Digital Imaging Introduction

Make-up of a digital image

Most digital images you see on the Internet are either JPEG or GIF format. These formats, along with some others, are known as "raster" images, and they are made up of colored squares called "pixels."

When we refer to "resolution" we are referring to the number to pixel wide and the number of pixels high an image is. Images with higher resolution can be viewed larger without seeing the individual pixels of the image.

Digital Image Formats

JPEG

(Joint Photographers Expert Group)
  • This format is best with digital photographs and images that have complex color make-ups like scanned photographs, etc.
  • Results in unnecessarily large file sizes on images with few colors
  • JPEG images can use millions of colors to make up an image.
  • JPEG images can be saved at different "quality" settings that will effect the appearance of the image on screen or when printing.

GIF

(Graphics Interchange Format)
  • GIF images can only use a maximum of 256 colors and a minimum of 2 colors.
  • When saved, the color pallet of GIF images can be reduced to remove unused colors and result in a smaller file size.
  • GIF is best for images like logos, buttons, etc., but does not result is very good photographs.
  • Some software can produce "animated GIFs" in which a series of GIF images are combined into one file. When displayed, they are displayed in series like a flip-book animation.

Examples

Photograph

JPEG Format, Medium quality Setting

File Size: 12K
  Notice that the file size for this image is 1/3rd that of a GIF of the same image. Plus the image is much clearer. Because JPEGs can use million of colors, they can result in good photographs with smaller file size. However on other images that are not a complex color-wise, GIF is better because the palette can be reduced to use fewer colors, with no visible loss to the image.

 
Photos by Alison Meyer, a fantastic photographer of the Palouse and other Inland Northwest areas

Photograph

GIF Format, 32 Colors

File Size: 37K
  Notice the shading problems in the sky are of the photograph. This is a result of the limits colors, in this case 32 colors. For photographs, GIF will often result in larger files with lower quality. However, for other items like buttons, logos, etc., GIFs can produce simpler and smaller files. Most of the other images displayed on this web page are GIFs because of the smaller file size.