convert

# imagemagick utility

# To resize an image to a fixed width and proportional height:
convert original.jpg -resize 100x converted.jpg

# To resize an image to a fixed height and proportional width:
convert original.jpg -resize x100 converted.jpg

# To resize an image to a fixed width and height:
convert original.jpg -resize 100x100 converted.jpg

# To resize an image and simultaneously change its file type:
convert original.jpg -resize 100x converted.png

# To resize all of the images within a directory:
# To implement a for loop:
for file in `ls original/image/path/`;
    do new_path=${file%.*};
    new_file=`basename $new_path`;
    convert $file -resize 150 converted/image/path/$new_file.png;
done

# convert pdf to image
convert -density 150 filename.pdf -quality 90 output-%03d.jpg

# convert multiple images to single pdf
convert "*.jpg" -quality 85 outfile.pdf

# rotate image by 90 degrees
convert input.jpg -rotate 90 output.jpg

# force dimensions without respect to aspect ratio
-resize 64x64\!

# make gif from images
convert -delay 3 *.png giffile

# remove transparency layer if present from pdf or images
-alpha remove

# join two images side by side 
convert img1 img2 +append result.jpg

# convert images to gif using image magick
convert -delay 20 -loop 0 *.jpg myimage.gif