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Understanding File Formats

by Steph Doran (follow)
Blog (332)      Articles (155)     

Photographs are being taken on many different types of devices these days, which all use different file formats. However, there are so many image file types and file extensions (from capture-type images to viewing-type images and images that are used for web or print output), it’s easy to become overwhelmed. It's also frustrating when you can't view or upload images across different devices unless the file type is compatible with the device.

The reason that all of these different kinds of files exist is that they all have different features and uses.

Here are the most common file types:

RAW Files

A RAW file is an uncompressed collection of data, and is the biggest type of file your camera is capable of capturing. What this means is that the camera records information across all areas of the image (highlights, shadows, colour, contrast, etc), and does not process or lock in any set values for this data. The benefit of a RAW file is that you can then use this extensive amount of information to make adjustments to your image in post production. RAW images allow you to make these changes without damaging the image, or reducing its quality. Professionals generally shoot in RAW, as it gives them the most flexibility with post-production.

Pros: Shooting RAW allows you to make lossless changes to your image in post-production.

Cons: RAW images can only be read by RAW-processing software, and need to be converted to another image type if you want to print, email, or upload them.

When To Use RAW: At the capturing stage, as RAW files are created by digital cameras (as opposed to computers.)

JPEG Files

JPEG files are perhaps the most popular kind of image to work with. However, just because they are the most popular does not mean they are the best. JPEG files are compressed files and although many beginners like to shoot in JPEG because they can fit more images onto their memory cards, and because they don’t have to process or convert the images before uploading them to the internet, there are downsides to using JPEGs.

This is because the heavy compression makes it almost impossible to make adjustments or corrections to the image (such as changing the white balance, or adding contrast, for example) without drastically reducing the quality. Every time that you make an adjustment to a JPEG image, there is a reduction in quality, even when saving it at the ‘highest quality’ option. Think of it like making a photocopy of a photocopy; every time another photocopy is made, the quality is reduced. Compressed JPEG images degrade easily, and this is why they can often look pixelated, blurry, or have strange looking colours. That being said, JPEG images are fine to use most of the time, but when you are planning to edit your photos, shooting in RAW and converting your final shot to JPEG is preferable.

Pros: Easy to use, recognisable by most software, and readily uploadable to the web.

Cons: Heavy and lossy image compression, and a reduction in quality every time you make and adjustment.

When To Use JPEG: When you want to email some snapshots or upload to Facebook to share with friends.

Image taken by Thomas Hawk

TIFF Files

TIFF stands for Tag Image File Format, and is a lossless image format, which means that when it is saved, no image data is lost. Because of this, TIFF files tend to be very large – too large to send to people or to upload. TIFF files are recommended for archiving because many keywords and details can be saved in the metadata, like in the photo above.

Their lossless compression also means that you can come back and make changes to your image without reducing the quality each time you make a change. If you use Photoshop, you can also save multiple adjustment layers into a TIFF file, which allows you to come back and make changes to your image at any time, without losing quality.

There are two types of TIFF files, 16-bit and 8-bit. 16-bit is a larger file, but it offers more information to work with when manipulating the file. For example, more data in the tones and colours that can be worked with. An 8-bit TIFF is smaller, and is great for saving your ‘finished’ photograph, ready to archive or print. Again, because of the lossless nature of TIFF files, they are perfect for printing high-quality images, even at large print sizes. Professional photographic labs prefer TIFF files when making prints.

Pros: Very high quality, and a lossless image format. Metadata can be retained.

Cons: Large file sizes, not suitable for the internet.

When To Use TIFF: When saving your final images to your computer to retain the highest quality, particularly if you have made adjustments, or when printing photographs in a professional lab.

GIF Files

GIF type images were designed when 8-bit video games were created for computers, before JPEG images were invented. They are quite a small file, relative to the other file types we have looked at. The reason they are so small is that they were invented at a time when dial-up internet was the norm, and so they had to be small enough to load quickly at slower internet speeds.

GIF images are still used on the web, as they support image transparency and animation. Transparency is great for web, as it allows you to place the image over any background without seeing an image border. However, GIF files can only replicate a very small range of colours, so they are better suited to graphics, logos or icons, and are not recommended for photographs. In addition, GIF files do not retain the EXIF data, which you means you can’t look at the metadata to see which shutter speed or focal length you used.

Pros: Small image size, readily uploadable for web. Can be animated or transparent. Lossless compression.

Cons: Very small amount of colours, and no embedded metadata.

When To Use GIF: To create icons or logos for the web, or to create animations.


PNG Files

PNG (Portable Network Graphics) are a more recent file type, invented to build on the benefits of GIF images. They are usually only used for web (smartphone photos are saved in PNG format). PNG files also use lossless compression, which means that all image information is restored when the file is decompressed during viewing. This makes them a little larger than compressed JPEG images. Like GIF files, PNG files allow you to work with transparency, but they also allow shifts in opacity (or different ‘levels’ of opacity.) However, unlike a GIF, PNG files can only contain one image, so they cannot be used to make animations.

Pros: Lossless compression, and retention of image sharpness.

Cons: Can be large, so may not be as easy to share online (depending on file sizes.)

When To Use PNG: When you want to retain quality in images being sent or uploaded through the web.

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