A marked progress has been made in the field of image compression and its application in various branches of engineering. Image compression is associated with removing redundant information of image data. It is a solution which associated with storage and data transmission problem of huge amounts of data for digital image. Compressing an image is significantly different than compressing raw binary data. Of course, general purpose compression programs can be used to compress images, but the result is less than optimal. This is because images have certain statistical properties which can be exploited by encoders specifically designed for them. Also, some of the finer details in the image can be sacrificed for the sake of saving a little more bandwidth or storage space.
Overview of Image Compression
Image compression is an application of data compression that encodes the original image with few bits. The objective of image compression is to reduce the redundancy of the image and to store or transmit data in an efficient form.
Image compression is a type of an application for data/image compression in which the basic image gets encoded with the limited bits. To lower the irrelevance and the redundancy of image data is the major target of the image compression is to enable them to get saved or transmit the data in the better form. Image compression is the lowering of the image data size, also with maintaining the required details. The basic objective of the image compression is to show an image in small quantity of bits also the needed content of information is not lost within the actual image. Compression techniques are developed rapidly to compress huge files of data like images. By the rapid growth of the technology a large quantity of image data should be managed to store those images in the proper manner by the use of effect.
Image compression is one of various known techniques in the image processing. This technique may have various implementations and performs a vital role in the effective storage and transmission of the images. The image compression targeted at decreasing the redundancy in the image data to record or sends only few numbers of the samples and by this also a good accession can be reconstruct for the actual image corresponding with the perception of human visual.
Figure 1: Image Compression Example
Image compression is minimizing the size in bytes of a graphics file without degrading the quality of the image to an unacceptable level. The reduction in file size allows more images to be stored in a given amount of disk or memory space. It also reduces the time required for images to be sent over the Internet or downloaded from Web pages.
Image Compression Techniques
Images are very important documents nowadays; to work with them in some applications they need to be compressed, more or less depending on the purpose of the application. Images are very important documents nowadays; to work with them in some applications they need to be compressed, more or less depending on the purpose of the application. There are some algorithms that perform this compression in different ways. Compression is obtained by eliminating any of one or more of the below three fundamental data redundancies:
- Coding redundancy: This is presented when the less than best (that is the smallest length) code words were used.
- Inter-pixel redundancy: This results from the correlations between the pixels of an image.
- Psycho-visual redundancy: This is because of the data which is neglected by human visual-system (that is, visually not required information).
There are some techniques that perform this compression in different ways. Compression can be divided into two categories, as Lossless and Lossy compression. In lossless Compression, the reconstructed image after compression is numerically identical to the original image.
1. Lossy Compression Technique
Lossy compression reduces a file by permanently eliminating certain information, especially redundant information. When the file is uncompressed, only a part of the original information is still there (mostly not noticed by user). Lossy compression is generally used for video and sound, where a certain amount of information loss will not be detected by most users. The JPEG image file, commonly used for photographs and other complex still images on the Web, is an image that has lossy compression. Using JPEG compression, the creator can decide how much loss to introduce and make a trade-off between file size and image quality.
The Lossy data-compression methods are aware by the researches on how the people anticipate data in the question. As an example, the human eye is very sensitive to slight variations in the luminance as compare that there are so many variations in the color. The Lossy image compression technique is used in the digital cameras, to raise the storage ability with the minimal decline of the quality of picture. Similarly in the DVDs which uses the lossy MPEG-2 Video codec technique for the compression of the video. In the lossy audio compression, the techniques of psycho acoustics have been used to eliminate the non-audible or less audible components of signal.
2. Lossless Compression Technique
With lossless compression, every single bit of data that was originally in the file remains after the file is uncompressed. All of the information is completely restored. This is generally the technique of choice for text or spreadsheet files, where losing words or financial data could pose a problem.
These types of compression are also known as noiseless as they never add noise to signal or image. It is also termed as the entropy coding as it uses the techniques of decomposition/statistics to remove/reduce the redundancy. It is also used only for the some specific applications along with the rigid needs like a medical-imaging. Below mentioned techniques consists in the lossless compression:
- Huffman encoding
- Run length encoding
- Arithmetic coding
- Dictionary Techniques
Benefits of Image Compression
Below are few benefits of the Image compression technique:
- It enables a reliable cost of savings that is included with the sending of less data on the network of switched telephone in which the cost of call is normally dependent on its duration.
- It is not only to decrease the requirements of storage but also decrease the entire time of execution.
- It decreases the chances of the errors transmission as
- Some bits have got transferred.
- It enables a level of the security against monitoring the unlawful Activities
 Manjari Singh and Sushil Kumar, “Various Image Compression Techniques: Lossy and Lossless”, International Journal of Computer Applications (IJCA), Volume 142 – No.6, May 2016
 Khobragade P. B. and Thakare S. S, “Image Compression Techniques- A Review”, (IJCSIT) International Journal of Computer Science and Information Technologies, Vol.ume5 (1), 2014, pp. 272-275
 Wei, Wei-Yi. “An introduction to image compression.” National Taiwan University, Taipei, Taiwan, ROC (2008).