image["format"]      #=> "TIFF"
image["height"]      #=> 41 (pixels)
image["width"]       #=> 50 (pixels)
image["dimensions"]  #=> [50, 41]
image["size"]        #=> 2050 (bits)
image["original_at"] #=> 2005-02-23 23:17:24 +0000 (Read from Exif data)
image["EXIF:ExifVersion"] #=> "0220" (Can read anything from Exif)

require ‘mini_magick’
img = MiniMagick::Image.from_file “1.jpg”

w,h = img[:width],img[:height] #=> [2048, 1536]#取得宽度和高度
shaved_off = ((w-h)/2).round #=> 256
img.shave “#{shaved_off}x0″ #此处表示宽度上左右各截取256个像素，高度上截取0像素

img.write “2.jpg”

#!/usr/bin/ruby

require "mini_magick"

def  resize_and_crop(image, square_size) 
	if image[:width]<image[:height]
		shave_off=((image[:height]-image[:width])/2).round
		image.shave("0x#{shave_off}")
	elsif image[:width]>image[:height]
		shave_off=((image[:width]-image[:height])/2).round
	end
	geometry=to_geometry(square_size,square_size)
	image.resize(geometry
	return image
end

new_image=resize_and_crop(MiniMagick::Image.from_file("1.jpg"))