Working with Aspect Ratios
This month we tackle the simple but often misunderstood topic of aspect ratios and how to handle cases where the aspect ratio of the image doesn't match the aspect ratio of the print.
Aspect ratio: the simple definition
Aspect ratio is nothing more than width divided by height. The higher the aspect ratio, the wider the image (or screen). For example, standard televisions have an aspect ratio of 1.33. That is because the screen is 1.33 times as wide as it is tall. This 1.33 aspect ratio can be written as 1.33, 1.33:1, or 4:3. HDTV sets have an aspect ratio of 1.78, sometimes displayed as 1.78:1 or 16:9. The higher number (1.78 versus 1.33) indicates that the HDTV set has a wider, more rectangular screen than the more "square" standard set.
This same concept applies to digital photographs. Most consumer digital cameras capture a picture that is about the same aspect ratio as a standard television: 4:3 or 1.33:1 while professional dSLR cameras often use the 3:2 or 1.5:1 standard that matches the typical 35mm negative, slide, and 4x6 photograph. As you can see below, a dSLR produces a picture that is a little more rectangular (wider) than the more square photo from the consumer camera.
Pro dSLR Camera
Matching aspect ratios
Now that we know the definition of an aspect ratio, it becomes clear that we have a problem. First consider aspect ratios that match. For example, the 3:2 photo from a pro dSLR camera (displayed above right) can be printed at the popular 4x6 photo size because the aspect ratio of the image (3:2) matches that of the print which is also a 3:2 ratio. That means that the entire photograph from the pro dSLR camera can be printed as a 4x6 print with no cropping and the final print will be exactly 4x6. Here, we have no problem because we have a match between the aspect ratio of the image and the print size we have chosen.
The problem occurs when we have a mismatch. For example, if we have a consumer camera that produces 4:3 photos, we cannot print a 4x6 photo without either distorting the image (making the subjects look wider than normal) or cropping some of the image. Let's consider three methods for obtaining a 4x6 photograph from a consumer camera that records a 4:3 "mismatched" image.
Method 1: Fit in frame
With method 1 above, we fit the entire 4:3 photo inside a 4x6 frame. Using this method, the actual photograph is 4 inches tall but only 5.3 inches wide. The white bars on the left/right fill out the rest of the 4x6 photo and would show if mounted in a 4x6 photo frame. This method is often not desirable when placing photos in a frame because the white bars show inside the 4x6 frame. The advantage to using this method is the fact that the entire photo can be printed with no cropping.
Method 2: Crop to Size
With method 2, we crop out a portion of the center of the photo using a 3:2 crop. Using this method, we lose a little off the top and bottom (notice the flags are missing on the bottom) but we lose nothing on the left/right. This method is often the preferred method since the photograph will be exactly 4x6 inches and will fit in a 4x6 frame with no borders. The compromise, of course, is that we must lose a bit of the image on the top and/or bottom.
Method 3: Distort (stretch)
The third and least preferred method is to "stretch" the image from left to right so that the entire image fits in the 4x6 photo. Since this method distorts the image, it should not be used with photographs. The distortion is not as obvious in the above photo as it would be with people as subjects. We can see that the tall/skinny building near the right/center of the photo looks "fatter" in the distorted image. This effect is more noticeable with people/faces than with buildings for which we have no internal reference in our mind.
Dealing with the differences
While any photo editor will allow you to achieve any of the above aspect-ratio-matching methods, the best way to deal with this issue is to use software specifically designed for photo printing. Most photo printing software will allow you to easily switch between methods 1 and 2. Method 3 is not offered in most photo printing applications as it is considered an "error" since it distorts the photo.
As an example, in my own Qimage photo printing software, you can easily switch back and forth between "fit in frame" and "crop to fit" by simply selecting photos on the page and clicking the crop button (scissors icon on the main window). With the button in the up position, photographs will print via method 1 above. With the button down, method 2 is used. When using method 2, the default cropped area is the exact center of the photo (equal portions of the top/bottom are cropped in the above example) but the area that gets cropped can easily be changed.
When using method 2, it is desirable to have a quick and easy way of adjusting the part of the photo that is cropped. For example, if the flags are important, you may want to drag the crop down a bit so that the flags are included in the photo, losing a little more of the tops of the buildings. If the flags are not important or are considered a distraction, you need to be able to drag the cropped area up so that the flags disappear and you get more of the tops of the buildings. In Qimage, this task can be performed simply by clicking the "Full page editor" button under the preview page on the main window and then dragging the small image on the "Cropping" tab on the right side of the page editor window.
Other photo printing software may offer similar methods of fitting/cropping and adjusting but most multiple-photo-printing programs do offer the option at some point in the user interface.
While this entire topic may be trivial to the advanced amateur or pro, I'm still surprised by how many inquiries I get on a daily basis regarding how to effectively deal with this issue. I often get the same question, for example, asking how to print a 4:3 photo at exactly 4x6 inches without cropping. After reading this article, hopefully the answer is clear: the only way to do this is by distorting the image. Other than distorting the image, your only other options are to adjust the size (to 4 x 5.33) or crop some of the image (on the top and/or bottom). Obviously, this article focused on one example but similar situations exist when printing other sizes. For example, we have the same problem when trying to print a 3:2 photo from a dSLR at a size of 8x10 or 5x7. Also note that depending on the orientation of the image (portrait/landscape) and the image-versus-print aspect ratios, sometimes the cropping method will require cropping from the top/bottom rather than the left/right. I hope this article will help in the basic understanding of aspect ratios and the handling of "mismatched" aspect ratios.
-- Mike Chaney
Mike Chaney is president and chief software programmer for Digital Domain Inc and is the author of Qimage and Profile Prism software. He has a bachelor's degree in computer science from the University of Maryland, College Park. Mike worked for the federal government for 14 years as a senior software engineer, designing and deploying large scale workload tracking systems. He began developing digital imaging software in 1996 as a part time venture and due to the success of his software was able to resign from the government in 2001 to pursue his passion for digital photography and development of related software. Mike continues to develop and update his software and is also an active member of many online communities related to digital imaging. He enjoys helping others by discussing the latest topics, doing independent research, and sharing with others in order to take some of the "mystery" out of some difficult but key concepts in the field of digital photography.