How do I choose the appropriate file type for saving/editing/creating images?

The main factors in your choice of an image file type are compression, color, and accessibility.

Compression

Some file types compress images in order to reduce file size.

  • Lossy file types lose information (small bits of detail) each time the image is opened and re-saved. The effect is often undetectable, but can be problematic over a long period of time, or if high-quality, archival images are needed. For example, JPEG, GIF*.
  • Lossless compression, which means that no information is lost when the file is compressed. For example, PNG, GIF*.
  • Uncompressed file types result in large file sizes and are useful mainly for archival purposes. For example, TIFF, PSD, RAW, and BMP. *GIF is lossless for images with 256 colors or less; for most images (especially photographs), color information is lost.

Color

Color options are also variable. Some file types (GIF in particular) support a limited palette of 256 colors. This allows for great file size compression, and is well-suited for logos, abstract images, and other flat images; it is inappropriate for photographs. Most file types (JPEG, PNG, TIFF, etc.) support 24 bit color, meaning a palette of 16 million colors or more.

Accessibility

Lastly, accessibility is an issue for some file types. Proprietary file types such as PSD can only be opened in the required software (in this case, Photoshop). PSD and BMP (a Microsoft file type) are both proprietary. In addition, some file types (TIFF, PSD) are not widely supported by Web browsers.

File type

Compression

Color

Use

BMP

Not compressed

24 bit

Microsoft's proprietary file type. Not widely used.

GIF

Compressed

256

Best: Simple graphics with solid colors for web because colors will render true in all browsers, files are small. Not for photographs or richly/subtly colored images.

JPG

Lossy compressed; degree of compression is variable.

24 bit

Best: photographs for web and email attachments. Not well-suited for archival collections because of the lossy compression. Also not suited to line art, solid-color logos, etc.

PNG

Lossless compression

24 bit

Best: Images for a web site. Better compression than GIF, with more color options.

PSD

Not compressed

24 bit

Best: for editing in Photoshop because it maintains layers, text editability, and more editable features. Cannot be opened in any other program, so final version should be saved as an other file type (such as JPEG) for use in other programs.

RAW

Not compressed

24 bit

The raw file from a digital camera. Best saved as another file type. Different camera makers have distinct RAW file formats, so the type is often proprietary.

TIFF

Either not compressed or lossless LZW compression

24 bit

Best: archival purposes. Not for web pages, not for low quality photos or simple graphics. Large file size.

These concepts are explained in more detail, and examples are given in this source document: Matthews, Rick. "Digital Image File Types Explained." 5 March 2006.

This guide was last updated on 2 March 2006.

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