Ramon F Herrera wrote:
Let’s say I have scanned 2 documents which are very similar and I need to quickly find out the parts (words) in which they differ. A very useful technique is to alternatively display both images and the eye will quickly spot the differences. The catch is that the similar parts of the images have to be aligned as precisely as possible. I could attempt to do this by trial an error, moving one of the images around, measuring pixels, etc., but I bet there is a better way.
Is there?
TIA,
-Ramon
Yes, there’s a very simple way to do this.
Instead of pasting to layers, rotating images by half a degree, resizing by a pixel or two and shunting left and right until everything lines up – a task which could take hours to do correctly, why not let your computer do all the hard work instead. It can do the exact same job for you in a matter of seconds.
Open both images, and then click on File>Automate>Photomerge When it asks you which files you want to use, select the option "Use Open" and tick the box labelled "Attempt to automatically align images". Now click okay to proceed.
Photoshop will now present you with a composite image with both the source images correctly aligned over each other.
On the right hand side of this window, place a tick in the box labelled "Keep as layers", and then click Okay.
You should now have a new image open in your workspace, with two separate layers. Each layer contains one of the original source images, and they should be perfectly aligned.
Now just toggle the top layer on and off to highlight any changes between the two.