DPI – Myth, Mania, or Massive? v.2

^{I’ve shuffled parts of the original post around and created this secondary post with new enlightened data. After three days of reading, writing, thinking and learning, I’ve 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.

I’d been informed recently that 72 dpi is enough for most web-images and could also be used for printing purposes. I’m guessing the person didn’t consider that I might like my work printed at A2 size! BUT … I am still not convinced that 72DPI is enough for printing photographs at the LARGE size available in RedBubble. Can anyone help answer this question more succinctly?

OK, I have finally worked out a lot more about DPI and how it affects the quality of photographs. And I’ve worked out why REDBUBBLE and so many other print-houses want our photographs in the BIGGEST possible dimensions possible. But we’ll get to that in a minute…

First, let me read the comments in the original post from James and Peter . Then my notes and some things my coughwifecough said. Now I am going to write this in such a way that makes a lot more sense (at least to me!).

First, let’s choose a photograph shot with my Canon EOS 400D dSLR. It measures 3,888 pixels by 2,592 pixels. Although that’s the highest setting this camera can do, I can actually print a far bigger image. Choosing an ISO of 100 helps, but knowing I can reach the required DPI helps!
To determine the total amount of pixels in the photograph, multiply 3,888×2,592 pixels to reach 10,077,696 pixels !

Now we define DPI again. That’s DOTS PER INCH. DOTS are the pixels of your photograph. You cannot delete nor increase the amount in each photograph, but you can increase/decrease the DPI of of the photograph, therefore affecting the size.

When you want to print the image above at 20 inches by 32 inches (similar to the largest size offered by RedBubble), the DPI is determined like this:

^{Divide 10,077,696 pixels (total pixels in image) by 640 square inches (print size of 20×32inches) = 15,746.4
Determine the Square-root of 15,746.4 = 125.48 = This is the DPI.}

Did you understand that calculation? I’ve been through it with a number of people (including my coughwifecough), and they all say it makes sense – mathematically and photographically.

Where does this leave us now? Basically, when you upload any photograph to RB, you need to ensure it has sufficient pixels to create printable images, particularly the largest size offered by RB. Ah ha! That explains why RB want our BIGGEST images. Because they can/will increase the DPI to create the smaller images. (Packing more dots in the inch uses up more pixels in the photograph, therefore decreasing the entire size.)

Well, I think I have this sorted out. Maybe this produced more questions than answers! I’m sure James and Peter can assist! Either here or in the forums .

^{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.}

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Tags:

adelaide, australia, dpi, myth, photograph, photography, printing, redbubble, resolution, stephen_mitchell and stephentrepreneur