Digital Images

There are two basic image types:

• Vector image.
• Raster image (pixelmap, bitmap).

Vector image

“Take a 100×100 mm sheet of paper. With a 3 mm wide green pencil draw a line from point [10,10] (a point 10 mm from left edge and 10 mm from bottom edge) to point [90,90]. Draw another line from [10,90] to [90,10]. Now take 10 mm wide red pencil and draw a circle with center at [50,50] and radius of 25 mm.”

Computer uses similar commands when storing vector images. And here is the result:

A vector image – note that the zoomed-in region is smooth.

Storing images using this method is effective if they are drawing or diagrams. It would be very hard to have a photograph stored as a vector image. Current internet browsers cannot display vector images on their own. They need an external SVG or FLASH plug-in.

The rest of this article deals with raster images, because they are what most users work with.

Raster image

Take a photograph and cut it to 1x1mm squares. Remember where each square was in the photograph and for each square choose one color that describes it best. Remember what color you assigned to each square. This is how raster image is stored.

Raster image – squares (pixels) are visible in the zoomed-in area.

Compare the zoomed-in areas in raster and vector images. While you simply see a larger circle and a larger line in the vector image, the raster image contains the mentioned squares – called pixels (picture elements). In case of raster image, we do not know that there is a circle and a line. This information was lost; all we have now is a bunch of colored squares. Therefore the zoomed-in region is not accurate.

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Vector File formats: 

 Raster File Formats:

Photos on most devices are stored as .jpg’s with varying percentage of quality.  For lossless digital storage, you can use .tif which many cameras have as an option.