What does DPI mean?

  • What does DPI mean and how does it affect images displayed on screen versus printed?

  • Chris

    Chris Correct answer

    11 years ago

    DPI, or Dots Per Inch relates to the dot density when printing.

    To help better understand the relationship of DPI to pixel dimensions, take an 800x600 pixel image for example:

    • Using 300dpi, an 800x600 image will print 2.6x2 inches.
    • Using 200dpi, an 800x600 image will print 4x3 inches.
    • Using 100dpi, an 800x600 image will print at 8x6 inches.

    Notes:

    • As the DPI gets less dense, or lower, the print quality degrades.
    • The pixel dimensions don't change in the example, only the printed pixel density
    • Extremely large prints may be printed at lower DPI because they are viewed at a distance
    • When changing DPI in a photo editing program, you can choose to resample which will change pixel dimension, or, if you choose not to resample, the pixels remain unchanged, only the print dimensions change.

    Thanks for a clear answer. Showing exactly how the DPI affects the pixel dimensions when printing helped! Is there a standard DPI I should use?

    @Canon Gangsta: The DPI setting you use affects the print quality, what you use depend on the printer. Note the difference between DPI (resolution of the printer output) and PPI (resolution of the image). A reasonable resolution for an image to be printed is 200 - 500 PPI.

    @Canon Gangsta: If you want a detailed explanation of how to choose a proper DPI for prints, check out my thread on the subject here: http://photo.stackexchange.com/questions/1715/how-do-i-generate-high-quality-prints-with-an-ink-jet-printer

    It should be noted that the numbers quoted above (i.e. 300dpi) are actually the resolution, not the DPI. DPI and PPI are distinct factors, and depending on the type of printer used, may be identical or may be very different. DPI is the resolution of actual dots printed by the printer, and there may be many dots per pixel. Particularly with ink jet printers, DPI is usually much higher than PPI (i.e. Canon 9500 is 4800x1200 dpi, but native resolution of 600ppi). I would change DPI to PPI in all examples above.

    But also note that the EXIF standard uses dpi when it should use ppi, because the EXIF "dpi" field is really a description of pixels per inch, not printed dots per inch.

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Content dated before 7/24/2021 11:53 AM