Image CompressionImage Compression

Submitted By : Kriti Jaiswal

Branch : Computer Science & Engg.

Roll no. : 0834310012

Overview

Image compression is the image Data Elaboration Branch dedicated to the image data representation.

Image compression addresses the problem of reducing the amount of data required to represent a digital image.

The underlying basis of the reduction process is the removal of redundant data.

Information vs. Data

Redundant Data

Information

Data = Information + Redundant Data

Information

Data RedundancyData redundancy is a central issue in digital image compression.

It is not an abstract concept but a mathematically quantifiable entity.

If n1 and n2 denote the number of information carrying units in two data set

Then, relative data redundancy RD of the first data set (n1) is

RD =1 - ( 1 / CR )

where CR = compression ratio

CR = (n1/n2)

Information

What is Image compression ?

Image compression is minimizing the size in bytes of a graphics file without degrading the quality of the image.

The reduction in file size allows more images to be stored in a given amount of disk or memory space.

The objective is to reduce redundancy of the image data in order to be able to store or transmit in an efficient manner.

Information

Why Image Compression ?

The bytes number to store an uncompressed image can be really huge !

Real time video conference (bandwidth, cost).

Sending with MMS (upper bound limit).

For data storage and data transmission.

Storing in a physical device.

Sending with GPRS (cost).

Information Sending with GPRS (cost).

Types of Image Compression

Lossless or Information Preserving

There is no information loss, and the image can be reconstructed exactly the same as the original.

Lossy Compression

Information loss is tolerable.Information loss is tolerable.

Information

Formats of Images

BITMAP FORMAT

Files with .bmp extension.

Each pixel is represented by a fixed no. of bits (integral power of 2).

A typical BMP file usually contains the following blocks of data:

BMP Header stores general information.

Bitmap Information stores detailed information

Color Palette stores the definition of the colors.

Bitmap Data stores the actual image pixel by pixel.

Information

AdvantagesAdvantages :Simple.

Widely used.

Relatively well documented.

Free of patents.

Disadvantages:Minimum or zero compression.

Information

AdvantagesGRAPHICS INTERCHANGE FORMAT

256 colors out of a palette of 224 color are indexed.Amongst the oldest formats available. Supports animations

Palette: In computer graphics, a palette is either a given, finite set of colors for the management of digital images .

PORTABLE NETWORK GRAPHICS FORMAT

Developed to improve upon and replace GIF.Supports 2D interlacing, transparency and variable color depth.Uses lossless data compression.

Information

AdvantagesA PNG image with an 8-bit transparency channel (left). The same image is overlaid onto a checkered background (right), to highlight the transparency.

The only disadvantage of PNB is that it doesn’t support animations.

Information

AdvantagesTAG IMAGE FILE FORMAT

Developed by Aldus and Microsoft .

Tags used to indicate how data is arrange.

Advantages :

Highly flexible and platform independent.

Widely used by scanning, faxing, word processing, image manipulation applications.

Capable of describing grayscale, palette-color and full color image data.

Disadvantages :

TIFF image can’t have more than 4GB of data.

AdvantagesStandards or Techniques of Image Compression

JPEG

JPEG 2000

Why standardization is important ?

Standardization allows to obtain a multi-environment file.

Why do we need International Standards?

Standards provide state-of-the-art technology that is developed by a group of experts in the field.

What is JPEG ?

“Joint Photographic Expert Group” Voted as International Standard in 1992 for photographs.

Works with color and grayscale image.

Lossy.

JPEG is not an algorithm but rather a framework with several algorithm and user settings.

Coded bit-string

TransformationInputInfo.

Reconstructed Information

Codeword decoder

Inversetransformation

Codewordassignment

QuantizationCodedBit String

JPEG Framework

JPEG Compression

JPEG is commonly used method of lossy compression for image.

This is ideal for large images that will be displayed while downloading over a slow connections

EXAMPLE:

EXAMPLE

Very high quality , Size 83,216 bytes

(9 bits / Color pixel)

Medium quality ,Size 9553 bytes

(1 bit / Color pixel)

Low quality ,Size 4787 bytes

(0.75 bits / Color pixel)

Lowest quality, Size 1,523 bytes

(0.13 bits / Color pixel)

Advantages :

Compression ratios of 20:1 are easily attained .

24-bits per pixel can be used leading to better accuracy.

Disadvantage :

Doesn’t support transparency.

Doesn’t work well with sharp edges.

Almost always lossy .

JPEG 2000

This standard finalized in 2001.

It defines a new image coding scheme using state-of-the-art compression techniques based on wavelet technology.

The standardized file name extension is .jp2 .

It provides flexibility.

It fully supports transparency.

Example:

Original image

Wavelet used for lossless compression

An example of the wavelet transform that is used in JPEG 2000.

Applications of JPEG 2000

Internet image distribution.

Security systems.

Digital Photography.

Medical Imaging.

Consumers applications such as multimedia devices (e.g. 3G mobile phones, printer, scanners).

Military (e.g. HD Satellite images, Motion Detection, Remote sensing).

Digital Cinema.

Video editing. Etc.

Advantages of JPEG 2000

Good Performance.

Significant flexibility of the code stream.

Compression of an image with JPEG2000 is scalable in nature, meaning that it can be decoded in a number of ways.

Lossless and lossy compression.

Disadvantages of JPEG 2000JPEG 2000 has been published is an ISO standards, ISO/IEC 15444. As of 2010, JPEG2000 is not widely supported in web browsers and hence is not generally used on World Wide Web (W W W) .

Benefits of Image Compression

The smaller file size provide ,can take up on your hard disk or digital cameras.

Allow for more images to be recorded on other media such as a photo CD.

Take less time to load.

Possible to view more images in a shorter period of time.

On the internet, it reduces a web-page’s uploading and downloading time.

Take up less space on the server in terms of space and bandwidth.

In email, compressed images take much less time to send and receive.

Software

Blubox

AlSee 6.2

Picshrink 2.3

Rea Compressor 1.95

Web Image Guru Suite 5.5

Application of Image Compression

Televideo-conferencing.

Remote sensing (the use of satellite imagery for weather and other earth-resource applications).

Facsimile transmission .

Hazardous waste management applications .

Military

Space etc.

Conclusion

Every format has its own advantages and disadvantages.

Depending upon the application the appropriate format should be used.

Only redeeming feature of gif : support animations.

TIFF is appropriate where flexibility is needed.

JPEG is good for photography.

JPEG2000 is an all encompassing standard.

Image Compression is necessary in any instance where images need to be stored, transmitted or viewed quickly and efficiently .

References

www. google. co. in

www. en. wikipedia. com

www. answers. com

http://www. jpeg.org

“Digital Image Processing” by Gonzalez & Woods

Thank You