Representation of Text, image and sound in computer

Q1.  Describe what is meant by File format.

• File format is a standard way that information is encoded for storage in a computer file.
• It specifies how bits are used to encode information in a digital storage medium.
• It tells the computer how to display, process, save and print the data by the application program which created the file.

Q2.  How file format is often recognized?

• File name contains two parts, the first part is the name of the file and the second part is it's extension (suffix) separated by dot. The extension name of the file indicates it's data format.

Representation of Text in computer

Q3.  Describ why we need to convert the data like text, image and sound into binary form for computers.

⇒  Computer is made up of silicon chips that contains millions of transistors or switch which could be in either 'ON' or 'OFF' state.

⇒  A switch in 'ON' state is represented by '1' and 'OFF' state is represented by '0'.

⇒  Computer can only understand these binary digits called Bits (1's and 0's).

⇒  Hence, everything that need to be processed by computer has to be converted into Binary format.

Q4.  When converting text to binary a character set is used.

a)  Describe what is meant by  Character set. 

⇒  A set of characters and symbols that can be represented by a computer system.

⇒  Each character and symbols is assigned a unique numerical value to represent it digitally in computers.

b)  Why do computers need character set?

⇒  To store textual characters used by human in computers.

⇒  To communicate and exchange text between different computer system.

Q5.  All data inside a computer is transmitted as a series of electrical signal that are either ON of OFF. Therefore, in order for a computer to be able to process any kind of data, including text, image and sound, they must be converted into binary form.

a)  Describe how Text, Numbers and Symbols are stored in Computer.

⇒  Each character is assigned an internationally accepted numerical value called ASCII code or UNICODE.

⇒  These values are stored in binary format to represent each character in computer.

b)  Describe  ASCII code  and its use.

⇒  ASCII stands for American Standard Code for Information Interchange.

⇒  It is internationally accepted 7-bit binary code (0 to 127 in denary or 00 to 7F in hexadecimal) to represent English alphabets, numbers and symbols found on a standard keyboard.

⇒  It could represent 128 possible characters including 32 control codes for control keys.

⇒  It provides the most common text file format like *.txt and *.html.

Note : Extended ASCII uses 8-bit code (0 to 255 in denary or 00 to FF in hexadecimal). It gives another 128 codes to allow for characters in non-English alphabets and for some graphical characters to be included.

c)  Describe  UNICODE  and its use.

⇒  UNICODE is Universal Character encoding standard, designed to represent characters of all languages around the world.

⇒  It uses 16-bit or 32-bit binary code which could represent 2¹⁶ or 2³² possible characters.

⇒  It is more efficient character encoding system than ASCII, used to store text files, web-pages and other types of documents.

⇒  It contains reserved part of code for private use to enable a user to assign codes for their own characters and symbols.

d)  Give difference between ASCII and UNICODE.

ASCII code	UNICODE
A character encoding standard for electronic communication, designed to represent english alphabets, numbers and symbols.	A computing industry character encoding standard, designed to represent characters of all languages around the world.
Stands for American Standard Code for Information Interchange	Stands for Universal Character Encoding
Supports 128 characters	Supports a wide range of 216 to 232 possible characters
Uses 7-bits to represent a character	Uses 16-bit or 32-bit depending on the encoding type
Requires less space	Requires more space

Representation of Images in computer

Q6.  Describe how  Bitmap images  are represented and stored in computer.

• Bitmap image is made up of tiny dots arranged in rows and columns called Pixel.
• A Pixel is the smallest addressable area of an image which is assigned a colour.
• Each pixel can be represented as binary number, and is stored in a series of binary codes.
• A black and white image requires only "one-bit" to represent a pixel, which could be either '1' for black or '0' for white colour.
• An image with 256 colour requires 8-bits to represent each pixel.

Q7. a)  State what is meant by  Pixel. 

• A Pixel is a Picture element.
• It is a smallest addressable area of an image.
• The basic unit used to define colour on a computer display or printed digital image.

b)  Describe  pixel dimension  of an image.

• Pixel dimension refers to the total number of pixels along an image’s width and height.
  Example, 640 x 480.

c)  Describe  resolution  of an image.

• Resolution refers to the density of pixels in an image.
• The greater the density, the greater the image sharpness and clarity.
• It is measured in pixels per inch (ppi) or dots per inch (dpi).

d)  Describe  Colour Depth  of an image.

• Colour depth is the number of bits used to represent the colour of a single pixel of an image.
• If an image contains 2^N colours, then ‘N’ will give the colour depth.

e)  How many bits per pixel would be required for an image with a palette of 256 possible colours?

• 256 = 2^N = 2⁸ ; N = 8
• Hence, Colour depth is 8 (number of bits required to represent a pixel).

Q8.  The example below show two digital photographs captured by different cameras.

A	B

a)  Describe why image-A looks better than image-B.

• The resolution of image-A is higher than image-B which contains fewer pixel to represent the image.
• The image-A contains large number of pixels, smaller in size and tightly packed, so it looks better.
• Whereas the image-B contains less number of pixels, larger in size and loosly packed, so it looks blurred or fuzzy or pixelated.

b)  Describe how does increasing the image resolution affect the file size.

⇒  Increase in resolution means increase in number of pixels or the density of pixel. As the number of pixels used to represent the image is increased, the size of the file will also increses.

c)  Explain the relationship between image quality and file size.

• Image quality depends on the resolution of an image.
• A higher resolution image has more pixels or more picture information.
• Hence increase in quality of image increases the size of file.

d)  State two factors that affects the file size of a bitmap image.

1. Image Resolution (or Pixel dimension) : Increase in number of pixels, increases the file size.
2. Bit depth (or Colour depth) : Increase in number of bit to represent a pixel, increases the file size.

