Here’s the real power of the curves tool…being able to easily control how feathered your adjustment is by manipulating the “curve” of your line. This is my preferred tool for processing tones in both Photoshop and Lightroom because the result is more natural…and is especially useful for enhancing the mood and atmosphere of your image.
To demonstrate how the curves tool makes a tapered adjustment , let’s start with a simple increase in brightness by adding a point in the center and dragging it up slightly.
The actual pixels we are moving here are at Input 122 and Output 156. So, I am brightening these pixels up by 34 points. However, notice that the tones around this point have also increased in brightness.
If I add another point to the left of our first adjustment, we have an Input of 75 and an Output of 100. So, that is an increase of 25 in brightness.
Let’s add another point further down the line. Here we have an Input of 19 and an Output of 26; that’s an increase of 7 points in brightness. So, the further away we get from our first anchor point, the increase in brightness becomes less.
Whenever you make any tonal adjustment (whether with curves or another tool), you almost always need to change the tones surrounding the pixels that you are adjusting. Otherwise, it gives you noisy and pixelated results.
To demonstrate this, I’ll select a narrow band of tones in the circle below.
Now, if I make the same curves adjustment to only the selected tones, see how sharp and pixelated the result is?
In order to avoid this separation of tones, you need to feather the adjustment out….gradually dropping off in strength the further you move away from the tone you are adjusting (where the point is placed on the curves graph)
Said another way…
A curves adjustment will automatically feather itself to the surrounding tones on a scale in order to keep a natural appearance (And avoid the pixelation seen above).
Before the curves adjustment
After the curves adjustment
The same curves adjustment, but not feathered to surrounding tones.
To bring it all back to my earlier discussion….
Notice how the greatest distance between the curves line and the baseline is at the anchor point we added to the image. And as we travel further away from this point, the distance becomes less…demonstrating a gradual feathering of this adjustment.
Adding Anchor Points to Adjust Smaller Groups of Tones
When you add a single point to the curves graph and make an adjustment, the feathering zone can be quite large. If we take a look at the image below, this is a rather big adjustment….so almost the entire tonal range is affected to some degree.
What you can do is add additional anchor points to the curves graph in order to restrain the adjustment to specific “ranges” of tones.
If I add an additional point further in the shadows (below) and drag it back down to the baseline, I’m telling Lightroom to remove this adjustment between pure black and this new anchor point.
In other words…the zone between these two points now directly mirrors the baseline…which means that this adjustment will not be visible over these deeper shadows (below). By making that curves line steeper and restraining it to only a portion of the tonal range, we’re controlling the breath of the feathering zone.
I’ll also make the same restriction for the highlights by adding another point (below), removing this adjustment from my brightest tones.
So now, the adjustment has been restricted to just the midtones.
What Happens When the Curve is Too Steep
You do have to be careful when you manipulate a curve like this because if your curve is too steep, it will result in pixelation and artifacts…so you always want to keep an actual curve to your line.
For example, if I go too steep here, the pixelation comes back into the photo.
For the most part, you always want to maintain a natural and soft curve, but you can add a little bit of steepness to target a specific range of tones.
The Target Adjustment Tool
The Target Adjustment Tool for curves is a way to sample the tone you want to adjust by clicking on the actual image…instead of trying to guess which tone to adjust by clicking on the curves line.
This simple tool is often underrated, but the value that it can give you is priceless.
Adjusting Highlights and Shadows
To use the target adjustment tool…first, you need to click on this hand right here (the Target Adjustment Tool icon).
Then, click and hold over the tone you wish to adjust…and drag up or down to lighten or darken that tone. You’ll notice that a new anchor point is automatically added to the curves line, and the input will be whatever tone you were hovering over when you clicked on the image.
In either Lightroom or Photoshop, a “preview” anchor point will appear on the line as you move your target adjustment tool around the image. This is in live-time, so the point will jump to a different place on the line as you move your mouse around.
If you notice here, when I hover over the brightest part of the tonal sphere…a new temporary point appears near pure white on the curves graph.
And if I hover over middle grey, that point instantly jumps to that value along the curves line.
And if I sample the darkest shadows, that point now appears all the way down near the black point on the curves graph. Remember: you have to actually click on the image in order to add this point to the curves line.
So, if you don’t know the exact value number of the area you want to change…you can use your mouse to sample that area. I prefer to use curves this way since I find it easier to work visually and simply click on the area I want to adjust.
And of course, you can come back here to your curves (the actual graph) and manipulate this point even further if you have to after it has been added through the target adjustment tool.
Let’s add a very simple “S” curve with the target adjustment tool to add some contrast. First, I hover over my shadows…then click, hold, and drag down to deepen the shadows.
Then, I’ll repeat the same for the highlights: I hover over the brighter tones…click, hold, and drag upwards to lighten them up a bit.
This is a very light increase of contrast, and is quite standard for landscape photography. And since we have the black and white points “anchoring” the curves line down, it’s helping to not overexpose your highlights even more or underexpose your shadows. Without these points, the added contrast would start to clip detail.
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