Raster images or bitmaps: are formed by many points that, as a whole, define the final image; each of these points has specific colour, luminosity, contrast…The image files contain the information of the image in a dot matrix (pixels), so-called raster. When you save a bitmap image on a file, the characteristics of all points are stored.  • Vector images: the images are created using lots of vectors or individual objects, each of which has its own definition (size, type of line, colour, fill, etc.). The vector image files store the definition of all their components through mathematical expressions; this makes, commonly, this type of images has a size smaller than the bitmap type. • 3D images: such images may be created with different techniques, but its purpose is always to transmit the projection of something visual in three dimensional space; they are usually linked to animated pictures or animations. • Animated pictures (animations):are a first approximation to videos, since allow transmitting a running sequence, but without sound.
The quality of an image depends on several factors: • Number of points (pixels) that compose it; the larger the number of points used in the image, the better quality it has, since each point will be smaller and the image will be shown with more detail. • Colour depth: refers to the number of colours that has the image, and the larger it is, the more shades it has. 
• Compression of information: when saving a bitmap image on a file, the information of each of their points or pixels is stored, consequently the file size is very big. To avoid it, the most of the graphical formats use some compression method, which implies a loss of quality to a greater or lesser extent. 
A sound wave is expressed as a sine function with the following parameters: • Amplitude: indicates the intensity of sound and is measured in decibels (dB). Noise levels above 85 dB can be dangerous its continuous exposure causes hearing damage. • Wavelength: is the separation between the crests of the wave and indicates the true distance that the sound travels over a time period. • Frequency: is the number of oscillations per second. The more frequency, the lower wavelength. High frequencies are translated into high-pitched sounds and low frequencies into bass sounds. Frequency is measured in Hertz (Hz). • Spectrum: represents the intensity of sound for each one of the frequencies
The digitalisation of sound consists of the conversion of the analogic wave into digital values that a computer system can interpret. To make this process, a microphone that converts wave sounds into electrical signals is used. Then, the sound card performs the analogue/digital conversion. In order to listen the digital sound the inverse process has to be made, that is to say, the digital/analogue conversion. This conversion is made by the sound card, amplifying the sound to the levels needed for vibrating the speaker cone that will again generate the sound waves which can perceive the human ear. The digitalisation process takes place in three phases: Sampling consists of taking samples periodically from the original sound at regular intervals. The number of samples that are taken in about a second is called sampling frequency and is expressed in Hertz (Hz). 
Phase 2; quantification of the analogue signal: Quantification consists of assigning to each sample a numeric value. The smaller the interval between the possible values, the more approximate the measurement will be. If the value of the sample remains 
phase 3: binary coding
Uncompressed formats MIDI (Music Instrument Digital Interface). Communication protocol between the computer and other electronic music devices , being the most used in musical composition. CD-A or CDDA (Compact Disc Digital Audio). Uses as support the optical disc  where the recording is carried out through a laser beam. Is a high quality non-compressed format WAV (Waveform Audio File). Microsoft´s format that is normally used in Windows for storing sound in different resolutions and sampling rates. Is not very popular on the Internet because the files are very large. Lossless compression formats FLAC (Free Lossless Audio Codec). Is an free-licence open format. Allows compressing an audio file up to half of the original size and decompressing it into a file identical to the original one. AIFF (Audio Interchange File Format). Developed by Apple, can be distinguished by its fast signal processing, 
Lossy compression formats MP3 . One of the most popular formats due to its sound quality and small size. . Ogg Vorbis. Free open format, based on the public GNU licence. Can multiplex independent channels for audio, video, text and metadata.  WMA (Windows Media Audio). Audio compression technology,. Real Audio. Widely used around Internet because of its real time playback without generating an audio file, for instance, on an online radio station. This format is often associated with the RealPlayer audio player. AAC (Advanced Audio Coding).