Raster Images

A raster image is used in a certain way to represent digital images and is quite often referred to as a bitmap. There is a wide variety of formats that a raster/bitmap image can be created in, including .gif, .tiff, .jpg, .png, .psd (Photoshop) and .bmp. The image contains many bits of information which then translate into pixels when displayed on the screen. The pixels then convert to form points of colour which creates the overall image.

Each pixel has been given a specific value that decides what colour that pixel is going to be. To assign a colour to the pixel, it uses a RGB (Red, Green and Blue) colour system. There are a total of 256 colour values to choose from allowing it to have a wide range of values.

In order to scale a raster image to a certain size, it all depends on the resolution of the image. If the image was to have a large resolution then it would be able to be viewed on a large scale without any of the pixels being on show. However, if an image had a low resolution, the larger that image got, the easier it would be to see the pixels in which it would be quite difficult to see the image. Below is an example of how pixalated the image is when zoomed in.

 

Raster compression is the process that reduces the size of a raster file resulting in saving space on any system. This can be done in a couple of way; a JPEG file format is a lossy compression method which is mainly used with full colour images and also grey scale images, however, this can lower the quality of the image as pixel values are lost. The other way is to use a LZ77 file which is lossless format where no pixel values are lost.