Multimedia Object - Image
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Transcript of 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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