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Aspect Ratios and Cropping Considerations for
Digital Images
The ratio of the width to height (or long to short side) of an image or print is the aspect ratio. Cameras and scanners capture images in varied aspect ratios, and the ratio also varies for common print sizes. This means that decisions must be made about cropping portions of many images to size them for specific uses. This article describes common aspect ratios and image cropping considerations.
Aspect Ratios and Image Capture
Before discussing image display and printing, it is useful to understand common image capture aspect ratios.
The image sensors in most common compact digital cameras record pixel information in a ratio of 4:3 (4 pixels of width for each 3 pixels of height) for an aspect ratio of 1.33. The larger sensors typically found in digital SLR cameras capture pixel information in a ratio of 3:2 resulting in an aspect ratio of 1.5.
Images captured by scanning will simply reflect the same aspect ratio as the item being scanned. This can vary considerably, since over the years, photos and documents have been produced in many different sizes and aspect ratios. These photos of varied sizes reflect past iterations of competition among equipment and film makers, as well as different approaches taken by photo developers.
Aspect ratios for non-photo images will vary widely as scans are created of other images such as vintage postcards, documents , and other sorts of memorabilia.
Aspect Ratios and Display and Printing
Common image print sizes reflect a variety of aspect ratios, as can be seen below:
| Print Size | Aspect Ratio |
| 4 x 6 | 1.50 |
| 5 x 7 | 1.40 |
| 8 x 10 | 1.25 |
| 11 x 14 | 1.27 |
| 16 x 20 | 1.25 |
| 20 x 30 | 1.50 |
It is interesting to note that the compact digital camera aspect ratio of 1.33 does not perfectly match any of the above common print sizes. However, the 1.33 is a pretty flexible compromise. On the other hand, the digital SLR aspect ratio of 1.5 is a good fit for some, but less so for the majority.
Computer display monitors are typically engineered to an aspect ratio of 1.33 (600 x 800 pixels a common setting).
This understanding of aspect ratios can be important as you begin to contemplate how a captured image will be displayed in print and on monitors.
Cropping and Resizing Images
If we are planning to print an image in a different aspect ratio, we can often simply allow our software or printing service to use default and arbitrary cropping methodology to make our image fit a specified size. Alternatively, we can often specify no cropping, in which case white borders will be added to two sides as necessary to keep all image information in the boundaries of the print size.
A third option is to crop each image to the proper aspect ratio with digital image editing software.
It is current industry default practice for most photo printers, including online printers, to enlarge an image as necessary to fill the print area of a specified size of print. If the aspect ratio of the image is different from the aspect ratio of the specified print size, the portion of the image enlarged outside of the targeted aspect ratio will be cropped/trimmed equally on both sides. This default is often referred to as a "zoom & trim" approach. Alternatively, you are often provided the opportunity to turn off this default crop. When the default is disabled, your full mage is placed onto the designated print size, and borders are added as necessary.
