I have some new things in store for my blog - photography tips.

Chris Baldwin of Graham River Productions is working with me in producing some top notch video tutorials. I have lots of topics in mind, ranging from camera basics to flash (always a popular topic).

Keep an eye out for the video clips!

To start off, here's a common question I see on photography forums:

DPI and Resolution

I see people ask all the time what DPI they should set their high resolution images at. With printer resolutions achieving 2400DPI and higher, the old printing standard of 300DPI, many cameras have a default DPI of 72, it's not surprising that there is so much confusion surrounding this issue.


First off, we should start with a definition. DPI, or Dots Per Inch, is a number which tells how many pixels or dots can be printed in a single row, 1 inch long. Technically, it is only applicable when printed. To keep things simple, we will use DPI (dots per inch) and PPI (pixels per inch or points per inch) interchangeably.

The human eye can see detail at about 250-300 DPI, so even under close scrutiny, any print with at least this much information will look "photo quality" - meaning there won't be any noticeable quality issues from any viewing distance.

For the following examples, let's assume a 4MP (4,000,000 pixel) square image. This gives us 2000x2000 pixels of information.

If we wanted to print this image as a 2" x 2" print, we would have 1000DPI (2000 pixels / 2 inches). Obviously, no problem.

If we print it as a 4"x4" print, we would have 500DPI (2000px / 4"). Again, no problem.

If we print it as an 8"x8" print, we would end up with 250DPI (2000px / 8"). We're close to the low end of what the human eye can see, but for the most part, we can assume this would print just fine.

Let's say we want a wall print - a 20"x20". Now we're down to 100DPI (2000px / 20"). This may or may not be acceptable.

How so?

Because of the viewing distance. A 2x2, 4x4, or even an 8x8 print will usually be held by hand, resulting in a viewing distance of 1 to 2 feet. A wall print, on the other hand, will usually be viewed from a distance of 3 to 5 feet. Since the viewer won't be as close to the image, the human eye won't be able to see the details as easily as the smaller prints.

This is evident in billboards. These huge format prints are regularly printed at 10 to 25 dots per inch. Since the viewing distance is several hundred feet, the image appears perfectly smooth.

So, back to the original question - what DPI should be set?

The simple answer: It doesn't matter. When I crop an image, I usually leave the DPI setting blank. Rather than discard existing information, or have software try to "create" information, I simply send the full sized image to be printed.

If you're a bride, groom, or client, here's the easy way to tell if you are receiving the full sized (often mistakenly called high-resolution) images. Ignore the file size (as high quality full sized JPGs can range from less than 1MB to over 15MB) and ignore the DPI number. What you're looking for is the pixel count (the image size). Take the width and multiply it by the height - that will tell you what size file you have.

2000X3000 pixels = 6MP
2336X3504 pixels = 8.2MP
2592X3888 pixels = 10.1MP
2912X4368 pixels = 12.7 MP

If you use photoshop, you may see a number in the bottom left corner that shows 3x the image size. This is because the image is a composite of three layers - Red, Green, and Blue. A 6MP image will show 18MP in photoshop.

I hope this helps clear things up about DPI!

Lots more to come, with video!

Shan