Cropping can be an incredibly useful tool for your photography , and it is one that is often necessary if you are planning on printing your images. This post will explain aspect ratio and when you will need to crop to match your finished print size.
Photos via Boost Your Photography
Cropping and aspect ratio
Before you begin cropping your photographs, you need to understand aspect ratio. Aspect ratio is a comparison of the length and width of your image. For most DSLR digital cameras, that ratio is 2:3. For most point-and-shoot and phone cameras, that ratio is 3:4. Shooting in a square is an aspect ratio of 1:1.
If you do not already know the aspect ratio that you are shooting in, look at the height and width of one of your photographs in pixels and divide the height by the width. My camera records images that are 3648 by 5472 pixels, which is 0.667, for an aspect ratio of 2:3.
You need to know aspect ratio because different print sizes also have different aspect ratios. If you are shooting at 2:3 and want to print your photograph as a 4 x 6 inch print, then your printed image will exactly match your original photograph. But, if you want to print an 8 x 10 inch print, you will have to crop your image to match a different aspect ratio, 4:5.
Your 2:3 original photograph would become an 8 x 12 inch print, so you will need to crop the equivalent of 2 inches off your image at that size. The image above shows the relative impact of that crop. The faded bars on the side represent the one inch on each side of the image that would have to be cropped out to print as an 8 x 10. (You do not have to crop the same amount off of each side, of course, but this is just one example.)
Shooting and cropping for wrapped canvases
This aspect ratio cropping is even more pronounced if you want to print a photograph as a wrapped canvas. Not only will you need to crop your image to fit the aspect ratio (a 16 x 20 canvas has the same aspect ratio as an 8 x 10), but you will also need to keep in mind that some of the edges of the image will be used to create the wrapped effect around the edge of the canvas.
This can create a problem if important parts of your image are near the edge of the frame. With the image above, you can see that part of the building and the tree are now wrapping around the edge of the canvas.
If you want to be successful when printing photographs on wrapped canvases, then you need to plan ahead while you are shooting. Leave some space around your main subject(s) and the frame of your photograph. You can always crop down a little bit later for the perfect image, but you cannot expand a photograph that was taken in too close.
Particularly if you are shooting images for a client, you want to make sure that they can utilize your photographs in a wide range of print sizes and aspect ratios. Aim for a range of close and wide compositions to give your clients, and yourself, options. Because I shot a range of different compositions, I could substitute a wider version of the scene (above) that would better lend itself to a wrapped canvas without losing any parts of the main subjects.
Pay attention to pixels and dpi
Any time you crop an image, you are making it smaller and losing pixels. The fewer pixels you have, the more limitations there will be on your maximum printed size. Many photographers recommend printing at a minimum resolution of 300 dots per inch. The problem with dpi is that dpi changes with both the amount of pixels you have as well as the size of your final print.
Dots per inch is a ratio of the number of pixels (dots) for each inch of your printed image. To determine the dpi of a given image, take the number of pixels on one side divided by the number of inches of the final print. For a photograph with 2400 x 3000 pixels, it would have a dpi of 300 when printed as an 8 x 10 but only a dpi of 150 as a 16 x 20.
Before printing, always double-check your dpi to make sure that you have adequate resolution to keep your photographs looking great.
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