Both in my day job as a magazine art director and in my personal life, “Is this photo big enough”, is the most popular question I get asked. Experienced designers take this simple information for granted, including myself, because we use it on a daily basis, and we have tools readily available to help us determine the answer.
To figure out if an image is of adequate size or not, I drop the photo into a program like Adobe Photoshop and pull up the detailed sizing information. This takes mere seconds, but if I had to do it for every single photo that I worked with, I wouldn’t do anything else, so I encourage people to learn how to figure it out on their own. However, I’ve struggled in the past on finding an adequate way to explain it to people who don’t have the correct tools, and without using vernacular, but I think I’ve figured it out.
A Short Primer on Pixels
For the completely uninitiated, pixels (tiny dots of color) are the unit of measurement for any rendered image. The computer monitor you’re reading this on most likely renders images at 72 DPI (dots per inch), in other words, a single line of pixels across a 20-inch monitor is going to have 1,440 (72×20) pixels of color. No matter how big or small the monitor, most of them render at 72 dpi; that is the constant.
Contrary to that, most professional printing projects (magazines, brochures, calendars, product packaging, etc.) use images that render at 300 DPI; the dots are much, much smaller, which is necessary for creating crisp, clean lines in the print process. Because of this much higher amount of dots/pixels needed, it creates a resolution problem for images that were meant to be viewed on a monitor, like web images.
If you have an image that is 4×6″ at 72DPI, your pixels are 288×432. A 4×6″ image at 300dpi is 1200×1800 pixels. You would need to increase the size of the 72DPI image quite a bit in order to get to 1200×1800. You can enlarge the image using Photoshop or any image editing program, but what you end up doing is enlarging the size of the pixels, which creates blurry images, and because the software is trying to figure out which pixels to increase to make up the distance between 72 and 300, you get what are called “artifacts”, or blocks of color that look unnatural to the image. Photoshop is a very intelligent program, and can make a low res image look decent at high res, but there will be a loss in quality.
Is My Photo Big Enough?
Let’s say one of your friends has a photo on Facebook that you like and you want to have a copy to hang on your wall. Chances are, that photo is no where close to being big enough for print if its currently displayed on some website unless your friend had the presence of mind to upload the high resolution version. Some photo sites like Flickr, SmugMug or Picasa allow you to upload high resolution images, but not everyone knows or wants to put the high res on their accounts. If they do have high res up on those sites, the normal display image is NOT the high res. You’ll likely have to dig to find the high resolution image, so you’re better off asking your friend for a link to the high res, or have them send you the photo via email.
Let’s say they send you a photo and you’re looking at it in some image viewing program like iPhoto or Windows Photo Viewer. It looks the right size on the screen, but does that mean it will print correct? Truth be told, it’s hard to say, because all photo programs work differently when showing the image on screen. However, if your there’s something somewhere that shows what percentage you’re viewing the image at, this can help you. If the image is displayed at 100% and it looks like normal 4×6″ image, most likely, you’re looking at a low-res version. If that same photo is only being displayed at 30%, and at 100% is fills your entire screen; you’re definitely looking at an adequate high resolution photo, but who wants the guessing game?
The one constant for images is their pixel dimensions. Maybe you’ve adjusted your monitor settings in the past and saw options like 800×600, 1024×786 or something similar. These are standardized screen sizes, but the concept has its place in digital images as well. An 800×600 pixel image is equal to an 8×11″ image at 72 DPI, but at 300 DPI, it’s only 2.5×2″. The pixel dimensions remain the same regardless. Therefore, if you really want to know if your image is high enough resolution for a certain size image, make note of the pixel dimensions. Finding this information is File Properties (PC) or Get Info (Mac) menu when you right-click. Once you find that out, you can use a basic scale like the one below to see how close you are.
Lead image created by Dave Conrey, but inspired by our friends at Candy Sign.