Ceci est une ancienne révision du document !
If you have been following our Darktable tutorials, you will know we are working with the latest version, not the version that is bundled in the Ubuntu Software centre. Disclaimer: In no way am I an expert in photo manipulation, I just know a guy who had a dog that gave me some fleas. I thought I may help you scratch an itch also. White balance, what is it? Well, it is the process of removing unrealistic color casts, so that objects which appear white in person are rendered white in your photo. Sounds simple, doesn’t it? Whilst most of us play it by eye, there is a way to set your white balance without ogling the picture every five seconds. Truth!
Si vous suivez nos tutoriels sur Darktable, vous savez que nous travaillons avec la dernière version, et non celle du Centre de logiciels d'Ubuntu.
Avertissement : je ne suis nullement un expert en traitement des photos. Je connais simplement un gars qui a un chien qui m'a donné des puces. Je pensais que je pouvais vous aider à vous gratter aussi.
La balance des blancs, c'est quoi ? C'est le processus de suppression des couleurs non réalistes, de sorte que les objets qui apparaissent blancs en réel soient rendus blancs sur votre photo. Ça paraît simple, n'est-ce pas ? Si la plupart d'entre nous la faisons à l'œil, il existe un façon de régler la balnce des blancs sans lorgner la photo plus de cinq secondes. Vraiment !
What you need to know: Though you can adjust the white balance on .jpeg-files, this is easier and more common to adjust it on RAW files. Because of the compression used in .jpeg-files, you adjust more than just the white balance afterwards. Before I ramble on about white balance, know that I live in sunny Africa, where clouds are few and far between. So my reference to white balance is usually the sun. You may live in an area where it is more cloudy, so the white balance in your photo may be an average of the light. The same goes for you guys in the city, with all its lights and reflective surfaces. (As well as night photography). So the fastest way to set the white balance is to select a pure white, or neutral reference, in your photo. That’s it, and I will show you how a bit later. The other way is to change your histogram in Darktable to waveform and try to align the colors. The two modules you will need are white balance and color correction.
Ce que nous devons faire
Bien que vous puissiez ajuster la balance des blancs sur des fichiers .jpg, c'est plus fcile et plus habituel de l'ajuster sur les fichiers RAW. À cause de la compression utilisée dans les fichiers .jpg, au final, votre ajustement déborde largement la balance des blancs.
Avant que je m'aventure dans la balance des blancs, sachez que je vis sous le soleil d'Afrique, où les nuages sont peu nombreux et dispersés. Aussi, ma référence de balance des blancs est en général le soleil. Vous vivez peut-être dans un endroit où il y a plus de nuages, et, ainsi, votre balance des blancs pour votre photo peut être une moyenne de la lumière. Même chose pour vous qui vivez en ville, avec toutes ces lumières et ses surfeces réflécissantes. (Et aussi pour la photographie de nuit).
Aussi, la façon la plus rapide de régler la balance des blancs est de sélectionner un blanc pur, ou une référence neutre, dans votre photo. C'est ainsi et je vous montrerai comment un peu après. L'autre façon consiste à modifier votrehistogramme dans Darktable pour onduler et essayer d'aligner les couleurs. Les deux modules dont cvous avez besoin sont la balance des blancs et la correction des couleurs.
If you look at my histogram here, you will see that blue is high and red is low. To get a more natural color, I need to raise the reds and lower the blues, without creating color casts. As this picture is a .jpeg-file, my chances of changing it much without making it unrealistic are slim. With RAW images, it is another ball-game altogether. This is why any photographer worth his salt shoots in RAW format. My father used to spend hours fiddling, setting his camera settings, before taking a photo. In effect, doing all this processing prior to getting a shot off. Let’s call it pre-processing, as film was not really editable afterwards. This is the appeal of digital photography for me. I can go out, snap pictures of animals, before they run away, and fix the small things later. Also, Darktable allows me to save my presets, as, when taking photos up the skeleton coast, the environment and lighting seldom change. The sky is always blue, the sand always white, and the sea is always green. But it may be different for you, so white balance may be more of a “thing”.
Open your picture in Darktable with the two modules that I mentioned. Go to your white balance module and you will see this: You will see ‘preset’ with a triangle to the right. Expand that and change it to “spot”. This will allow you to select a spot in your picture that is as white as possible. That selection will direct Darktable’s algorithm to do an “auto white balance” for you. Click and drag a rectangle on anything white. If your photo contains no white, find a neutral spot to do this and you can fine tune it afterwards. Don’ t be afraid to zoom in to 1:1 to find a nice white spot. You can also tweak it by hand. Open your color contrast and you will see “green vs. magenta” and “blue vs. green”. Right-click on the sliders to get the mouse adjustment curves or inch your sliders left and right very carefully. You should be able to get the same results as with the white balance. When adjusting a landscape photo, keep your eyes on the clouds, Pink clouds are not uncommon, but you do not see them in the middle of the day.
Don’t be afraid to open the same picture in another editor like RawTerapee and adjust it there. Different tools have different algorithms and sometimes one makes it perfect in one go. You can now mimic those settings in Darktable to get your perfect picture. Once you have your white balance sorted, you can start layering things on like HDR and masks. However, keep your eye on your histogram always. TIP: When you are done adjusting your white balance, and your picture was in direct sunlight add the color balance module. Now adjust your shadows offset by .010-0.20 negative, to keep that feeling of depth in your picture. That’s the low down-and-dirty on white balance. Obviously there is a lot of theory and practice behind it, but this should be enough to get you up and running without bogging you down in the details. It is instant results that will speed up your workflow. When the workflow is a slog, nobody enjoys it. Darktable post processing is actually relaxing therapy. Enjoy it. Questions? Comments? E-mail us on misc@fullcirclemagazine.org