h1. FastImage

h4. FastImage finds the size or type of an image given its uri by fetching as little as needed

h2. The problem

Your app needs to find the size or type of an image.  This could be for adding width and height attributes to an image tag, for adjusting layouts or overlays to fit an image or any other of dozens of reasons.

But the image is not locally stored - it's on another asset server, or in the cloud - at Amazon S3 for example.

You don't want to download the entire image to your app server - it could be many tens of kilobytes, or even megabytes just to get this information.  For most common image types (GIF, PNG, BMP), the size of the image is simply stored at the start of the file.  For JPEG files it's a little bit more complex, but even so you do not need to fetch much of the image to find the size.

FastImage does this minimal fetch for image types GIF, JPEG, PNG, TIFF and BMP.  And it doesn't rely on installing external libraries such as RMagick (which relies on ImageMagick or GraphicsMagick) or ImageScience (which relies on FreeImage).

You only need supply the uri, and FastImage will do the rest.

h2. Features

Fastimage can also read local (and other) files, and uses the open-uri library to do so.

FastImage will automatically read from any object that responds to :read - for
instance an IO object if that is passed instead of a URI.

FastImage will follow up to 4 HTTP redirects to get the image.

FastImage will obey the http_proxy setting in your environment to route requests via a proxy.

You can add a timeout to the request which will limit the request time by passing :timeout => number_of_seconds.

FastImage normally replies will nil if it encounters an error, but you can pass :raise_on_failure => true to get an exception.

h2. Examples

<pre lang="ruby"><code>
require 'fastimage'

FastImage.size("http://stephensykes.com/images/ss.com_x.gif")
=> [266, 56]  # width, height
FastImage.type("http://stephensykes.com/images/pngimage")
=> :png
FastImage.type("/some/local/file.gif")
=> :gif
FastImage.size("http://upload.wikimedia.org/wikipedia/commons/b/b4/Mardin_1350660_1350692_33_images.jpg", :raise_on_failure=>true, :timeout=>0.1)
=> FastImage::ImageFetchFailure: FastImage::ImageFetchFailure
FastImage.size("http://upload.wikimedia.org/wikipedia/commons/b/b4/Mardin_1350660_1350692_33_images.jpg", :raise_on_failure=>true, :timeout=>2.0)
=> [9545, 6623]
</code></pre>

h2. Installation

h4. Gem

bc. gem install fastimage

h4. Rails

Install the gem as above, and add it to your Gemfile.

Then you're off - just use @FastImage.size()@ and @FastImage.type()@ in your code as in the examples.

h2. Documentation

"http://sdsykes.github.io/fastimage/rdoc/FastImage.html":http://sdsykes.github.io/fastimage/rdoc/FastImage.html

h2. Benchmark

It's way faster than conventional methods (for example the image_size gem) for most types of file when fetching over the wire.

<pre lang="ruby"><code>
irb> uri = "http://upload.wikimedia.org/wikipedia/commons/b/b4/Mardin_1350660_1350692_33_images.jpg"
irb> puts Benchmark.measure {open(uri, 'rb') {|fh| p ImageSize.new(fh).size}}
[9545, 6623]
  0.680000   0.250000   0.930000 (  7.571887)
  
irb> puts Benchmark.measure {p FastImage.size(uri)}
[9545, 6623]
  0.010000   0.000000   0.010000 (  0.090640)
</code></pre>

The file is fetched in about 7.5 seconds in this test (the number in brackets is the total time taken), but as FastImage doesn't need to fetch the whole thing, it completes in less than 0.1s.

You'll see similar excellent results for the other file types, except for TIFF. Unfortunately TIFFs tend to have their
metadata towards the end of the file, so it makes little difference to do a minimal fetch. The result shown below is
mostly dependent on the exact internet conditions during the test, and little to do with the library used.

<pre lang="ruby"><code>
irb> uri = "http://upload.wikimedia.org/wikipedia/commons/1/11/Shinbutsureijoushuincho.tiff"
irb> puts Benchmark.measure {open(uri, 'rb') {|fh| p ImageSize.new(fh).size}}
[1120, 1559]
  1.080000   0.370000   1.450000 ( 13.766962)
  
irb> puts Benchmark.measure {p FastImage.size(uri)}
[1120, 1559]
  3.490000   3.810000   7.300000 ( 11.754315)
</code></pre>

h2. Tests

You'll need to @gem install fakeweb@ to be able to run the tests.

bc.. $ ruby test.rb 
Run options: 

# Running tests:

Finished tests in 1.033640s, 23.2189 tests/s, 82.2337 assertions/s.             
24 tests, 85 assertions, 0 failures, 0 errors, 0 skips

h2. References

* "Pennysmalls - Find jpeg dimensions fast in pure Ruby, no image library needed":http://pennysmalls.wordpress.com/2008/08/19/find-jpeg-dimensions-fast-in-pure-ruby-no-ima/
* "DZone - Determine Image Size":http://snippets.dzone.com/posts/show/805
* "Antti Kupila - Getting JPG dimensions with AS3 without loading the entire file":http://www.anttikupila.com/flash/getting-jpg-dimensions-with-as3-without-loading-the-entire-file/
* "imagesize gem documentation":http://imagesize.rubyforge.org/
* "EXIF Reader":https://github.com/remvee/exifr

h2. Licence

MIT, see file "MIT-LICENSE":MIT-LICENSE