The other big news is vastly-improved control over levels and the long-awaited addition of curves, which Mueller says is his most-requested feature from longtime Photoshop users. Hopefully the documentation for Acorn 4 makes this clear, because it would be a shame for casual users to miss out here. On the downside, many of the most useful effects aren’t going to look right unless the user switches the blend mode away from 'Normal,' which he or she is only going to know to do after a lot of experience with Photoshop or a similar app. Coupled with the speed improvements I mentioned earlier, Acorn 4 lets you see your changes instantly reflected on the canvas, which is immediately rewarding and really encourages experimentation and playing around. For Acorn 4, Flying Meat borrows heavily from Pixelmator with a Spotlight-searchable list of layer filters (it subsumes Acorn 3’s separate lists for filters and layer styles), but it adds a big improvement - the filters are now non-destructive, and can be stacked, reordered, and readjusted after they’ve been applied. Image editors typically offer a ton of different styles and effects that you can apply to images, but the UI doesn’t usually make them very inviting if you don’t know what you’re doing. If you're coming from Acorn 3, it’s not immediately obvious that anything has changed, but that’s only before you click the 'fx' button and see the new Layer Filters palette for the first time. In the top half of the right-hand panel you get contextual settings for your current tool, and down below, a layers list complete with most of the features a Photoshop user would expect - grouping, layer masks, locking, and blending and opacity controls. 'I try and target the people who have used iPhoto,' says Mueller, giving an indication of the kind of visual simplicity he's aiming for. If you’ve used Photoshop you’ll be able to find your way around easily, and many of the keyboard shortcuts carry over, but the UI is stripped down to the bone. Over the years, Mueller has focused on making the app feel (and behave - more below) as 'Mac-like' as possible, and it shows. As far as aesthetics go, Acorn 4 is a good-looking app but it isn't trying to break the mold - everything is subdued, but clean and easy to navigate.

Mac photo preview ui