Image Compression

Introduction

Nearly all files can be compressed without losing any of the original data at all. For example, take the following text:

‘the cat sat on the mat’ --22 characters.

Simple text compression occurs by replacing symbols for common words or letter combinations.

Using the following substitutions where, ‘_the_’ becomes ‘#’ and ‘at’ becomes ‘^’ the text above becomes:

#c^ s^ on#m^ --12 characters

0% compression means that the file has not changed size. 99% compression means the file is now only one hundredth of its original size. In the case above the file has been compressed by about 45% using only 2 simple substitutions.

Images, especially photographic images, are harder to compress. This is because they infrequently contain identical strings of characters that can be easily substituted. Many different solutions have been devised to solve this problem, one of the most successful being JPEG compression. To be precise, the JPEG solution is not true compression. As you compress your image, more and more information is lost. If you compress an image too much it looks grainy. However the power of JPEG compression is that you can heavily compress a picture before it begins to look perceptibly different. Compression levels of up to 50% are common.

Using Image Lab to compress your Images.