If the previous article talked about bulk resizing, this article talks about reducing multiple image files size. This can be achieved by many ways. We give some examples in the way of reducing the colors (PNG) and using -quality option (JPEG). We separate PNG and JPEG because they have these different commands.
1) PNG
Color 128
for i in *.png; do convert -verbose -colors 128 "$i" "`echo $i | sed 's/.png/-converted.png/g'`"; done
Note: this command will reduce the image colors into 128. In our example, every image size reduced approximately in half.
Color 32
for i in *.png; do convert -verbose -colors 32 "$i" "`echo $i | sed 's/.png/-converted.png/g'`"; done
Note: this command will reduce every image colors into 32. In our example, every image size reduced approximately 1/5 of the original file.
2) JPEG
value=50
for i in *.jpeg; do convert -verbose -quality 50 "$i" "`echo $i | sed 's/.jpeg/-converted.jpeg/g'`"; done
value=20
for i in *.jpeg; do convert -verbose -quality 20 "$i" "`echo $i | sed 's/.jpeg/-converted.jpeg/g'`"; done
Sample Results
value=50 resulting in about 1/4 of the original.
value=20 resulting in 1/8 of the original.
