Question about file size when saving JPEGs

Discussion in 'Photoshop Tutorials' started by pixel_a_ted, Sep 15, 2007.

  1. pixel_a_ted

    pixel_a_ted Guest

    I am running PS 7 on a Mac, OS 10.4. To meet the size requirement for
    posting an image to a certain forum, the image must be less than 100
    kByte in size. So I use Save As / JPEG and as I select Quality with
    Preview checked it apparently shows me the file size at the bottom of
    the window with an estimate of the time to transfer the file. But I
    find quite often that if I choose Quality to get the size below 100
    kB, the image is actually saved at a larger size (as confirmed by
    using Get Info as well as the fact that the forum site often doesn't
    accept the image). So I have a couple of questions.

    1. What does the size estimate based on the Quality level actually
    mean and why is it apparently inaccurate?

    2. When I instead use Save For Web, I usually get much smaller file
    sizes even when I choose fairly high quality settings. What is Save
    For Web doing differently from Save As / JPEG?

    Thanks.
     
    pixel_a_ted, Sep 15, 2007
    #1
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  2. pixel_a_ted

    C Wright Guest

    Can't really answer your first question since I don't use PS7. The answer
    you your second question is that Save for the Web strips out the EXIF data
    so that the overall file size will be smaller than Save As / Jpeg.

    While you don't say, I do assume that you are down-sizing the pixel
    dimensions of your originals either at the same time or prior to saving as a
    Jpeg.
     
    C Wright, Sep 15, 2007
    #2
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  3. pixel_a_ted

    pixel_a_ted Guest

    While you don't say, I do assume that you are down-sizing the pixel
    Yes, the requirement is 800 pixels as the largest dimension.

    Thanks.
     
    pixel_a_ted, Sep 15, 2007
    #3
  4. pixel_a_ted

    Bob Williams Guest

    That's an interesting observation.
    I just created an image in PS 7 on a PC.
    The image was 800 x 580 pixels, "Saved As"..at Quality 8
    PS said the image was 92 KB.
    I mailed it to myself via Seamonkey and it came in at 125KB.
    Very Perplexing.
    Bob williams
     
    Bob Williams, Sep 15, 2007
    #4
  5. pixel_a_ted

    pixel_a_ted Guest

    Yes, that's exactly what I'm talking about.
     
    pixel_a_ted, Sep 15, 2007
    #5
  6. pixel_a_ted

    tacit Guest

    The file size in Save As shows the size of the actual compressed JPEG
    data. By default, unless you explicitly instruct it not to (in the
    Preferences command), Photoshop includes other information in the file
    as well. This other information makes the file larger. The other
    information can, depending on on how you have your preferences set,
    include:

    - Digital camera EXIF data
    - A thumbnail of the image
    - A full-size preview of the image
    - A color profile
    - An icon of the image
    - Pen paths, if there are any
    When you use Save for Web, it strips out all extraneous information.
    Save for Web by default includes only the actual JPEG data. It removes
    EXIF data, previews, color profiles, and so on.
     
    tacit, Sep 16, 2007
    #6
  7. pixel_a_ted

    pixel_a_ted Guest

    Thanks all. I guess that explains why the Save As / JPEG image seemed
    to have a minimum size that reducing the JPEG quality didn't affect.
     
    pixel_a_ted, Sep 16, 2007
    #7
  8. Bob Williams wrote, On 15/09/07 9:58:
    Is 125KB the reported size of the email or of the attached file?

    The mail is very inefficient at sending binary files, and implies
    typically something like 25% overhead because of the base64 encoding.
     
    Olivier Croquette, Sep 25, 2007
    #8
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