RMagick remove white background from image and make it transparent

Question

I need to remove the white background from this image and make the background transparent. So it\'s just a black tick on the transparent background exported as a png.

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Answer 1

I know I am pretty late to the party, but a lot has changed since this question was first posted, so here is how you can do it today using at least version 2.15.4 of rmagick

Assuming you have the image somewhere accessible:

image = Magick::Image.new(path_to_file)
image.background_color = 'none'

If you also want to trim the image so it's only as big as it boundaries, simply use .trim!

image.trim!

EDIT:

Turns out the solution above does not really work for all use cases. A more general solution is this:

# the image needs to be in 'PNG' format
image.format = 'PNG'

# set a fuzz on the image depending on how accurate you want to be
image.fuzz = '10%'

# get the image background color
background_color = image.background_color

# convert pixels based on their color to being transparent
# the fuzz set above controls how accurate the conversion will be
image.paint_transparent(background_color)