FastImageInline – inline images in your html code

You may not know this, and I didn’t until recently, but you can place images directly in your img tags. Not just the address of them, but the whole binary data – base 64 encoded.The technique is based on the Data URI scheme.Take a look at the source of Google News. Scroll down a bit and you should start to see image tags that contain base64 encoded data (well you will if you are on IE8 or another make of browser – not IE7). That’s what I’m talking about.The technique is particularly suitable if you have have small images that change often and you do not need the browser to cache them. In this case, the saved http connection and fetch that inlining the images affords you is a performance win.In case you find it useful I have extended my FastImage series with FastImage Inline, which is a gem and rails plugin that will take care of inlining your images.It’s simple to use – just like image_tag there is now a helper method inline_image_tag (and inline_image_path for image_path). Example


Result for request from a data-uri capable browser:

<img alt="Bullet" src="data:image/gif;base64,R0lGODlhCAANAJECAAAAAP///////wA  AACH5BAEAAAIALAAAAAAIAA0AAAITlI+pyxgPI5gAUvruzJpfi0ViAQA7" />

Result for a non-capable browser (eg IE7 or below):

<img alt="Bullet" src="/images/bullet.gif?1206090639" />

 InstallationNote that the FastImage gem must be installed first, check the requirements section below. As a Rails plugin

./script/plugin install git://

 As a Gem

sudo gem install sdsykes-fastimage_inline -s

Install the gem as above, and configure it in your environment.rb file as below:

... do |config|    ...    config.gem "sdsykes-fastimage_inline", :lib=>"fastimage_inline"    ...  end  ...

 Requirements* FastImage Browser supportAll modern browsers support this technique except for IE versions 7 and below. This is still a major segment of the market of course, but as IE users migrate to IE 8 this will become less of a problem. FastImage Inline uses a simple browser detection mechanism by looking at the user agent string. If the browser is known to not have support, or if we do not recognise it at all, we serve a normal image tag which includes the path to the image file in the src attribute. But if we know the browser can handle it, we send the image inline, and the browser won’t need to fetch it separately. LimitsReportedly IE8 will not handle data strings longer than 32k bytes. But it is probably unwise to inline images this big anyway. Google news serves images that are up to about 3.5k in length, and this seems a reasonable approach. However, FastImage Inline does not enforce any particular constraints, it is for you to decide.FastImage Inline does not cache the images it has read – so every time an image is sent it will be read from disk. This feature may be added in a later release. ConclusionInlining images is not for everyone, but it’s a useful technique in your toolbox for optimising delivery of certain kinds of pages or content. For more information check the comprehensive list of advantages and disadvantages on the Data URI scheme wikipedia page.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s