watermark transparency

[luchiayu]

Hi, I am new for nconvert, I don't know how to set the watermark transparency. For example:
./nconvert -npcd 2 -size 256x256+0 -ctype grey -corder inter -out jpeg -wmfile 10mm_02.png -wmpos 0 3 -transparent 0.5 10mm_02S.png 10mm_02X.png 10mm_02Y.png
not work javascript:emoticon(':?:')
CY

[xnview]

Ok, currently i use alpha from source file, so i'll add an option