Paint.NET is one of the first things I get when I install windows somewhere. It's actually pretty frustrating that there isn't a nice simple image editing tool like that for Mac (or Linux). There's Gimp but...
I actually run paint.net inside a windows vbox on OS X. Pixelmator doesn't cut it. People say paint.net is simple but it's actually very powerful. It's just designed so well that it fools people into thinking it's simple.
One downside of pixelmator (as compared to Acorn) - you can't cut/paste Excel spreadsheets and get all the nice formatting and gridlines - Acorn handles that.
Also wondering what is wrong pixelmator. My trial ran out before I could decide whether it was really capable enough. It seemed like something wasn't quite right with it though.
The OSX alternative is Seashore. It's got the same goal as Paint.Net, to be a simple and easy to use image editor and is based on gimp, so it's stable and supports many things.
Krita is an impressive painting app, but not really designed for photo-editing. The developers of Krita currently have a Kickstarter campaign running to fund new features and possibly port it to the Mac
I'm too stupid to use Gimp. It's like every time I want to do something I think is really simple (and in other tools it is really simple) takes me longer to do in Gimp. Sometimes I can't get it right, give up and try something else.
While acengiano here is being downvoted, this is really one of my biggest gripes with Gimp. I'm having a terrible user experience.
It also doesn't help that I'm already well used to the paint.net/photoshop keyboard shortcuts. Besides Gimp having its own, different keyboard shortcuts, it also has some unique (and again different) conventions for how to use the mouse to select regions and stuff like that.
It may be equally productive once you're used to it, but I never liked Gimp enough to get into how the different ways it has chosen to do things actually works.
Gimp shortcuts aren't displayed, most often. Try creating a path and draw a line on it: You'll have to use the mouse very, very often. And you'll only find the shortcuts if you search online.
That's sad because you could be much more efficient with it.
GIMP is too complex (and too slow to startup) for simple image editing tasks.
None of the substitute photo viewer type apps on Linux really seem to stand in particularly well either - I like Shotwell at the moment, but it still lacks an easy to use crop/copy/paste workflow.
gThumb has been my favourite for years for quick resize/crop/rotate/white balance edits and image folder browsing. I don't know why it never was picked as default on Linux Desktops.
Depends on what you need on the Mac. For many common image editing tasks like rotating, cropping, resizing, saving in a different image format, some simple levels, exposure, saturation, sharpening and white balance adjustments as well as a few mark up tools (adding text, arrows, various shapes) Preview is perfectly adequate.
That’s probably more than enough for people who don’t actually create any images. Maybe the photo editing is a bit anaemic, but Photoshop’s photo editing tools are cryptic and hard to use for occasional users and those probably benefit a lot more from a simple editing panel with a few relevant sliders than from all the hard to unlock power of Photoshop.
The only notable absent thing is some sort of image straightening tool (only 90° rotations are possible).
If you want to do actual image editing there are a couple of excellent apps, namely Acorn and Pixelmator, both modern and frequently updated. You have to pay for them but that’s Mac software. You should have to pay for them. That’s only proper.
There's a large amount of free software available on Windows that doesn't have an equivalent on Mac. It matter less over time as more things move to the web, but Paint.net is still a good example.
I had a similar situation and came across... "Pinta" (Linux), I think it was. Did enough while retaining relatively simple and straight-forward controls. (It was no Paint.NET, but neither was it the beginner-adverse Gimp.)
I'd have to have another look to refresh my memory, and it was only a brief need, but might be worth having a look.
P.S. And of course, for vector graphics, "Inkscape".
And, oops: I see now that someone else mentioned Pinta already.
Preview is a markup tool, not an image editing tool.
On OS X it is either Acorn (my preferred tool, because you can cut/paste excel spreadsheets into it elegantly), or Pixelmator (which I also use occasionally)
Depends on what you mean by 'editing'. I can crop, resize, rotate and stitch together images in Preview which is editing in my book and covers about 95% of all image editing I ever need.
I've used Paintbrush for this use case because it gets the job done and is free; it hasn't been updated in a while but still seems to work fine under Maverick.
