better to compress the jpeg or reduce resolution or reduce pixel size?

Discussion in 'Digital Photography' started by Mr.Will, Sep 23, 2004.

  1. Mr.Will

    Mr.Will Guest

    Heya guys,

    If anyone can offer me some science on the matter I'd be most grateful. I am
    taking shots at high jpeg setting on my Canon d60. These files come out
    between 3 and 4 Mb.

    The people that want the photos want the size to be no bigger than 2mb so
    that their server can handle each one. Problem is, with photoshop I arent
    entirely sure what is the best way of achieving this file size, or how to
    calculate it without saving as a different filename and previewing using the
    "properties" of the image icon.

    If I reduce resolution this brings down the file size, as does reducing the
    image dimensions (pixels) as does compressing. Which would you reccomend as
    the best method? I notice photoshop has THREE maximum settings (10,11,12).

    Also I arent entirely sure how much of each does to the filesize. For
    instance I started with a 3 mb file, I reduced it in size and saved it, and
    the file, despite being smaller was now 3.5 mb!!!

    Any light ANYONE can shed will be most appreciated.

    Mr.Will, Sep 23, 2004
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  2. If you decrease the resolution of the pictures via Photoshop, Paint Shop Pro're losing picture image quality.

    If you simply reduce the photo size in the camera, it will be more than
    sufficient for viewing, unless you're going to blow these things up.

    It's best likened to developing an 8X10 of a photo that was shot at 100 ISO,
    to doing the same picture 8X10 of a photo using 800 ISO.

    I use Paint Shop Pro's Photo Album sofware. It's GREAT for batch resizing
    (or renaming) of photo's. I can do 50 12MB files into 50 500k files in
    about 20 minutes. If you did them'd take all night!

    Hope this helped you a bit.
    Not Dick Daley, Sep 23, 2004
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  3. Mr.Will

    Peter Guest

    The pixel dimensions you want are primarily determined by how someone will
    view your images. If they're always going to be viewed on a 800x600
    computer screen, there is no point in making the image pixel size bigger
    than that. On the other hand, if the images are going to be printed in high
    quality, you should plan on 100-300 pixels per inch of printed size. (This
    wide range reflects differing opinions on this).

    Once you have determined the pixel dimensions, the file size will be
    determined by the amount of detail in each image and by the JPEG
    compression level (or inversely the quality setting).

    [In tests I conducted on photo images with the same pixel dimensions and
    the same JPEG compression level, file sizes vary over a range of more than
    3-to-1, depending on the detail present in the images.]

    Sounds like you could use a versatile image resizer that will automatically
    figure out what JPEG compression level is needed to achieve your desired
    file size. Suggest you try the link below.


    Need to resize images for email attachments or web pages?
    Try Jpeg Sizer at:
    Peter, Sep 24, 2004
  4. Mr.Will

    Bob Guest

    First - you need to know what dimensions are needed, not the file size...

    Once you know that, you can worry about the file size... :)

    But generally speaking, for the Internet, you decrease file size by increasing
    the compression of the image. This is because Internet images are usually just
    for viewing, and not blowing up or printing, therefore you can get away with
    huge compressions.

    On my own web site, I re-size to 1024x680 or so, to fit the biggest screen, and
    then I compress to an average 125k bytes. The originals are 3m, 3000x2000....

    I use Micrografx software but Photoshop has a 'quality' option in saving as

    You need to manipulate both the image size and image compression to achieve the
    results you want.
    Bob, Sep 24, 2004
  5. Mr.Will

    Tony Morgan Guest

    In message <>, Not Dick Daley
    Really? I always thought that the higher ISO introduced noise and not
    artefacts, but that it did not reduce resolution.

