Is there a simple way to get image dimensions in Ruby? - ruby

Question

I'm looking for an easy way to get width and height dimensions for image files in Ruby without having to use ImageMagick or ImageScience (running Snow Leapard).

Answer 1

As of June 2012, FastImage which "finds the size or type of an image given its uri by fetching as little as needed" is a good option. It works with local images and those on remote servers.
An IRB example from the readme:
require 'fastimage'
FastImage.size("http://stephensykes.com/images/ss.com_x.gif")
=> [266, 56] # width, height
Standard array assignment in a script:
require 'fastimage'
size_array = FastImage.size("http://stephensykes.com/images/ss.com_x.gif")
puts "Width: #{size_array[0]}"
puts "Height: #{size_array[1]}"
Or, using multiple assignment in a script:
require 'fastimage'
width, height = FastImage.size("http://stephensykes.com/images/ss.com_x.gif")
puts "Width: #{width}"
puts "Height: #{height}"

Answer 2

You could try these (untested):
http://snippets.dzone.com/posts/show/805
PNG:
IO.read('image.png')[0x10..0x18].unpack('NN')
=> [713, 54]
GIF:
IO.read('image.gif')[6..10].unpack('SS')
=> [130, 50]
BMP:
d = IO.read('image.bmp')[14..28]
d[0] == 40 ? d[4..-1].unpack('LL') : d[4..8].unpack('SS')
JPG:
class JPEG
attr_reader :width, :height, :bits
def initialize(file)
if file.kind_of? IO
examine(file)
else
File.open(file, 'rb') { |io| examine(io) }
end
end
private
def examine(io)
raise 'malformed JPEG' unless io.getc == 0xFF && io.getc == 0xD8 # SOI
class << io
def readint; (readchar << 8) + readchar; end
def readframe; read(readint - 2); end
def readsof; [readint, readchar, readint, readint, readchar]; end
def next
c = readchar while c != 0xFF
c = readchar while c == 0xFF
c
end
end
while marker = io.next
case marker
when 0xC0..0xC3, 0xC5..0xC7, 0xC9..0xCB, 0xCD..0xCF # SOF markers
length, #bits, #height, #width, components = io.readsof
raise 'malformed JPEG' unless length == 8 + components * 3
when 0xD9, 0xDA: break # EOI, SOS
when 0xFE: #comment = io.readframe # COM
when 0xE1: io.readframe # APP1, contains EXIF tag
else io.readframe # ignore frame
end
end
end
end

Answer 3

There's also a new (July 2011) library that wasn't around at the time the question was originally asked: the Dimensions rubygem (which seems to be authored by the same Sam Stephenson responsible for the byte-manipulation techniques also suggested here.)
Below code sample from project's README
require 'dimensions'
Dimensions.dimensions("upload_bird.jpg") # => [300, 225]
Dimensions.width("upload_bird.jpg") # => 300
Dimensions.height("upload_bird.jpg") # => 225

Answer 4

There's a handy method in the paperclip gem:
>> Paperclip::Geometry.from_file("/path/to/image.jpg")
=> 180x180
This only works if identify is installed. If it isn't, if PHP is installed, you could do something like this:
system(%{php -r '$w = getimagesize("#{path}"); echo("${w[0]}x${w[1]}");'})
# eg returns "200x100" (width x height)

Answer 5

I have finally found a nice quick way to get dimensions of an image. You should use MiniMagick.
require 'mini_magick'
image = MiniMagick::Image.open('http://www.thetvdb.com/banners/fanart/original/81189-43.jpg')
assert_equal 1920, image[:width]
assert_equal 1080, image[:height]

Answer 6

libimage-size is a Ruby library for calculating image sizes for a wide variety of graphical formats. A gem is available, or you can download the source tarball and extract the image_size.rb file.

Answer 7

Here's a version of the JPEG class from ChristopheD's answer that works in both Ruby 1.8.7 and Ruby 1.9. This allows you to get the width and height of a JPEG (.jpg) image file by looking directly at the bits. (Alternatively, just use the Dimensions gem, as suggested in another answer.)
class JPEG
attr_reader :width, :height, :bits
def initialize(file)
if file.kind_of? IO
examine(file)
else
File.open(file, 'rb') { |io| examine(io) }
end
end
private
def examine(io)
if RUBY_VERSION >= "1.9"
class << io
def getc; super.bytes.first; end
def readchar; super.bytes.first; end
end
end
class << io
def readint; (readchar << 8) + readchar; end
def readframe; read(readint - 2); end
def readsof; [readint, readchar, readint, readint, readchar]; end
def next
c = readchar while c != 0xFF
c = readchar while c == 0xFF
c
end
end
raise 'malformed JPEG' unless io.getc == 0xFF && io.getc == 0xD8 # SOI
while marker = io.next
case marker
when 0xC0..0xC3, 0xC5..0xC7, 0xC9..0xCB, 0xCD..0xCF # SOF markers
length, #bits, #height, #width, components = io.readsof
raise 'malformed JPEG' unless length == 8 + components * 3
# colons not allowed in 1.9, change to "then"
when 0xD9, 0xDA then break # EOI, SOS
when 0xFE then #comment = io.readframe # COM
when 0xE1 then io.readframe # APP1, contains EXIF tag
else io.readframe # ignore frame
end
end
end
end

Answer 8

For PNGs I got this modified version of ChristopeD's method to work.
File.binread(path, 64)[0x10..0x18].unpack('NN')