File Formats

So you've scanned, tweaked and touched up your image to your heart's content. Which file format are you going to save your masterpiece in? To some, this is a deceptively simple question, but your choice of file formats can have some pretty surprising consequences. There are lots of different ways of saving images - PhotoShop itself can recognise and save in more than 20 different file types. For our purposes, we'll just restrict ourselves to the most common ones.

As any regular web-surfer worth his/her salt will tell you, the vast variety of images out in the Internet comprise of mainly 2 file types: JPEG and GIF.

JPEG (Joint Photographic Experts Group) files are by far the most common, and certainly the most popular. JPEG encoded files usually have the .JPG extension to the file name. Most digital cameras store their images as JPEG files. There is a good reason for this. JPEG is a compressed file format, which means that the saved files are much smaller than the actual image size. So what's the big deal? There are other types of  compressed file formats, GIF being a notable example.  The beauty of JPEG files is that it can offer incredible compression with no appreciable loss in quality.

OK, let's quote some numbers. An 11 by 6 inch 300 dpi image in 24 bit colour (16 million colours) is about 25 MB in size. If you save it in JPEG, the file size ranges from about  2.5 MB to 500K, depending on the settings you use. If you're short on storage space, JPEG is the way to go. No other format even comes close to JPEG in shrinking file sizes. What's the secret to its incredible compression abilities? Well, JPEG utilises a "lossy" compression scheme. What this means is that during the process of saving the image, the compression algorithm tosses out "non-essential" information from the image. You have absolutely no say in the matter, except to determine the level of compression through the quality settings. The highest quality setting gives the least compression. The compression routine mostly does a pretty good job. An image saved under JPEG using the highest quality setting is indistinguishable from the original. And because the format can suppport 24 bit colour, JPEG is particularly well suited to saving photographic images.

GIF stands for Graphics Interchange Format, and is also a compressed file format. GIF, however, uses a lossless compression scheme, which means that its file sizes are typically larger than an equivalent JPEG file. GIF used to be very popular until JPEG came along. The greatest disadvantage of the GIF format is that it can only save up to 256 colours. Thus the GIF format is quite unsuitable for the saving of photographic images, because the 256 colour limit produces grainy, dithered images. However, GIF is particularly well suited for images with large patches of solid colours, or with lots of fine detail, clearly defined lines or edges. Thus most of the banners or logos we see out in the web are saved in the GIF format. JPEG can introduce image artifacts with such images, especially at low resolutions.

TIFF stands for Tagged Image File Format, and like the GIF, has been around for a while. It was introduced back in the early days of the Apple Mac, and is thus quite popular among printing bureaus and graphic design shops. TIFF files can also be read interchangeably between PC's and Mac's, so it's an attractive format if you intend to submit your scans to a commercial printing bureau (which typically uses Apple Mac's). A TIFF file can be compressed through a lossless process, but the results are nothing to write home about. A typical 25 MB file usually reduces to about 21 MB, which pales in comparison to results obtained through JPEG compression.

There are also a whole bunch of other file types, but they are either too oddball, proprietary, or too specialised to be of use to us. The 3 formats mentioned are the ones you will encountering most often, and they have the advantage of being recognised by nearly every image editing software out there.

OK, so what exactly are the consequences I was alluding to earlier? Well, each format has its own advantages and disadvantages, so you should be familiar with them and use them accordingly. The JPEG format does have one VERY important point (or disadvantage) you should be aware of. Because JPEG uses a "lossy" compression scheme, each time you open, edit and resave the image, pixels get dumped and the image becomes progressively degraded. And once the information gets discarded, it's gone forever. So although it saves you a lot of space, the JPEG format is unsuitable if you need to edit your files very often. Save in JPEG ONLY when you're absolutely sure you don't need to edit your image anymore.

If your scans archive are of mostly photographic images, your best bet may be to save them in the TIFF format. 

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