Image pixels/inch vs printout.

Discussion in 'Photography Beginners' Forum' started by Nacho, Apr 18, 2008.

  1. Nacho

    Nacho TPF Noob!

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    Hello all, really new here and to editing photos in prep for printout at the proper size.
    I have done quite a bit of photo tweaking before, but never in an attempt to print it out as a 5x7, or whatever.
    What I am confused about, is if I have a jpeg that has a pixel/inch count of 72, does that mean anything when it is printed? Or is the output printed size of the photo dependent strictly on the size of the jpeg (say 2400x3000) and the dpi the printer is set to (like 300?) I am kinda baffled as to what that image resolution of 72 even means.
    Thanks in advance!
     
  2. davebmck

    davebmck TPF Noob!

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    72 pixels per inch (ppi) is not appropriate for printing. This is a resolution used for monitors. For printing you need at least 240 ppi. You can resize your image to improve your resolution. Take your example of an image that is 2400x3000. You can divide each of the pixel sizes by your resolution of 72 to determine your picture size in inches. 2400/72=33 and 3000/72=42, so the picture size at this resolution is 33x42 inches. You can resize this picture to a resolution of 300 ppi and you will get a picture size of 8x10. Your software should be able to do this for you.
     
  3. Garbz

    Garbz No longer a newbie, moving up!

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    Actually it's PPI Pixels Per Inch. DPI is how much ink the printer lays down and should always be set as high as it can be in the printer driver.

    PPI means everything when printing and nothing when viewing.

    Your 3000px wide image printed at 72ppi will (look like ass) but be 41" wide!!
    300ppi is the standard where no pixellation is visible to someone with 20:20 vision at arms length (I think that's the definition anyway) at 300ppi you can print maximum 3000/300 = 10" wide print.

    Rule of thumb. Leave the resolution untouched and when you print adjust the PPI to get the desired size. However if the PPI drop below 300 or 200 if you're less pedantic, then put the image through some kind of resampling. As in upscale the image to 4800x6000 using a bicubic, billinear, or better yet lanczos resampling algorithm.
     
  4. Nacho

    Nacho TPF Noob!

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    OK thanks guys, I was wondering since I am using Paint Shop Pro 9 and noticed that 72 ppi when resizing a photo that I already had setup for an 8x10 printout, and when I resized again for 300 ppi, I think my 4 year old computer actually groaned at me.
    So basically what you guys are saying, have the images at 300 ppi on the computer with the appropriate dimensions, 1200x1800 for 4x6, etc etc? Then as long as the printer is setup for 300dpi it will look ok and be the right size? Basically match the image ppi with the dpi I am printing at, and adjust the pixel size of the image accordingly?
    I don't have a printer here at home, otherwise I would have just tested this all out myself. I could do it at work, but "the man" would probably not approve.
    Thanks again guys, I plan on being here awhile, lots of wildlife I want to get shots of here in my area.
     
  5. davebmck

    davebmck TPF Noob!

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    You don't have to match your picture resolution (ppi) to your printer resolution (dpi). Just adjust your picture size to the size you want to print and make sure the picture resolution is above 240 ppi before you send it to the printer. Set your printer to the best quality photo setting and you should be OK.

    Beyond that, this can get very complicated and if you want to perfect your printed images you need to do a lot of reading.
     

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