Can not calculate the right sha1 checksum to the file from pm.sendRequest response

My question:
I want to get the file’s sha1 from postman’s pre-request script, but get the wrong result all the time.

Details (like screenshots):

The result from postman is ‘3adcb668d79fdb661d44722baea18a712cfcb8a2’, and the result from other tools is ‘6b56023928e22d703a6803a152da99838aae4140’, they are not same.