Digital image files can be saved and/or sent as various file formats. The optimal file format depends on how the image will be used.
Some common file formats and their uses/applications:
Halftone (pixel) files:
RAW (Camera RAW)
‘Native’ file format that comes directly from a digital still camera. This format has the highest possible image quality and colour depth, but needs to be processed with a RAW converter to create usable files for webpages or printed matter.
TIF (or TIFF)
File format that comes either from a digital camera or is saved by an image-editing program (e.g. Photoshop).
TIFF files can contain maximum image quality. When you save images in this format, you can make use of a compression option (LZW compression) to reduce the file size at the expense of quality. Alternatively, you can save the image without LZW compression to retain maximum quality. TIFF files can contain layers and transparency.
Native Photoshop format. This file format preserves the maximum image quality, with no compression. PSD files are often very large files that contain a lot of information: layers, layer effects, layer masks, transparency, gradients, etc.
JPG (or JPEG)
File format developed to compress halftone images and thus reduce the file size. When you save the image, you can choose between 12 different degrees of compression (1 = minimum quality, 12 = maximum quality). The degree of compression you choose depends on the purpose for which you wish to use the image.
JPG compression compromises image quality and is irreversible. The more often a JPG is saved, the more compression and loss of image quality occurs. It is therefore advisable to save original image files as PSD or TIFF files (without compression) and then to use these to create JPGs for sending or using online.
Another compression format. The compression is performed using a different technique, but also comes at the expense of image quality and is irreversible. GIF files are mainly suitable for online applications and are ideal for logo-like images (illustrations, line art).
A special variant of this format is the animated GIF, an image file that contains a number of moving ‘frames’ like a mini-movie.
Yet another compression format. The compression involves a different technique but comes, again, at the expense of the image quality and is irreversible. PNG files are mainly used online and are well-suited for combinations of halftone and line art (illustrations, etc.).
Vector (line) files:
Native Adobe Illustrator file. Can store vectorised lines, curves and surfaces. May also contain halftone information. Pure vector image is in principle resolution independent; it can be enlarged as needed with no restrictions on image sharpness and quality. The image can also be saved any number of times without loss of image quality. Especially suitable for digital illustrations, logos, graphics, etc.
File format that can store vectorised lines, curves and surfaces as well as halftone images. EPS files can be generated from various applications, such as Photoshop and Illustrator. An important property of EPS images is that they can contain additional digital information such as ‘duotone’ techniques.
File format that can store vectorised lines, curves and surfaces as well as halftone images. PDF files can be generated from various applications, including the Windows Office suite, Acrobat, Photoshop and Illustrator.
PDF is the international standard for sharing platform-independent digital files.