How to decode base64 image file with mini_magick in Rails?

Question

In our Rails 4 app, the image is uploaded to server in a base64 string:

uploaded_io = "data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2....."

We would like to to retrieve the content type, size and so on and save the file as image file on file system. There is a gem 'mini_magick' in our app. Is there a way to process base64 image string with mini_magick?

Topple

did you solve that ? – After

Answer 1

Yes, there is a way to do that.

Strip metadata "data:image/jpeg;base64," from your input string and then decode it with Base64.decode64 method. You'll get binary blob. Feed that blob to MiniMagick::Image.read. ImageMagick is smart enough to guess all metadata for you. Then process the image with mini_magick methods as usual.

require 'base64'

uploaded_io = "data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2....."
metadata = "data:image/jpeg;base64,"
base64_string = uploaded_io[metadata.size..-1]
blob = Base64.decode64(base64_string)
image = MiniMagick::Image.read(blob)
image.write 'image.jpeg'

# Retrieve attributes
image.type        # "JPEG"
image.mime_type   # "image/jpeg"
image.size        # 458763
image.width       # 640
image.height      # 480
image.dimensions  # [640, 480]

# Save in other format
image.format 'png'
image.write 'image.png'

Deputy

This saved my day. ImageMagick return false when we validation image after writing base64 image string into tempfile under binmode. This is helpful. Thanks – Diverse