There are two types of compression you can pick when optimizing your images: lossy and lossless compression.
Lossy image optimization applies a variety of techniques and processing steps to input images to recompress them to a lower quality level which falls below the human perceptible threshold. When being viewed on a computer or mobile device this loss of quality is often not detectable to the human eye. We strongly recommend that you try out our lossy compression. However, you can restore the original from our backup if needed or reoptimize your images using lossless compression. We use this mode ourselves, as do most of our customers. Typical file weight reductions range from 5%-70%.
Lossless image optimization means that your images will get compressed to some extent without changing their informational value in any way whatsoever. Reductions in terms of file weight are usually in the 5%-30% range, however, sometimes greater savings can be achieved.
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