Q9.  The example below show a small section of an image is zoomed in or enlarged.

A	B

a)  Describe why the enlarged image-B appears blurred.

• The resolution of image-B is decreased, because the number of pixels per inch (PPI) has decreased.
• Less number of pixels is made to occupy more space that increases the size of pixel to make it looks blurred or fuzzy.

b)  The image-A uses 24-bit RGB colour to be displayed on screen at a resolution of 250 x 400 pixels.

Construct an expression and calculate the file size of the image-A in KB (Kilobytes).

⇒  To find the size of an image file, you multiply the resolution of the image by the colour depth :

Size of image file (in bits)	=	width (in pixels) x height (in pixels) x colour depth
	=	250 x 400 x 24 bits
Size of image file (in bytes)	=	250 x 400 x 24	bytes
since 1 byte = 8 bits		8
Size of image file (in KB)	=	250 x 400 x 24		(Or)	250 x 400 x 24	approximately
since 1 KB = 1024 bytes		8 x 1024			8 x 1000
(1000 bytes approximately)
	=	292.97 KB		(Or)	300 KB	approximately

Q10. a)  Calculate the file size of 256 colour photo with dimension of 50x50 pixel.

256 Colour = 2⁸ Colour

Hence, Colour depth = 8 bits. (i.e. number of bits needed to represent 256 colours)

b)  What would be the file size if the photo is converted into Black and White.

Black and White means 2 colour = 2¹ Colour

Hence, Colour depth = 1 bits. (i.e. number of bits needed to represent 2 colours)

Q11. a)  Describe what is meant by  Metadata. 

• Metadata is a set of data that provides information about the contents of the file (like file headers, its profile, technical details, and copyright).
• It is embedded with the file in a way that can be understood by other software, hardware, and end users, regardless of the format.

b)  Give four examples of metadata.

• File header like title, subject, author, and creation date/time.
• File profile like dimension, resolution, colour depth etc.
• Technical details like file types, size, and type of compression.
• Copyright information about the file or copyright holder.

Q12.  Describe JPEG file format.

• A JPEG file is a bitmap image saved in a compressed graphic format standardized by the Joint Photographic Experts Group (JPEG).
• It is commonly used for storing digital photos and used by most digital cameras to save images.
• It supports up to 24-bit color and is compressed using lossy compression.

Q13.  Digital Images are of two types Bitmap (Raster) image and Vector image.

Give difference between  Bitmap  and  Vector Image .

✬   Bitmap (or Raster) Image : 

⇒  Bitmap image is made up of tiny dots arranged in rows and columns called Pixel.

⇒  It stores the details of each pixel, like its location, colour depth, etc. Hence, its size is much larger than Vector image.

⇒  When enlarged, it loses its quality due to increase in distance between the pixel (i.e. reduced resolution).

✬   Vector Image : 

⇒  Vector image uses geometrical formulas to represent shapes and images.

⇒  It stores the details of lines to be drawn from one node to another, hence its file size is much smaller than Bitmap image.

⇒  When enlarged, it does not loses its quality.

Bitmap Image	Vector Image

Representation of Sounds in computer

Q14.  Give difference between  Analogue  and  Digital Signal  with example.

✬   Analogue Signal : 

⇒  Analogue signal is a continuous value that keeps on changing over a time period, like temperature, pressure, wall clock etc.

⇒  Analogue is a real value which cannot be read accurately.

⇒  It is represented by sine wave.

✬   Digital Signal : 

⇒  Digital signal is a discrete fixed set of values like 1, 2, 3, 4, ... etc.

⇒  Digital is a discrete in nature which can be read accurately, like digital clock, calculator etc.

⇒  It is represented by square wave.

Red Colour wave : Analog Signal / Blue Colour wave : Digital Signal		Sound is in Analog, which is converted to Digital using ADC (Analogue to Digital Converter) because Computer don't understand Analogue.

Q15.  Sound waves are converted into digital by sampling.

a)  Describe what is meant by  Sampling. 

• Sampling is the process of recording the amplitude of sound digitally at a regular interval of time.
• Each measurement is then saved in binary format converting analogue signal to digital data.
• Number of samples per second is called 'sample rate' measured in hertz (1 hertz equals 1 sample per second).
• Higher sample rate means the samples will be closer together and will not miss the peaks and troughs of sound wave.

A Sound Wave being Sampled.

b)  Digital audio has a sample rate, sample resolution and bit rate.

Describe the following :

c)  Explain how the quality of sound recording on a computer could be improved.

⇒  The increase in Sample rate increases the sound quality, because the sound samples will be closer together and will not miss the peaks and troughs of sound wave.

⇒  The higher the Sample resolution, the better the sound quality, because more levels of sound details can be captured.

Note : CDs have a 16-bit sampling resolution and a 44.1kHz sample rate - that is 44100 samples every second. This gives high-quality sound reproduction.

Q16.  Give the benefits and drawbacks of using larger sampling resolution when recording sound.

Q17.  A 32-second sound clip is be recorded, sampled 1600 times a second. Each sample is be stored using 8 bits.

Calculate the file size in kilobytes. You must show all of your working.

Q18.  A typical, uncompressed high-quality audio file has a sample rate of 44,100 samples per second, a bit depth of 16 bits per sample and 2 channels of stereo audio.

a)  Calculate the bit rate of the audio file.

b)  Calculate the file size of 4 minute song with the above bit range in megabytes.

Q19.  Describe MP3 file format.

• MP3 stands for MPEG (Motion Picture Experts Group) Layer-III.
• It uses lossy compression to reduce the original sound by 90% without losing its quality; by eliminating the sounds which human ears cannot hear.
• It the most common audio file format that most digital player uses.