Raw Therapee RAW converter - update

Posted on 29 March 2008, 22:19

As usual, this is not really a detailed review, but more of an “overview” user report, intended just to give a flavour of the very favourable impression RawTherapee has made on me.

I’ve updated this piece slightly to reflect my latest thoughts.

Keith 29 March 2008

I’ve been using a free RAW converter called RawTherapeeRT – for a while now, and it compares very well indeed with the alternatives.

Previously I was a long-time fan of Rawshooter Essentials but (presumably because I’ve changed a setting in the software somewhere that I can’t track down – or perhaps because of the need to “hack” it to get any joy at all with 40D files) I’ve noticed that something about the colours has changed for the worse.

Capture One 4 does an excellent job in terms of colour, and has good batch processing, which speeds up large conversion jobs: but its highlight recovery is rather disappointing, and it can be computer resource intensive.

Bibble Lite is quick and intuitive, but it doesn’t extract details nearly as well as the others, making it less than ideal for bird photography, and most Bibble conversions result in a colour shift I can’t fix: this is not a problem, but it means that I’m not seeing colours as I want them to be.

I also have Lightroom and CS3/ACR to choose from, both of which are excellent – but I like the idea of a lean, focused, “one-trick pony” RAW converter.

So, having seen a few recommendations for RT I thought I’d have a go, although if I’m honest I didn’t expect too much from it, based on experiences of other free converters.

Proof, if proof were needed, that you should never make assumptions…

RT comes with an impressive array of functions.

It uses the pretty ubiquitous DCRaw to decode RAW images, but (and I didn’t realise this until I was gently corrected by Bytec from the RT team) all subsequent processing from demosaicing onwards is based on RT’s own proprietary algorithms.

That’s astonishing. I freely admit that I’d initially assumed RT to be, in essence, an effective “front end” for DCRaw (there are a lot of those about) and the fact that everything about it beyond the decoding is original, impresses the hell out of me.

Its main features are:

Selectable high performance demosaicing algorithms (EAHD and HPHD)
Image post processing in 16 bit/channel mode
Exposure control in RGB space
Auto exposure with adjustable clipping point, Exposure compensation, Shadow and highight compression, contrast adjustment, curve editor
White balance adjustment in RGB space
In-camera, automatic and spot white balance options
Temperature/Green tint fine tuning
Highlight Recovery
Shadows/Highlights control in RGB space
Basic Luminance curve tool to modify the luminance channel in CIELab color space
Brightness/Contrast adjustment, curve editor
USM sharpening applied on the CIELab luminance channel
Classic USM parameters (Radius, Amount, Threshold), option to avoid noise amplification, sharpening halo control
Color shift control in CIELab color space
Allows color shift by shifting the CIELab “a” and “b” channels
Color booster applied on the CIELab “a” and “b” channels
Amplifies color channels “a” and “b” together or separately
Avoids color overamplification in high chrominance areas
Option to avoid clipping caused by too high color boosting
Luminance denoising algorithm applied on the CIELab luminance channel
Edge sensitive method to preserve as much details as possible
Color denoising tool applied on the CIELab “a” and “b” channels
Classic gaussian blur or edge sensitive blurring of the color channels
Fast switching between different postprocessing profiles
Image flipping horizontally or vertically, rotation by 90 degrees clockwise or counter clockwise
Arbitrary image rotation (straightening tool)
Simple lens distortion correction
Crop tool
Chromatic Aberration correction tool
ICC based color management
Change History with bookmarks to support before/after checking
Output options:
Supported file formats:
JPEG (8 bit), PNG (8 or 16 bit), TIFF (8 or 16 bit)
EXIF data is preserved in JPEG output (except crw files)
Output directory and automatic file naming highly customizable
File browsing with thumbnails

The things that matter to me

It’s an impressive feature set, many of which you really want to see in a good RAW converter, and quite a few which are a surprise, possibly more to be expected in image editing applications rather than converters – but if that means that more work can be done at the RAW stage, so much the better.

Highlight recovery is particularly important to me (which is one reason why I don’t use Canon’s DPP, good as it is otherwise).

RT would fail at the first hurdle if its highlight recovery tool wasn’t up to the job.

