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Thread: How does the DPI setting affect the print size?

  1. #1

    How does the DPI setting affect the print size?

    The DPI (dots per inch) value is stored in the image to define the print resolution, for example if your image is 1600x1200 pixels and DPI is set to 300, the print size will be 5.3 x 4 inch.

    Why is that? As DPI defines the number of dots per inch, the width and height are divided by the DPI value (300) and we get the print size in inch.

    In Light Image Resizer you can resize the image to the desired print size based on the image's DPI value, in inches or centimeters (A)
    or just change the DPI value itself (B)

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  2. #2
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    so actually, we can consider DPI is just a meta information ? it could be redefined at any time and doesn't really change the output quality ?

  3. #3
    Yes, it only defines the print size.

  4. #4
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    it is useful only to define a default size for printing ? nothing else ?

  5. #5
    Nope, nothing else.

    In case you're bored:
    http://www.rideau-info.com/photos/mythdpi.html

  6. #6
    Dots per inch doesn't affect screen size. At least based from my tests. Am i missing something?

  7. #7
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    This is something I can't seem to work out.

    I usually use pixels for image size, so say I have several pics which are the same width but different heights, when posted on Facebook, ebay or elsewhere I would have thought they would have come out looking as if they were the same width, but no they come out different.

    I get easily confused and have not been able to work out if that is because the height is different of the resolution is different? (I think the resolution is the same as the dpi dots per inch or megapixels?)

    Or could it be because they are different heights - surely not but then that could be to do with the way Facebook or other sites handle images of the same width but different heights?

    At times I have driven myself up the wall with this, and have not been able to work it out yet, so I would be grateful for help to sort this out.

    I had the idea that if the images were the same width in pixels, but looked like they were different widths because the resolution was different, I could use the resizer to change the resolution while keeping the pixel size the same, but there doesn't seem to be a way to do that.

    With the program that I use, the only way to change the resolution seems to be to save it as 90% quality but then I would know what resolution I would end up with, so that wouldn't work either.

    Help on this would be much appreciated!

    My goal is really to be able to post two or more pictures one underneath each other - which I often do - and have them coming out the same width.

    I would prefer to stick to measuring the pics by pixels if possible as that is what I am used to.

    Thank you for your time.

  8. #8
    As mentioned above, the DPI resolution doesn't affect the display size. It's only used for printing the image. So for uploading you don't have to mind the DPI setting.

    The layout issues are probably caused by the resizing done by the respective website. I guess you need to crop your images to have consistent pixel dimensions.

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