Probably this is a simple question, however I really don't understand this behavior in Mathematica. It particularly leads to a memory leak in a huge program I have to do processing of 3D images. I broke it down which took me quite a time and had to figure out that the problem occured in a simple function that includes a GaussianFilter in Block. The following simple code increases the memory each time I execute it and I can't figure out how to stop this:

image = Import["ExampleData/CTengine.tiff", "Image3D"]; oldMem = MemoryInUse[]; GaussianFilter[image, 1]; N[(MemoryInUse[] - oldMem)/1000/1000] 

58.6569

Meaning that the consumed RAM increases by about 58 MB when the filter is applied even though nothing is returned. I checked for the data type that is produced by the GaussianFilter. The data type changes from Byte to Real32. I know that Mathematica stores output internally but nothing is returned. Especially, I don't understand why the memory is never freed even if I put the stuff into scoping structures like Block. By the way, setting $HistoryLength to 0 doesn't help either.

ImageType@image ImageType@GaussianFilter[image, 1] 

Byte

Real32

fun[image_] := Block[ {}, GaussianFilter[image, 1]; ]; oldMem = MemoryInUse[]; fun[image]; N[(MemoryInUse[] - oldMem)/1000/1000] 

58.6571

$HistoryLength = 0; oldMem = MemoryInUse[]; fun[image]; N[(MemoryInUse[] - oldMem)/1000/1000] 

58.6571

System specifictation

• OS: Windows 7 Professional, Service Pack 1 (64-bit)
• Processor: Intel Xeon CPU E5630 @ 2.53 GHz (2 Processors)
• Installed memory: 96 GB
• Mathematica 10.0.1