Article by Robin Whalley - www.lenscraft.co.uk
If you read my earlier article on using the Develop module in Lightroom you may have wondered why I didn’t cover the Tone Curve tool. My reason is that the tool just has too much functionality and really needs an article of its own to do it justice. So here then is that article.
Introducing the Tone Curve
The Tone Curve is found in the Develop module, on the right side of the screen, just below the group of sliders used to adjust the exposure of the image. To users of Photoshop it will be instantly recognisable although the operation is different. Its purpose is to adjust the tones in the image so that they can be made lighter or darker and the interface will look something like the screenshot below. I say “something like” as there are two different views of the Tone Curve. If you look at the bottom right corner of the panel you will see a square icon that appears as a curved line with a dot on it. If your view of the Tone Curve doesn’t match that below simply click this icon to switch to the other view.
Looking at the Tone Curve in the screenshot above you can see that I have selected a ”Point Curve” of type “Linear”. This means the diagonal line shown in the top part of the screen is straight and no adjustment is being applied to the image. This line is the “Tone Curve” that controls how each tonal value in the image will be mapped to a new value as a result of the change. Behind the line you will see the image histogram so you can understand which part of the histogram your changes will apply to.
In addition to the “Linear” Tone Curve you will see there are two other values in the menu (“Medium Contrast” and “Strong Contrast”). Select either of these and you will see the shape of the diagonal line change. My suggestion however is that you make the “Linear” tone curve your default curve and starting position before you make any changes to your image. Once you have made all your changes to the exposure, contrast and saturation sliders (as described in my previous tutorial) you can move on to adjust the tone curve. I also suggest you don’t bother with the standard “Medium Contrast” and “Strong Contrast” curves as you will be able to achieve much better results with a little understanding.
Using the Tonal Sliders
There are a few ways you can make your adjustments to the Tone Curve but the most obvious is perhaps the sliders that appear in the lower part of the panel. The “Highlights”, “Lights”, “Darks” and “Shadows” all act on different areas of the tone curve. Whilst the names are somewhat intuitive, you can visual see the tones affected when you begin to move the slider left or right. Move the slider and you will see a highlighted area appear around the line of the tone curve so you can understand which tones the slide can change. Just remember that the lightest tones appear on the right of the curve and the darkest on the left.
If you want to make the lightest areas of the image lighter move the “Highlights” and “Lights” sliders to the right. To lighten the darker areas of the image move the “Darks” and “Shadows” slider to the right. To darken these areas simply move the sliders to the left. What you need to understand is that these adjustments act on the entire image unlike the Gradient or Brush tool and are said to be global adjustments.
When you make these adjustments to the Tone Curve you are altering the contrast in the image. If you make the line of the tone curve steeper you are increasing the contrast whilst reducing the angle of the line will reduce contrast. With this in mind, you should be able to see that your adjustments will reduce contrast in some tonal areas whilst increasing it in others. This is something you can’t avoid so it’s often best to increase the contrast (line steepness) in the mid tones at the expense of the darkest and lightest areas. This would create a classic “S” curve shape which is often used to enhance contrast in the mid tones (which have the greatest visual impact) at the expense of contrast in the highlights and shadows.
Adjusting Tonal Ranges
Having read the above you might be wondering how you can target your adjustments to specific areas of the tone curve. The answer is be redefining the area of the tone curve each slider affects. You can see this in the screen shot below where I have dragged one of the regional sliders over to the right. After my change the “Shadows” slider affects the darkest 38% of tones in the image rather than the default 25%. The “Darks” slider however now only affects from 38% to 50% of tones. Experiment with these sliders and you realise you have some real flexibility at your disposal.
Dragging the Curve
The sliders however are not the only way to adjust the curve. An alternative, and one most people are probably familiar with is to pick a point on the tone curve and drag it either up or down. Dragging the curve up will lighten the image whilst dragging down will darken the image. When you do this you will also notice that Lightroom will move the sliders accordingly as shown in the screen shot below.
Something that I haven’t yet mentioned is that the possible tonal range of each image is divided into 100 areas with 0% (black) being the darkest and 100% (white) being the lightest. If you look to the top left of the curve screen shot above you will see the numbers “27/21% displayed. This is telling me that I am targeting the tones that appear at 27% in the tonal range and that I am making them darker so that they will appear at 21% in the finished image. As this is a curve, the surrounding tones in the range are also changed but by a lesser amount.
Working with Channels
The next way to adjust the tone curve is using the icon in the bottom right of the panel that I mentioned earlier. You can see this in the screen shot below where I have also picked a point on the curve and dragged it down to make the tones of the image darker. You will know when you are in this mode as the “Highlights”, “Lights”, “Darks” and “Shadows” sliders have disappeared.
You might be wondering how this differs from the previous adjustment described above and to some degree it is the same. This screen does however give access to being able to target tone curve changes to different channels of the image. The default is to target the RGB channel (the composite channel of Red, Green and Blue) but you can target individual channels by selecting them and then making a point adjustment on the curve. You will see this menu just below the tone curve. This is very similar to the curves tool in Photoshop and opens up the ability to make adjustments to colour and contrast on a channel by channel basis.
Dragging The Image
The final method I would like to cover with you is the point and drag. In the screen shot below, at the top left of the Tone Curve panel there is a circle with a smaller circle inside it. When you click on this your mouse pointer will change to the same icon as you move it over the image area. Find the point on the image that you would like to lighten or darken then click and drag. Drag the cursor down to darken those tones and drag up to lighten them. Again this is a global adjustment so other similar tones in the image will also be adjusted. Whilst I think this method is intuitive I don’t personally use it very often as I feel the other methods described give me greater control.
Bringing It Together
As you can see then, there are a number of choices in how you use the Tone Curve. The adjustments are however separate to those made to the Exposure sliders that I discussed in my earlier tutorial on the Develop module. What I have found is that the adjustments made through the Tone Curve can be much more severe than through the Exposure sliders and sometimes a little hard to control. For example I might find it hard to drive my images tones to pure black using the Black slider (without getting a very strange histogram) but using the Tone curve I can achieve this relatively easily and with a much better spread of tones in the histogram. My approach therefore is to use the Exposure sliders to achieve the best exposure and histogram that I can and then make further adjustments in the Tone Curves tool. Once I have done this I find that it’s often good to return to the Exposure sliders and adjust them further to fine tune my image.
I hope after reading this you will agree the Tone Curve hides a great deal of power and make it part of your own workflow.
Article by Robin Whalley - www.lenscraft.co.uk