photo enlargement question

Discussion in 'Photography Beginners' Forum' started by grodr, Dec 3, 2009.

  1. grodr

    grodr TPF Noob!

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    hello,

    i have an image with the following specs: (straight from 10megapixal camera)
    width - 137,16 cm
    height - 91,44 cm
    dpi - 72

    and I would like to change the size to: (for high quality printing - exhibition)
    width - 110cm
    height - ? will crop
    dpi - 300

    Any tips, sorry I have never done photo enlargements before.
    Thank you,
    grodr
     
  2. The_Traveler

    The_Traveler Completely Counter-dependent Supporting Member

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    Post-processing a digital image, including enlarging the file, requires specific software and specific experience.

    If you have no experience in post-processing or making enlargements, you really don't have enough experience to make satisfactory, very large prints and you will probably be disappointed in the result if you try to do it yourself. There are issues of sharpening, etc. that you are unfamiliar with.

    Rather than spending some amount of money and getting a mediocre result, consider going to a color lab, giving them the file and asking if a satisfactory large print can be made from that image.

    You could start by posting a reduced version of the image here and the viewers can give you some feedback on whether it will hold up as a larger print.

    Lew
     
  3. Misfitlimp

    Misfitlimp TPF Noob!

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    Im not sure what that is in inches or whatev but i made the mistake of saving work at 72 dpi and when i changed it to 240 the biggest i could print was about 13x19 and 300dpi brought it down to about 11x14 or so so yeah
     
  4. KmH

    KmH Helping photographers learn to fish Supporting Member

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    Here are some number definitions:

    DPI = Dots Per Inch. Digital cameras don't have dots! They have pixels.

    PPI = Pixels Per Inch. Now we're talking digital images.


    To make this discussion simple we will start with an uncropped image that will be printed at a resolution of 100 PPI.

    Look at the pixel dimensions of your image. It will be something like 3426 x 2872 pixels.

    Printing that image at 100 ppi yields an image that is 34.26 inches by 28.72 inches. Do you follow the math there? 3426 pixels divided by 100 PPI = 34.26 inches (82.224 cm).

    Printing that image at 300 ppi yields an image 11.42 inches by 9.57 inches. Again the math, 3426 pixels divided by 300 ppi = 11.42 inches (27.41 cm)

    This is a key concept: The ppi (dpi) is meaningless until the image will be printed.

    For computer screen viewing and online only the pixel dimensions have meaning.

    It looks that the pixel dimensions of your image are 4128 pixels x 2743 pixels?
     
    Last edited: Dec 3, 2009
  5. itsjustbrandy

    itsjustbrandy TPF Noob!

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    keith .. i have a question re: your very helpful info.. to make it even simplier, for myself anyway...
    Based on what size I would like the photo to be, is determined by changing the ppi only.. that simple? And I will not even mess with the pixel size for printing.. ?

    (I just posted a thread asking a similar question.. you're very helpful!)
     
  6. The_Traveler

    The_Traveler Completely Counter-dependent Supporting Member

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    In order to manage the correct size for printing, assuming that you want to print at 240-300 DPI, you need to resize the image to match. Otherwise the printer software will resize it for you and your careful sharpening, etc will be in vain.
     
  7. KmH

    KmH Helping photographers learn to fish Supporting Member

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    No, it's not that simple. Sorry.

    A rule-of-thumb used in the industry is that for a print made from a digital image to have the same print quality as a print made from film, the digital image needs to be printed at a resolution of 300 ppi.

    As a practical matter the visual difference between a 200 ppi print and a 300 ppi print is very close to nil.

    So the no part of my answer means that as you decrease the ppi value to make the print larger, you also decrease the visual quality of the print to one extent or another. The quality of the native image has a lot to do with the range ppi can be decreased to achieve a larger print.

    The other part of the no answer has to do with the aspect ratio of the image. Most digital SLR cameras make images in a 3:2 aspect ratio, the same aspect ratio of 135 film (35mm). The long side of the image is 1.5x the length of the short side (4x6, 6x9, 8x12).

    An 8x10 is a 5:4 aspect ratio, the long side is only 1.25x the length of the short side.

    To make a 5:4 aspect ratio print (8x10) from a 3:2 aspect ratio image (8x12), you have to crop some off the long side of the 3:2 aspect ratio image.

    If you didn't shoot the image in anticipation of cropping later, you could wind up being forced to crop away something important in the image to get to 8x10.

    You can't just resize one side of the image in an image editor because it will introduce distorion.
     

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