Multimedia Object - Image

Multimedia SystemImage

Nyoman Bogi Aditya Karna, ST, MSEESisfo IM Telkom

Image• Introduction• Compression• Types: GIF/JPEG

Sound• Introduction• Compression• Types: WAV/MPEG

Video• Introduction

• Compression• Types: MPEG

Multimedia Object

Lossy

• data might be truncated if it is not important

• based on human’s sense limitation (sight and hearing)

• example:JPEG and MPEG

Lossless

• data must be in the way it is (whole data is important)

• example:BMP, ZIP, GIF, Drive compression agent

Symmetric

• Compression process is the reverse algorithm from decompression process

• example:JPEG

Asymmetric

• Compression process is not equal to decompression process

• example:GIF

Compression

Image can be described as 2 dimensional data array (M x N) where each element (picture element or pixel) represents a function of light intensity f(x,y) (x and y represent spatial coordinate)

If

M = number of Column

N = number of Row

L = maximum intensity (gray level)

Then

0 x M – 1

0 y N – 1

0 f(x,y) L – 1

0 1 1 1 00 1 0 1 00 1 1 1 00 1 0 1 00 1 0 1 0

1 2 3 4 5

2345

1 Pixel

X

Y

Digital Image

0.001nm 400 nm10 nm 25000 nm 1 m 1000 m700 nm1 nm

Gamma Ray

UltraViole

t

X-Ray

Violet Blue Green Yellow Orange Red

400 nm 700 nm

InfraRed

MicroWave

Electronic Communicati

on

Color

All scanner devices scan an image pixel by pixel (dots per inch). Each color in every pixel must be converted (separated) to a specific color space used to determine the color. The most common color space used are RGB (red+green+blue additive primaries) and CMYK (cyan-magenta-yellow-black subtractive primaries) color spaces.Other Color Spaces :

grayscale 256 levelYCbCr or YUV (Luminance ChrominanceBlue Chrominance Red)

greenred

blue

cyanmagenta

yellow

black (CMYK) black (RGB)

Color Space

C = 1 – R R = 1 – CM = 1 – G G = 1 – MY = 1 – B B = 1 - Y

|C| |m1 m2 m3| |1 - R||M| = |m4 m5 m6| |1 - G||Y| |m7 m8 m9| |1 - B|

|Y | | 0.299 0.587 0.114 | |R| | 0 ||Cb| = |-0.1687 –0.3313 0.5 | |G| + |128||Cr| | 0.5 –0.4187 –0.0813| |B| |128|

Color SpaceTransformation

GIF• 1987 by Compuserve

• Lossless• LZW compression• 256 color max• Patented by Unisys• Transparency mode• Interlaced mode• Animated GIF mode• GIF 87 and GIF89a

JPEG• 1988 by Joint Photographic

(Picture) Experts Group• Lossy (quantization)• Huffman coding

compression• All color (no max color)• Free• No Transparency mode• Progressive mode• Motion JPEG• JPEG and JPEG2000

GIF vs. JPEG

Facts about GIF

• GIF, which stands for Graphics Interchange Format, is a lossless method of compression called substitution

• If the algorithm comes across several parts of the image that are the same, say a sequence of digits like this, 1 2 3 4 5, 1 2 3 4 5, 1 2 3 4 5, it makes the number 1 stand for the sequence 1 2 3 4 5 so that you could render the same sequence 1 1 1, obviously saving a lot of space

• It stores the key to this (1 = 1 2 3 4 5) in a hash table, which is attached to the image so that the decoding program can unscramble it

LZWcompression

RawImage

GIFImage

Graphics Interchange Format

About LZWLZW compression using a table-based lookup algorithm invented by Abraham Lempel, Jacob Ziv, and Terry Welch. Two commonly-used file formats in which LZV compression is used are the GIF image format and the TIFF image format. LZW compression is also suitable for compressing text files.

LZW ProcessLZW algorithm takes each input sequence of bits of a given length (for example, 12 bits) and creates an entry in a table (sometimes called a "dictionary" or "codebook") for that particular bit pattern, consisting of the pattern itself and a shorter code.As input is read, any pattern that has been read before results in the substitution of the shorter code, effectively compressing the total amount of input to something smaller.Unlike earlier approaches, known as LZ77 and LZ78, the LZW algorithm does include the look-up table of codes as part of the compressed file. The decoding program that uncompresses the file is able to build the table itself by using the algorithm as it processes the encoded input.

LZW Compression

Source Image

bitmap

114862 bytes

GIF 256 color

21821 bytes

GIF 128 color

17566 bytes

GIF 64 color

13553 bytes

Graphics Interchange Format

Joint Photographic Expert Group

Based on human’s sight limitation which can not see clearly a high-frequency part of the image

three types: arithmetic, standard, progressive

JPEG Encoding

Subtract

2n-1

Subtract

2n-1

Quantization

Quantization

Forward DCT

Forward DCT

Reordering(2-D-to-1-D)Reordering(2-D-to-1-D)

Image Codin

g

Image Codin

g

s(j)

Original subimage

sTable Look-

Up

Table Look-

Up

Table Look-

Up

Table Look-

Up

JPEG Decoding

Image Decodin

g

Image Decodin

g

Reordering(1-D-to-2-D)Reordering(1-D-to-2-D)

Inverse DCTInverse DCTs(j)

Table Look-UpTable

Look-UpTable

Look-UpTable

Look-Up

DequantizationDequantizationAdd 128Add 128

Recovered

subimages

JPEG

Source Image

bitmap

114862 bytes

JPEG 10

12995 bytes

JPEG 40

8052 bytes

JPEG 90

2886 bytes

JPEG

Source Image

bitmap

37854 bytes

GIF

JPEG 10

7701 bytes

JPEG

JPEG 40

4294 bytes

JPEG 80

2631 bytes

JPEG 65

3351 bytes

GIF vs. JPEG

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