Take center part of image while resizing

Question

I have a problem with resizing image with Carrierwave-MiniMagick-ImageMagick.

I wrote custom method of resizing, cause I need to merge 2 images together and make some processing on them, so standard process methods from MiniMagick are not enough. The problem is with resize method. I need to take center part of the image, but it returns me the top part.

def merge
  manipulate! do |img|
    img.resize '180x140^' # problem is here

    ...

    img
  end
end

Thanks for any help!

Answer 1

I would approach this as follows:

• Resize image to a 180x180 square
• Remove (180-140)/2 from the top
• Remove (180-140)/2 from the bottom

Something like this should do it:

def merge
  manipulate! do |img|
    img.resize '180x180' # resize to 180px square
    img.shave '0x20' # Removes 20px from top and bottom edges

    img # Returned image should be 180x140, cropped from the centre
  end
end

Of course, this assumes your input image is always a square. If it wasn't square and you've got your heart set on the 180x140 ratio, you could do something like this:

def merge
  manipulate! do |img|
    if img[:width] <= img[:height]
      # Image is tall ...
      img.resize '180' # resize to 180px wide
      pixels_to_remove = ((img[:height] - 140)/2).round # calculate amount to remove
      img.shave "0x#{pixels_to_remove}" # shave off the top and bottom
    else
      # Image is wide
      img.resize 'x140' # resize to 140px high
      pixels_to_remove = ((img[:width] - 180)/2).round # calculate amount to remove
      img.shave "#{pixels_to_remove}x0" # shave off the sides
    end

    img # Returned image should be 180x140, cropped from the centre
  end
end

Answer 2

This is what resize_to_fill does:

Resize the image to fit within the specified dimensions while retaining the aspect ratio of the original image. If necessary, crop the image in the larger dimension.

Example:

image = ImageList.new(Rails.root.join('app/assets/images/image.jpg'))
thumb = image.resize_to_fill(1200, 630)
thumb.write('thumb.jpg')

The method takes a third argument which is gravity, but it's CenterGravity by default.

Answer 3

You should use crop instead of resize.

Take a look at crop ImageMagick description of crop command here: http://www.imagemagick.org/script/command-line-options.php#crop

MiniMagick just a wrapper around ImageMagick, so all arguments are the same.