DPI - Myth, Mania, or Massive?
Dots per inch (dpi) – A measurement of printer resolution that defines how many dots of ink are placed on the page when the image is printed.
I’ve shuffled parts of the original post around put new enlightened data into a new post .
Yes, I have spent three days of reading, thinking, and revising my thoughts on DPI. It’s still the same information, plus a bit more – which helped me so much that I hope it helps others!
I’ve been concerned over the last few nights that my photographs were not of a satisfactory DPI for printing. I searched the RB forums and found a great article by Xavier on the subject, but it didn’t really answer my questions.
So much so that I did a bit of research. I googled photographs printing dpi to discover the sites outlined below. I am now a lot more educated from much reading of some interesting facts.
The Myth of DPI
Good piece of reading. Personally, I consider it the most important to read. Both well-written and concise whilst still giving the facts in a such a way that you’ll say “Now I get it!” – and still keep reading.
How Many Pixels Do I Need for Printing Photos?
This one gives an easy to understand definition of both PPI and DPI:
Pixels per inch (ppi) – A measurement of image resolution that defines the size an image will print.
The higher the ppi value, the better quality print you will get—but only up to a point. 300ppi is generally considered the point of diminishing returns when it comes to ink jet printing of digital photos.
Dots per inch (dpi) – A measurement of printer resolution that defines how many dots of ink are placed on the page when the image is printed.
Today’s photo-quality ink jet printers have dpi resolution in the thousands (1200 to 4800 dpi) and will give you acceptable quality photo prints of images with 140-200 ppi resolution, and high quality prints of images with 200-300 ppi resolution.
Why are my images only 72 dpi?
From the fotolia site comes a great and simple explanation. Worth having a careful read.
How Big Can I Print This Photograh
This says it all. Yes, it is from that place that RB doesn’t like to talk about, but it is worth a few minutes of your time. (No, it is not one of my photographs.)
How Many Megapixels Do I Need? (Link doesn’t want to work now, but it did earlier!)
They have one paragraph that should help most photographers:
To factor how many pixels you need, multiple the dpi by the size of the photo. Thus an 11×14 image at 150 dpi will need 11 x 150 by 14 x 150 pixels, or 1,650 by 2,100 pixels (3.465 million pixels).
And This is just chucked in for those looking for the latest software – and want to know more before they commit any money!
See new entry entitled DPI – Myth, Mania, or Massive? v2 for new information
For anyone who says they’ve already written some story about this, glad to hear it! I did this for me because I find it interesting to do the research, the reading, and then to write it about. I find writing a great way to reinforce the information in my own mind. So publishing it helps me as much as it might help everyone else.
peter
To print the largest size (16 by 24 inches) on RedBubble we currently require a 2560 by 3840 pixel image (160 PPI). Given that we’re printing on photo paper (which is continuous tone) I’m not 100% sure how we then relate this to DPI. The manufacturer’s website suggests that the printer provides a resolution equivalent to 1200 DPI.
I guess that means for each pixel we print the equivalent of (12001200)/(160160) = 56 dots! That’s a lot of dots.
Stephen Mitchell
O…k… I admit to still being a little confused. I never really thought about this before!
I currently upload my photographs at either 3600×5400 or vice-versa – because I thought it would help. According to my coughfreewarecough editor, they are all 72 DPI. and about 2 to 7meg (depending on hex-range)
I’ve just discovered how to increase the DPI : Should I increase to 160 DPI? I’m guessing that will increase the megabytes somewhat…
rawbun
Im not an expert on this field.. and especially when it comes to printing photographs, but at uni we are told that the best dpi to use for an A4 print (for our images created via photoshop or corel or what ever) is 240 – 300 dpi.
According to All About Graphics (a small printing company in West Melbourne) they usually ask their clients to have their images at min 150 to max 300 dpi (btw I am talking abot RGB format)
Not really sure if what I just said was much help at all. But I usually don’t use 72dpi if I know the final image will be printed out
James Pierce
So there are two things to worry about.
1) The pixel resolution of the file … eg. 2000×3000
2) The dpi of the file eg. 200 dpi
The pixels resolution AND the dpi says how big the file will be when printed.
2000×3000 @ 200dpi is going to be 10×15 inches. 2000/200×3000/200
But the DPI can be changed at will.
If I want a larger print from the same file I can decide to make it 100 dpi (or ppi)
2000×3000 @ 100dpi is going to be 20×30 inches. 2000/100×3000/100
When we print an image at RedBubble the DPI is automatically changed to suit the print size. So what does it all mean ?
Worry about the number of pixels in your image, not the DPI, the DPI can be changed … but if you want to make a big print and you don’t want it to look to soft etc, then the DPI does need to be high enough at the size you print. It’s probably more useful to look at how big your file is in pixels, how big you want to print it and then work that back to DPI.
eg.
20×30 inch print, from a 2000×3000 file means 2000/20 = 100 dpi
Now that’s not going to look that sharp – The reccomendations above are about right, somewhere around 200dpi for small reproductions pushing down towards 150 or even 140 for larger prints … The reason for this is we tend to view larger prints from futher away so there is a bit more margin.
rawbun
oooooo…..
Stephen Mitchell
Thanks everyone. I’m still digesting this information. Will give longer reply shortly. Big thanks to James for the info’.
Stephen Mitchell
You can see my response in my modifications to this entry and the follow up DPI – Myth, Mania, or Massive? v.2
I’m fairly sure I have this figured out now. And I am very sure my photographs have sufficient pixels to produce high quality LARGE framed, mounted or laminated images! ...right?