1. A method of optimizing the compression of image data in accordance with at least one compression objective including: an initialization phase including the steps of: compressing a plurality of test samples in accordance with at least two different compression conditions, associating with each of said test samples at least one item of information characteristic of the content of said sample and at least one measurement of the corresponding compression results, and establishing at least one reference function associating at least one of said compression objectives and/or at least one compression result measurement and/or at least one of said items of characteristic information for each of said compression conditions, and a selection phase including for each set of image data to be compressed the steps of: determining at least one item of information characteristic of said set of image data to be compressed, and selecting the optimal compression condition that maximizes at least one of said compression objectives in accordance with said item or items of characteristic information and said reference functions.