Problem of etcpack command line on Mac

I meet problem when using command line tool "etcpack". I have succeed to use it on Windows. But when I use same options to convert the file on Mac, it failed.

The error message was "conver: command not found"

I have already make the working dir to Mali..../bin, And use ./etcpack as the command.

The command line is:

./etcpack /XXX/a.png /XXX -c etc1 -ext PNG -as

The result is:

sh: convert: command not found

Error: Could not convert input image /XXX/a.png to .ppm

the files in bin fold are:

astcenc   composite   convert    etcpack