Photo Size and Compression

On the Web today, GIF, PNG and JPG are the most common and widely-supported image file formats. But which should you use? The GIF and PNG formats are ideal for graphics that contain flat areas of plain color, transparency, as well as text. The JPG is ideal for photographs, as it is very efficient at compressing natural looking images. Another format occasionally seen is the BMP. Even though Internet Explorer will allow you to place an image as a BMP, other browsers may not be able to display it - simply, do not use it.

Images on a computer are not like photographs. Computer images are made up of a lot of little colored dots known as "pixels". The more pixels per inch the image has, the better they will look when printed. You're going to find that most images on the Web are 72 (72dpi) and 100 (100dpi) pixels per inch. Printed images are usually 300 (300dpi) pixels per inch.

IMPORTANT: Image size and file size are not the same thing. Your image size may be 400x350 and the file size may be 45k. Compression will affect the file size, not the image size.

The images below show the difference in file size and quality depending on what format you save your image in. Compressing your images is important if you have a lot of images on your page, or are using large photos - the smaller the size without loosing quality, the faster your page will load.

150x116 JPEG file - 19.1k save quality 100	150x116 JPEG file - 7.65k save quality 70	150x116 JPEG file - 3.37k save quality 30
150x116 GIF file - 6.55k 128 no dither	150x116 GIF file - 6.55k 128 dithered	150x116 GIF file - 2.4k web palette
150x116 PNG file - 16.3k 24	150x116 PNG file - 6.42k 128 dithered	150x116 BMP file - 51.2k *Image may not appear

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