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Photography Tips: Image Size

Digital cameras have settings to control the size and compression quality of the images they store. This tip discusses what image size is, what compression does, and how to set the camera for the highest quality results.

The size controls how big the images are, up to the maximum resolution of the camera (for example, my old 7.1 megapixel camera creates 3072 x 2304 pixel images. This means the picture is made up of a rectangle of coloured dots 3072 across and 2304 down. My digital SLR stores 20 megapixel images at 5472 by 3648 pixels.

The more dots you store, the more detailed the photo can be, but more pixels usually mean smaller sensors, meaning less sensitivity and/or more noise (usually seen as unwanted coloured dots all over the image). Its possible to take photos smaller than the camera's capability, which allows more images to be stored in the camera, and sometimes makes processing faster.

Compression controls how the images are processed for storage. You still get the same number of dots, but the camera uses compression to store the photo in a lot less memory. The more compression used the smaller the image is (on the memory card, the photo itself is the same size) but highly detailed areas tend to become blurry. Its also possible to store images without compression, but they can get really big, for example only a few images might fit on a small memory card (not such a big problem today, now that memory cards are so big and relatively inexpensive).

Left is a highly compressed image, right is a moderately compressed image, which is the same size. Notice that the compression blurs detailed areas, such as the clock. The less compressed image required 5 times more memory than the small one to store though.

My policy has been to use the highest quality settings available, even if I don't need all the detail that provides. For example, I display most pictures on my high resolution computer screen (several million pixels) or my UHD TV (3840 x 2160 pixels) but my camera takes 5472 by 3648 pictures (20 megapixels). The reason I take the photos at the highest quality is to give me some extra information to work with when rotating, cropping and doing other manipulations. You can see on the image above how I zoomed in on the church by cropping the bigger photo. Because the image was big to start with I still got good detail. Also, it gives extra detail when printing on high resolution printers.

The disadvantage is, of course, that the memory card in the camera gets full more quickly, but the price of high capacity cards isn't that much so I use a large card which can store hundreds of the highest quality images. If I was going to be away from a computer for a long time I would consider using a second card instead of reducing the picture quality.

One other factor to consider is redundancy. If you have a single large card storing hundreds or thousands of images, and it gets corrupted, they might all be lost. Note that there are tools to recover files from damaged cards, but this recovery cannot be guaranteed. Using several smaller cards, or swapping them before they get full, means that if a card gives problems, at least only one card of images will be affected. Note that modern cards and cameras have good reliability, so this isn't as big an issue as it was in the past.