1- Information Representation Flashcards
Denary prefix
Denary Factor value
kilo (K) x10^3
mega (M) x10^6
giga (G) x10 ^9
tera (T) x10^12
Binary prefix
Binary Factor value
kibi (Ki) x2^10
mebi (Mi) x2^20
gebi (Gi) x2^30
tebi (Ti) x2^40
ASCII characteristics
- Only English
alphabets can be
represented - Each character
encoding takes up 7
bits, hence 128
possible characters - Smaller storage
space.
Extended ASCII characteristics
- ASCII’s extension -
Also includes most
European
languages’
alphabets - ASCII’s extension -
Also includes most
European
languages’
alphabets
UNICODE Characteristics
- Superset for ASCII
& extended ASCII -
recognized by
various global
languages - Greater range of
characters, as it
uses 2 or 4 bytes
per character - 2 or 4 times more
storage space per
character.
Bitmap Images Process
1.Data for a bitmapped image is encoded by assigning a
solid colour to each pixel, i.e., through bit patterns.
2.Bit patterns are generated by considering each grid
row as a series of binary colour codes corresponding
to each pixel’s colour.
3.These bit patterns are ‘mapped’ onto the main
memory.
4.Bitmap images also contain the File Header, which
has the metadata contents of the bitmap file,
including image size, number of colours, etc
Image resolution facts
Pixel density, which is measured by no. of pixels/cm
If image resolution increases, then the image is
sharper/more detailed
Screen resolution facts
Number of pixels which can be viewed horizontally &
vertically on the device’s screen
Number of pixels = width × height
E.g. 1680 × 1080 pixels
Colour depth facts
= number of bits used to represent the colour of a single pixel
An image with n bits has 2n colours per pixel
E.g. 16-colour bitmap has 4 bits per pixel ∵
Colour depth↑: colour quality↑ but file size↑
File Size = Number of Pixels × colour depth
Convert bits to bytes by dividing by eight if necessary.
Applications: scanned images and general computer
usage ∵ small file size and can be easily manipulated
How Vector Graphics work
-Made up of drawing objects
-The properties of each object are the basic geometric
data which determine the shape and appearance.
-Data is encoded using mathematical formulas to
generate properties in order to draw lines & curves to
create the image
-If object is resized, properties are recalculated.
- scalable without losing quality unlike bitmaps
How sound works
-Analogue signals converted (encoded) to digital
signals by sampling:
-Sound wave’s amplitude (height) sampled at set
time intervals
-These samples (amplitudes) are encoded as a
binary number sequence
-This sequence provides a digital representation of
the sound wave
-Increasing the sampling rate increases the accuracy
of digitized sound wave representation but increases
the file size.
-Increasing sampling resolution increases accuracy of
digitized sound wave but increases the file size
Lossless Compression
Type of compression that allows original data to
perfectly reconstructed from compressed file when
the file is opened by utilizing some form of
replacement.
E.g. bitmap (.bmp), vector graphic (.svg) and .png
images, text file compression, database records
Run-Length Encoding (RLE)
Form of lossless compression which is used for
compressing text files and bitmap images.
Reduces file size of a sequence of elements which
has adjacent, identical elements (characters in text
file and pixels in bitmap images).
Repeating sequence of elements encoded in two
values: run count and run value.
E.g. RLE of bitmap image:
We can represent the first row as a sequence of
pixels: “W B B W W B B W” | W: white and B: black
After applying RLE: “W 2B 2W 2B W”.
In ‘2B’ 2 is the run count and B is the run value,
which represents a run of two adjacent black pixels
Process is repeated for other rows.
Lossy Compression
Type of compression which irreversibly eliminates
unnecessary data
File accuracy/quality lower than that of lossless but file
size is lower (~10% of lossless).
E.g. Sound files (.mp3), .jpeg images
Sound files compression (.mp3) utilizes Perceptual
Coding to remove certain parts of sound that are less
audible/discernible to human hearing.
