ImageMagick Tutorial

How to convert from gif to png?

convert p1.gif p2.png

How to convert from png to jpg?

convert -scale 50% -quality 80% old.png new.jpg

How to scale a image?

convert -scale 50% old.gif new.png

How to autocrop border?

convert -trim cat.png cat.png

How to crop (cutting) a image?

convert -crop 853x368+0+56 old.png new.png

The 853 and 368 would be the new image's width and height. The 0 is the offset on x-axis, and 56 is the offset of y-axis. The x and y axes's origin starts at the upper left corner.

To crop by specifying percentage of sides to cut, use “-shave”.

How to increase brightness?

convert -modulate 150,100,100 old.png new.png

The above increase brightness by the multiplier 150%. To decrease, use values less than 100.

The 3 numbers means: brightness, saturation, hue. They are all interpreted as percentages.

How to increase saturation?

convert -modulate 100,130,100 old.png new.png

The above increase color saturation by the multiplier 130%. To decrease, use values less than 100.

How to replace transparency/alpha with white?

convert -flatten old.png new.png

How to change color image to gray scale?

convert -type Grayscale old.png new.png

Note: this does not force the png image format to use indexed color for smaller file size.

How to reduce bits per pixel?

Use -depth. In particular, for a grayscale line art in png, you can do: convert -depth 8 old.png new.png. That makes it 8 bits. For clean black and white line art, you can use “-depth 2”. This is great for reducing file size. (see also “-colors”)

How to reduce color?

convert -dither -colors 256 old.png new.png

(dither adds dots)

To reduce color without dithering, use +dither instead of -dither. Note that reducing colors does not necessarily reduce file size.

To reduce png file's size when reducing color, use -depth for values of {2, 3, 4, 8}.

How to sharpen a image?

convert -sharpen 2 old.png new.png

How to blur a image?

convert -blur 1 old.png new.png

How to insert copyright notice?

convert -fill red -draw 'text 20 20 "© 2006 example.com"' old.png new.png

Use -gravity SouthEast -font helvetica to put the text in other corners, and change font.

How to add a border?

convert -border 1 -bordercolor black cat.png cat2.png

How to rotate a image?

convert -rotate 90 x.png x.png

Positive degree means counter-clockwise.

How to flip a image?

# left/right flip
convert -flop x.png x.png

# up/down flip
convert -flip x.png x.png

How to combine 2 images?

montage -mode concatenate -tile 1x cat1.jpg cat2.jpg out.jpg

or

# join images vertically
convert x1.png x2.png x3.png -append out.png

# join images horizontally
convert x1.png x2.png x3.png +append out.png

How to batch process?

There are many ways to process all files in a directory in one shot. You can use the unix shell utils “find” and “xargs”.

Suppose you want to convert all files in a dir from png to jpg. Here's GNU/Linux example:.

find . -name "*png" | xargs -l -i basename "{}" ".png" | xargs -l -i  convert -quality 85% "{}.png" "{}.jpg"

The “-l” makes it process one line at a time. The “-i” makes the “{}” to stand for file name. The “basename” strips the suffix.