Tutorial: How to edit image tones using a “Curves” adjustment layer.

I’ve had a few people ask me to do a little demo on how to use the “curves” adjustment in Photoshop recently and, seeing as it’s pretty much one of my favourite colour editing tools ever, I couldn’t quite resist. The only real downside here is that you’re going to have to look at an old close-up of my mug multiple times while I’m explaining this stuff. I do apologise.

Colour curves are the proverbial bee’s knees. By using a curves adjustment layer in Photoshop, you can non-destructively tinker with your image tones to your heart’s content and create colours and contrast which are as subtle / batshit crazy as you like. To best show you the power of the curve, I’ve done a little self-portrait edit avec many, many screenshots. I’m well aware that this guide may not be technically perfect when it comes to the language and terminology I’m using – it just feels like the best way I can possibly describe it to you all.

Ready to learn this business?! Here we go…

This here is a super basic JPG, sans any kind of colour edit. If you look at the little grey box to the right of this screenshot, you’ll see what appears to be a histogram on a grid with a line throught it. The grid is divided into four boxes across, each box representing a tonal range. From left to right, these boxes / sections represent the following tones:

Shadows -> Mid-darks -> Midtones -> Mid-highs -> Highlights

Now, looking at the verticals on the grid, we can establish how much of each type of tone we have already in the image. The higher the level on the histogram, the more of that tone there is. Looking at the histogram for this example image, I can see that there is a spike in the quarter representing shadows to mid-darks but next to nothing in the mid-highs to highlights, so none of the tones in my image are blown out to white or pure-black. Make sense? Understanding the tonal range of your image is part of the key to perfecting your use of the curves tool, because the next step involves manipulating it.

You can use the RGB channel of the curves layer to accurately tinker with the contrast levels in your image. One of the most common ways of doing this is by creating an “S-shape” curve. Click right in the centre of the grid to begin with and you’ll see a little dot appear – this has now anchored your midtones. Next up, click and drag the line down on the mid-darks area to make them darker and then click and drag the line up over the mid-highs area to boost those and make them brighter. See how contrasty that just made things?

On the other hand, you might want to make your image somewhat less contrast-tastic. If this is the case, anchor those mid-tones again and then click and drag the line up from the bottom left corner to make the shadows (and everything up to that midtone anchor) lighter, then click and drag the line down from the top right corner to make the highlights (and everything from the midtone anchor) a bit darker.

If you want to really start being brave and adding more points to warp your image tones, here’s a little peek at the RGB channel points I’ve used to create a slightly filmic overall tone. I’ve dragged some of the mid-darks down to create contrast, but also opted to bring the shadows up and the highlights down a bit to add some vintage-style fade to the effect. The best thing to do is just have a play and see what effects you can create by wiggling various points around on the graph. Sometimes it’ll look dreadful, sometimes it’ll look mega – don’t be afraid to experiment here.

Hopefully you’re starting to see how super freakin’ powerful this adjustment layer is / understand where the main tone points are now? Yep? Good, because the next step is:

Colour Toning

Ohhh yesss! As if the contrast tricks weren’t enough, you can also use curves to do beautiful things to the colours in your image. This adjustment just keeps on giving.

First of all, you’re going to need to find the “red” channel on the adjustment layer. If you look just above the graph where it says “RGB” you should see a little arrow on the far right of that box? Click that and scroll down to the “red” option to select our new colour channel of choice.

Now, in the same way that shadows are opposite to highlights on the grid, each of our colour channels has its opposite colour. Learning these will ultimately help you out with a huge number of other colour editing tools, not just curves, so they’re well worth memorising. Here’s what you need to know:

Red – Cyan

Green – Magenta

Blue – Yellow

Let’s start with red. Any point now pulled upwards or left will increase the amount of red in that tonal area. Any point pulled downwards or right will therefore increase the amount of red’s opposite colour, cyan, in that tonal area. In the above image, I’ve set the midpoint once again and pulled the shadows end of the red right up – can you see how the shadows and mid-darks have now taken on a much redder hue?

To then do the opposite, keeping that midpoint anchored, I’ve dragged the highlights point right down. All of the mid-highs to highlights are now somewhat cyan-tinted.

If I wanted to be a bit more subtle and just give a slightly warmer red tint to the shadows only, I could add another anchor point over the mid-darks intersection and then drag the shadows point slightly upwards. Using those same / similar anchor points I could also choose to give the shadows a cyan tint by dragging the shadow point to the right across the bottom of the graph.

This colour opposites theme continues through the “Green” and “Blue” channels. I’ll not show you the extremes of each because the theory remains the same as above, but here a couple of my personal favourite tricks:

For slightly pinker highlights, select the green channel and set an anchor point or two over the midtones and mid-highs, then drag the highlight end down. This increases the magenta in the highlights and can do lovely things to skin tones if done subtly enough.

If you’d like to get super vintage about things, get yourself over to the blue channel right now! For that slightly fairytale vibe, push the shadow point right up and pull the highlight point down, midtone anchoring optional. I usually tend to go for the slightly more subtle option here, which is just to slightly tint with this technique:

And there you have it! Photoshop Colour Curves in a few easy steps. Hopefully it made some modicum of sense and I haven’t just confused you further. If there’s anything you’d like clarification on or if you think I’ve made any glaring omissions in this guide, hit the comment button! If you’d like to book a Zoom call to learn a few more editing tricks with me, get in touch via the Contact page for more information.

Love to the lot of you,

E x

P.S. If you edit something awesome using what you’ve learned from this tutorial, I’d LOVE to see it! Send me your Flickr / Facebook / Instagram links or just post your work in a comment.