I don’t remember the class or professor who drilled it into my head, but
ever since college, I have embraced the mantra of 300 dpi. If you have
ever spoken with your printer, you have probably heard that number as
well. But, what does it mean? Why is it important?
Image quality: More dots per inch, better image
DPI stands for “dots-per-inch,” which is how printing ink is applied to a
page. Each dot has a combination of the four colors: Cyan, Magenta,
Yellow, and Black. At 300 dpi, the naked eye cannot see the individual
colors, but it sees the blend that makes a clean image. Images with less
than 300 dpi can appear blurry or pixelated when printed because the
computer used for printing made some color assumptions when filling in
missing information. Often, this results in photos that aren’t as sharp
and easy to read. In other words, hello, blurred image.
With the dawn of digital photography, we were introduced to another
measurement called pixels-per-inch (ppi). While ppi and dpi do not
technically mean the same thing, they are often interchangeable when
considering equipment and photo quality. One big addition with digital
photography was a term introduced to help consumers make decisions based
on a simple number: the megapixel. We have all seen cameras boast five,
10, or possibly 20 megapixels, but, what do those numbers mean?
One megapixel is an area measurement of 1 million pixels. It is
calculated much like square feet. Typically, a 10-megapixel camera will
produce images that are 3872 x 2592 pixels. If you multiply those
dimensions, you have 10,036,224 or 10 million pixels.
Why images “shrink”
One complaint printers or editors usually have is that when they receive
an image for publication, it isn’t nearly large enough. The person who
submitted the image doesn’t understand. After all, when they sent the
image, it measured 500k, or maybe even one 1MB, and it took up the
entire computer screen.
So, why is the printer now saying the image is only an inch or two wide and not nearly big enough to print?
To determine the maximum size photo quality image you can produce,
divide each dimension of your photo file by 300. In this example, 3872 /
300 equals 12.91 inches, and 2592 / 300 equals 8.64 inches. (See
below.) As you can see from the chart, if you have an image that only
measures 600 x 300 in its original form, it will only measure to 2
inches by 1 inch at 300ppi.
So, you may be thinking to yourself: But, what about gigantic images,
like on billboards? You might think that those photographs can only be
created by a 100-plus megapixel camera. There is one other calculation
you must consider: distance.
The distance from which your audience views the image allows for certain
freedoms in regards to image quality. As shown below, the farther away
from a picture you view it, the less dpi is required because human
eyesight is unable to differentiate the image’s imperfections.
Armed with these numbers, you can begin to plan your marketing around
your capabilities. If you plan to mail a postcard promoting your next
real estate auction, an image from a six-megapixel camera may be just
fine. But, if you put that same picture across the top of a large folded
brochure, six megapixels may not cut it.
Many other factors can affect the quality of your photograph, such as
lighting conditions or lenses used. But, keep DPI in mind from the
beginning and you won’t have to worry about the final step of printing
ruining a great photo.
Andrew Imholte, ATS, BAS, is a second-generation Auctioneer who has a
degree in marketing and graphic design. His unique perspective to both
industries has helped him create a blend of experience and knowledge
that he shares as a presenter at the NAA International Auctioneers
Conference and Show.
*This article first appeared in the February 2014 issue of Auctioneer magazine