21-04-2012, 10:44 AM
image compression
1.INT TO IMAGE.docx (Size: 24.43 KB / Downloads: 35)
INTRODUCTION
Image compression means minimizing the size in bytes of a graphics file without degrading the quality of the image to an unacceptable level. The reduction in the file size allows more image to be stored in a given amount of disk more memory space. It also reduces the time required for image to be sent over the internet or downloaded from web pages. Uncompressed multimedia (graphics, audio and video) data requires considerable storage capacity and bandwidth. Despite rapid progress in mass storage density, processor speeds, and digital communication system performance, demand for data storage capacity and data transmission bandwidth continues to outstrip the capabilities of available technology. The recent growth of data intensive multimedia based web application have not only sustained the need for more efficient ways to encode signals and images but have made compression of such signal central to storage and communication technology.
NEED FOR COMPRESSION
An image 1024 pixel *1024 pixel *1024 pixel *24 bit ,without compression would require 3MB of storage and 7 minute of transmission, utilizing a high speed ,64 kbs, ISDN line .If the image is compressed at a 10:1 compression ratio, the storage requirement is reduced to 300 KB and the transmission time is reduced to less than 7 second. Images file in an uncompressed Form are very large, and the internet especially for people using a 56 kbps dialup modem, can be pretty slow. This combination could seriously limit one of the webs most appreciated aspects –its ability to present images easily.
The examples above clearly illustrate the need for sufficient storage space, large transmission bandwidth, and long transmission time for image . Audio and video data at present, the only solution is to compress multimedia data before its storage and transmission and decompress it at the receiver.
TYPES OF COMPRESSION
In the case of video, compression ratio causes some of the information to be lost some information at a detailed level is considered not essential for a reasonable reproduction of scene.This type of compression is called lossy compression, audio compression on the other hand is not lossy, it is called loss less compression.
1.3.1 Lossless Compression
In lossless compression scheme, the reconstructed image after the compression is numerically identical to original image. However lossless compression can only achieve a modest amount of compression. Lossless coding guaranties that the decompressed image is absolutely identical to the image before compression. This is an important requirement for some application domain, e.g. medical imaging, where not only high quality is in demand but unaltered archiving is a legal requirement. Lossless technique can also be used for the compression of other data types where loss of information is not acceptable, e.g. text document and program executables.
Lossy Compression
Lossy is a term applied to data compression technique in which some amount of the Original data is lost during the compression process. Lossy image compression applications attempt to eliminate redundant or un necessary information in terms of what the human eye can perceive. An image reconstructed following lossy compression contains degradation relative to the original image. Often this is because the compression scheme completely discards redundant information. However lossy scheme are capable of achieving much higher compression. Under normal viewing condition, no visible loss is perceived (visually lossless).
Lossy image data compression is useful for application to the world wide images for Quicker transfer across the internet. An image reconstructed following lossy compression contains degradation relative to the original. Often this is because the compression scheme completely discard the redundant information.
APPLICATIONS OF COMPRESSION
Applications of data compression are primarily in the transmission and in storage of information. Image transmission application are in broadcast television remote sensing via satellite, military application via aircraft, radar and sonar, teleconferencing, computer communication, facsimile transmission, etc. Image storage is required for educational business documents, medical images, that rises in computer tomography, magnetic resonance imaging and digital radiology, motion picture, satellite image weather maps, etc. Application of data compression is also possible in the development of fast algorithm, where the number of operations required to be implement an algorithm is reduced by working with compressed data. Over the year, the need for image compression has grown steadily. Currently it is recognized as an enabling technology. It plays a crucial role in many important and diverse applications such as:
1. Business document, where lossy compression is prohibited for legal reasons.
2. Satellite image where the data loss is undesirable because of image collect cost.
3. Medical image where difference in original image and uncompressed one can compress
diagnostic accuracy.
4. Tele -video conferencing.
5. Remote sensing.
6. Space and hazardous waste water application .
7. Control of remotely piloted vehicle in military.
8. Facsimile transmission (fax)
CHARACTERISTIC OF COMPRESSION:
Image quality describes the fidelity with which an image compression scheme recreates the Source image data. There are four main characteristics to judge image compression algorithms
1. Compression Ratio
2. Compression Speed
3. Mean Square Error
4. Peak Signal to Noise Ratio
These characteristics are used to determine the suitability of a given compression algorithm for any application.
Compression Ratio
The compression ratio is equal to the size of the original image divided by the size of the compressed image. This ratio gives how much compression is achieved for a particular image. The compression ratio achieved usually indicates the picture quality. Generally, the higher the compression ratio, the poorer the quality of the resulting image. The trade off between compression ratio and picture quality is an important one to consider when compressing images.
