means that if my picture
    > is origally approximately 2400 x 1200 and I reduce it to 1024 x 768,
    > that means that the width was 2400 pixels and now it's 1024 pixels
    > (and same thing for the height). So basically what the software is
    > doing is compressing the file, and shouldn't the software call that
    > "picture compression" instead of "picture size". I just think that
    > calling it "picture size" can be confusing to people who are not too
    > familiar with digital photography.
    >
    > My second question is about printing these pictures. If I'm going to
    > email them to someone, it's probably better to drop the size down to
    > 1024 x 768, to get a reasonable file size to email. But if I'm going
    > to upload them to a site and print them, it's better to upload the
    > full 4 MB file, right??
    >
    > Just wondering, because I don't want to print pictures and get them
    > back and find out they're blurry when they looked fine on my monitor.
     
    Robert E. Williams, Jan 6, 2004
    #5
  6. cnavazio

    Don Stauffer Guest

    No- compression does not mean changing image size in pixels. It means a
    reduction in digital storage size, with the same number of pixels.
    Compression routines do this by removing inherent redundant information
    in most images. This is just like disk compression for reducing size of
    data files on hard drives, or audio file compression, i.e, MP3.

    cnavazio wrote:
    >
    > I have a question regarding image size of digital pictures from my
    > Nikon Coolpix 3100. I set the camera to take pictures in the highest
    > resolution. When I download them to my PC they are typically about
    > 4MB in size. Now within the software that Nikon provides, there is an
    > editing option that let's me change picture size. It will let me
    > select different sizes such as 1024 x 768 or 800 x 600, which really
    > reduces the file size (typically down to less than 1MB).
    >
    > Correct me if I'm wrong, but that basically means that if my picture
    > is origally approximately 2400 x 1200 and I reduce it to 1024 x 768,
    > that means that the width was 2400 pixels and now it's 1024 pixels
    > (and same thing for the height). So basically what the software is
    > doing is compressing the file, and shouldn't the software call that
    > "picture compression" instead of "picture size". I just think that
    > calling it "picture size" can be confusing to people who are not too
    > familiar with digital photography.
    >
    > My second question is about printing these pictures. If I'm going to
    > email them to someone, it's probably better to drop the size down to
    > 1024 x 768, to get a reasonable file size to email. But if I'm going
    > to upload them to a site and print them, it's better to upload the
    > full 4 MB file, right??
    >
    > Just wondering, because I don't want to print pictures and get them
    > back and find out they're blurry when they looked fine on my monitor.


    --
    Don Stauffer in Minnesota

    webpage- http://www.usfamily.net/web/stauffer
     
    Don Stauffer, Jan 6, 2004
    #6
  7. cnavazio

    SmartyPants Guest

    > No- compression does not mean changing image size in pixels. It means a
    > reduction in digital storage size, with the same number of pixels.
    > Compression routines do this by removing inherent redundant information
    > in most images. This is just like disk compression for reducing size of
    > data files on hard drives, or audio file compression, i.e, MP3.


    And compression always removes quality... sometimes not noticable, sometimes
    very noticable. It is a tradeoff. I save digital photos in their original
    size and format even if I save a cropped or compressed version... "just in
    case". Digital storage is so inexpensive it is a crime not to do so.
     
    SmartyPants, Jan 6, 2004
    #7
  8. cnavazio

    Tom Thackrey Guest

    On 6-Jan-2004, "SmartyPants" <aipeasr@hot(remove_this)mail.com> wrote:

    > > No- compression does not mean changing image size in pixels. It means a
    > > reduction in digital storage size, with the same number of pixels.
    > > Compression routines do this by removing inherent redundant information
    > > in most images. This is just like disk compression for reducing size of
    > > data files on hard drives, or audio file compression, i.e, MP3.

    >
    > And compression always removes quality... sometimes not noticable,
    > sometimes
    > very noticable. It is a tradeoff. I save digital photos in their
    > original
    > size and format even if I save a cropped or compressed version... "just in
    > case". Digital storage is so inexpensive it is a crime not to do so.


    Wrong. Lossey compression (like JPEG) always removes some information from
    the data (loss of quality). Lossless compression, like disk compression, LZW
    TIFF, PNG, etc do not alter the data so no quality is lost.

    --
    Tom Thackrey
    www.creative-light.com
    tom (at) creative (dash) light (dot) com
    do NOT send email to (it's reserved for spammers)
     
    Tom Thackrey, Jan 6, 2004
    #8
  9. cnavazio

    Frank H Guest

    On Mon, 05 Jan 2004 23:26:23 -0800, "Robert E. Williams"
    <> wrote:

    >Since most viewers still set their monitors to view 800 x 600 pixels,


    !! Really? I'd have thought the majority were running at least
    1024x768. Even my cheap 2-year old laptop runs at that resolution.
     
    Frank H, Jan 6, 2004
    #9
  10. cnavazio

    Donald Gray Guest

    On Mon, 05 Jan 2004 23:26:23 -0800, "Robert E. Williams"
    <> wrote:

    >Since most viewers still set their monitors to view 800 x 600 pixels, and
    >e-mail windows are smaller than that, it is probably best to send pictures
    >at 640 x 480 pixels or less, to avoid having to scroll to see the entire
    >picture.
    >Bob Williams


    The webstats on one of my web site give the following resolutions used
    buy viewers:-
    (In order of popularity)

    1024x768 = 42.50%
    800x600 = 27.92%
    1280x1024 = 18.67%
    1152x864 = 4.95%
    1600x1200 = 2.77%
    640x480 = 1.65%
    Other = 1.51%

    In real terms, that makes 68.89% using OVER 800x600 Vs 27.92%!

    I would recommend that unless that are very real reasons, email and
    web images should not be much larger than 400* pix over the biggest
    dimension. Not everyone is on wideband.

    *there will always be exceptions to any rule (written or not), If
    large images have to be sent by email, always ask the recipient first.

    If it has to be published on the web make 2 images. A small image of
    about 250 - 350 pix which links to the large image, ideally with some
    indication in Mb, the size of the big one. At least that way the
    viewer has the choice of going for it and not have it thrust at 'em

    Several website authors still publish the full-size image and get the
    viewers browser to resize -down- to the thumb-nail size.

    Tip: If you find a site that seems to be slow in rendering apparently
    normal size images, copy the image to a photo editor and see the huge
    sizes that are about!
    --
    Donald Gray
    Putting ODCOMBE on the Global Village Map!
    www.odcombe.demon.co.uk
    You do not have to email me, but if you wish to...
    Please remove the SafetyPin from my email address first
    Thanks
     
    Donald Gray, Jan 6, 2004
    #10
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