Sound travels in waves and its therefore analogue in form. To be stored in a computer, the analogue signal must be converted into digital form. The wave that is input through a microphone is sampled at regular intervals by an analogue-to-digital converter. This device measures the height of the wave at the time of sampling and stores this as binary code. The number of times that the wave is sampled for a given time period is known as the sampling rate. The more frequent the sampling, the more accurate the representation of the sound.
Data compression techniques are used to reduce the amount of storage space required.
Compressed Bitmap Files
Data compression techniques are used to minimise the amount of storage space needed for graphical images. The Joint Photoghic Experts Group (JPEG) has defined standards for graphical image compression. JPEG is now commonly used format.
Direct Data Capture
Direct Data Capture is the collection of data for a particular purpose. Examples of direct data capture are:
- Reading barcodes at a till so that the product is identified
- Account details being read directly from the chip embedded in a credit card
- An MICR device automatically reading the number on the bottom of a cheque
- Data from an automatic weather station being downloaded into a computer.
What is Information?
Information is data that has been processed and given a context which makes it understandable to the user.
Information is siad to be of good quality if it is accurate, up to date and relevant for a particular use.
A bitmap is the binary stored data representing an image. A picture is broken up into thousands of tiny squares called pixels. The number of pixels stored for a given area determines the resolution of the image. The more pixels that are used per square unit, the greater the resolution of the image. The greated the resolution of the image, the more memory is required to store its bitmap.
Each pixel is allocated a number of bits in the bitmap to represent its colour. the more bits allocated to each pixel the greater the choice of possible colours.
Bitmapped graphics can be created by using a drawing package where individual pixels can be set or lines "Drawn". this is achieved using some kind of pointing device to modify an image displayed on a screen. An image can be input using a scanner or a digital camera. A software package can then be used to modify the image.
Indirect Data Capture
Indirect Data Capture is the collection of data as a byproduct from another purpose. Examples of indirect data capture are:
- Using data from reading bar codes at a supermarket till to work out stock levels
- Using records of transaction generated at a store when a customer uses a loyyalty car to build up a profile of that customer.
How data can arise?
Data capture means the collection of data to enter into a computer. Data can be input into a computer in a variety of ways depending on the source:
- Speech recognition
- Touch screen
- Bar-code scanners
Data can be capture Directly or Indirectly.
A mordern computer must store data of many types. When data is input into an ICT system it has to be converted from its current form into a form that can be processed digitally. This means that it has to be represented by a binary code made up of binary digits which can be written as either 0 or 1.
The term "Encoding Data" means putting the data into an appropriate binary code.
The following are examples of files stored in the computer in binary code:
- Text such as DOC files
- Digital picture, such as Bitmap, JPG or GIF files
- Digital videos, such as MPG or AVI files
- Sound files, such as WAV or MP3 files
Different binary codeing systems are used to represent different types of data. The smallest unit of storage is a bit. A bit can be in two states, 0 or 1
Computers store numbers, as all other data, in binary coded form. There are three main ways of coding the numbers that we use:
- Integers are whole numbers. When integers are stored in a computer, the number of bits assigned to the code determines the range of numbers that can be stored. The coding can be designed to store negative as well as positive integers. Integer arithmetic provides fast and accurate results; problems only occur if a calculation results in an integer that is too large to be stored in the number of bits assigned to the code.
- A Real Number is a number that can have a fractional part. Unlike integers, real numbers can rarely be stored exactly in the bits assigned to store the number. Whatever you write will not be exact; the representation of real numbers in a computer always involves some loss of accuracy. Performing calculations on real numbers is a more complex operation than performing calculations with itegers and therefore slower.
- in systems where fractional values are needed but where accuracy is very important, such as when data is representing money, then a third form of coding can be used. There are a number of appliactions where numbers that represent cureency values are stored in a special format.
Coding Data - Why?
Codes are used because:
- They are often easier to remeber
- They are usually short and quick to enter - fewer errors made
- They take up less storage
- They ensure that the data stored is consistent
- It is easier to check that data is valid if the range is limited.
