You’ve taken some beautiful digital photographs and want to edit them in in your favorite graphics program. Once done, you click “Save As” and see a multitude of options in the drop-down menu labeled “Format.” There is “JPG, BMP, PSD, PNG, GIF and more. What do all of those file extensions mean? What is the best format for your purpose? This post will answer these questions.
There are two main types of computer images: Raster and Vector. Raster images are typically what most people deal with day to day. Raster images are made up of numerous tiny squares called pixels. Each pixel is a mixture of Red, Green, and Blue. The pixels combine to make an image, and usually can’t be seen. However, the more you zoom in on an image, the more “pixelated” it becomes. Vector images use mathematical equations (called algorithms) to create the image. Unlike Raster images, you can zoom in on Vector images and the edges don’t become pixelated. Popular programs that use Vector imaging are Adobe Illustrator and Corel Draw. In this post I’ll focus on different types of Raster images and their uses.
- BMP – Stands for “Bitmap”. It is an uncompressed image file format originally introduced by Microsoft for its Windows Operating System. This format stores information for each pixel in the image, therefore it is a large image file format and used mainly for print media. JPEGs and GIFs are compressed Bitmap formats that are better suited for use on the Web.
- GIF – Stands for “Graphics Interchange Format”, and was originally developed by CompuServe as a way to transmit images over a network or the Internet. The GIF format uses indexed colors, meaning that GIF images can contain a maximum of 256 colors. Use this file format for icons, illustrations, and small animated images, but not for high quality photographs. You can use GIFs on the web with a transparent background, making this image file format very versatile (such as for a an image of a logo on a background of a different color).
- JPEG – Stands for “Joint Photographic Experts Group” and is a compressed Bitmap. It has a “lossy” image compression, which means that each time you save it, a little more data is lost in compression; so, avoid saving a JPEG image multiple times. The JPEG image format has no restriction on the amount of colors used and is cross-platform compatible, therefore it is the best for transmitting high quality images on networks and the Internet.
- PNG – Stands for Portable Network Graphic. This format was originally created as an alternative to the GIF format. It compresses images with up to 48-bits for color and 16-bits for gray scale. However, PNGs do not support animation. Like GIFs, you can use PNG’s on the web with a transparent background.
- TIF (TIFF) – Stands for Tagged Image File Format and was introduced in the 1980s as an attempt to make image files universal across all computer platforms. Its main feature is that it uses “lossless” compression, meaning that no image data is lost when you save and re-save the image. TIF images are ideal for print media because they are high resolution.
- Camera RAW – This is an uncompressed and unprocessed image file usually taken by a digital camera. If you do not have image editing software that can process the RAW image format, it is advisable that you don’t take pictures in this format. Otherwise, refer to your camera’s instructions if you would like to shoot your pictures in the RAW format.
- EPS – Stands for Encapsulated Post Script. Post Script is a page description language and is used in conjunction with Post Script printers, which are printers that are able to read and render a Post Script document. EPS image files are designed for high resolution images intended for print, thus it is not suited for rendering images on the Web.
- PSD – Stands for “Photoshop Document” and is the proprietary file format for Adobe’s Photoshop image editing program. This file format can also be used in the GIMP program, which is an open source image editing program similar to Adobe Photoshop. This file format allows for much more than image data. It also stores layers, filters, adjustments, meta data, etc. If you would like to know more about the PSD format, see Adobe Photoshop’s support web page.
In addition to the file formats described above, computer image resolution requirements are different for the web and print publication. If you are publishing an image to the web, you want to focus on the lowest resolution you can obtain without distorting the image so that you can reduce page-load time. The conventional resolution for web is 72 dpi/ppi (dots per inch/pixels per inch). Any less than that will distort the image and anything more is considered too big for optimum download. The proper resolution for print depends on the printer, but standard practice is nothing less than 150 dpi/ppi. However, for all-around good quality, I use 300 dpi/ppi. Most desktop printers can print at least 600 dpi/ppi, but the difference between 300 and 600 is not noticeable to the naked eye.
Choosing the right image format can be a little confusing, but it’s really not that complicated. For more information on image formats you can visit the links below: