Crop and resize an image using MiniMagick in Ruby on Rails. Two approaches.

resize_nocrop_noscale

  def resize_nocrop_noscale(image, w,h)
    w_original = image[:width].to_f
    h_original = image[:height].to_f

    if w_original < w && h_original < h
      return image
    end

    # resize
    image.resize("#{w}x#{h}")

    return image
  end

resize_with_crop

  def resize_with_crop(img, w, h, options = {})
    gravity = options[:gravity] || :center

    w_original, h_original = [img[:width].to_f, img[:height].to_f]

    op_resize = ''

    # check proportions
    if w_original * h < h_original * w
      op_resize = "#{w.to_i}x"
      w_result = w
      h_result = (h_original * w / w_original)
    else
      op_resize = "x#{h.to_i}"
      w_result = (w_original * h / h_original)
      h_result = h
    end

    w_offset, h_offset = crop_offsets_by_gravity(gravity, [w_result, h_result], [ w, h])

    img.combine_options do |i|
      i.resize(op_resize)
      i.gravity(gravity)
      i.crop "#{w.to_i}x#{h.to_i}+#{w_offset}+#{h_offset}!"
    end

    img
  end

  # from http://www.dweebd.com/ruby/resizing-and-cropping-images-to-fixed-dimensions/

  GRAVITY_TYPES = [ :north_west, :north, :north_east, :east, :south_east, :south, :south_west, :west, :center ]

  def crop_offsets_by_gravity(gravity, original_dimensions, cropped_dimensions)
    raise(ArgumentError, "Gravity must be one of #{GRAVITY_TYPES.inspect}") unless GRAVITY_TYPES.include?(gravity.to_sym)
    raise(ArgumentError, "Original dimensions must be supplied as a [ width, height ] array") unless original_dimensions.kind_of?(Enumerable) && original_dimensions.size == 2
    raise(ArgumentError, "Cropped dimensions must be supplied as a [ width, height ] array") unless cropped_dimensions.kind_of?(Enumerable) && cropped_dimensions.size == 2

    original_width, original_height = original_dimensions
    cropped_width, cropped_height = cropped_dimensions

    vertical_offset = case gravity
      when :north_west, :north, :north_east then 0
      when :center, :east, :west then [ ((original_height - cropped_height) / 2.0).to_i, 0 ].max
      when :south_west, :south, :south_east then (original_height - cropped_height).to_i
    end

    horizontal_offset = case gravity
      when :north_west, :west, :south_west then 0
      when :center, :north, :south then [ ((original_width - cropped_width) / 2.0).to_i, 0 ].max
      when :north_east, :east, :south_east then (original_width - cropped_width).to_i
    end

    return [ horizontal_offset, vertical_offset ]
  end

resize_with_nocrop

# see details - http://maxivak.com/crop-and-resize-an-image-using-minimagick-ruby-on-rails

def resize_with_nocrop(image, w, h)

    w_original = image[:width].to_f
    h_original = image[:height].to_f

    if (w_original*h != h_original * w)
      if w_original*h >= h_original * w
        # long width
        w_result = w
        h_result = w_result * (h_original / w_original)
      elsif w_original*h <= h_original * w
        # long height
        h_result = h
        w_result = h_result * (w_original / h_original)
      end
    else
       # good proportions
       h_result = h
       w_result = w
    end

    #
    image.resize("#{w_result}x#{h_result}")
    return image
  end