Export *.psd to *.png using ImageMagic.

psd2png.sh

#!/bin/sh

mkdir out

for f in *.psd
do
    echo ${f/psd/png}
    # 1.trim
    # 2.resize with in (512 x 512)
    # 3 convert to png
    convert $f[0] -trim +repage -resize '512x512' out/${f/psd/png}
done