# Why does using Discrete Cosine Transform lead to data compression?

DCT is used in JPEG standard along with Huffman encoding to further compress the result. I understand that most of the data in spatial domain which is an image is "present in low frequencies". This is because most adjacent pixels change only little in the color value.

An image which is represented numerically in signal processing, with numbers representing the pixel color intensity. When we do a DCT on it we still get numbers in result. Where exactly does data get compressed via DCT?

• Both JPEG and MP3 are lossy compression, designed around the limits of human perception. A JPEG compressed image may have subtle visual artifacts not present in the original image, that result from the attenuated high frequency components lost during compression. – MarkU May 12 '15 at 0:13