Ceci est une ancienne révision du document !
For the people just joining us, you can install Darktable from the software centre, however you may see: Look at the version when installing and If you roll your own, be aware that once you hit 2.6, you cannot downgrade. There are BIG changes from 2.4 to 2.6. The PPA for version 2.6 is:
sudo add-apt-repository ppa:pmjdebruijn/darktable-release
When you install Darktable, you will notice Lensfun is also installed. You can see if your lens is supported here: http://lensfun.sourceforge.net/lenslist/
Do not worry if yours is not, you can always calibrate yours.
That out of the way, let us step into some more photo editing and workflow.
Lets face it, Photo’s seldom look like the scene we remember. Sometimes the colours look faded, sometimes you just do not feel what you felt looking at the scene. One of the features of Darktable is the improved tone curve. In this issue, we would like to spend some time exploring this feature. For me, photos are about the feeling - so let us see if we can get the feeling back with colour manipulation. Feels? No, I thought not.
Quick tip - if you use Open Camera on your mobile phone, rename the .dng files to .raw
I was walking in the rain the other day and saw a rainbow, bright as can be and a double rainbow to boot. Yet every photo I took was washed out and the second rainbow was missing. Bear in mind that this is a mobile phone camera, it is not meant for anything more than ‘selfies’. As you can imagine, I was pretty disappointed, but as it was a phone, I did not delete it immediately. Usually, I would discard these type of photos and I am sure many of you would too. This, I thought, would be the best test for the L*a*b tone curve. Those of you who are used to RGB tone curves, may say, hey hold on….
Don’t feel alone if you do not know what L*a*b colour space is; I had to look it up on Wikipedia: https://en.wikipedia.org/wiki/CIELAB_color_space
The math is actually beautiful, but we are here for Darktable.
TL:DR version, it matches colours better to what your eyes see. Let us put it to the test.
As you can see it is rather boring, now where is the L*a*b colour?
To find the L*a*b channels, you need to open the Tone curve and change it with the little down triangle, to lab independent channels. Now, when you click on “a” or “b”, you’ll get a green to red and blue to yellow histogram? (Sorry, English is not my first language and if I used the incorrect word, just roll with it).
Now, drag a point on the line until you get the desired result. If you make a mistake, just double-click the little circle that you were dragging around and it will reset to default. The way it works is that the changes are more drastic the closer you drag around the centre. If I drag the “b” channel in a sort of s-curve, you will notice the green in the trees pop. I am going to adjust the “a” channel in more or less the same way: Now you can see the roof pop.
Lastly, I will adjust the “L” channel, which is the greys and contrast your eye sees. Again, I will make just a basic s-curve. S-curves are not always the best idea - it is high contrast, I am just using it as an illustration – it produces dramatic changes and this dreary picture needed dramatic change. S-curves are nice if the white balance on your picture is okay. Dragging below the line is darker and above lighter, and should you drag the top left, you will start seeing overexposure. Pay attention to the colour histogram in the top right. Do not squash your histogram into any of the sides.
Long story short, I drag it just enough to see the different greens on the tree and the grey’s in the clouds - with the blue smattering popping. If Darktable can do this to a random picture with no value, imagine what it can do for your high value pictures. This is not about applying a snapseed filter, this is about fine grained control over every aspect of your photo. This is by no means all you can do with Darktable, this is but a tiny part of what this powerhouse can do.
For those who want a bit more, I will give the penny tour. “L” (lightness) is roughly comparable to dragging all three R,G,B values in RGB or the sum thereof. The width is 256 (not a coincidence) from -128 to +128 for all three settings. The histogram of what you are editing is shadowed in the background of each of the channels (colour space). There is no substitute for practical experience; go play with it! The little hamburger menu (right above the “L”) has presets defined and you can save your own for future use. Happy editing!
We will cover another feature soon, but if there are any features you would like us to cover first, you know where to find us!