Image file formats.

A good starting point when you first begin to understand your images is to know a little bit about the common file formats or the way that your images are saved. So here we have seven, (one for each day of the week).

JPEG

The most commonly used image file format in both digital cameras and on the web today is JPEG. JPEG actually stands for Joint Photographic Experts Group. If you are of a technical bent you might wish to go and visit the groups website at www.jpeg.org. For the rest of us when we refer to JPEG we simply mean the file format.

One of the reasons JPEG is used so widely is because, (compared to some of the other file formats) it produces a very small size file. The downside to JPEG images is that the small file size is achieved by degradation (loosing pixel clarity) of the image. Because of this degradation the file format is referred to as Lossy compression.

You can also choose to save these images at different resolutions as shown below.
Maximum size image 73.92K
Maximum resolution 73.92K
High resolution image 31.7K
High resolution 31.7K
Low resolution image 9.238K
Low resolution 9.238K

Lossy Compresion

Refers to a data compression techniques in which some of the data is lost. Now this is important:

Every time you save a JPEG image you loose digital information.

So if you are working in Photoshop (and I am going to assume that you are working in Photoshop or Photoshop Elements) if you are starting with a JPEG image before you touch anything else I would highly recommend that you save the image as either PSD (PhotoShop Document) or as a TIFF (Tagged Image File Format).

Lossless

Lossless is the opposite of lossy, and no image data is lost.

GIF

Graphic Interchange Format or *GIF is probably the second best known on the web.

*Note

One of the most controversial things about GIF is way you pronounce GIF. Having been brought up in England and living almost all of my adult life in Canada I learned to pronounce the acronym as GIF with a hard G. I was completely taken aback a few years ago while, at a tutorial I was attending in Seattle, the presenter began saying “JIF”.

It turns out that the originally intended pronunciation was in fact JIF and the acronym was a play on words to echo a highly popular TV Ad at the time for JIF peanut Butter. I must confess that in speech I still use GIF unless I’m really thinking about it, and I’m obviously not alone as both versions are accepted.

The cool thing about GIF’s (however you say it) is they allow animation. It is also a lossless (no data is lost). format, allows 256 colors per image.

PSD

A PSD is a Photoshop document and is the native file format of Photoshop. When I’m working in Photoshop I prefer to save and work on my images as PSDs.

*Note

Now I have to let you in to my little world of paranoia. Once I’ve downloaded my images and decided which ones I’m going to keep, if I shot them as a JPEG I always like to keep a backup copy as a PSD preferably on a separate drive on my computer.

BMP

Bitmap or BMP means a range of bits (computer code) that make a map. Usually a Bitmap is one bit per pixel (but not always). This is a vast over simplification but for the moment all you really need to be aware of is the name.

TIFF

Tagged Image File Format or TIFF was originally mainly used by the print industries. Because TIFF is a lossless format it is good for saving images where you want to retain detail but all the file size will be much larger than that of a JPEG.

Camera Raw

Camera Raw is the new darling of the photographic world. The files are huge but you loose no information.

The files have “raw” information and can be thought of like an old fashioned negative. Because Raw files are not ready to be edited they open (in Photoshop) in their own dialogue box which allows you to manipulate the image without any destruction before opening the image in Photoshop itself. The huge advantage is that you always have the original image in its original state with all its information intact. (As long as you don’t delete the file of course.)

DNG

Digital Negative Format DNG is another Raw file format developed for digital cameras developed to enable greater sharing capabilities over different software platforms.

This is the first of a series of Core Articles. These articles are designed to get you up to speed on fundamental terms and their meaning. Subscribe using RSS feed to make sure you don’t miss the next in the series.

Leave a Reply

Your email address will not be published. Required fields are marked *