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Comment by eponeponepon | Hacker News Reader

Neat... I can see a use case for this in comparing pre- and post-final HTML documents (though I don't relish the headaches involved in actually acquiring both relevant sets of images at the same time out of our CMS).

Presumably it gets deeply murky when dealing with compressed jpegs?

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Rather than use this, you can use a custom tool built for comparing websites, for reasons similar to your use-case:

http://responsivenews.co.uk/post/56884056177/wraith

http://bbc-news.github.io/wraith/index.html

Thanks for sharing this. I actually had this exact idea last year, but BBC News implemented it better than I probably ever would have.

Thanks for the links! Wraith looks really useful for my current project.

There was a web dev addon that would take your comp images and overlay them while you were firebugging a pixel-perfect layout. I found it highly useful early in my career.

Edit: found it https://addons.mozilla.org/en-US/firefox/addon/pixel-perfect...

css filters work on any element, not just images. Maybe you could overlay two absolutely positioned documents on top of each other for a visual diff.

I've actually done that with text before - in particular, ensuring that links in a document had the same URL in their text content as in their href - by making one red and one green (and putting them in a monospace font for good measure), you can see straight away when they don't match.

I went with red and green because I intended to try using 3d glasses, but as it turned out, 'vaguely pinkish' was enough to see a match without actually looking.

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