File Formats For Digital Images

August 11th, 2009

The four most common image file formats are: TIF, JPG, GIF, and PNG. Programs like Photoshop and Elements support each of these formats.

These are not the only options just the most accepted. A web page requires a jpg, gif, or png because those are the file types that a browser can read.

TIF supports most color spaces and the file format contains many options such as the option to add tags to each image- but the biggest benefit is that a TIF file can be exchanged among platforms with no problem.

When saving a TIF file you can use the LZW lossless compression as an option. Lossless compression simply means that there is no loss of quality from compression. That means that you can always read back exactly what you thought you saved. Bit for bit with no data corruption. TIF files are generally very large. But the size is not a disadvantage because it just means there is a lot of detail saved within the file. A TIF should be used when high quality and archiving are a major consideration.

There may be times when quality is less a consideration than file size such as web pages or email- in this case choose a jpg.

JPG uses lossy compression which means that there is loss to image quality. But JPG was designed to be lossy to allow for major size reduction in the image. So when we open a JPG file the data expands so that we may view it and it is not exactly as it was before. This is loss of quality, purity and integrity. And it is unrecoverable. So depending on your image you need a good reason to use a JPG since its purpose is to create a smaller file. A good reason would be email or for the web.

Photoshop and other image editing programs will allow you to choose a quality setting when saving a JPG. Always use the highest setting.

When using JPGs you must also realize that each time the image is opened and then saved again it further compresses creating more data corruption. Each time it is rotated or added to- it is further compressed and more data is lost. Opening and viewing the JPG file is no problem. But every time you perform a save operation more data is lost. You can begin to see that this compression is leaving artifacts (or blurry spots) in your image over time by zooming in by 300% and the data loss becomes apparent. Over time these corruptions will become apparent when viewing the image at regular size.

So rather than continuing to edit and save a JPG file you should just begin with an archived Master TIF file and begin anew.

When using a camera that uses JPG files you should immediately save the image as a TIF and keep that as your master as you can then feel comfortable that there will be no quality or data loss with in the file. From the TIF file you can create JPG copies if needed. Keep in mind that you will not gain quality by transferring your JPG images that you already have to TIF format. But you can feel secure that you will not lose anymore quality. So if your JPGs already contain data corruption they will keep these if transferring to a TIF format. Which is why saving to a TIF to keep as a master copy that you will never rewrite is the first thing you should do if your camera does not support TIF files. Save any new changes to a different file. Never rewrite over your master copy.

The small JPG file size is great but it comes with a price.

GIF has no real value in photo quality images and is best suited for the web. JPG is a much better choice for the web for both quality and file size. However if your image has any transparency then use a GIF or PNG file as JPG does not support this. PNG will produce the better quality image but GIF is still the better choice as Internet Explorer does not always read the transparency information in a PNG file as other browsers do. So although I don’t feel that GIF is the better choice for quality it is the better choice for browser compatibility.

PNG supports lossless compression and is well suited for master copy like TIF files. It will also create a smaller file size than TIF. But TIF is the undisputed leader for image quality. When nothing less than maximum quality is required than always choose a TIF file to save your images. TIF is also the most common file asked for by commercial printers.