Image quality manipulating in JPEG is done by quantization tables. JPEG has two quantization tables - one table for the luminance information and one table for the chrominance information. These quantization tables have been designed in support of images with few sharp changes; however, typically most GPS image maps have many sharp changes and as a result, the images are not optimally compressed. The designers of the quantization tables have presumed that sharp changes in the colors will rarely occur. Therefore, they divide the values that represent sharp changes in the frequency space by large numbers and divide other values by smaller numbers. As a result, when there are sharp changes in an image, the proportional allocation for each kind of data in the compressed image is inappropriate and results in an inefficient compression. In this paper the standard quantization tables have been modified as to handle the different kinds of GPS image map data appropriately. Consequently, the experimental results show that images with sharp changes are compressed more efficiently when making use of the new quantization tables.
Bibliographical noteFunding Information:
Dr. Wiseman is an international expert who has reviewed and evaluated several large projects of the European Union, Israel Science Foundation, Marie Skłodowska-Curie actions in Ireland and the Ministry of Education and Science of Kazakhstan. His more than 50 journal papers have been published in many venues around the world.
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- Image compression
- Quantization tables