Unit 2 Text and Image Processing

Question 1

Types of text:

Answer 1

1. Unformated text (plain text, ASCII character code)
2. Formatted text
3. Hypertext

Question 2

Text file formats

Answer 2

File formats are application specific
TXT - plain text document without much formatting options

DOC - created by document editing softwares like Microsoft word and is in binary format

RTF - Rich Text Format using Microsoft

PDF - Portable Document Format (binary format)

PS - Post Scripts (programming language the defines look of a printed page)

Question 3

What is meant by text compression?

Answer 3

Reducing the size of a text document without changing the contents of the document while storing on a disk

Question 4

Components of a compression technique:

Answer 4

Encoder
Storage or network
Decoder

Question 5

What is the compression ratio?

Answer 5

The ratio of the total number of bits required before compression to the total number of bits required after compression

Question 6

What is Huffman coding?

Answer 6

Instead of fixed sized code words variable length code words are derived such that the shortest code words are used for the words occurring frequently

Question 7

What is the requirement of Huffman coding?

Answer 7

Used in applications where the text to be compressed has some known characteristics in terms of characters and their relative frequency of occurrences

Question 8

Applications of Huffman coding

Answer 8

Fax machines, JPEG, MPEG

Question 9

Image file formats

Answer 9

BMP - lossless, developed by Microsoft
TIFF - lossless file format, high quality, large size
JPEG - lossy, small size
GIF - lossless compression, larger size than JPEG, limited color range(256 colors)
PNG - lossless, support 16 million colors

Question 10

Run–Length–Encoding (RLE)

Answer 10

• Applied across a sequence of characters
• Sequence contes repetition of characters
• Main idea is to replace the repetition of character by the frequency count of occurrence of that character
• Can easily encode images which are binary that is only black and white with continuous regions
• Can be used for two dimensional image data for every row

Question 11

Shannon-Fano Algorithm

Answer 11

• It is a variable length coding (VLC) method, codewords generator is variable
• Uses top-down approach
• can be implemented using binary tree

Question 12

Arithmetic Coding

Answer 12

• Modern coding method that outperforms Huffman coding

Question 13

Vector Quantization

Answer 13

• Lossy compression
• Algorithm:
  1. Vectorisation
  2. Codebook generation
  3. Encoding
  4. Decoding
• Key points: Variable bitrate, vector size and complexity, codebook design

Question 14

Fractal Compression technique

Answer 14

• Depends on the concept of fractals
• Algorithm:
  1. Partition (image divided into smaller non overlapping blocks or regions)
  2. Iterative Matching (affine transformations)
  3. Error calculation (differences in pixel values)
  4. Encoding (parameters of transformation and errors)
  5. Decoding (application of inverse transformation)

Question 15

Transform Coding

Answer 15

• Lossy compression technique
• Algorithm:
  1. Dividing image into blocks
  2. Apply transform like DCT(discrete cosine transform) on each block to generate transform coefficients
  3. Quantization
  4. Encoding (any symbol encoding algorithm is used)
  5. Decoding entire above process reversed
• Used for JPEG compression

Question 16

What is image processing?

Answer 16

It is the manipulation and analysis of visual information contained in an image.

Question 17

Elements of image processing:

Answer 17

Acquisition - capturing visual information from real world and convert it into digital form

Storage - storage of acquired digital information of image for later retrieval and processing

Communication - transfer of image from one location or system to another

Display- rendering digital image data on a visual output device

Enhancement - improvement of the visual quality or image data to make it more suitable for analysis and interpretation