module DynamicImage::Model

DynamicImage Model

ActiveModel extension for the model holding image data. It assumes your database table has at least the following attributes:

create_table :images do |t|
  t.string  :content_hash
  t.string  :content_type
  t.integer :content_length
  t.string  :filename
  t.string  :colorspace
  t.integer :real_width, :real_height
  t.integer :crop_width, :crop_height
  t.integer :crop_start_x, :crop_start_y
  t.integer :crop_gravity_x, :crop_gravity_y
  t.timestamps
end

To use it, simply include it in your model:

class Image < ActiveRecord::Base
  include DynamicImage::Model
end

Usage

To save an image, simply assign to the file attribute.

image = Image.create(file: params.permit(:file))

This will automatically parse and validate the image when your record is saved.

To read back the image data, access the data attribute. This will lazily load the data from the store.

data = image.data

Cropping

Images can be pre-cropped by setting crop_width, crop_height, crop_start_x and crop_start_y. The crop dimensions cannot exceed the image size.

image.update(
  crop_start_x: 15, crop_start_y: 20,
  crop_width: 300, crop_height: 200
)
image.size # => Vector2d(300, 200)

By default, images will be cropped from the center. You can control this by setting crop_gravity_x and crop_gravity_y. DynamicImage will make sure the pixel referred to by these coordinates are present in the cropped image, and as close to the center as possible without zooming in.

Public Instance Methods

cmyk?() click to toggle source

Returns true if the image is in the CMYK colorspace

# File lib/dynamic_image/model.rb, line 76
def cmyk?
  colorspace == "cmyk"
end
gray?() click to toggle source

Returns true if the image is in the grayscale colorspace

# File lib/dynamic_image/model.rb, line 81
def gray?
  colorspace == "gray"
end
rgb?() click to toggle source

Returns true if the image is in the RGB colorspace

# File lib/dynamic_image/model.rb, line 86
def rgb?
  colorspace == "rgb"
end
safe_content_type() click to toggle source

Finds a web safe content type. GIF, JPEG and PNG images are allowed, any other formats should be converted to JPEG.

# File lib/dynamic_image/model.rb, line 92
def safe_content_type
  if safe_content_types.include?(content_type)
    content_type
  else
    "image/jpeg"
  end
end
to_param() click to toggle source

Includes a timestamp fingerprint in the URL param, so that rendered images can be cached indefinitely.

# File lib/dynamic_image/model.rb, line 102
def to_param
  [id, updated_at.utc.to_fs(cache_timestamp_format)].join("-")
end

Private Instance Methods

read_image_metadata() click to toggle source
# File lib/dynamic_image/model.rb, line 108
def read_image_metadata
  metadata = DynamicImage::Metadata.new(data)
  @valid_image = false
  if metadata.valid?
    self.colorspace = metadata.colorspace
    self.real_width = metadata.width
    self.real_height = metadata.height
    self.content_type = metadata.content_type
    @valid_image = true
  end
  true
end
safe_content_types() click to toggle source
# File lib/dynamic_image/model.rb, line 125
def safe_content_types
  %w[image/png
     image/gif
     image/jpeg]
end
valid_image?() click to toggle source
# File lib/dynamic_image/model.rb, line 121
def valid_image?
  @valid_image ? true : false
end