1.INT TO IMAGE.docx (Size: 24.43 KB / Downloads: 35)
INTRODUCTION
Image compression means minimizing the size in bytes of a graphics file without degrading the quality of the image to an unacceptable level. The reduction in the file size allows more image to be stored in a given amount of disk more memory space. It also reduces the time required for image to be sent over the internet or downloaded from web pages. Uncompressed multimedia (graphics, audio and video) data requires considerable storage capacity and bandwidth. Despite rapid progress in mass storage density, processor speeds, and digital communication system performance, demand for data storage capacity and data transmission bandwidth continues to outstrip the capabilities of available technology. The recent growth of data intensive multimedia based web application have not only sustained the need for more efficient ways to encode signals and images but have made compression of such signal central to storage and communication technology.
NEED FOR COMPRESSION
An image 1024 pixel *1024 pixel *1024 pixel *24 bit ,without compression would require 3MB of storage and 7 minute of transmission, utilizing a high speed ,64 kbs, ISDN line .If the image is compressed at a 10:1 compression ratio, the storage requirement is reduced to 300 KB and the transmission time is reduced to less than 7 second. Images file in an uncompressed Form are very large, and the internet especially for people using a 56 kbps dialup modem, can be pretty slow. This combination could seriously limit one of the webs most appreciated aspects –its ability to present images easily.
The examples above clearly illustrate the need for sufficient storage space, large transmission bandwidth, and long transmission time for image . Audio and video data at present, the only solution is to compress multimedia data before its storage and transmission and decompress it at the receiver.
TYPES OF COMPRESSION
In the case of video, compression ratio causes some of the information to be lost some information at a detailed level is considered not essential for a reasonable reproduction of scene.This type of compression is called lossy compression, audio compression on the other hand is not lossy, it is called loss less compression.
1.3.1 Lossless Compression
In lossless compression scheme, the reconstructed image after the compression is numerically identical to original image. However lossless compression can only achieve a modest amount of compression. Lossless coding guaranties that the decompressed image is absolutely identical to the image before compression. This is an important requirement for some application domain, e.g. medical imaging, where not only high quality is in demand but unaltered archiving is a legal requirement. Lossless technique can also be used for the compression of other data types where loss of information is not acceptable, e.g. text document and program executables.
Lossy Compression
Lossy is a term applied to data compression technique in which some amount of the Original data is lost during the compression process. Lossy image compression applications attempt to eliminate redundant or un necessary information in terms of what the human eye can perceive. An image reconstructed following lossy compression contains degradation relative to the original image. Often this is because the compression scheme completely discards redundant information. However lossy scheme are capable of achieving much higher compression. Under normal viewing condition, no visible loss is perceived (visually lossless).
Lossy image data compression is useful for application to the world wide images for Quicker transfer across the internet. An image reconstructed following lossy compression contains degradation relative to the original. Often this is because the compression scheme completely discard the redundant information.
APPLICATIONS OF COMPRESSION
Applications of data compression are primarily in the transmission and in storage of information. Image transmission application are in broadcast television remote sensing via satellite, military application via aircraft, radar and sonar, teleconferencing, computer communication, facsimile transmission, etc. Image storage is required for educational business documents, medical images, that rises in computer tomography, magnetic resonance imaging and digital radiology, motion picture, satellite image weather maps, etc. Application of data compression is also possible in the development of fast algorithm, where the number of operations required to be implement an algorithm is reduced by working with compressed data. Over the year, the need for image compression has grown steadily. Currently it is recognized as an enabling technology. It plays a crucial role in many important and diverse applications such as:
1. Business document, where lossy compression is prohibited for legal reasons.
2. Satellite image where the data loss is undesirable because of image collect cost.
3. Medical image where difference in original image and uncompressed one can compress
diagnostic accuracy.
4. Tele -video conferencing.
5. Remote sensing.
6. Space and hazardous waste water application .
7. Control of remotely piloted vehicle in military.
8. Facsimile transmission (fax)
CHARACTERISTIC OF COMPRESSION:
Image quality describes the fidelity with which an image compression scheme recreates the Source image data. There are four main characteristics to judge image compression algorithms
1. Compression Ratio
2. Compression Speed
3. Mean Square Error
4. Peak Signal to Noise Ratio
These characteristics are used to determine the suitability of a given compression algorithm for any application.
Compression Ratio
The compression ratio is equal to the size of the original image divided by the size of the compressed image. This ratio gives how much compression is achieved for a particular image. The compression ratio achieved usually indicates the picture quality. Generally, the higher the compression ratio, the poorer the quality of the resulting image. The trade off between compression ratio and picture quality is an important one to consider when compressing images.