ImageMagick Visual Reference
Example sprite sheet with consistent sprite sizes and no spacing or margins
To extract the sprites, use tile cropping
convert bobs.gif -crop 32x32 +repage d%03d.gif
Results
To crop horizontal strips from a sprite sheet
convert bobs.gif -crop 0x32 +repage b%02d.gif
For vertical strips just swap the dimensions.
Automatic filename numbering is done with %02d which means two digit numbers padded with zeroes, starting at 00. But what if we want it to start at 01? Use null:
convert null: b00.gif -crop 32x0 +repage f%02d.gif
^ f01.gif ^ f02.gif
Example row of sprites
I can crop the sprites if I know their dimensions. In this case 32 pixels wide
convert dude-cropped.png -crop 32x0 +repage d%02d.png
Example image
Crop 10 pixels from the top
convert in.gif -crop +0+10 +repage ftop.gif
Crop 10 pixels from the right
convert in.gif -crop -10+0 +repage fright.gif
Crop can also extract an area of the image if you include an offset
convert in.gif -crop 50x10+10+20 +repage out.gif
By the way, +repage readjusts the canvas to match the final image size after cropping. Without it, the original canvas remains with transparent background
convert in.gif -crop 50x10+10+20 out.gif
Example images
, 
, 
Append the images in a row
magick tvfuzz1.gif tvfuzz2.gif tvtest.gif +append tv1.gif
Append the images in a stack
magick tvfuzz1.gif tvfuzz2.gif tvtest.gif -append tv2.gif
If the filenames follow a consistent number pattern then a Bash range can select several files
magick d%03d.gif[9-11] +append tv1.gif
To generate an animated gif, use several input images and one output image. A Bash range can help
magick d00%d.gif[0-7] bl.gif
Built in images:
xc: - Block colour. State the size
logo: - 640x480 ImageMagick Logo
wizard: - 480x640 ImageMagick mascot
rose: - 70x46 rose
null: - 1x1 transparent pixel
Generate a builtin image
magick rose: rose.gif
Generate a black box
convert -size 100x100 xc:black black.gif
Convert a png to gif
convert dude.png +repage dude.gif
Convert all files in the current folder
convert * +repage %03d.gif
Scale with -scale. Use a whole fraction to avoid blur.
Blow up double size
convert in.gif -scale 200% out.gif
Shrink half size
convert in.gif -scale 50% out.gif
To add a 1px white border to the left side (spritesheets)
convert null: v01.png +append a3.png
Rotate
convert in.jpg -rotate 90 out.jpg
convert in.jpg -rotate -90 out.jpg
The origin (0,0) is in the upper-left corner.
Dimensions and offset take this syntax: (w)x(h)(+right)(+down).
The "-negate" option negatively colours an area.
Negate an area, topL corner, 10px to the right, 20px down
magick rose: -region '100x200+10+20' -negate rNeg1.gif
Area spills off the left edge
magick rose: -region '100x200-10+20' -negate rNeg2.gif
Set the origin (0,0) to the centre. Negate an area below and left of the origin
magick rose: -gravity center -region '100x200-10+20' -negate rNeg3.gif
Negate an area centre
magick rose: -gravity center -region '100x200' -negate rNeg4.gif
Tips:
Convert a PNG to GIF before cropping to see the whitespace that PNGs hide.
Pad the output to 3 digits with %03d, up to 999. Pad more if more than 10 by 10 tiles in a sheet.
Remember Bash tricks when selecting input images, globs, wildcards, ranges, expansions.