Set device-compression level. Only used for drivers that provide
compression. This function, if used, should be invoked
before a call to
The desired compression level. This is a device-dependent
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.
This function is used in example 31.