Rubber-band.

For some reason, Photoshop has this feature and Illustrator doesn't. Rubber-band is a feature of the pen tool that shows you what the path will look like after you click to set the anchor point, before you click to set the anchor point. This live preview is sorely missing from Illustrator, even though there's no reason not to have it. (Do they think it's too CPU-intensive or something? Ask the Photoshop team!)

Lineform has this feature, as well it should. Once you've tasted rubber-band, there is no doing without it.

The other feature I would suggest is Core Image, with a twist: Add the ability to apply a Core Image filter within a selection or path. It'd be work (you'd have to rasterize that area of the image, then apply filter, and of course it'd be for display only in a special Core Image type of layer), but it'd be yummy. I'd use this for blurring out sections of screenshots (e.g. people's email addresses or IM handles).

More generally: Non-destructive editing. Adjustment layers; filter layers (as I mentioned rather obliquely in my previous comment); being able to do anything (or as much as possible) with persistent paths rather than transient selections, so that the path could be changed in order to change the thing that was done with the path in the past.

Non-destructive editing is a very good general goal. You could probably think of even more cool features if you headed in that direction.

Lately I've been using Photoshop Elements, because it was all I ever needed from a PShop kind of program. I actually never really got into MacPaint, even all those years ago.

I did, however, fall deeply in love with MacDraw and still mourn its loss. I switched late to Adobe Illustrator, but have since stopped doing so much technical style drawing (used to be for games and the like). I don't mix much vector and pixel style so much - pixel is messing with images, vector is technical drawing. I'm pretty plain that way I guess.

Cropping.

I was born to crop.

Cropping with feedback on the exact image size is very handy.

As is Photoshops canvas dimensions dialog that allows you to shift the image based on how you resize the canvas.

Simple but very handy functionality.

Jonathan Wight's mention of the Canvas Size dialog reminded me of another feature that I always miss every time I'm without it: The ability to do things with numeric input. I regularly want to move this anchor point or this image 50 points this way or one-and-a-half centimeters that way. It'd be nice to have a dialog to do that, rather than having to hit shift-⇢ five times or (in the case of metric) approximate it.

That gave me another idea: Customizable origin. At the very least, top-left or bottom-left; I don't believe that anybody needs to go to Photoshop's extreme of having an origin at any random point. Bottom-left would be handy for me to study numbers to plug into my PostScript source files, besides also being useful for Carbon and AppKit programmers to mock up views and then later turn their mock-ups into real code/nibs. The rest of the world can use top-left.

Can you tell that I think a lot about what features I want in a graphics program? :)

As an aside, the RSS feed had a broken link to this post. There was a question mark before ".html" in the generated link.

Since you disqualified layers (harumph), I'll have to go with levels. I am starting to get comfortable with the much more powerful curves feature, but levels is the one effect that I at least try out on every single photo I edit. Brightness/contrast has its uses, but is a sucker's game for the most part.

Having just discovered Photoshop's ability to refine selections through addition, subtraction, and intersection, I am very excited about it, but that feature will never see the kind of use that levels does.

--mkb

My favorite is the crop feature of Photoshop. I can input dimensions I want the resulting image to be, and then crop the image with the box maintaining those proportions. Then, after I hit crop, it also automatically resizes the image for me.

Extremely useful.

Hard to say what my *favorite* is, but I've always been a big fan of the Healing Brush"in Photoshop, or the similar Retouch tool in iPhoto. I'm not sure if purists scoff at those or not, but I'm certainly impressed.

That's easy! The Gimp's grid-view font finder. Makes "seeing" the right font just that much easier.

I like the cloning tool and the magic lasso.

Curves.

Photoshop's curves tool is the most important and powerful color adjustment tool in the application. When an image is switched to L*a*b* color mode, curves adjustment layers combined with masks allow very fine control of color balance and contrast.

Hmm, somehow my name got swallowed in the last comment.

Anyway, I should add that the curves tool is a lot easier to use when a histogram is simultaneously visible. And also, stick to 16 bits/channel mode for L*a*b*, because in 8bit/channel mode, L*a*b* has such a high dynamic range that some amount of detail will probably be lost. Fortunately, with RAW images, they start out with 16 bits/channel.

Invert Selection!

I, for one, would like to see selections go away.

There's no need for them if your app can do paths (as Photoshop can): everything that selections do today can be easily transferred to paths (presuming that you have rectangular-path and freehand-path tools). And paths are persistent and mutable, unlike selections, which are transient, and therefore can't be mutated after they've been put to their purpose.

Consider the case of running a filter in Photoshop using a selection. Once you've done it, saved, and quit the app, you can't go back and run the same filter over some other part of the image; you can only run the filter anew, which breaks things like Gaussian Blur, and various lens-effect filters such as Core Image's Kaleidoscope.

Now consider a persistent filter layer constrained to a path and masked with an alpha channel. At any time, you can go back and add segments, remove segments, add or delete whole subpaths, reverse subpaths (= Invert Selection), and the effect of the filter is updated accordingly. Even if you save, close, quit, shut down, and move to a Himalayan summit for ten years.

Non-destructive editing is the way of the future. You heard it here first. :)

And by the way, there's no need to restrain it to filters. You could do plain fills, gradient fills, strokes — all the basic vector-app requirements. It would then be a hybrid, and with a good Mac-like UI on it, it would be a very powerful one.

Cropping, resize, and red-eye thing in iPhoto.

Peter:

Yes, we need filter layers masked with alpha channels. No, we don't need it all to use paths. My alpha channel mask can use 8 or 16 bits of transparency. This is way more powerful than any path is going to ever be. I can use the paintbrush tool to add or subtract transparency with fine control. Without very serious filesize and processor overhead, that's not going to be adequately replaced with paths.

I wasn't saying that alpha channels should be replaced by paths. In fact, I said “consider a persistent filter layer constrained to a path and masked with an alpha channel”. We should have both, with the path used first, and then the alpha channel.

Empty clipping paths do not clip (more precisely, they are of infinite bounds), so if you do not set a clipping path, it will not clip, and only the alpha channel will have any effect.

I'm no artist, so unlimited-undos is probably my most used feature ;-)