These will convert an audio signal into a digital form that can be stored and processed by a computer.
Video Digitisers
These will convert a video signal into a digital form that can be stored and processed by a computer. These are useful for capturing pictures of three dimensional objects.
Scanners
These will convert an image on a flat sheet of paper into a digital form that can be stored and processed by a computer.
The speed, resolution, data transfer rate and connecter interface are essential features of a scanner.
How a scanner works
For a black and white picture the scanner measures the reflected light from each position on the paper (Say at 100 dots per inch). If the reflected light is above a certain level the dot is assumed to be white which is recorded as the digit 1.
If the reflected light is below the certain level the dot is assumed to be black and recorded as the digit 0. The picture is thus made up of a string of 0’s and 1’s like 01101101110011010101100. This is in digital form.
For a grey scale picture each dot may be one of several different shades of grey and this cannot be represented by just 0’s and 1’s is used to represent a shade. So for example
11111111= White
11111110= Light grey
…………
00000001= Dark grey
00000000= Black
Using an 8-bit code like the one above gives us 256 different possible codes and so 256 possible shades of grey.
For a colour picture a similar technique is used. Normally 3 different lights are shone on the picture and the reflected light from each is used to measure the colour value.
Different colours are then represented using a collection of 0’s and 1’s as above. An 8-bit code will give us 256 colours. A 16 bit code will give us 65536 colours.
Data capture
Input methods that use a keyboard usually involve the transcription of the source data from the source document. This process clearly creates extra work, and if verification is employed to reduce errors made during transcription then the workload and the time taken is increased still further
Documents readers are an automated method for putting data from the source document without the use of a keyboard.
In most cases the data will be read by the document ready and stored on magnetic tape or disc ready for batch processing.
Optical Mark Reading (OMR)
Here the marks are detected optically measuring reflected light. The readers use CLOCK MARKS to determine which areas of the card to read, so the cards can vary in size and in format. Coding methods need to be employed to allow the marks to represent different types of data so the range of the data that can be represented is limited.
The original source document can be pre-marked by the computer so that turnaround documents can be used (i.e. Documents that are produced by the computer, have some information added and then are re-input to the computer). Special care needs to be taken over correction procedures so that badly marked or damaged documents do not cause confusion in the system.
Advantages Disadvantages
-Fairly reliable - Unsuitable for alphabetic data
-No special marking equipment needed
-Can be used for turnaround documents
Optical character recognition (OCR)
Here carefully produced characters can be read by the machine. It is possible for documents typed on a normal typewriter or computer printer or even carefully hand printed documents to be read. The reliability of the reading depends on the clarity of the shape of the characters. The reader will expect a particular design of character (font) to be used.
OCR is now quite common, and examples of OCR turnaround documents may be found on Gas and Electricity bills where the bill has figures printed on by the computer which can be read by OCR and enable the transfer of funds to take place.
Advantages Disadvantages
-Natural method for non-technical users -Cost of OCR readers
-Data may be read by people -Not as reliable as OMR
-Careful hand printing may be used
Magnetic Ink Character Recognition (MICR)
Here the characters are printed in special ink, which may be magnetised.
Fonts used enable accurate reading of data.
The typical example of this is it is used on bank cheques.
Kimball tags
Commonly used in fashion shops
Bar Codes
Commonly used in supermarkets
Magnetic Strip
Used for credit cards
Voice Recognition
Not yet good enough to become widely adopted
Handwriting Recognition
Progress being made on this but mainly used in specialist applications and with something other than normal handwriting e.g. PDAs.
