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SPEECH AND IMAGE PROCESSING LAB
Image file formats
Blessin Joseph & Pilmy PeterM.Tech Signal Processing
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
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INTRODUCTION
Image file format
Provide a standardized method of organizing and storing image data.eg: JPEG, TIFF, PNG, GIF
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bmp file formatgif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
List of File Formats
List of File Formats
1 BMP
2 GIF
3 PNG
4 JPEG
5 TIFF
6 PCX7 XBM
8 PPM
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bmp file formatgif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
BMP File Format
Short for bitmapped graphics format.
Simple graphics file format.
Usually not compressed.Unsuitable for transferring images on the Internet or other slow orcapacity-limited media.
Features
File extension : .bmp or .dibType : image
Type code : BMP
Developed by : Microsoft
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bmp file formatgif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
BMP File Format contd...
File Structure contains blocks of data.1 Bitmap Header : General information about the file.
2 Bitmap Information : Detailed information about the image.
3 Color Palette : Details of colors used for indexed color bitmaps.
4 Bitmap Data : Actual image in pixel by pixel.
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bmp file formatgif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
BMP File Format contd...
Bitmap header structure
Bitmap information structureapplication detailed information to display the image on the screen.
Matches the header used internally (Windows and OS/2) & hasdifferent variants.
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bmp file formatgif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
BMP File Format contd...
Color palette
Each pixel stored using one or more bytes.
Tells the application the actual color that each pixel corresponds to.
Uses RGB color model.
Number of entries - number of colors used in the picture (4 bytes -Windows & 3 bytes - OS/2).
Color palette is not used when the bitmap is 16-bit or higher.
Bitmap dataBottom left corner - left to right - row by row (bottom to top).
In a horizontal line, number of bytes not divisible by 4, then padwith null-bytes.
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bmp file formatgif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
GIF File Format
Short for Graphics Interchange Format.
Lossless data compression.
Palette up to 256 distinct colors from the 24-bit RGB color space.
Supports animations.
Features
File extension : .gif
Type : bitmap image formatType code : GIF
Magic : GIF87a/GIF89a
Developed by : CompuServe, 1987
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bmp file formatgif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
GIF File Format contd...
Two versions: 87a & 89a(GIF87a and GIF89a).
Distinguished by the first six bytes of the file.
GIF89a : Support multiple images in a stream.
Suitable for sharp-edged line art (logos).
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pgif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
PNG File Format
Short for Portable Network Graphics.
Lossless data compression.
Created to improve upon and replace the GIF format.
Supports palette-based (24-bit RGB) or greyscale or RGB images.
Designed for transferring images on the internet, not professionalgraphics.
Features
File extension : .png
Type : lossless bitmap image format
Type code : PNGf
Developed by : PNG Development Group, October 14, 1996
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gif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
PNG File Format contd...
PNG header structure
Chunks
Compatibility with older versions.
Chunk have header specifying their size and type.
Immediately followed by the actual data & checksum of data.
4 letter case-sensitive name.
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bmp file format
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gif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
PNG File Format contd...
Color depth
Use palette-indexed color or made up of one or more channels.
Number of channels depends on greyscale or color & alpha channel.
Animation
MNG : An extension to PNG - supports animation.
More complex than PNG.
APNG : Based on PNG, supports animation and is simpler thanMNG.
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
bmp file formatif fil f
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gif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
PNG File Format contd...
Comparison with GIF
Greater compression than GIF.
Wider range of color depths than GIF.
GIF supports animation while PNG does not.
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gif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
JPEG File Format
Short for Joint Photographic Experts Group.
Lossless & Lossy compression.
Storing and transmitting photographs on the World Wide Web.Not suitable for line drawings and other textual or iconic graphics
Features
File extension : .jpeg, .jpg, .jpe
Type : image/jpeg
Type code : JPEG
Developed by : Joint Photographic Experts Group, 1992
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
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gif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
JPEG File Format contd...
