After further studying the behavior of the exposure and brightness sliders and discovering how strong upward exposure adjustments can cause serious color shift, I am modifying my workflow as shown below. Instead of relying mostly on exposure adjustment I am beginning to think that brightness adjustment is a more stable tool. On a photograph +2 exposure or +150 brightness produce almost identical results the latter being slightly more restrained. Ideally, this much adjustment should not be necessary, but in a pinch try the brightness first. Now I understand better why Lightroom “Auto” tonal adjustment almost always uses the brightness slider.
I have been using Lightroom since its original public beta before version 1 was released. It has become an indispensable tool in my workflow like many other photographers. It offers a very good set of tools for photographers in a very usable interface. Those of you who go back that far may remember another product before Lightroom was even announced, Raw Shooter Essentials and Professional. The Essential was free and the Professional was worth every penny I paid for it. Adobe thought likewise and purchased the company and its technology along with it. Several tools in Lightroom, later in Photoshop are descendent of Raw Shooter series. The most notable ones that are visible outside are Recovery, Fill Light, Vibrance, and Clarity sliders. Along with these, I would not be a bit surprised if the entire “Basic” group descends from RSE including brightness, blacks, and exposure. Interestingly, I have found the information on the “basic” group the most spotty and “soft” in presentation and explanation. Generally, explanations go like this “brightness is kind of exposure control but leaves the endpoints alone”, “it is a kinder and gentler exposure slider”, and so on. There are many discussions on a variety of forums and you will read a variant of these explanations peppered on the Internet. Even Martin Evening in his quite encyclopedic volume on Lightroom does not provide a fully satisfying explanation of how the Exposure slider adjustment differs from the Brightness slider adjustment.
To better understand the behavior of these sliders, which seem to do very similar but not identical things, I decided to study their behavior on an artificial gray-scale ramp. In Photoshop, I created a 1200×1200 blank image and filled it from left to right with a gradient map going from black to white. To make reading values more consistent, I posterized the gradient fill with 16 steps. After importing the PSD file into Lightroom, I took RGB readings from each strip and recorded them on each strip in Photoshop. The resulting file had the steps all identified as Lightroom saw the RGB values. Since they were all identical, I did not repeat the numbers for R, G, and B channels.
I created an Excel spreadsheet with the original measurements as the baseline. Then proceeded to increase the Brightness adjustment in three large steps of 50, 100, and 150. After each adjustment, I measured the value of brightness (RGB values) on each step and recorded along the baseline measurements. Then I went in the negative direction, -50, -100, and -150 and recorded the brightness values. The intention here was to measure the change affected by each step of adjustment on different values of grays.
Next, I zeroed the Brightness slider and changed the Exposure slider in +1, +2, +3 and -1, -2, and -3 settings while measuring and recording the resulting values in each step of the gray-scale ramp. I charted the observed differences in tonality in the following graphs, one for Brightness adjustments and one for the Exposure adjustments.
Now, let us take a look at the charts and see what we can observe. Clearly, the overall behavior of both sliders seems to be similar. However, some important points to note are:
- None of the settings produce a linear response, the effect starts low, peaking at some point, and then diminishing again
- When increased, Exposure seems to affect the shadows more than Brightness
- When decreased, Brightness appears to impact the highlights more than Exposure
- Since the endpoints are black and white they do not register any change
- Reducing Brightness seems to be a better way to tame the highlights and high values
- Increasing Exposure seems to be a better way to deal with opening the shadows and low values
- The effects mentioned in 5 and 6 are most pronounced with extreme adjustments, probably not used often
- Some settings produce nearly identical results, see Exposure = – 1 and Brightness = -50 graph
In practice, neither adjustment will likely be used alone. When used in combination with Blacks, Fill Light, and Contrast the results can vary significantly depending on the choice of tools. Real images bring their own problems that may stem from using one adjustment over the other. So, a generalized statement on which tool to use is difficult to make. However, the shape of the histogram will likely give clues as to the best starting point. The Lightroom’s built-in “intelligence” seems to favor using Brightness more than Exposure when the “Auto” option is used, and I have not yet seen only one slider adjustment being sufficient.
Here is my workflow for tonal adjustments: (Modified after the follow-up analysis of how these adjustments affect color shift)
- Set the “appropriate” white balance (I am avoiding “correct” since the WB depends on context and sensibility of the photographer)
- Set the “White” point, the highlight end using Exposure Brightness; remember not every photograph has a “White” point in Zone 9, don’t push it
- Set the Black point using the “Blacks” slider; these two adjustments will likely provide the necessary contrast
- If necessary, adjust the mid-tones with the “Brightness” Tone Curve, Exposure, even brightness
- If there are blown highlights, gently introduce “Recovery”
- If there are blocked shadows that need a hint of detail, use the “Fill Light” slider
- For finer tuning, use the Tone Curve adjustment either in parametric or point curve mode
- Use the HSL panel, starting with the Luminosity group and fine tune the brightness of each channel as well as saturation as necessary (easy, a little goes a long way!)
Here are some more graphs each showing a pair of Exposure-Brightness adjustment results for easier comparison. Of course, some of you may be wondering why I chose 50 unit increments for Brightness and 1 stop increments for Exposure. I have no scientific reasoning behind it other than I wanted to divide the Brightness and Exposure ranges into 6 and these numbers seemed “reasonable”. Also look at the sample photographs resulting from different adjustments. You will be hard-pressed to tell the difference in some instances (well, most instances) except the “Auto” setting which I left without further tweaking. As you see, at least depending on the image, it is possible to create virtually identical results with significantly different adjustments.
Although this post has not reached a definitive conclusion on the behavior of these two adjustments, it at least has provided you with carefully measured results and how they compare. I am sure you can develop your own conclusions that will work for your workflow.