A lossless compression algorithm compresses image data without discarding any of the data. Therefore, when the image is decompressed, there is no evidence that the image was ever compressed. A lossy compression scheme discards some of the image data in order to achieve higher compression ratios. For a full discussion of lossless image compression, click here. The degree of compression is controllable.
Some images can withstand more lossy compression than others.
Images should be tested to discover their compression threshold. Image quality is great considering the amount of data that is discarded. Disadvantages of Lossy Compression Compression artifacts, such as blocking and ringing begin to appear at higher degrees of compression. Repeated compression gradually degrades the image. It is often necessary to keep a master version of the image file that has never been compressed with a lossy technique, or has only been compressed once.