Here’s a nice summary of Photoshop CS4 new and upgraded features that pertain to photographers, from John Nack of Adobe:
There are a couple new very powerful features, and then there are alot of changes that make it easier to get around in Bridge and Photoshop, and easier to do things that you could already do before.
The first new feature is the ability to do local adjustments in Camera Raw using the graduated filter and the adjustment brush. Scott Kelby has a video demo of these at www.photoshopuser.com/cs4
These were also introduced into Lightroom 2, so if you use Lightroom (and followed my advice from an earlier post to upgrade to Lightroom 2), you already have these features and you aren’t using Camera Raw anymore. If you don’t use Lightroom, then the introduction of the ability to do your dodging and burning, local contrast, saturation and sharpening enhancements right in Camera Raw is a powerful reason to upgrade in itself. Imagine not having to go into Photoshop anymore for many of your images that don’t require sophisticated selections and masks. I consider it a huge efficiency boost. The one word of caution I have on this for you to be prepared for these tools to challenge your machine’s processing power, unless you have upgraded recently. I don’t think this is a reason not to upgrade to CS4, but you will have to be a little patient at times. (And if it is time for a new computer, check out my colleague Dave Marx’s blog, www.computersforphotographers.com for thoughtful articles and recommendations.)
The second brand new and cool feature is Content Aware Scaling. Consider those situations where you need to crop your image to different proportions, such as 5×7 or 8×10. But you don’t want to get rid of any of the image, and you also don’t want to squish it, making everyone really thin and tall, or widen it, making your paying customers fat. Assuming that there is negative space in your image, content aware scaling will try to find this negative space (or you can tell it where it is with an alpha channel), and will just shrink that down or expand it, preserving important areas like people at the right proportions. Russell Brown has an excellent video demonstration of this tool that I highly recommend you watch at http://av.adobe.com/russellbrown/ContentAwareScale_SM.mov
If this interests you but would be your only compelling reason for upgrading, I suggest downloading the 30 day trial version and experimenting with the tool. It is good, but it does have its limitations in terms of how smart it is and what situations it is useful for.
Whoops, there is one more cool new feature — it allows you to automatically combine multiple images shot at varying focus points, to get sharpness throughout the image. So when your depth of field is too shallow, shoot multiple images and use this Blend feature.
Ok, just one more major change — the ability to leverage 64 bit Windows processing. With this you can finally exceed the 4 GB limit that PS has been restricted to working with before. Of course if you don’t have or anticipate buying a new 64 bit machine in the next year, then this isn’t applicable to you.
Otherwise I consider most of the other features as nice to have. They make your day a little easier and the experience more pleasant.
Is it worth the $199? It depends on how dear $199 is to you these days, how much tolerance you have for learning new features, and how you value the new ones introduced. Unless you use Camera Raw and can take advantage of its local enhancement tools, the decision is not so clear cut as, in my opinion, the decision to upgrade from Lightroom 1 to Lightroom 2.