I have createt large Tif files (150MByte) with -colorspace cmyk -flatten -compress LZW to make sure, I have only the four Channels and a working compression. (I recompiled gm with lzw enabled before).
When I load this tif file to photoshop and save a copy, Tif with lzw, the copy is only 2/3 of the size, around 100MB
I cannot find a reason for this. Can you?
I would love to have the smaller size in the first place.
Please execute 'tiffinfo' on the original TIFF file and the version written by Photoshop and post the output here. There are various factors which might result in a smaller file size.