Foundations of Digital Image

09. Compression

Compression is a process of reducing file size by reorganizing data. The data format can change multiple times through compression to make the file smaller and easier to send or store. Sometimes information is discarded in compression and interpolation is used to make up for the losses.

Ex. Beach Vacation

Imagine you are packing to go on a vacation to the beach. You start packing your suitcase; throwing in your swimsuit, sandals, a towel, suntan lotion, a book, etc. You are compressing the essentials for your beach vacation into a suitcase. The smaller the suitcase, the quicker and easier you travel independently. After your relaxing beach break, you unpack. Now, unless you left your book on the beach, you should be able to obtain all the items you previously packed. You can use this analogy to better understand the compression of data. When packing for a short trip, you can’t shrink all your clothes to bring with you! You have to organize the essentials for that trip.

The two types of compressions: Lossy and Lossless



A LOSSLESS compression algorithm discards no information. It looks for more efficient ways to represent an image, while making no compromises in accuracy.

In contrast, LOSSY algorithms accept some degradation in the image in order to achieve a smaller file size.

A lossless algorithm might, for example, look for a recurring pattern in the file and replace each occurrence with a short abbreviation, thereby cutting the file size. In contrast, a lossy algorithm might store color information at a lower resolution than the image itself, since the eye is not so sensitive to minor changes in color.

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