Bring on the GIMP
Feature-wise, Shotwell lags well behind F-Spot offering only very basic editing controls. In fact, at this point Shotwell is basically just a photo organizer. However, the roadmap indicates the next release should support opening your images in external editors like GIMP or UFRaw.
Shotwell is also a native Gnome app with no need for the overhead of Mono, which appears to be the reason both Fedora and Ubuntu have embraced it.
If you're looking for a lightweight, speedy photo organizer and prefer to do your editing in GIMP, Shotwell fits the bill.
Early signs are RawTherapee is headed to a strong, third installment
The last option on my list is not really a Linux app, but Google does make a version of Picasa for Linux that runs under Wine. Frankly, Picasa for Linux doesn't offer much that you won't find in Shotwell or F-Spot, but if you're used to the interface from the Windows version then it may be a good choice.
If your photos are in camera RAW format, none of these editors are going to do you much good. That's where you'll need an advanced editor.
Camera RAW images are uncompressed and offer post-production controls that far outstrip what you can do with a JPEG, but the cost is greater complexity and a swamp of proprietary file formats - neither of which lead to good open source software.
One of the best options for editing and organizing RAW images on both Windows and Mac is Adobe's Lightroom 3. Other options include ACDSee or Apple's Aperture.
There are several quite capable RAW editing programs for Linux, but the best of the free options is undoubtedly RawTherapee.
RawTherapee offers impressive RAW processing tools (decoding is done by dcraw, but the image processing is all RawTherapee) that generate excellent results. Check out the comparison page which, though slightly out of date, shows how RawTherapee's algorithms stack up against those of Adobe, Bibble Labs and other software.
RawTherapee is also on its way to what looks like a very impressive update. Version 3, currently an alpha, is slated to bring a new curves editor, some additional perspective correction tools, true multi-image processing and more.
Transitioning from Lightroom or Aperture to RawTherapee can be a little bumpy, but if you give the app a chance you'll find it can do almost everything its competitors do.
Bibble: confusing but a match for anything on Windows
The last option is neither free, nor open source. Despite that, Bibble Labs continues to turn out a Linux release of its flagship Bibble Pro.
You can download a 14-day trial, so I took the latest version (5.1) for a test drive. I found that while the interface can be a little confusing, the processing tools themselves are every bit as good as what you'll find in the much more expensive Windows software.
Where Bibble falls on its face is in its failure to support the DNG file format. If you're coming from Lightroom especially, you probably have a lot of DNG files, which renders Bibble quite useless.
And of course at $200, with no source available, Bibble Pro 5 is definitely not for everyone.
While Linux has some capable photo editors that can handle the basics, whether you're an advanced or just casual photographer, the apps lack some extra features and polish found in similar offerings on other platforms.
That said, upcoming versions of Shotwell and RawTherapee look to close the gap considerably and should provide Linux users with enough options to fit everyone's needs. ®
What about Digikam?
I'm surprised that this review has left out what's probably the most sophisticated photo management app on Linux - Digikam. Digikam is KDE based, but runs just as happily under gnome, and offers several features that are not present in F-Spot. Definitely worth a look.
I hate to put it bluntly, but The Gimp, which I use and like, is no way near Photoshop for picture editing. Don't misunderstand me : I use it a lot, but it comes very far down my post processing path, in fact as the last tool before uploading to the web, because The Gimp is still limited to 8 bits, and not so good for archiving pictures without losing an enormous quantity of colour information. This said, for converting a 16 bits colour managed image into something optimized for the web, it's a treat.
The reviewer also forgot a fantastic combo found with KDE 4 : digikam and showfoto. It's really all you wish a raw software to be for filing, geotagging, archiving and uploading your pictures. From raw to web or print in a couple of minutes. It does correct chromatic aberrations, geometric aberrations, allow finely tuned perspective corrections and levelling. Truly a thing of beauty. The list of raw supported cameras is about the one of dcraw. And icing on the cake, it's of course colour managed and full 16bits. The digikam package also includes everything you should need to work on DNG raws that are now the de facto standard for high quality archival of raw images.
This is not photoshop for now (it might become when Krita is finally useable), but for conscious amateurs worry of degrading their files, it's got all you need and more.
No mention of DigiKam? It's aimed at the 'professional' user, incorporates both organising and editing tools and is purportedly cross-platform (Win, Mac, Linux). I've never got around to evaluating it myself, but it seems like a pretty serious contender.