Or: what not to do!
The wavelet engine in RawTherapee is a powerful tool for image processing but is equally capable of producing terrible results as well: excessive noise and artefacts, strange colors, unnatural tonemapping or a lack of sharpness, to name a few. In this article we’ll have a look at how to use the wavelets the wrong way. Once understood, it’s easier to use them the other way around!
For this article I use a photo that I took in a harbour in the south of France. It is a raw file (NEF), opened with the neutral profile and rotated a tiny little bit. That looks like so, not too bad as a starting point.
For the following example I use 7 wavelet levels, as can be set on the top of the wavelet panel (and what happens to be the default value).
Contrast
With the sliders in the Contrast section of the wavelet tool you can adapt the contrast of the different detail levels. This can be used, among other things, to give the sensation of depth or 3D to a photo. In the following example I used values of 200 for the levels 5, 6 and 7. As you can see this is way too much, but you might see the depth effect. With lower values you can indeed create a realistic – that is not exaggerated – depth effect.
I reset the photo to Neutral with the button with the same name and I position the sliders in the form of a stairway by clicking several times on the Contrast+ button, until the finest level 1 is at 198.
That gives this.
The boats show more profound shadows and the clouds as well.
Now change the ‘Apply to’ setting under the sliders from Shadows/Highlights to Whole luminance range…
… and we’ll get this.
Burk!! Nonetheless, judging on the number of photos like this on photosites like Flickr, there are many people out there who love this effect. I don’t, personally.
Switch the ‘Apply to’ setting back to Shadows/highlights, drag the left two (coupled) sliders of the highlight luminance range to the left and the two coupled sliders on the right in the shadow luminance range to the right, like so.
That results in this photo.
Still ugly but a bit less than the one we saw before! Remember that you can always decrease the effect of the wavelet sliders by using the Strength slider at the top of the wavelet panel. In this case, values around 60 lead to a pleasant looking image, but that is not the topic of this article – here we uglify!
Please understand that with these very same sliders we can have excellent results when used in a more balanced way.
Chromaticity
We can combine our contrast settings from above (66 for level 7, 198 for level 1) with the chrominance method ‘Link contrast levels‘, to be found under the Chromaticity entry of the wavelet tool. Set strength to 100 and the colors will be amplified based on the strength of the contrast settings. When the contrast sliders are set to neutral, this chrominance method will have no effect of course.
That gives this.
We are my 3d glasses?! Ugly again of course, so take care with this chroma method or dampen the effect by dragging the chroma-contrast link strength slider to lower values, or again with the main strength slider at the top of the wavelet panel.
The other two chrominance methods – Whole chromaticity range and Saturated/pastel – do not affect the photo in a dramatic way.
Denoise and refine
The denoise tool is very useful to reduce noise due to high iso or to reduce artefacts in blue skies that appear even at low iso values. In many cases it’s enough to place the upper slider of level 2 above the bottom slider of the same level.
But beware, even when the photo in the image window fits the screen (so you see the whole photo), you can already notice some changes in the image. Especially persons’ hairs might loose their details and transform into a kind of funny tulband, depending on the coiffure! So use with care.
Edge sharpness
This tool can be very determining – and often is – in how your photo will look in the end, especially the combination of the local contrast curve and the main strength slider.
First I uncheck all the other sections, including the contrast section, and then set the strength slider of Edge sharpness to 50 (that’s a lot), like so.
That gives this.
Screendump of the center of the photo at 100%.
Now we move the middle node of the local contrast curve up to the upper axis…
… and the photo starts to deteriorate a lot.
It is advisable when you use this tool to often switch between a zoomed view at 100% (keyboard shortcut Z) and a view where the photo fits in the image window (shortcut F). Photos taken with higher iso levels can profit – noise wise – when you lower the middle node below the horizontal dotted line. Drag the left node further down to reduce noise in the shadows. As already mentioned in another article, drag the right node up above the horizontal dotted line to increase the local contrast in the highlights.
Changing the ‘First level’ choice under the three main sliders to Unchanged or Reinforced makes things even worse.
Another recipe to ruin a photo is to move the contrast sliders in the contrast section above to values of 100 and more, and to use this edge sharpening tool at the same time with higher strength settings.
I repeat: this article is about what not to do with the wavelet tool! Using the sharpness tool in a controlled way can give excellent results.
How to ruin a photo using the sliders in the Residual image section is left as an exercise for the reader. I end this article with a photo that was tonemapped with the residual image tool and, in the Final touchup section, combined with an adapted d/v-h curve like so.
The d/v-h curve or slider alters the contrast balance between the wavelet directions vertical, horizontal and diagonal. In the resulting (ruined) image the diagonal dimension of the wavelets is clearly visible.
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