Understanding Aspect Ratios

Question:  "Can I have an 8" x 10" enlargement of that photo?"

Answer:  "Well... yes and no, it kind of depends."

Definition

"Aspect Ratio" is the relationship between the width and height of a photographic image. The image can be a print, a negative or a digital file. Aspect Ratios are typically expressed as a numerical ratio between the length of the short side and the length of the long side.

Units Of Measure

Inches remain the most common unit for expressing photographic print size. The word "inch" is abbreviated with a double quotation mark. Prints from places like Wal*Mart typically measure 4" on the short side and 6" on the long side. Common enlargement sizes are 8"by 10" and 11" by 14".  The word "by" is abbreviated with the letter "x" and the quotation marks are dropped. A print that is 11 inches on the short side and 14 inches on the long side is described as 11x14.

As with picture dimensions, Aspect Ratios are typically expressed with two numbers. Unlike picture dimensions, a colon (":") separates the numbers rather than an "x".. Also unlike picture dimensions, the fraction implied by the Aspect Ratio numbers should be reduced to its lowest terms. For example, a 4x6 print would have an aspect ratio of 4:6, but this is properly expressed as 2:3 when reduced to its lowest terms. An 8x10 print would have an aspect ratio of 8:10, properly expressed as 4:5. Enlargements such as 8x12, 12x18 and 24x36 have an aspect ratio of 2:3 because all of these ratios reduce to the same value, that is, 2:3.

Why It's Important

People need to understand Aspect Ratio because prints that faithfully reproduce the original digital files must have the exact same aspect ratio as the image in the source file. If there is a mismatch between the print size requested and the aspect ratio of the digital file, some of the image will be lost when the file is printed. This may or may not be a serious issue depending on whether or not there is important subject matter located in the portion of the image that does not get printed. The digital cameras that I use are all designed to produce digital image files that have a 2:3 Aspect Ratio. As a result, 2:3 is the most common Aspect Ratio of the images that you will find on my website. Sometimes however, this strong rectangular shape doesn't match well with the image's subject matter. In these situations, I often post images cropped to a 4:5 Aspect Ratio. Occasionally I'll crop to a nonstandard Aspect Ratio because it better fits the subject matter than any of the standard ratios. Panorama images always have extreme Aspect Ratios. Something like 1:5 might be typical.

It's very common for me to receive requests from people who want to have an 8x10 enlargement printed from a source file that has a 2:3 aspect ration. Conversely, people also ask me to provide them with a 4x6 print from a source file that has a 4:5 Aspect Ratio. With one exception (which I'll describe when I get to Figure 5), this can not be done without losing some of the original image.

Examples

Figure 1 is an image from my website. Suppose that you request a digital copy of this image. I send you the file but you get it printed as an 8x10 enlargement. Figure 2 shows the sort of thing that will happen to the print. Some of the image is lost ("cropped" in the language of photographers). When you upload the file to the processing company, you often have an opportunity to specify how the picture is to be cropped, so the end effect may be somewhat controllable. For example, you could lose less of the penny but more of the Twonie or you might want to keep more of the Twonie and lose the penny entirely. Either way, you can NOT avoid losing a substantial portion of the original image when you mismatch Aspect Ratios between source files and prints.

Sidebar

TV & Aspect Ratios

Aspect Ratios for television and motion picture images, are often expressed as decimal fractions.  In this situation, the longest dimension of the image is divided by the shortest. 'Stanndard TVs have an aspect ratio of 4:3, that is, 1.33.  Wide-screen HDTVs are built to display images with a 16:9 Aspect Ratio; that is, 1.78.  Motion pictures often have wider Aspect Ratios. Two example are 1.85 and 2.35. This is why DVDs of motion pictures often produce black bars above and below the image even on wide screen TVs.  This happens when the Aspect Ratio of the movie is wider than the 16:9 aspect Ratio of the TV. This is completely analogous to the situation seen Figure 5 on this page

Some TVs and DVD players can be set to 'stretch' the picture and eliminate the black bars.  You could do that with photos too but I don't know of anyone who wants to look at photos like that.  For the life of me I can't understand how so many people seem oblivious to stretched images on their televisions.

Most digital photo frames follow TV standards and are built with a 16:9 Aspect Ratio. This is a good thing for displaying wide-screen home videos but a bad thing for displaying still photos which are almost never 16:9.  Some frames can stretch the photos to fill the screen but I wouldn't want to look at them then.

I can only pray that photo print processors don't start offering a 'stretch' option for mismatched aspect ratios. Looking at stretched TV in Sports Bars is bad enough.  Imagine looking through a friend's photo album where everybody looks fat!  

A similar problem occurs when someone requests a digital file for an image with a 4:5 Aspect Ratio, like shown in Figure 3, and uses that file to produce a 4x6 print. The result will generally be something like the image shown in Figure 4. Again, the negative effects can be minimized by being very careful when you upload the file to the processing company and taking care that you specify what portion of the image is to be lost. Still, you WILL lose some of the image. As a work-around for this problem, I often produce a modified version of my image files that adds blank areas to the sides of the image, thus forcing it to have a 2:3 Aspect Ratio. This type of file will produce a 4x6 print like shown in Figure 5.

Advice

At first, the concept of Aspect Ratio can be tough to grasp.  Once understood, however, it's almost second nature to work with it.  Next time you're tempted to ask a photographer for an 8x10 enlargement from a 4x6 proof, think twice.  You may realize that an 8x12 enlargement is what you really want.