Formats and Transforms

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IntroductionList of file formats

Transforms

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
http://find/http://goback/


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Transforms

INTRODUCTION

Image file format

Provide a standardized method of organizing and storing image data.eg: JPEG, TIFF, PNG, GIF



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Transforms

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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Transforms



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


b fil f


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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.


bmp file format


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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.


bmp file format


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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.


bmp file format


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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


bmp file format


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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).


bmp file format


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Transforms

pgif file formatpng 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


bmp file format


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Transforms

gif file formatpng 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.


bmp file format


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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.


bmp file formatif fil f


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Comparison with GIF

Greater compression than GIF.

Wider range of color depths than GIF.

GIF supports animation while PNG does not.


bmp file formatgif file format


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Transforms



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




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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



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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




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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.




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Transforms

gpng 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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Transforms

gpng 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.




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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.



fil f


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Transforms

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


DFT


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Transforms


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.


I d iDFT


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Transforms


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


I t d tiDFT


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Transforms

DCTHadamard TransformWavelet Transform

DFT Transform contd...

PropertiesInvertible linear transformation.

Orthogonality condition is satisfied.

Parsevals theorem is satisfied.

DFT sequence is periodic.


IntroductionDFT


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Transforms


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.


IntroductionDFT


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Transforms


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


IntroductionDFTDCT


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Transforms


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.


IntroductionDFTDCT


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List of file formatsTransforms


Hadamard Transform contd...

Hadamard transform Hm

is a 2mx2m matrix, given by,

Hm=12

Hm1 Hm1Hm1 Hm1

,

where 12

is the normalization factor.


IntroductionDFTDCT


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Examples:

H0 = +1

H1 =12

1 11 1

H2 =12 H1 H1H1 H1


IntroductionDFTDCT


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Hadamard Transform of an N x 1 vector u is given as,

v = Hu

The inverse transform is given by,

u = Hv


IntroductionLi f fil f

DFTDCT


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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



DFTDCT


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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



DFTDCTH d d T f


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Wavelet Vs Fourierwavelet-localized in both time and frequency.

fourier-localized in frequency.

DWT is computationally less complex.



DFTDCTH d d T f


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TransformsHadamard TransformWavelet Transform


ApplicationsDWT-data compression.

CWT-signal analysis.

JPEG 2000-uses biorthogonal wavelets.



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.


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