Flickr style resizing with attachment_fu

Question

I want attachment_fu to resize my thumbnails in a similar way to how flickr, facebook and twitter handle this: If I want a 100x100 thumbnail I want the thumbnail to be exactly 100x100 with any excess cropped off so that the aspect ratio is preserved.

Any ideas?

Answer 1

To set up the 100x100 thumbnails, add the following to your model:

  has_attachment :content_type => :image,
                 :storage => IMAGE_STORAGE,
                 :max_size => 20.megabytes,
                 :thumbnails => {
                   :thumb  => '100x100>',
                   :large  => '800x600>',
                 }

(In this example, I am creating a 100x100 thumbnail, and also an 800x600 'large' size, in additional to keeping the original size.)

Also, keep in mind that the thumbnail might not be exactly 100x100; it will have a maximum dimension of 100x100. This means that if the original has an aspect ration of 4:3, the thumbnail would be 100x75. I'm not exactly sure if that is what you meant by "exactly 100x100 with any excess cropped off so that the aspect ratio is preserved."

Answer 2

There's a cropping directive that can be given in the specification:

has_attachment :content_type => :image,
  :thumbnails => {
    :thumb  => '100x100#'
}

Memonic: '#' looks like the crop tool.

Edit: Correction

has_attachment :content_type => :image,
  :thumbnails => {
    :thumb  => '100x100!'
}

The previous method was for Paperclip which has a different notation.

Answer 3

Add this to your model

protected  

  # Override image resizing method  
  def resize_image(img, size)  
    # resize_image take size in a number of formats, we just want  
    # Strings in the form of "crop: WxH"  
    if (size.is_a?(String) && size =~ /^crop: (\d*)x(\d*)/i) ||  
        (size.is_a?(Array) && size.first.is_a?(String) &&  
          size.first =~ /^crop: (\d*)x(\d*)/i)  
      img.crop_resized!($1.to_i, $2.to_i)  
      # We need to save the resized image in the same way the  
      # orignal does.  
      self.temp_path = write_to_temp_file(img.to_blob)  
    else  
      super # Otherwise let attachment_fu handle it  
    end  
  end

and change the thumbnail size to:

:thumbnails => {:thumb => 'crop: 100x100' }

source:

http://stuff-things.net/2008/02/21/quick-and-dirty-cropping-images-with-attachment_fu/

Answer 4

My solution was to delve into the attachment_fu plugin folder (vendor/plugins) and edit the rmagick_processor.rb file. First I renamed resize_image to resize_image_internal, then added:

  def resize_image(img, size)  
    # resize_image take size in a number of formats, we just want  
    # Strings in the form of "square: WxH"  
    if (size.is_a?(String) && size =~ /^square: (\d*)x(\d*)/i) ||  
        (size.is_a?(Array) && size.first.is_a?(String) &&  
          size.first =~ /^square: (\d*)x(\d*)/i)  
        iw, ih = img.columns, img.rows
        aspect = iw.to_f / ih.to_f
        if aspect > 1
            shave_off = (iw - ih) / 2
            img.shave!(shave_off, 0)
        else
            shave_off = (ih-iw) / 2
            img.shave!(0, shave_off)
        end
        resize_image_internal(img, "#{$1}x#{$2}!")
    else  
      resize_image_internal(img, size) # Otherwise let attachment_fu handle it  
    end  
  end

I can now use 'square: 100x100' as my geometry string. Note that the above code assumes the required output is square.