Part 1. Digital Imaging Theory

Digital Image Theory

Pixels

The name pixel derived from the combination of picture and element. A pixel is a single dot on a digital screen/video display system, and all digital imaging is made up of a collection of pixels, with each pixel being on or off, dark, being off and illuminated, being on, a turned on pixel will possibly be in colour. The number of pixels that can be on a digital image at any one time varies on the resolution of the screen itself. Some common resolutions include, 640x480, 1024x600, 1280x720, 1280x960, 1600x1200 and 1920x1080.

Types of Digital Graphics

Digital graphics comes in many forms and styles, the main types of digital graphics are raster images and vector images.

Raster Images, otherwise known as bit-mapped images, are a data assembly representing generally a square or rectangular grid of pixels, or points of colour, viewable on a screen, paper, or other display medium. The density of the dots on the screen is the image’s resolution, which determines how clear the image appears when it is printed on paper or viewed on a digital display. Resolution is often listed as the image’s dots per inch (dpi). A vector Image is the use of geometrical primitives such as points, lines, curves, and shapes or polygons, which are all built upon mathematical calculations, to signify images in computer graphics.

File Extensions

A file extension is a suffix for the name of a file stored on computers used to show the file format of its contents. Examples of filename extensions are BMP, PNG, GIF, JPG and PSD.

BMP is a bitmap image used in Windows. BMP images store graphics in a format called device-independent bitmap (DIB). The naming of this is because of the independence of the final output device. When a DIB image is output, for example being sent to a printer, the device driver will translate the DIB colours to colours the output device can display.

GIF is Graphics Interchange Format, a graphics imaging format which is supported by the web. With GIF format, you can compress files more as the GIF format only supports 256 colours. Therefore it becomes better than JPG (see below), for images with only a few colours. GIF also can support animation files, and transparency.

JPG or JPEG is Joint Photographic Experts Group, the original name for the group that originally wrote the standard. JPG like the GIF can be supported by the web, and is a lossy compression technique that is designed to compress colour and greyscale images. The information that is discarded within the compression is information that the human eye cannot portray. The JPG format can support up to 16million colours and is best used for photographs, and graphics that are complex.

PNG stands for Portable Network Graphics, is another graphics standard supported by the web. The PNG was developed as a patent-free to the GIF, however it also turned into an improvement for the GIF technique. Images in a lossless PNG can be 5-25% more compressed than a GIF image file of the same image. PNG builds on the idea of opacity in GIF images and allows the use of the degree of opacity. Saving, restoring and re-saving a PNG file image will not change the output or quality of the image, however unlike the GIF file format doesn’t support animation.

PSD is a Photoshop document, a PSD file format can be opened within Photoshop and can be edited and turned into a GIF, BMP, JPG, or PNG. Photoshop can support many layers of images, which can be merged/flattened to make a compete image, or exported individually to make its own image.

Compression

Lossy compression allows big reductions in file size by eradicating some of the data. Lossy compression classically attains far greater compression however reduced quality than lossless compression by shortening the complications of the data. A number of techniques are used to eradicate data with slight reduction in the quality of production. For many everyday listening situations, the loss in data is unnoticeable. The MP3 format is the most well-known example of this, however the AAC (advanced audio coding) format which can be found on the iTunes Music Store is also communal. Most formats offer a range of degrees of compression, usually measured in bit rate. The lesser the rate, the lesser the file and the more vital the quality loss.

Lossless compression is a compression technique in which no data is lost. WinZIP is a form of lossless compression which can compress a file without the loss of any data. Lossless compression can reduce the size of the file/ files by up to 50%. To compress data files and programs lossless compression is the only type of compression that works however lossy compression can compress only certain types of data such as graphics, audio and video.

MIP Maps

MIP mapping means “multim in parverm” which literally translates to “many in few” in Latin. MIP mapping is used in 3D graphics, it is used as textures for objects to give them a sense of realism. It is used to help stop pixilation and when the distance of the object is from the viewer the texture also has to change. Mipmapping carries out a function which uses many bitmap images to texture a map. This in turn means that when an object is further away from view the bitmap changes resolution to a lower resolution. This process was invented by Lance Williams in 1983, during the times when consoles started to appear in homes and video games started becoming more widely acknowledged. The MIP maps each have a several bitmaps which are altered versions of the original image or texture, the detail within each bitmap file will change and so does the image resolution. By using MIP maps the rendering time taken will decrease as unwanted texture pixels will not be needed. Thus MIP mapping makes the map a game is played on for example more efficient and quicker to render.