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If you’ve never driven a standard transmission, it’s possible you’ve wondered why anyone would bother with a car that involves extra work to drive. Sure, you look cool doing it… But seriously, foot-hand coordination? Why?
One word: Control. The Tone Curves tool is like the stick shift of photo light and color adjustments. Yes, you can use lighting and exposure tools, but Tone Curves gives you a whole other level of control over the tonal range. You can select specific colors, (red, blue, or green), to adjust, or the entire range of the image. And then still adjust lighting and exposure after and beyond to get the image just how you like it.
Let us first look at adjusting contrast and learn how the tool works. Begin with an image in Edit mode (or Develop for non-destructive adjustments if you’re a Pro or Ultimate user). In the Exposure/Lighting section, open the Tone Curves tool.
Inside the tool, notice the bars on either side of the x and y axis of the graph.
The dark area of the bar represents the shadows in your image. The middle represents the midtones, and the white area is the lightest parts of your image. You’re ultimately trying to improve the contrast of the image by changing which pixels map to the brighter area of the graph and which map to the darker area.
Let’s take a closer look. The following photo is nothing special, but it is helpful for demonstrating the concept behind the graph. The input, represented on the x axis, shows you what tonal range the pixels in your image fall into. The Output, or the y axis, shows you where any of the given tones are mapped to. Look at any point on your x axis, find where it hits on the curve (the line through the graph), and then find where that hits the y axis: this is where the tone is being mapped to. As you can see in the histogram of this image, most of the pixels are concentrated in the area closest to where the axes converge — the shadows. And, as we haven’t made any changes yet, their output is also mapped to the shadows.
Now, for the sake of understanding, check out what happens when I move the curve down.
Even the pixels at the lightest point on the x axis are mapped low into the shadowy area on the y axis, hence the image is almost entirely black. Conversely, on this image below, I have moved the curve up, so even the darkest pixels on the x axis are mapped high into the light area of the y axis, and therefore, the image is significantly lightened.
Generally, you want to achieve heightened contrast in your image. And this is done by what we call an “S curve”. It’s when you make an S with the curve, (you don’t say!), dragging the shadow section down, darkening the darkest pixels, and dragging the lights up into the highlight section, lightening the whitest pixels in the image. However, it’s important to note that you can’t add contrast to one tonal region without decreasing it in another region. The steeper you make the curve in the shadow region, the more detail you will get.
This image starts out kind of flat.
But then—Tone Curves tool! Through an S curve, I made the dark darker and the light lighter, achieving greater overall contrast.
But this is what happens if you get out of hand….Ok, it’s kind of fun.
Adjusting the Tone Curves tool is a useful time to take advantage of the Exposure Warning. In the upper left corner of the tool, enable the button in order to display clipped shadows and highlights. Click the icon or press E on the keyboard, to highlight over- and under-exposed areas of the image.
You can also adjust the tonal range on a color by color basis. From the Channel drop-down menu, choose a color channel.
Play with the curve to get the effect you want. Less is more if you are seeking a natural look.
From this point, you can really take it wherever you want, be that adjusting it in other tools, or being satisfied and sharing it in a variety of ways. That’s basically it. Hopefully this has shed some light on how to use the Tone Curves tool. I know at first I found the look of this graph as daunting as my first hill start in a standard. (A graph?? I don’t do math!) But once you understand how it works, it’s easy to get your lighting, color, and contrast show on the road. ;D