Raster Images are a kind of computer graphics made of a matrix of tiny dots called pixels. Each of these pixels have their own color values and are arranged in a specific pattern to form an image. This image is then viewable via a particular medium such as a computer screen or a sheet of paper. High resolution photographs are always formatted as raster images. Their complex color profile (even black and white photos have many tones) makes it impossible to non-destructively format them with vector paths.
Raster images, also known as bitmap images, are made of many small squares called pixels. As the name bitmap suggests, these dots (also referred to as bits) are mapped precisely throughout the document to form an image. Raster graphics can be identified by zooming in closely and observing the appearance of each pixel. If the image is enlarged enough, the square pixels will become visible. If the image is magnified past a certain point, it will appear distorted and blurry. This occurs because raster graphics are designed to be accurately viewable only at 100% or less magnification. If the magnification exceeds 100%, the image quality will erode. Raster graphics are not scalable beyond their origin size.
Raster graphics typically have larger file sizes than their vector counterparts. Higher DPI (dots per inch) and PPI (pixels per inch) settings also contribute to larger files because any given viewing software must keep track of each pixel. File size can become a concern if storage space is limited or if files have to be transmitted electronically.
The main disadvantage of raster graphics is its lack of scalability. Raster graphics can be scaled down with little to no loss of quality. However when scaled above their origin size, the pixels wont map on the document accurately. As a result, the rendering software has to estimate a comparable position for each dot. This leads to images that can have blurry lines or distortions. Vector graphics, on the other hand, are able to scale up infinitely without any loss in image quality.
A raster image can be difficult to modify without loss of information. However, they can be edited by changing the color values of the individual pixels they are made of. This is may be done using raster graphics editing softwares such as Adobe Photoshop. In most cases, the entire image is adjusted. For example a picture might be edited by increasing its exposure, which has the effect of lightening the image.
Raster is the most common format for high resolution photography. When photos are taken with a digital camera or copied on a scanner, the resulting files are raster images. Raster Images are typically avoided in creating and working with logos and illustrations that are meant to be scaled and used for different applications. In some instances however, a raster image can be used effectively with logos, especially if there the logo is an image rather than text or a shape.