For this lesson, I’ll show you how to set tonal limits in Lightroom with the curves tool and the histogram.
We previously learned that the space between black and white points in the curves tool will determine the environment of your tones…
And the actual line between these two points – the curve – will adjust the tones within the environment.
Now before we jump too deeply into setting the tonal limits, I want to make sure we are all on the same page as to what exposure is. In the field with your camera, if we increase exposure by one stop, the amount of gathered light would be doubled and affect all tonal groups evenly (highlights, midtones, and shadows). This means that the brightest areas of your image would most likely become over exposed.
However…when you adjust the exposure here in Lightroom, the exposure slider is weighted heavily on the midtones and is a much more delicate adjustment. This is what you would use to set the majority of your tones without having to worry about crushing shadows or clipping highlights.
Setting Tonal Limits
Here is a rather muted image that could use with a bit of added contrast. Take a look at the point curve (located under the Tone curve panel). Let’s take the white point and bring it down vertically:
Making a shift like this to your curves will redefine the environment of your tones….which will change the tones that the tonal sliders in the basic panel adjust.
So, by bringing that white point down vertically, I’m telling Lightroom to restrain the tonal environment so that the brightest pixel in my image will never cross 85.9% brightness (as opposed to 100% brightness)….no matter what I do to those tonal sliders.
In other words, the absolute white point is not 100%, it is now down to 85.9% brightness. Any pixel that was above that in brightness has now been brought down, and any pixel you adjust later on will not cross that threshold.
Let’s increase whites to 100 and bring up the exposure to 0.75 (below). See how the tones are now being pushed up against an invisible wall on the histogram? This “wall” is the point we set with curves, at 85.9% brightness.
If you keep increasing the brightness of your tones, more of them will be pushed up against this wall and further remove detail (variation of tones) from the image.
If I take my exposure up all the way to 3.50, crushing all of my detail and pushing all that information towards the right of my histogram, those pixels are now (almost) all set to 85.9% brightness.
So to summarize: the curve panel determines the environment that your tones are in, and the tonal sliders under the basic panel will work within that environment.
This works a lot like setting the color profile, as that determines the environment of your colors…and the HSL panel will adjust those colors within the environment set by the profile.
Notice how if I turn off my tone curve all those pixels get push back up to pure white:
However, when I turn the tone curve back on, those tones are pushed back to the right side of the histogram.
To summarize: any adjustment you make to the exposure will never go above the absolute white point or below the absolute black point that is set with your tone curve.
Over here in Lightroom the tools of the tone curve are basically the same, just a little more basic. You can add actual points to your curve line and drag them around just like over in Photoshop:
We also have the target adjustment tool that can help to add points:
However, many of the advanced features in Photoshop are missing here…such being able to enter actual values for your points (input and output). Of course, all the benefits of adjustment layers, blend modes and layer masks are also missing in Lightroom.
You can use the curves tool to set new absolute limits for your white and black points. In other words, you can set new “limits” for your highlights and shadows…so when you make adjustments, your tones will not go past that point.
You do need to be careful as to not make too dramatic of a shift as that will flatten detail. For example, if you bring your white point down from 255 to 200….all of the values between 255 and 200 will now be the same.
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