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! In this issue, I would like to take your hand and guide you to an often underutilized module in Darktable. That is the ‘Equalizer’ module. Let’s dive right in, shall we? Open a RAW image and go to Darkroom. Any one will do.
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 une façon de régler la balance des blancs sans devoir lorgner la photo toutes les cinq secondes. Vraiment !
Dans ce numéro, j'aimerais vous prendre par la main et vous guider dans un module si souvent sous-utilisé dans Darktable. C'est la module « Égaliseur ». Plongeons directement dedans, n'est-ce pas ? Ouvrez une image RAW et allez dans la Chambre noire. N'importe laquelle conviendra.
As you can see (below), we have “luma”, “chroma” and “edges”. You can keep your mouse over each word for a nice description. The description for “edge” says: “only changes results for luma and chroma tabs”. What this means is that ‘edge’ does not work on its own. It works only on edits from the previous tabs. In other words, it is dependent on changes in the previous two tabs. If you mouse-over any one of the three “empty” boxes, you will see white circles appear. These are your nodes. Some words will also appear in the four compass directions, these will change with each tab. In luma, they are, “coarse”, “bold”, “fine”, and “dull”. You may wonder what is “coarse” in a photo. Well, those are large areas with little detail and more-or-less uniform color. If you look at our picture, the Rondavel roof’s are a great example. The opposite of coarse is fine, obviously, but in our picture, it is the flowers, where there is a lot of color change, and dark parts and highlights. However, I want to stress that on the luma tab, color is not the target; that is what the chroma tab is for. When you mouse-over the words that line the block, you will notice that you cannot mouse-over the word “smooth”. As soon as you do, it acts like those old windows 3.1 viruses and changes the word at the last second. Suddenly you have “noisy”. The word smooth now went and replaced “contrasty”. How now brown cow? Don’t panic, it is perfectly “normal”. Think of noise as the basement level to smooth. Drag some nodes or click inside the square to make some changes. At any point you can undo any change with ctrl+z as usual. To simply reset the graph, double-click. If you went into the basement by mistake, just go there again and double-click your mouse there to reset those graphs. To get an idea of what is happening, make some ‘s-curves’ in the positive and negative direction (Sine waves).
Reset the graph once you have an idea of how it works. Now I want you to raise each node, one-by-one, to the maximum of three, and have a Mexican wave run across the graph from left to right. At first, it will seem awful. Then get better, then sort of not really make big changes as the wave rolls out the right-hand side of the screen. Now lift node two (2) and node four (4) somewhat. Take a snapshot of your image, then reset it. Compare the two images. There are also shortcuts built into the module, so if you right-click, a drop-down menu will appear. Choose denoise. Suddenly that noise basement will get a linear value (it displays darker). Zoom into your image at least 1:1 and now adjust that line accordingly. Now switch from luma to chroma. You should still be able to see the darker triangle at the bottom. This works just like luma, but instead of light, obviously color. The same with the noise, it addresses color noise. Please feel free to play with this too, creating s-curves and Mexican waves across the graph. Don’t do it only in the positive, but in the negative too, so you can see where it changes. The only teacher here is experience. Notice that even if you make massive changes, the histogram changes only slightly. (We are tweaking only intensity).
Though you can go totally nuts, you will find that bell curves make the best bases to edit from. Although my photo has clipping, it is clipping in an area I was going to cut off anyway, so pay that no heed. My phone camera’s sensor – is a lot smaller than that of my camera – so I need to take that into consideration. You may also have noticed, whist dragging, that there is an odd shape that follows your mouse inside the graph block. This is the amount of detail that you change at a time. To change this, you simply select a node and scroll your mouse wheel forward or backwards. The circle will increase or decrease. This, in turn, adjusts that sort of diamond shape behind your mouse cursor. Think of this as your z-axis edit. You can click your mouse pointer between nodes, and the cursor will create a high or a low without your nodes moving. They seem to be locked horizontally and move only in the vertical plane. However, if you look at the bottom of the box, you will notice four (4) triangles. They will allow you to move the nodes along the x-axis.
Now for edge, you need to zoom in to the maximum, then move to a spot where low detail and high detail meet, for instance a wall and flowers. Even if you drag the nodes to the top and the bottom, the changes are minuscule. Remember I told you that it acts on the previous changes you made in the other tabs. Think of it as very fine tuning. Most of the time I do not even bother with this tab. You also may have noticed a slider below the graph box. Mix will take your edit and amplify or condense your edit already made. You can turn on blend and change any one of those, but I recommend that you leave it off as this is what you are adjusting. Don’t be afraid to try out the right-click menu short-cuts, as this can save you a lot of time. The denoise feature is also great for using at the end, after fiddling, as one can remove those pesky color noise one introduces with some coloring edits, without then fiddling with the denoise module again. I hope this opens up some more editing avenues for you. Calm your spirit and edit some photos! Questions? Comments? E-mail us on misc@fullcirclemagazine.org