Post-processing tutorial #1: Working with Curves adjustments
01 November 2015
My last post, ‘Street Portraiture – the 100 Strangers Project, Part II‘, received a lot of positive feedback regarding the post processing tips about fixing in-camera mistakes, so I thought it may be helpful to write more about this particular topic for those who would like to delve deeper into the subject!
First, a question: do you have a question or request for me to write about in my next post? It could range from a question about how I processed a certain photo, to more general areas of editing you’d like to read about. If you do, please comment below or contact me directly, and I will aim to answer in the next instalment! Otherwise I will pick topics I think would help the most people.
Working with the tone curve in Lightroom or Photoshop
When I was a newbie at photo editing, I was quite scared of Curves adjustments. I had no idea what they did, how they worked, and which channel option I should select – RGB, Red, Green, or Blue? Without knowing what they are doing, I ended up randomly clicking on the curves, adding and moving points, and 99% of the results looked absolutely terrible.
But Curves are in fact really useful, and they’re a super quick (and surprisingly easy!) way to alter the mood of your image, so it’s worth learning more about them.
So what do Curves actually do?
I don’t have a textbook explanation, so please bear with the unscientific explanation as I understand it – I will try to explain in simple terms.
There are two things Curves can do.
The RGB curve (which is the default setting when you open the panel) can control the exposure at any given point of the histogram, across the whole dynamic range of the image. However, the name is misleading because by default the curve is actually a straight line!
By changing the exposure level at certain points on the curve, we can adjust contrast and make our image pop.
A rule of thumb to get images looking better without going overboard is to create a gentle S-curve. You can also lift the midtone area (exactly in the middle of the curve) just a bit if you need to. This keeps the deepest shadows intact but brings out the rest of the details more. How much you tweak will vary by image but it’s safe to say that I never leave my RGB curve as a straight line!
Notice the difference between the SOOC shot below, and the same shot with only the RGB curve adjusted. It already looks much better.
The individual Red/Green/Blue curves control the colour tones in the image, again, across the entire range from blacks to whites. They also start as a straight line by default, but if we adjust them we can tint areas of the image to have more or less red, green or blue tones in them.
Adding more of any of these colours, though, will remove the same amount of their ‘opposite’ colours from that area of your image. The opposites are as follows:
Red ⇔ Cyan
Green ⇔ Magenta
Blue ⇔ Yellow
Less is more with colour curves; a subtle change is most often the best to obtain a slightly film-like look. My favourite curve to adjust is the Blue one. I add some blue to the darker parts of the image, usually up until the midtone range (in the middle of the graph).
Our demo photo doesn’t actually need colour adjusting as I’m happy with it as it is, but for the sake of the example, here it is with a few variations on colour curves. You can see how I increased or decreased the Reds, Greens or Blues and how that affects the look.
You have to be careful not to make skin tones look unnatural, and they are most often in the midtone or highlight range, so for portraits we have to avoid too much messing about in those areas. Of course if you use Photoshop, you have the option of using layer masks and not worry about this, but in Lightroom you don’t have that option so readily available.
Playing with the colour curves is quite subjective, and what may look all right to one person may look over-processed and unnatural to others. If I’m not sure about something I’ll leave it until the next day, then go back to it and review it with a fresh eye. I like my images to look mostly natural but with a slight cinematic quality to them, hence the blue and sometimes red in the shadows.
Note: in Photoshop you can achieve very similar effects by using the Colour Balance or the Selective Color (using only the whites/neutrals/blacks settings) adjustment, but I find that Curves is a nice one-stop-shop and gives you finer control.