The desired compression level. This is a device-dependent value. Currently only the jpeg and png devices use these values. For jpeg value is the jpeg quality which should normally be in the range 0-95. Higher values denote higher quality and hence larger image sizes. For png values are in the range -1 to 99. Values of 0-9 are taken as the compression level for zlib. A value of -1 denotes the default zlib compression level. Values in the range 10-99 are divided by 10 and then used as the zlib compression level. Higher compression levels correspond to greater compression and small file sizes at the expense of more computation.