MrSID accesses image data in 'blocks' of pixels. Blocks in MG2 encoding are different from blocks in MG3 and MG4 encoding.
Different block sizes affect system resources. While a smaller block size in MG2 encoding uses less RAM, the opening and closing of multiple image blocks may impact a system in other ways, sometimes resulting in an encoding failure. If sufficient RAM is available, a larger block size is recommended for encoding projects approaching or exceeding a gigabyte in size.
By default, GeoExpress automatically selects a block size for MG2 encoding based on a calculated memory usage curve that is dependent on the input image. The block size corresponding to the lowest point in the memory curve is selected.
Block size may be set manually by selecting the Block Size check box and entering a value in the field that becomes available. When compressing imagery in excess of a gigabyte in size, use a block size of 1024. For imagery equal to or greater than three gigabytes, a block size of 2048 is recommended.
Changing the block size setting will not affect the rate of compression or the quality of the output image.
Minimum value: 32.