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The 5 Most Commonly Used Digital Image File Formats

by Dan Bailey on September 20, 2010 · 70 comments

The 5 Most Common Digital Image File Formats

One of the most confusing aspects of digital photography for some people is how to choose among all the different file types. I mean, c’mon, can’t an image just be an image? Why do we need so many formats?

Size, my friend. That’s why.

If we lived in a perfect world and we had endless digital storage and internet bandwidth, (I can’t wait for the day…) we’d really only need one file type. Big. Full Size. Ok, so may be we’d need two, if you include RAW.

Unfortunately, that day is not here yet, and so we still need to worry about how long it takes to transmit our images through cyberspace and how much room it takes to store them on our computers.

Here’s a basic primer on the different file types that you’re likely to come across and how they’re commonly used in the world of digital photography.

RAW: A RAW file is the full set of uncompressed camera data that was recorded by your digital sensor. Technically, a RAW file is not an image, it’s just the ingredients for an image, which includes all the light and color data, as well as any metadata that was applied to the file as specified by your camera settings. A RAW file must be converted to another image format in order to view it as an image. This is done through your image processing software, although the camera also has an onboard processor, which allows you to view a JPEG preview of your RAW image on the LCD screen after you shoot it.

DNG: Since every camera manufacturer uses a proprietary format for their RAW files, Adobe came up with an open standard RAW image format called DNG (Digital Negative). Not every software can read every different RAW file type, but most can read DNG files. DNG also solves the potential problem of file compatibility for long term storage of digital files. We all know that most technology becomes obsolete over time, so converting and storing images files as DNG files can give you confidence that photos you take today will be readable by Photoshop, or whatever software is current in the future. You can convert RAW files to DNG using Adobe software, as well as some other digital imaging programs.

TIFF: TIFF (Tagged Image File Format) is one of the most popular formats for high color, high depth digital images. If you need to deliver an image in the highest quality for reproduction or publication, or if you have digital images that you need to save and work on later, then you’ll probably want to save it as a TIFF file. TIFFs store image data in a lossless compression format, which means that image quality remains constant, not matter how many times you open and resave the image.  TIFF is the format you’ll want to use to save your master final images after doing RAW conversions, color and tone corrections and other Photoshop edits.

JPEG: JPEG (JPG) is the most common format for compressing digital images. It works by analyzing the image data and essentially throwing away the data that you probably won’t see in order to reduce the file size. You can choose the level of compression when saving photos, which makes it ideal for a number of applications. Saving an image as a high quality JPEG will preserve almost all of the necessary color data at a much smaller file size. Very high quality JPEGs are good enough for publication or high resolution prints. Medium to high quality JPEGs are suitable for the web, as they allow faster load times for your images. Low quality JPEGs allow you to transmit images over limited bandwidth, although you tend to see fuzzy ‘artifacts’ with too much compression.

The main disadvantage to using the JPEG format is that it uses lossy compression, which means that every time you open and resave the image, you lose more information and reduce the quality. JPEGs are ideal for emailing photos, posting to the web or delivering preview shots to clients.

PNG: PNG is a bitmap file format that uses lossless compression. The file is mostly used for placing images on web pages. The advantage of using a PNG over a JPEG on a web page is that PNG’s offer varying color depths, as well as transparency, which allows you an easy way to place images, or images of text and other designs that aren’t just solid palettes, and have the background color or pattern show through in the spaces.

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Dan Bailey is a professional adventure, outdoor and travel photographer based in Anchorage, Alaska. Follow his own blog at danbaileyphoto.com/blog and see his daily updates at facebook.com/danbaileyphoto.

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{ 4 comments… read them below or add one }

@gilesguthrie September 22, 2010 at 3:19 pm

Canon RAW files are compressed using some form of lossless algorithm, probably LZW or a variant. This is why Canon DSLR users will note that card capacity varies: ISO 1600 images are noisier, and thus less compressible than ISO 100 images. The camera's smart enough to account for this and predict it in the shot counter.

Otherwise, a useful and interesting article. I only really use three formats: RAW, PSD and JPEG. I've thought about doing a DNG conversion, but haven't gone past the thinking stage. I'm a little surprised you didn't include PSD actually. It provides the photographer with an excellent intermediary step between input & output, most critically retaining image construction information by saving the layers.

Downside is that PSDs can get massive – I have several at 10 megapixels which are running to in excess of 150MB…

Tom Gaulton September 22, 2010 at 3:20 pm

I would add PSD to this list. Many people use PSD for saving images during editing work in Photoshop (you can use TIFF instead but PSD is still commonplace I believe).

Meekohi September 22, 2010 at 3:27 pm

I have to totally disagree on the TIFF point. TIFF is an archaic format that should be completely replaced by PNG. PNG isn't just for putting images on websites it's the ideal format if you want lossless compression!

Can anyone come up with a reason to use TIFF instead of PNG?

Good? old GIF? September 23, 2010 at 6:53 am

What about GIF? Still one of the most used formats for small images. Sure, it's totally the wrong format for something coming out of a camera, but for small images it actually compresses most with the least amount of loss (the 256 color palette makes it kind of lossy). And it has animation, which we all hate…

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