Computer Image File Types

File Formats

Digital images are saved in computer files. Computer files containing raw digital image information are huge. However, there are different ways of storing the color information.

Microsoft Windows-based computers identify image file types by the last three letters after the dot in the name of the file. There are open file formats and proprietary formats. The open formats can be viewed by almost any kind of image editing device or software.

Standard Formats

The standard formats include (but are not limited to):

• JPG, JPEG
• GIF
• PNG

JPG

Virtually all digital cameras currently on the market support this format. JPG is a format best suited for digital photos and any image that isn't line art (the MWCC logo is an example of line art). Any complex image that contains thousands of different colors, that doesn't consist entirely of clearly defined areas of solid unbroken color is best suited for JPG. JPEG images utilize compression to shrink the size of the computer file needed to store the image information.

EXIF Metadata

This is a standard developed by Japanese digital electronics manufacturers. Cameras and scanners supporting the EXIF standard store additional 'metadata' in the images when they create them. This metadata includes things such as the camera or scanner's maker and model. For digital cameras, there are fields for ISO speed, f-number, focal length, +/- stop values, photographer's name, date and time the photo was taken and even Global Positioning System information if the device supports it. EXIF information can be read by Paint Shop Pro v8 (still researching which versions of Photoshop support EXIF, if any). Since Nikon and Canon are both Japanese brands, both support this format. The EXIF data even includes rotation information on cameras that support it.

IPTC Metadata (IPTC-NAA comments)

Photoshop added support for creating your own fields to store metadata within Photoshop's proprietary image format (.psd). News organizations, such as the International Press Telecommunications Council or 'IPTC', standardized the types of data that should be included with a news image when transmitted to a news organization. The capability of Photoshop to support metadata was used by journalists to add this standardized news image information using Photoshop's proprietary image information block. Needless to say, the news organizations had to have Photoshop, as did the journalists. The IPTC standard (IPTC 7901) was developed for/by the International Press Telecommunications Council (http://www.iptc.org). IPTC is specific to photojournalism and does not contain fields for the camera's physical specifications or the settings for the shot. Those must be created and entered manually. Photoshop v7 or later supports the current XML-compatible IPTC standard.

GIF

Strictly speaking, the GIF format is not an 'open' standard as it is owned by UNISYS corporation. However, it is so widely supported and well known that it is a de-facto standard image format. GIF images are better suited to anything that isn't a photo. Line art, graphics and any other image that consists of primary shapes and colors. The GIF image format is limited to 256 colors. GIF also supports animation (multiple images shown in sequence) and transparency (bits of the image show whatever is beneath the image). No EXIF or IPTC support.

PNG

This image format is much like GIF, but it supports variable transparency (with GIF, a part of the image is see-through or it's not). PNG also supports interlacing, better compression than PNG and more colors than PNG. No EXIF or IPTC support.

Non-Standard or 'Proprietary' Image Formats

There are a number of proprietary image formats. Any proprietary format is usually supported only by the manufacturer who invented that format. While other software and devices may know how to open them, you can't rely on this.

• .psd, .pdd, .eps - Adobe Photoshop
• .bmp - Microsoft Windows computers
• .pict - Apple computers
• .raw - originally a photoshop file type, but rapidly becoming a standard of its own due to the popularity of digital cameras.
• .cr2 - Canon raw file format used by the Canon 20D and others.

Some cameras support .bmp; most do not support any of the above formats.

Which file format is best? For a photography club member, the answer is usually JPG, unless quality of the image is important. If you are a professional, you will work strictly with the raw image data.

• Graphics File Format Summary