JPEG codec
Encoding
Color space transformation: RGB into YCbCr.
Downsampling/ Chroma subsampling : Reduce the Cb and Crcomponents.
Block splitting: Each channel splitted into 88 blocks(pixels).
Discrete cosine transform: Each component of each 88 blockconverted to frequency-domain.
Quantization: Divide each component by a constant for thatcomponent, & round to the nearest integer.
Entropy coding: Arrange image components in zigzag order - RLEalgorithm - Huffman coding.
Compression ratio and artifacts: Compression ratio can be varied by
varying divisors used in the quantization phase.Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
bmp file formatgif file format
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gif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
TIFF File Format
Short for Tagged Image File Format.
Lossy and lossless compression.
For high color depth images.
Supported by Adobe Photoshop, GIMP, Corel Photo-Paint.
Format for raster graphics.
Features
File extension : .tiff, .tifType : image
Type code : TIFF
Developed by : Aldus, now Adobe Systems, 1980
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
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gif file formatpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
TIFF File Format contd...
Flexible and adaptable file format.
Used as container for JPEG and RLE compressed images.Useful method for archiving images.
Begins with 2-byte indicator of byte order: II for little endian andMM for big endian byte ordering.
Following 2 bytes represent the number 42.Composed of small descriptor blocks containing offsets into the file.
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
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gpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
PCX File Format
Short for Pacific Exchange.
Lossless bitmap image format.
Uses simple form of run-length encoding.
Supports palette-based and 24-bit RGB images.
Features
File extension : .pcxType : lossless bitmap image format
Developed by : ZSoft Corporation.
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gpng file format
jpeg file formattiff file formatpcx file formatxbm file formatppm file format
PCX File Format contd...
File Format
Device-independent bitmap image format.
File header stores information about the display hardware.
Compressed using run-length encoding.
MSB used as control flag - whether given data represents a singlepixel of a given palette index or color value / RLE pair - a series ofseveral pixels of a single value.
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
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png file formatjpeg file formattiff file formatpcx file formatxbm file formatppm file format
XBM File Format
Short for X BitMap.
ASCII monochrome image format.Stores cursor and icon bitmaps used in the X GUI.
Can be compiled directly into an application without anypreprocessing steps.
Data appears in headers & consist of series of static unsigned char
arrays containing the monochrome pixel data.Image data consists of a line of pixel values stored in a static array.
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
bmp file formatgif file format
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png file formatjpeg file formattiff file formatpcx file formatxbm file formatppm file format
PPM File Format
Short for Portable Pixmap file format.
PPM, PGM, PBM specify rules for exchanging graphics files.
Features
File extension : .ppm, .pgm, .pbm, .pnm
Type : Image file formats
Developed by : Jef PoskanzerExtended to : XPM
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DFT
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Transforms
DFTDCTHadamard TransformWavelet Transform
Transforms
DFT, DCT, Hadamard Transform, Wavelets
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
DFT
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DFTDCTHadamard TransformWavelet Transform
DFT Transform
Short for Discrete Fourier Transform.
Expresses i/p fn. as sum of sinusoidal components.
Input function is discrete and finite.
Used to analyze the frequencies contained in a sampled signal, tosolve partial differential equations, & to perform convolutions.
Computed using fast Fourier transform (FFT) algorithm.
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
I d iDFT
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DFTDCTHadamard TransformWavelet Transform
DFT Transform contd...
2D - DFT
v(k, l) =
m
n u(m, n)W
kmN W
lnN , where k,l=0,1..N-1
2D - IDFT
u(m, n) = 1
N2 kl v(k, l)WkmN WlnN , where m,n=0,1..N-1
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
I t d tiDFT
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DCTHadamard TransformWavelet Transform
DFT Transform contd...
PropertiesInvertible linear transformation.
Orthogonality condition is satisfied.
Parsevals theorem is satisfied.
DFT sequence is periodic.
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DCTHadamard TransformWavelet Transform
DCT Transform
Short for Discrete Cosine Transform.
