Ceci est une ancienne révision du document !
Welcome back to another quick(-ish) insight into the very powerful and highly underrated Darktable. We are working with version 2.6 – NOT the version that ships with Ubuntu. There are features in 2.6 that you will not find in previous versions. These are features we are looking at. Darktable 2.6 (or higher) can be obtained via snap / flatpak / appimage or PPA. (If you are attempting this, you know how to install software on your Ubuntu system).
Today everything is digital, it makes economic sense. However there are people who prefer analogue. Like music, some people prefer vinyl to CDs. The same with taking pictures. Instead of us wasting money on film, then having to dispose of it in a landfill, how about we emulate what a film camera would have done in software? This is one of the new features Darktable brings to the… erm… table. This is why it is called ‘filmic’. Today, however, we will be doing things slightly differently. This time the homework comes first. Have a look at the filmic author’s website here: https://eng.aurelienpierre.com/2018/11/30/filmic-darktable-and-the-quest-of-the-hdr-tone-mapping
Please pay attention to the “Place in workflow” section.
Before you even attempt the filmic module, you need to traverse these three mentioned bullet points in the workflow. Aurélien Pierre also recommends you turn off the base curve. Here: https://discuss.pixls.us/t/introducing-the-filmic-module-in-darktable/9758
I need you to select a picture from your stash that you think could benefit from a bit of filmic treatment. If you have done your homework, and followed the three steps (bullet points) above, we can continue.
If you look at the filmic module, it may seem a bit confusing at first, unless you are a professional photographer. You may trust the auto-tune algorithm, but, in my experience, it is horrible. Load up a photo and click the little “auto tune levels” eye dropper… (above the words “filmic S curve”). It should look like someone took a milky white paste and coated your photo with it. That obviously will not do! Undo!… That is where our tutorial starts. The filmic module tries to emulate film, in a way that it blends the outliers. Trimming the highs and lows, but leaving the mid tones alone. I will try to use music editing as a comparison, as I am not schooled in the terms for graphic editing. So, in music terms, you put it through a high pass filter and a low pass filter. This gives us a softer image, like that of a film camera.
If you look at the sliders, the first will be “middle grey luminance” and I am sure there is a reason it is always at 18%, but we need to drop it. I suggest 9%-11% as this is usually good for most pictures taken indoors with a flash. (Only experience will let you recall values like that from the top of your head. So please play with it!). Try it on for size and see. Remember, I am trying to guide you into understanding how Darktable’s filmic module works, so none of the values are set in stone. A photo shot in harsh sunlight may actually require you to move it to 21%! I need you to get a feel for it. You can calibrate your eyes… YES! I said your eyes, by clicking the eye dropper and seeing where the algorithm sets the slider. Please, at any time, stop and smell the flowers… I mean read the tool tips.
The next slider is the “white relative exposure” - which has nothing to do with your flasher redneck uncle. When moving this slider, I need you to keep an eye on your histogram, as it can easily leave the square. Here too you can click the eye dropper to ‘automagically’ set it for you. I have to point out that the setting here depends on your setting of the previous slider. To understand this, set your “middle grey luminance” to 7% and click the eye dropper next to “white relative exposure”, then change it to 21% and do the same. It is an algorithm, it takes the previous slider in to consideration, it does not see your photo. So try to keep yours close to where it would be if it were on auto. (It does not have to match exactly).
The next slider down is the “opposite” of the previous one, the “black relative exposure”. As the tool tip says, it is between grey and pure black. Again, this depends on the first slider – should you choose the auto setting. Thus, if your grey was standard at 18%, the white would be below and the black above on a slider, or left and right, if you prefer, but it all hinges on that first slider. When you move the slider, pay attention to the histogram! Like music , you lose quality when their levels go out of bounds. (In music editing, it is called clipping; I am not sure what to call it in graphic editing). You want your histogram to go to the left as far as possible without going out of bounds. This should deepen the shadows and bring up nice contrast. You have to decide the ‘depth’ of you photo here, I cannot tell you where it *should go. I can only tell you what to look out for. Just try not to be too far off the auto setting, lest your picture looks “shopped”.
Right. Looking at the module, you should see a line and the words “filmic S curve”. This is the second part of the module. Here you need to pay attention – like a drunken sailor.
Every slider we will now move, will affect the “s-curve”, so keep your eye on that curve. At any time you can right-click a slider to bring up an alternative way to adjust it. Should you move the “contrast” slider, you will see that it moves the “core” piece of the s-curve between the two dots, clockwise or anti-clockwise. This slider is not as sensitive as the others, so feel free to slide it a bit. Just realise that the third slider will also move the core. This in turn will have an effect on the highs and lows of the “shadows/ highlights” in turn.
The second slider is “latitude”. It is not a horizontal line but the distance between the two points on the “s-curve”. This is the mid tones I was talking about in the beginning. The wider they are apart, the more of your “core“ remains. All our editing, our so-called high pass and low pass filters, affect only what lies beyond these two points. It is like trimming the frayed ends of a string. The longer the frayed ends, the more you can trim, but the shorter the string will be. You cannot cut the string (core), only the frayed edges. I hope that makes sense to you. You will see the lowest the slider can go is 2EV. The higher you move the slider, the wider the gap between the two points in the centre gets and the higher your histogram climbs, leaving you less space to make edits before it “clips”.
The next slider down is “shadows / highlights balance”. This moves the ”core” part or the string itself. Unlike the fist slider, this moves the “core” diagonally. Like in life, we need balance, so my advice is to try and keep it in the centre, unless you are making an artistic piece. Again, this is your photo, it has to look good to you and there will be situations where it will not be dead centre. (But usually aim for more-or-less centre).
Next up is “global saturation”. The name of the slider may be misleading as it effects the outliers and not the whole. If you slide it down from 100%, the changes are drastic. Colours give way to grey-scale. The changes that occur first are where the outliers are, and only at the lower end does it start affecting the mid tones. This slider again is algorithmically attached to the one above it. Thus it affects the shadows and highlights first.
The “extreme luminance saturation” is like a fine tune knob for me.
“Intent” is something I can not wrap my mind around… It ‘fixes’ boo-boo’s from what I understand. I have not used it or needed to use it yet. If your colors are faded or reversed through over saturation, this ‘fixes’ it. I use fix loosely – I have made things horrible, then used this tool and it did not seem to fix anything.
The checkbox “preserve chrominance” does nothing but keep the RGB ratios. Clicking this may cause Red / Blue over saturation. You can read more here: https://discuss.pixls.us/t/darktable-filmic-and-saturation/10622/10
That brings us to “destination display”. This requires you to know something about the display you will be sending your image to. I suggest reading the full specifications and the range it can display. This helps fix that ‘but it works on MY computer’ nonsense. If the Gamma is out on a display, your image can look faded, for instance. This will help correct it before it is displayed, if the display itself cannot.
The last one is blend mode. It is off for a reason. Feel free to go through all the options, but there is nothing “filmic” here.