We regularly work with printers, or work with people who work with printers, and there’s an incredible amount of confusion about pixels, dots per inch and what the print shop really wants. In trying to explain it all to somebody, I stumbled upon two decent articles that can do the explaining for me.
The first is called The Myth of DPI, and covers the basics and the common mistake:
The client already has a beautiful digital photo with pixel dimensions of 2048 x 1536. The client notices that the photo editing software is showing that the photo is set to 72 dpi. So, following orders, the client types in 300 to reset the dpi to 300. In doing so the image is resampled and is enlarged over 4 times to pixel dimensions of 8533 x 6400. The client sends this enlarged 300 dpi photo. The print shop/graphics designer/magazine reject it (too grainy, too colour blotched). The client is crushed.
And here’s the second, on what the print shop really wants:
What they are really asking for is a photo that will print at a certain paper dimension in inches at 300 pixels per inch (PPI). If you remember from the Myth of DPI, the term DPI is a holdover from when this setting in a digital photo would set the paper output quality (resolution) of a printed image (number of printer dots per inch). This is no longer the case, but people still confuse DPI with PPI.
Go forth and print your materials with confidence, knowing they won’t come back all jaggy and blotchy.
UPDATE: Riny writes with her own article about the confusing world of DPI. Read it in both English and Dutch.
DarrenBarefoot.com 
Will use this for future reference 🙂
Working at a publishing house, means we have to make our authors/editors understand – this is our (badly translated) explanation:
When handing in digital images, remember:
– photo’s at a minimum of 300dpi
– linedrawings at a minimum of 600dpi
This is the minimum for the actual size of the image when it is printed in the book/journal.
Example 1: Printing a photo at the maximum width of the type area (12 cm), the photo needs to be at least 12 x 120 (120 dots per centimeter = 300 dots per inch) = 1320 pixels wide.
Example 2: Printing a line drawing which is 1200 pixels wide means the actual image can only be printed at 5 cm wide (600 dots per inch = 240 dots per centimeter –> 1200 / 240 = 5cm)
That was one of the most difficult things as a student 10 years ago to grasp. Even when I returned to college 8 years later only to find at another institution in another province were design instructors continuing to argue vehemently amongst themselves which translated to many students graduating still not understanding the dpi/ppi difference.
Nice expanation.
And you didn’t even approach the topic of LPI. I used to work with a newspaper and ‘lpi’ was the term to use. The math is far easier if you just ignore the lingo.
thanks, this is really helpful
So when the yearbook staff guy says, “We require a wallet-sized portrait-orientated photograph, 300dpi (minimum)” does he want a printed wallet-sized photograph, or a digital file that will print out to a decent-resolution wallet-sized photograph?
Darren, I’m working back from digital photos that have been sent (i.e. fait accompli). It’s been easy to work backward with your formula. I open the image sent in Preview, crop it and copy it, open a new window from the clipboard and read the horizontal size and compare that with a one-inch width I’m shooting for. Saved a lot of time and discussion even with the small files (well, 10 kb, ma’am, just ain’t gonna fly!). It makes me wonder, though, how would you suggest measuring going in the other direction? Will you have to physically print it out and measure? Enlarging your carbon footprint, unnecessarily. Do you view it at its “actual size” and then measure it on your screen? What’s your take on this? Thanks for your minimalist approach!
Never clear to me
so i still don’t understand is dpi and ppi the same thing. Because I was just on this printing site that required a 300dpi and I had the image set at a 300 ppi and it still did not work
No.
well i dont care too much about ppi or dpi, i just still confuse on how to see the length of an image without software.. i mean the physical length(cm, inch, etc) not the pixel..
Thanks, very helpful!
I have no photography background, but I have been told i take some pretty good photos and I am going to take a huge risk and send in some of my photos to a contest but they are asking that my photos be between 150 and 300 RGB.DPI. I read what has been written above and am still confused. I am guessing these numbers are refering to once I download the photos into my scanner…and from there I must check the pixels to make sure they fall into that numeric category? Oy, I am so out of my league right now! I am crazy for even trying this!!
I studied photography in Germany so if you guys need any advise, feel free to drop me an e-mail! I am happy to help.
In Photoshop, open the image in question, then click Image>Image Size… (Alt+Ctrl+I in Windows). In the box that comes up, the lower portion will tell you the size of the image at its current resolution (usually 72). Make sure that “Resample Image” is UNCHECKED, then change the resolution to 300 pixels/inch (ppi). The resulting height and width under Document Size will tell you how large the image can be printed at 300ppi.
Hope this helps. 🙂
Ben
I have photoshop elements 8. When I change it from 72 to 300 the document size goes from 48×32 to 11.52×7.68 inches. That seems contrary to what I thought 300 dpi is supposed to do.
I just left and then came back to comment because these links were SO useful! The Myth of DPI article clarified a million things I didn’t get or know how to link together to do it right. Thank you! (Also: you were the first Google result when I searched “how to take a digital photo at 300 dpi”. You + the Google = rawk.)
We are a small company in Tokyo, Japan that manufactures a product the we are being requested to produce a high resolution picture (300 dpi) and have no idea what this German customer is talking about. Can you help ?
Carl Brown
dumaghi
just read the article he mentions http://www.dpiphoto.eu/dpi.htm Everything you need is right there, pretty good explained
Hello I am an artist and I have to send an image of 300 dpi 6×9 Jpeg file to a publishing company. So what do enter in image size if I am using Photoshop. I hope you will answer soon it would be a great help.
greetings Samina
I am still a little confused. I think that I understand the dpi, but the publisher also says that the picture should be something like 900 x 1500 or higher. What does that mean?
Thanks in advance.
Thank You
I am writing a children’s book and the submission requirements for the illustrations were 300 DPI.
Of course I thought, ????
But now I understand.
Thanks again