I don't know why BWT beats LZMA sometimes. I know that BWT sometimes works better on text files (eg enwiki8 ), but I don't get it why it outperforms LZMA while compressing Photoshop PSD files.
I attached a sample PSD file. For this one (and most of the files with a BW layer and a RGB layer), Rings Archiver (of Nania Francesco) and Nanozip Optimum 1&2 compress better. Here are the commands used in FreeArc.
NZ 0.9: 9rep+9rep+nz9:co:m2g:t1:p1
Is there anyway to improve the compression in LZMA?
NZ 0.9 Optimum 1 4,684,064
I don't prefer to use an external compressor in FreeArc as LZMA mostly compresses better than BWT.