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Have I just totally misunderstood DPI?

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  • Have I just totally misunderstood DPI?

    Forgive me if this is a terrible question but I'm confused. So I'm purchasing a photo and want the highest resolution available.

    The options are:
    (1) Small: 968 x 725 PX at 72 DPI
    (2) Medium: 1937 x 1451 at 300 DPI
    (3) Large: 3874 x 2903 PX at 300 DPI.

    There is a significant price difference between these 3 options, but like I said, I want the highest res.

    Based on what I (thought) I knew about DPI/PX, there is literally no difference between the medium and large except what digital size the image has been constrained to. They're both 300 DPI, so which one I purchase should make no difference, I can scale the medium to the large size myself at the same resolution they're selling it at.

    ...but I'm paranoid I've misunderstood something all this

  • #2
    It all completely depends on what your using it for but if you scale the medium up to the large size, you've doubled it in size so your DPI has now gone down to 150dpi. If this was for the cover of a magazine it'd be unacceptable.


    • #3
      Designia is correct. You can reduce the w/h but you can't enlarge without blowing it out. Also, on those stock sites, you may notice a small tab to view as inches vs. pixels so you know exactly what you need. You can convert in your software or online, but just toggle to inches for convenience.


      • #4
        In this instance the DPI is extraneous information as you are dealing with pixel dimensions opposed to imperial dimensions. If you want the highest resolution image, you need to buy the one with the most pixel data, which is option 3, which translates to approximately 12.9" x 9.7" @ 300 DPI.

        When you are dealing with pixels as a form of measurement DPI or PPI have no real relevance to the image quality or size.
        Last edited by kemingMatters; 01-26-2016, 02:47 PM.
        Design is not decoration.


        • #5
          Don't enlarge a photo no matter what size the dpi is, like stated above you reduce the dpi then. Reduce yes, enlarge no.


          • #6
            Like KemingMatters said, the DPI of these files is completely irrelevant and meaningless in the context that it's used. What matters are the number of pixels contained in the image.


            • #7
              Actually, the 300dpi is necessary to tell you how large the image will be using those pixel dimensions.
              If you divide the pixel dimension by 300 that gives you the size in inches.
              You can use that quickly on websites that don't have an Inches tab (or one you can find easily)

              The last one is obviously the larger.


              • #8
                Well, yeah, but if you divide the pixel dimensions by any number you'll get the size in inches for that particular resolution.

                You know all this of course, but there's really nothing special about 300 other than it's been erroneously accepted by too many people as a quality indicator, when in reality a digital image has no inherent resolution attributes separate from its pixel dimensions. The necessary output resolution is completely dependent on how many of the image's pixels need to be crammed into any given physical measurement to meet the needs of the printing process being used.

                People without sufficient knowledge of how image resolutions relate to print quality have come to erroneously believe that 300 DPI is a measure of image quality when all it signifies is the number of pixels in a linear inch required for printing at a (traditional printing) dot frequency of about 150 to 200 LPI.

                To make matters even worse, DPI isn't even the right term. Most of the time when people say DPI, they actually mean PPI. There's really no such thing as DPI in a digital image since DPI is a measure of printed dots and not a measure of digital pixels -- two very different things.


                • #9
                  Yeah, well there is all that.

                  But when you do wide format and you know your file resolution only has to be 35ppi it helps to know how big an image you are going to get...
                  300ppi is a pretty meaningless number to me anyway. Way overkill.


                  • #10
                    So, yes, I have totally misunderstood DPI but this information is helping a lot. Thank you to all!


                    • #11

                      DPI stands for Dots Per Inch which technically means printer dots per inch. Today it is a term often misused, usually to mean PPI, which stands for Pixels Per Inch. So when someone says they want a photo that is 300 dpi they really mean that they want 300 ppi.
                      A high resolution photo is an image with high quality pixels, saved in either a non-lossy file format or a low compression (high quality) JPEG, that can supply the desired PPI (usually 300) for the intended print size.


                    • #12
                      Originally posted by Melissa Kanon View Post
                      A high resolution photo is an image with high quality pixels, saved in either a non-lossy file format or a low compression (high quality) JPEG, that can supply the desired PPI (usually 300) for the intended print size.
                      There's no such thing as a high- or low-quality pixel, and resolution has nothing to do with lossy compression.

                      Resolution is the amount of detail in an image and is typically measured by the number of pixels -- especially the number of pixels available in a given space, as in XXX pixels per inch. Detail is different from quality. A blurry, out-of-focus, highly compressed photographic disaster can still be a high-resolution photo if there are a sufficient number of pixels in the image. High resolution is not necessarily synonymous with high quality.


                      • #13
                        I'd take issue with the 300ppi at print size too...
                        Not always.


                        • #14
                          Thank you for everyone's opinion. Your suggestion will be helpful in taking good dpi.


                          • #15
                            When dealing with image sharpness or detail, I always want to know the viewing distance.






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