Raw vs JPEG: 240dpi vs 300dpi, Why?

Discussion in 'Digital Photography' started by babalooixnay@hotmail.com, Jan 8, 2006.

  1. Guest

    When I download RAW images into PS CS2 from a Nikon D50 they come in at
    3008 x 2000 at 240dpi and JPEGs come in at 3008 x 2000 at 300dpi. I
    download using OSX's Image Capture (3.0.3) program. Anyone know why
    there would be a difference? Same difference shows up if I shoot a
    combined RAW + JPEG. Viewing them they look identical in size even at
    the Show Pixels setting.
    , Jan 8, 2006
    #1
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  2. On 8 Jan 2006 08:18:45 -0800, wrote:

    >When I download RAW images into PS CS2 from a Nikon D50 they come in at
    >3008 x 2000 at 240dpi and JPEGs come in at 3008 x 2000 at 300dpi. I
    >download using OSX's Image Capture (3.0.3) program. Anyone know why
    >there would be a difference? Same difference shows up if I shoot a
    >combined RAW + JPEG. Viewing them they look identical in size even at
    >the Show Pixels setting.

    The DPI setting does not mean anything when the images come from the
    camera. In this case, it is probably just an arbitrary value set by
    the camera. DPI (dots per inch) is only meaningful when an image is
    printed or displayed. DPI is just a value used to calculate a
    hypothetical size of the image in inches. The DPI setting that comes
    form the camera is completely unimporant.

    The important bit is the size of the image in pixels. The size of the
    image is pixels is what determines the amount of information in the
    image. You can interpret DPI something like, "if I were to print this
    3008 x 2000 pixel image at 300 dpi, it would be 10.03" x 6.67". If I
    print the same image at 240 dpi, it would be 12.5" x 8.33". Since the
    two images have the same number of pixels, there is the same amount of
    information in the images.

    To be a bit more accurate, the amount of information in the image is
    determined by (1) the number of pixels in the image and (2) the number
    of bits of information per pixel. The RAW format on your camera stores
    12 bits (I think) of data for each of 3 colors for each pixel. That is
    36 bits of data per pixel. JPEG only stores 8 bits per color channel
    per pixel -- 24 bits of data per pixel. Furthermore, JPEG compresses
    the data in the image in a way that results in some loss of image
    information. In other words, the RAW image contains quite a bit more
    information than the JPEG version, but it doesn't have anything to do
    with DPI.
    Leonard Lehew, Jan 9, 2006
    #2
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  3. Guest

    Thanks, much ado about nothing. Sorry about the multiple posts.
    Google seemed to be in a tizzy yesterday.
    , Jan 9, 2006
    #3
  4. Martin Brown Guest

    wrote:

    > Thanks, much ado about nothing. Sorry about the multiple posts.
    > Google seemed to be in a tizzy yesterday.


    So long as dpi is not zero almost any number will do.

    "300" is a popular choice. Most software ignores it by default and
    scales the image to fit on the paper (unless the dpi value is zero in
    which case some programs fall over with a divide by zero fatal error).

    Regards,
    Martin Brown
    Martin Brown, Jan 10, 2006
    #4
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