Well I’m delighted to say that highlight recovery works extremely well. In fact it is as good, generally speaking, as the class-leading Highlights/Shadows tool in CS3, and even provides two recovery options.

The first is Luminance Recovery, where the recovery algorithm extrapolates the missing detail from the remaining luminance information in the image resulting in recovered detail being essentially monochrome.

There is also Colour Propagation, where the extrapolation is based on available RGB data, which should result in detail having some colour.

In reality I generally can’t a difference in results, and tend to stay with the default Luminance Recovery.

The only slight fly in the ointment there is that if highlight recovery is applied too heavily, it can generate a dark halo beyond the highlight area. You just need to be careful in applying it.

In addition, RT seems to be better at extracting fine detail and sharpness (thanks in part its unique conversion algorithms) than anything else on my PC.

But even here RT gives the user some interesting choices. In addition to classic USM, there is the option to sharpen using Richardson-Lucy (RL) Deconvolution, a sophisticated multiple-iteration algorithm which apparently results in better results than USM.

I haven’t even touched this option yet – RT USM is pretty good for capture sharpening – but I intend to take a serious look at it shortly – a comparison article will doubtless result if the differences are worthwhile.

Colours are very good – as good as Capture One – and I like the subtle Colour Boost tool too.

Among the welcome extras are a dedicated Local Contrast Enhancement tool. I’ve only recently discovered this trick myself and have found it to be very useful for adding “pop” to an image, and to have it built in to RT is a nice bonus.

Another favourite function is the ability to easily create a Postprocessing Profile – a preset “snapshot” of exposure and other settings to use as a starting point for conversion.

Importantly, the RT interface is user friendly, efficient and intuitive. Although a very good manual exists, it’s hardly necessary to anyone with a basic understanding of working with RAW files.

So, it has all of my “must have” functions, but do they work?

Yes. I’m delighted with the image quality of the conversions RT provides.

The results I’m getting from RT have a sharpness, depth of colour and “pop” to them which is every bit as good as anything I’ve managed to get from the other converters I’ve used, including such big hitters as Adobe Lightroom.

One important point – and this is something that nearly caught me out initially – is that while processing files in RT, the image will often look decidedly noisy as you work away, and the temptation is to apply some noise reduction as part of the conversion process.


Saved images are much cleaner than the preview image in the program’s workspace leads you to expect, and it’s likely that you won’t need any NR at all – but if you do, you can always apply it in dedicated noise reduction software like my favourite, Neat Image.

That said, the built-in noise reduction processing is pretty good – especially with chroma noise.

Now then, RT doesn’t really have batch processing capabilities (no loss to me) but as a dedicated RAW conversion application, it’s really about as good as it gets. (Note – from R2.4, it does have batch processing).

The current version – 2.3 – is very stable and usefully quick, user interface “quirks” notwithstanding.

Interface improvements are the priority for the next release, but in truth there’s nothing inherently problematic with the UI now, it’s just different here and there.

RT also supports 40D files converted to DNG, as well as 30D CR2s.

One thing it won’t do is process sRAW files – that isn’t a problem for me, but it’s worth knowing. (Note – from R2.4 sRAW is supported).

All in all this is a serious RAW converter: it’s easy to use, efficient, and the results speak for themselves.

It’s a small file too – the download is only about 8 mb – and because it doesn’t write to the Registry on installation, it is “portable” and can be used from a USB pen drive, which might be useful.

I recommend it very highly, and actually prefer it to RawShooter Essentials – and that’s praise indeed.

To close, a few examples of 30D and 40D files converted in RT and edited in Paint Shop Pro X.

Note that the 40D shots are all heavy crops (all taken without the help of the 1.4x TC I was using on the 30D shots) but I think they give a great indication of how good the 40D’s colours are; how well RT brings ‘em out; and how well it makes the most of any fine detail to be found.

Sanderlings - Raw Therapee Mandarin - Raw Therapee Black stork - Raw Therapee Knot - Raw Therapee Sanderling - Raw Therapee Herring gull - Raw Therapee Curlew - Raw Therapee Sanderling - Raw Therapee


What do you think?

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