    In answer to the OP, I'd suggest that it's best to shoot at max
    resolution (pixels) and minimum compression, then to resample to the
    size that you require in your photo editing software.
    Tony Morgan, Sep 24, 2004
  6. Mr.Will

    Tony Morgan Guest

    Do so with great care. Increasing compression introduces artefacts. And
    never resize (again it introduces artefacts), but rather resample to
    Tony Morgan, Sep 24, 2004
  7. Mr.Will,

    Because I had sorta the same question you have, I have done some tests.
    I have a 5 Megapixel Canon S60 camera. I ever changed the resolution of
    the images or the camera ... all images/files are, and will always be 5

    1) Take photo in factory default 'Fine' 5MPixel.
    2) Take photo in 'Super Fine' 5 MPixel (probably default on D60)
    3) Take photo in RAW

    Here are the sizes:
    1) 1500 KBytes
    2) 2500 KBytes
    3) 5200 KBytes

    Then I lokked at the cmpression I could get:
    1) Save the RAW image as JPG with 100% quality
    2) Save the RAW image as JPG with 90% quality
    3) Save the RAW image as JPG with 80% quality

    This gave the following sizes:
    1) 3600 KBytes
    2) 1000 KBytes
    3) 800 KBytes

    Here was the amazing part:
    When comparing the follwing photos:
    - RAW
    - the 100% compressed jpeg (3600 KByte)
    - the 90% jpeg (1000 KByte)
    - the 'Fine' photo (1500 KByte)

    I could barely see the difference between the first 3, and the Fine
    photo showed much more compression artifacts than the rest.

    My conclusion was that the camera does a bad job at compressing: It
    compresses to a larger file, with more damage to the photo. That is not
    a big surprise, because the camera has to be optimised for SPEED, while
    the computer that compresses the image is probably way faster, and is
    optimized for quality!

    So ... From now on, I take all photos in RAW 'Super Fine' and when I
    need the files smaller, I compress them on my computer ...

    Translating that to your 6.3 MPixels ... the file sizes would be
    somewhat bigger, but probably only by about 20% ... I guess if you do
    the same tests, you'd come to more or less the same answers.
    Please do those tests yourself ... do not believe everything you read
    here ...

    Have fun with it,



    Wouter F. Wessels
    Gouda, the Netherlands
    Wouter Wessels, Oct 7, 2004
  8. Mr.Will

    Pete Guest

    I always capture photos in the camera with the highest available JPEG
    quality (although some perfectionists use TIFF or RAW). These are the only
    ways to ensure that the images will be suitable for any future purpose you
    might encounter.

    For Internet images, I agree with others here: figure out the pixel
    dimensions first, then the JPEG compression level.

    If an image is going to be displayed on a computer screen, there's no point
    in delivering more pixels than will fit without scaling, and there are
    still a lot of 800x600 monitors out there. 640x480 images are good, because
    task bars etc consume screen real estate.

    When it comes to compressing, most programs only let you specify the JPEG
    quality (or compression) level. The file size you get is unpredictable, and
    varies over a range of at least 3-to-1, depending on the amount of detail
    in each photo.

    JpegSizer is a batch resizing utility that will let you specify the file
    size you want, and it figures out automatically what compression is needed
    to achieve that file size. You can find it at

    It's a little unusual to post images as large as 2MB. PhotoSIG for example
    has a limit of 300KB, and there are plenty of superb images on there. IMO,
    anything more than that is only needed if the recipient will output large
    high-quality prints, in which case the pixel dimensions should also be
    higher. In these situations, I'd recommend that you keep the original pixel
    dimensions, and simply compress down to the desired file size.

    Hope this helps

    Pete, Oct 8, 2004
  9. Since the OP said he had Photoshop, here is a fool proof method (until
    we can create better fools.....)

    Go to Edit menu, Save for Web. In right hand dialogue, lower box, change
    width of image to 640 pixels, leaving "constrain proportions" checked.
    Then choose jpeg above, and save at medium quality. Now send the result
    to a friend, cc to yourself.

    And the original image is untouched so you can keep the higher
    resolution to print later.
    John McWilliams, Oct 8, 2004
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