Image quality: Why 300dpi is critical

What is 300dpi? Why is it important?
Why do media people keep asking me for it?

By Andrew Imholte, AMM, BAS

Have you ever gone through your life with a piece of knowledge you know to be true, but don’t really know why?

For example, when you think of firefighters, what dog comes to mind? Your first guess, as well as mine, is probably the Dalmatian. Why is that? It’s a little known fact that 100-plus years ago, in the time of horse-drawn fire equipment, Dalmatians were used because of the calming effect they had on horses. During the chaos of a fire, the Dalmatian was a best friend to both man and horse.

We can apply the Dalmatian concept to photography. How? Think about your marketing and public relations efforts. When it comes time to pull together images or graphics, what number sticks out to you if you think about it long enough?
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.