Part 5. Wavelets as part of a broader workflow

In the previous articles I’ve demonstrated how to denoise and sharpen a photo using the wavelet tool in RawTherapee, how to treat the residual image and even how to ruin your photos! In all those cases the photos were treated with the different instruments of the wavelet tool only. In this article I’ll integrate the wavelets in a broader workflow to process a raw file and hope to show you why this can be a good idea.

I will work on a photo of an old and abandoned customs building on the French-Spanish border, that’s in Europe. My workflow is this. I start by adjusting the exposure with the tone curve tool in the Exposure section of the toolbox, then I move on to the Wavelets tool and I’ll end up with some sharpening and denoising using tools located in the Detail tab. In fact, this is my standard way of processing raw files in RawTherapee. Although the wavelet tool has instruments for edge sharpening and denoising, I prefer to combine them with the unsharp mask and noise reduction tools. Simply because I’m used to the last two tools and they work well in most cases.

So here we go. After opening the raw file the first thing I do is to apply the neutral profile (under Processing profiles at the top of the toolbox on the right).


The photo looks quite dull with this profile, but that’s exactly what I am after at this point.


1. Adjusting exposure

I underexposed this photo with 0,67 EV (two thirds of a f-stop) to avoid overexposed or washed-out areas, as I’m allergic to that. You can see that clearly in the histogram: the photographic information (the gray area in the graph) ‘stops’ somewhere at 80% on the x-axis as indicated by the red circle.


To correct for this underexposure I first activate the overexposure indicator by clicking on the corresponding button on top of the screen (or by hitting the < key [less than] shortcut).


Then I take the upper right node and drag it leftward, somewhere to a point above where the graph ‘stops’, like so.


If you should move this node further to the left, more and more of the light areas in the photo would loose their detail and turn to white. Here that is considered undesirable.

Now the white stripe in the middle starts to get black, which indicates overexposure. By dragging the node a little bit southwards, the indicator stops indicating so we have our highlights where we want them. To give more pitch and contrast to the photo, I apply a kind of S-curve to the graph, like so.

The photo looks already quite well, as shown below.

As a reference I include the unaltered but downsized jpg from the camera (I shoot raw+jpg usually).

As you can see the two photos are quite close, but I already prefer the raw with the adjusted tone curve. In general, in RawTherapee I prefer to work with the tone curve rather than to use the Auto levels button; the latter gives me too often photos with a suboptimal contrast.

2. Wavelets

Time for wavelets now. In the Wavelet Levels tab I leave the wavelet settings at their default values.


For this photo I use the wavelets mainly to work on the colors. (For others photos I use other wavelet sliders, that depends on the effects I want to achieve). Using the Contrast and Edge sharpening tools deteriorates very fast the gravel (the little stones) on the road on the foreground and left, so I keep these inactive.

After playing a bit around with the sliders in the Chroma section, I end up with these settings.


This results in the following. The detail windows are at 100%, first one is with chroma off…

… and the second one with chroma activated.


The differences are subtle but clear. Notice how the blues and the reds get more vivid.

When using the Chroma entry, it is important to switch often between full view and 100% view. Colors may be very pleasing when viewed at 100%, but disappointing when you see the whole photo and vice versa. This applies to most of the wavelet tools by the way.

Under the Gamut entry I check the option ‘Reduce artefacts in blue sky’. When viewed at 200% you can see a positive difference. You can also choose to use the sliders in the Denoise and Refine section to reach a similar effect.

I use the Residual entry to lift the shadows a tiny little bit (+10) and to set Chroma at 35. I have the impression that this last slider produces another effect than the Chroma entry above that I used earlier.

3. USM and NR

The last step is to make the image look somewhat sharper and to apply a little bit of noise reduction, mainly for the sky. I just activate the Sharpening filter in the Details tab of the toolbox (that is the second one from the left), and use the default method and default values. The same applies – that means using the defaults – for the Noise Reduction filter that can be found further below (not the Impulse Noise Reduction filter!).

The before/after photos are shown below. Click to see a greater version, use the left and right arrow keys to toggle between them or click View full size (1600px in this case), in a new window.