Data has to be processed to produce information. A code is used to represent the data to allow processing to be more effective and to produce more useful information for the user. Common examples are:
- Gender is stored as F or M
- Banks use branch sortt codes such as 60-18-46
- Date of births
Increasingly, computers are used to manipulate, store and display non-textual images. For example a photograph can be downloaded from a camera, stored and used on a web page. Computer games can contain complex graphical images. Indeed, the most commonly used interfaces on a personal computer are made up of graphical images in the form of icons. These pictures also have to be stored in binary code form.
There are two main ways in which images are stored: either as bitmapped or vector graphics
Problems associated with Bitmapped graphics
- Bitmapped graphics can be difficult to edit. For example, if a line needs to be redrawn, the pixels in the deleted line have all be changed to the background colour and the pixels that make up the new line have to be changed too.
- Image quality can be lost if enlargement takes place as the size of the pixels is increased and the resolution of the image is reduced.
- Distortion can occur if the image is tranferred to a computer whose screen has a different resolution as pixels can be elogated in one direction.
- A large storage space is required to store the attributes of every pixel
Data made up of words or symbols is stored in text or character form. The word processor is the most common software package that processes text data.
Each character (including spaces) that can be used is assigned a unique binary code. Standard codes have been agreed so that data can be transferred and correctly interpreted between two ICT systems.
The most widely used character coding system is ASII (American Standard code for Information Interchange). A character coded in ASII is made up of 8 bits. The 8th bit acts as a check bit to help ensure that any corruption of data is detected. The other seven bits can produce 128 unique codes, each a different comibination of 0s and 1s.
Animations consist of a number of images or frames stored together and displayed one after the other. The more frames and the smaller the change between frames, the more realistic is the effect of the animation. An animation stored as GIF files can take up considerable storage space.
The MPEG file format uses a method of compression for video information in a similar way to that used in JPEG files for single images. MPEG files also allow a soundtrack. In spite of the size reduction resulting from compression, even a short piece lasting only a few minuets wil have hundreds or thousands of frames and so the file size is likely to be larger.
What do we mean by Data?
The term "Data" means recorded facts - usually a series of values produced as a result of an event or transaction. For example, if i buy an ietm in a supermarket a lot of data in the form of facts is collected such as:
- My loyalty card number
- The identity numbers for each item bought
- The weight of apples to be purchases
- The number of the credit card used to pay for the goods
All this data has been generated by an Event. If i pay a cheque into my bank account, this is an event that collects a record of the transaction. The record might contain details such as:
- My bank account number and sort card
- The amount of the cheque
The meaning of the data may not be obvious, items of the data may not be much use to a person however data is very useful when its processed to create information.
Up To Date
If information is out of data, then wrong decisions can be made. It is very important that all reports produced include a date so that the person recieving it knows how old it is.
Information has to be up to date to be useful. Keeping the information up to date affects the costs of producing the information. The cost arise from the need to:
- Collect up-to-date data
- Enter the data into a system
- Delete out-of-date data
Traditionally many computer systems operated in batch mode, in which data was collected over a peroid of time before processing took place. The information then produced was only as up to date as the most recent processing run. Transaction Processing system update with new data as it arises, processing each change as it occurs. Information produced from a transaction-processing system is always as up to date as possible.
How accurate it needs to be will depend upon the use being made of information. For example, the informayion in a bank statement must be exactly right to the nearest penny otherwise the account holder could make inappropriate decisions over spending and would be fully justified in complaining to the bank.
The accurate information is very important. For example inaccurate stock figures may cause a store manager to re-order the wrong amount. This could result in items not being avaliable for costumers or too much stock being held which would take up extra space and tie up capital.
Information that is essential in one situation may have no use in another. For example, information intended for a branch manager of a supermarket, showing checkout till usage to allow them to allocate staff over a weekly perios, would not be of use to the regional manager wanting to see the efficiency of all branches.
For applications such as computer-aided design (CAD), where high precision is requires, bitmapped graphics are not appropriate. With vector graphics, the image is stored in terms of geometric data. For example, a circle is defined by its centre, its radius and its colour.
Vector graphics enable the user to manipulate objects as entire units. For example, to cahnge the length of a line or enlarge a circle, the user simply has to select the chosen object on the screen and then strech or drag the image as required. The bitmapped graphics requires individual dots in the line or circle to be repainted. Using vector graphics, objects are described mathematically so they can be layered, rotated and magnified relatively easily.