Raster Images.

Raster Images:

Raster images are digitally created on screen or captured, it generally represents  a rectangular grid of pixels or points of colour which are viewable on a monitor , paper for example, (if an image has been scanned) or another display medium. In the compression of a raster image, ‘Lossy’ along with ‘Lossless’ are terms which describe whether or not original data can be recovered when an image is uncompressed. Lossless compression is includes every piece of data within a file remaining after the file is uncompressed and all of the data is restored. In comparison to this, Lossy compression results in losing data within a file, along with quality.  This usually occurs in file extensions such as JPEGS, BMP, and sometimes GIF, however it can depend on the GIF format. However, according to the book “Controlling Image Output”, it states that a GIF is usually in the compression of Loseless.

Image source: http://vector-conversions.com/images/raster_vs_vector_1.jpg