Understanding Image Resolution

I work for Metal Clay Artist Magazine as an art and photography editor. One of my jobs is to prepare photographs for print. I see many images that are submitted to the magazine. A problem that comes up many times is a resolution problem—the images are too small and don’t have enough resolution to be suitable for reproduction in the magazine.

Resolution was a very hard concept for me to grasp when I first learned it. I’d like to share with you the way image re-sizing was taught to me that finally helped me understand it. There is another method of image sizing in Photoshop, called “resampling”, that I won’t be discussing here. I’m concentrating this article on re-sizing an image for print.

Every digital image contains a set number of pixels of information that you determine with your camera settings when you capture the image. Once that photo is taken, pretend those pixels are all you will have to work with.
So think of an image like a cube. The cube has volume. Think of the volume as the pixels in the image.

Now let’s say that cube is 2 inches wide by 3 inches high, and the depth is 72 dpi—the resolution of the image. That cube’s volume is 91.1K pixels. For our purposes, that is all the pixels that cube will ever contain.

If we decide to enlarge that image and stretch out the 2 inches by 3 inches to 4 inches by 6 inches, the depth of the cube has to get shorter. So the resolution will drop to 36 dpi.  Remember, in our case, we only have so many pixels in that cube to manipulate.

When you stretch the 2×3 cube to 4×6, the depth (dpi) gets smaller.

If you want to submit photos of your work for print, the resolution of that image usually must be 300 dpi. This is the industry standard for print resolution. If your image’s dpi is lower than that, then the image needs to be large in vertical and horizontal dimensions.

Here is an example—again using our cube idea. We have an image that is 17 by 25 inches at 72 dpi. So our cube is 17 inches wide, 25 inches high, and 72 dpi deep. It has a volume of 6.30M of pixels, and that is a set number for us. Now we want to stretch the resolution, or depth of the cube, out to 300 dpi. When we do that, the width and the height shrink down to approximately 4 inches by 6 inches.

When you squash 17×25 down to 4×6, the depth (dpi) gets greater.

To re-size your image the way we are illustrating, in Photoshop, go to Image—Image Size. You will get the Image Size dialog box. Uncheck the “Resample Image” box. Notice that the width, height and resolution proportions of the Document Size become linked together. Now type in one of the sizes you want to change. It doesn’t matter which one you change, they will all re-calculate according to how many pixels your image has. (If the cube gets stretched or shrunk one way, the rest of the cube adjusts along with it). Then click “OK”.

Notice how the width, height and resolution sizes become linked when the Resample Image box is unchecked.

The width and height sizes change when the resolution is changed.

This article is a brief and simplified overview on image re-sizing for print. As it always is with Photoshop, there is so much more to the topic. Most importantly, be sure when you are preparing your images for submission that you have plenty of pixels to accommodate the necessary 300 dpi resolution needed for print. When you take your photographs, be sure your camera is set to capture a high resolution image.



About Evelyn

I'm a metal clay artist who is learning something new every day. My goal in my work is to make things that are well crafted and distinctively from my own hands, like the work of a good tailor. My jewelry can be found at http://www.evelynpelati.com.


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