Yesterday I mentioned that Photoshop CS3 Extended features "image stack analytical filters." Er, yes, so that’s useful and relevant… how, exactly? In a nutshell, you can now treat multiple images as a single entity, running an algorithm across them non-destructively. So, for example, you could take a range of frames, then have Photoshop show you the average value of each pixel. Other algorithms include Entropy, Skewness, Summation, and Kurtosis*.
If this doesn’t yet sound scintillating, it’s probably because (I’m guessing) you’re not doing technical image processing work. It was to enable technical applications that image stack processing was added, and it’s the reason that one finds the feature in Photoshop Extended.
Having said that, photographer and author Martin Evening has come up with a great example of how combining multiple images into a stack, then aligning them and running the Median filter, can make moving objects (tourists, pigeons, bits of noise) disappear. Check out his story on Photoshop News for details and images. To demonstrate the process, I’ve whipped up this 75-second video demo using Martin’s images (hoping he won’t mind). And you can watch Russell Brown "reduce global warming" by removing the cars from the Golden Gate Bridge**.
Now, I’ll admit that seeing image stacks this way makes our marketing story a little more challenging. Didn’t we say that "Photoshop Extended" is meant to offer specific capabilities to people who need them, and that we haven’t withheld core photographic functionality in order to get every customer wanting/using Extended? We did say that, and it’s true. Image stacks are powerful and (I think) pretty cool, but I’d feel uneasy about overselling them a core photographic tool. There’s both power and potential here, but it’s a little more science-fair-ish than we’d like to sell for mainstream photography work.
Does that make sense? We are sincere in trying to group capabilities logically in Photoshop vs. Photoshop Extended. We did not want to be shady. (That’s why, for example, you’ll find "Video Frames to Layers" in both editions of PS: It was previously in ImageReady, and even though we’d have had an easier time saying "all the video stuff is in Extended," we didn’t want anyone’s arm to feel twisted.)
* Which, Chris Cox assures me, does not mean “bad breath.”
** This also demonstrates how stacks are related to video, which is core component of Photoshop Extended.