Why I Ignore DPI And You Should Too

http://cazillo.com/articles/37-photography/223-why-i-ignore-dpi-and-you-should-too.html

Here is a great question from a #Cazillion on DPI. In my video I explain how it works and why DPI/PPI really don’t matter when exporting your images.

Subject: resolution/printing

To: Gregory Cazillo

Hey Greg, I am new to printing and I am having a problem regarding resolution/printing. Some of my pics say x and y resolution 72 dpi and a pic taken minutes later will say 300 dpi.(I am getting this from the exif info in flickr). Also, at this time i have only edited in iphoto.

1. How do I set my resolution for the best possible quality?
2. How does dpi relate to printing size and quality?
3. How/Can I print large prints ex. 20×30 with my D90

Thanks for all your help….

Definitions from Wikipedia:

PPI: Pixels per inch (PPI) or pixel density is a measurement of the resolution of devices in various contexts; typically computer displays, image scanners, and digital camera image sensors.

DPI: DPI is used to describe the resolution number of dots per inch in a digital print and the printing resolution of a hard copy print dot gain; the increase in the size of the halftone dots during printing. This is caused by the spreading of ink on the surface of the media.

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19 thoughts on “Why I Ignore DPI And You Should Too

  1. frank zuco

    hi ,dose the  mb matter , might be a dumb question , thanks for your help , Its more clean to me now, good-day

     
  2. ᏳᏫᏜᏡᎦᏈᏜᏫᏳ

    Although I have been getting this right since 1995 – I had to check these videos out to see if I was missing something. Your video was the most concise with real examples and good rhetoric. Good Job. I'm glad I'm not doing it wrong after all these years. It is essentially very simple and depends on your application and source quality. Cheers.

     
  3. Jeff Blankenship

    Thanks, Greg, great stuff….light bulbs were going off, all over the place; this makes much more sense that what I've heard from others.

     
  4. Michael Ayers

    Great job explaining these concepts!  As an image creator and graphic designer, I see many who are confused on the issue.  It comes down to proper instruction– the terms are not taught properly in schools and amateurs don't understand the difference.  Well done!

     
  5. Siddhartha

    Greg, great video. Recently I came across an online photo contest which wanted the entries with the longer side of the photo at 1000px. As they would be printing the picture, this would give them a print of hardly 3 inches at 300dpi. How can that be ?
    Or does it mean that they will use this size for selection only, once selected they will ask for the bigger picture (may be 4000px longer side) which they will print and put up in the exhibition. What do you think ?

     
  6. Warndog

    That means you printed it at a reasonable size for the resolution and your resulting PPI was acceptable. Keep upping the size until you get about 10ppi, (should be about 35feet long) and tell me the resulting print is still acceptable. Thats what ppi is for and its far from meaningless. You're a very intelligent guy who really knows his shit about photography, I'm really surprised you think this way about ppi. But I guess I'll just agree to disagree cause I have a crazy amount of respect for you

     
  7. Warndog

    Yea ofc, but how do you check that the pixel dimensions are suitable for that print size? By setting the desired size and checking the PPI. It's irrelevant what you set PPI to, but what PPI you're getting on the print itself is extremely important and shouldn't be ignored.

     
  8. Gregory Cazillo

    they are both irrelevant. When we print photos on a photo printer or send out to a lab they don't check ppi, they check pixel dimensions to be sure the photo is big enough. PPI is a suggested value and can be changed at will unlike pixel dimensions.

     
  9. Warndog

    I get what you're going for here. But really in the end, it all does come down to the PPI. if you have a 100px image and print at 100PPI, it'll be 1"… if you take that same 100px image and print at 50PPI it will be 2". That's the whole point of PPI. But yea before it gets to the printer… PPI is meaningless.

     
  10. CacusOnUTube

    When printing you really need to know what your printing for and the distance it will be viewed (not to mention the stock it's on).
    If your viewing your images from 4ft then you only need to output at 60lpi which means you only need a 120ppi rez for your original image

     
  11. CacusOnUTube

    DPI is the resolution of an output device and is used in conjunction with your required LPI (rez of final print) to establish the number of 'levels' you can print. A 2400 dpi output device can produce full 256 levels at 150 LPI. Technically if you were wanting to print an image you use a quality factor of 1.5 to 2. Hence why people get it in their head about 300 ppi. Then there's the 'Rule of 240' that you use to associate distance with LPI hence billboards looking good at only 20 LPI.

     
  12. Steve Zimmer

    You're partially correct….ppi is pixels per inch and dpi is dots per inch; BUT dpi is NOT the dots per inch shown on the credit card you held up. DPI are the dots per inch used by an imagesetter/rip and is usually in the neighbor of 2400. The credit card you held up, and any other hard copy print is measured as LPI (lines per inch) – usually 85 lpi for newspaper and 133-150 lpi for magazines. A typical print might be a 240-300ppi image ripped at 2400dpi and printed at 150lpi.

     
  13. The Moment Mill | Design & Photography

    I'll also add that, the PPI resolution is halved when the image is translated into print, because pixels can be directly next to eachother, you can fit more, per inch .. dots however need a space, very small, on either side … so basically your "DPI" becomes half your "PPI" .. "300PPI" is effectively "150DPI" .. the only reason "huge billboards" still look sharp at low resolution is simply down to viewing distance. Hope this helps, but your video this time has missed the mark.

     

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