Fourier-related transform.Uses only real numbers.
8 standard DCT variants.
The DCT-II - for lossy data compression - energy compactionproperty.
Used in JPEG image compression, MPEG, and video compression.
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DCTHadamard TransformWavelet Transform
DCT Transform contd...
2D - DCT
c(k, l) = (k)(l)
mnx(m, n) cos
(2m+1)
2N k
cos
(2n+1)2N l
,
where k,l=0,1..N-1
2D - IDCT
x(m, n) =
m
n (k)(l) c(k, l) cos
(2m+1)
2N k
cos
(2n+1)2N l
,
where m,n=0,1..N-1
(k) = 1N
, for k=0
=
2N
, for k=1,2,..N-1
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DCTHadamard TransformWavelet Transform
Hadamard Transform
Known as Walsh-Hadamard transform, Walsh transform, orWalsh-Fourier transform.
Named after the French mathematician Jacques Hadamard.
Equivalent to a multidimensional DFT of size 2 x 2 x ...x 2.
Takes only binary values 1 - no multiplications required intransform calculation.
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List of file formatsTransforms
DCTHadamard TransformWavelet Transform
Hadamard Transform contd...
Hadamard transform Hm
is a 2mx2m matrix, given by,
Hm=12
Hm1 Hm1Hm1 Hm1
,
where 12
is the normalization factor.
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List of file formatsTransforms
DCTHadamard TransformWavelet Transform
Hadamard Transform contd...
Examples:
H0 = +1
H1 =12
1 11 1
H2 =12 H1 H1H1 H1
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List of file formatsTransforms
DCTHadamard TransformWavelet Transform
Hadamard Transform contd...
Hadamard Transform of an N x 1 vector u is given as,
v = Hu
The inverse transform is given by,
u = Hv
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
IntroductionLi f fil f
DFTDCT
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DCTHadamard TransformWavelet Transform
Wavelet Transform
Based on small waves - wavelets( scaled and translated copies ofvarying frequency & limited duration ).
Powerful approach to multiresolution theory-Mallat, 1987.wavelet - Morlet and Grossmann - French word ondelette,meaning small wave - transferred to English - onde into wave
Used for non-stationary i/p signals.
Gives both time & frequency information at the same time.
Classified into discrete wavelet transforms (DWTs) & continuouswavelet transforms (CWTs).
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DFTDCT
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Hadamard TransformWavelet Transform
Wavelet Transform contd...
CWT
CWT off
(t
) w.r.t wavelet (t
) is given as,
W(a, b) = f(t)
1|a|
tba
dt
where a, b are real.
a-scaling parameterb-location parameter
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
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DFTDCT
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Hadamard TransformWavelet Transform
Wavelet Transform contd...
DWTDWT of f(t) w.r.t wavelet (t) is obtained by puttinga = 2j & b = k2j in CWT
W(a, b) =
f(t)2
j/2 (2jt k)dt
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
IntroductionList of file formats
DFTDCTH d d T f
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Hadamard TransformWavelet Transform
Wavelet Transform contd...
Wavelet Vs Fourierwavelet-localized in both time and frequency.
fourier-localized in frequency.
DWT is computationally less complex.
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
IntroductionList of file formats
DFTDCTH d d T f
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TransformsHadamard TransformWavelet Transform
Wavelet Transform contd...
ApplicationsDWT-data compression.
CWT-signal analysis.
JPEG 2000-uses biorthogonal wavelets.
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IntroductionList of file formats
DFTDCTHadamard Transform
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TransformsHadamard TransformWavelet Transform
References
1 www.wikipedia.org2 Digital Image Processing in MATLAB,Rafael C. Gonzalez ,
Richard E. Woods.
3 Fundamentals of Digital Image processing, Anil K. Jain.
Blessin Joseph & Pilmy Peter M.Tech Signal Processing SPEECH AND IMAGE PROCESSING LAB Image file formats
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