Convert from a format to another

convert img-from img-to

Convert all the images in a folder from JPG to PNG

DESTFOLDER = './dest/'
cd .
for PHOTO in *.jpg
do
    FILENAME=${PHOTO%.jpg}
    convert "$PHOTO" "./$DESTFOLDER/$FILENAME.png"
    echo  "./$DESTFOLDER/FILENAME.png"
done

Crop and scale

Scale to a percentage of the original size

convert -scale 50% img-from img-to

Scale to custom dimensions preserving aspect ratio

convert -resize 600x600 screen.jpg

e.g.

1920x1200 => 600x375
600x1200 => 300x600
150x300 => 300x600
300x150 => 600x300

convert -resize 600x600\> screen.jpg

e.g.

1920x1200 => 600x375
600x1200 => 300x600
150x300 => 150x300 (is not resized to bigger size)
300x150 => 300x150 (is not resized to bigger size)

Scale to a percentage of the original size to create a thumbnail

convert -thumbnail 50% img-from img-to

Create a thumbnail image with a given width (e.g. 170 pixels)

convert -thumbnail 170x img-from img-to

Create a thumbnail image with a given height (e.g. 128 pixels)

`convert -thumbnail x128 img-from img-to

Create a thumbnail image with a given height (e.g. 128 pixels)

convert -thumbnail x128 img-from img-to

Set a filled background to image with transparent background layer

convert -background white -alpha remove -alpha off img-from img-to