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Crushing Contrast: Understanding Tonal Adjustments and Creating Different Contrast Styles

by | 2 years ago

In modern-day color photography, we tend to put more emphasis on our hues and neglect our tones; however, exposure and contrast are like the foundation of a building, so a good image relies more on tonal values than on color harmonies. The tools that can help us achieve tonal heaven are all grouped together at the top of Photoshop’s list of adjustment layers: Brightness/Contrast, Levels, Curves, and Exposure. In this article, we’re going to learn how to use these tools, and then we’ll apply our newfound understanding of them to create a couple popular looks through the application of stylistic contrast. 

The Histogram 

To effectively learn how to use Photoshop’s tonal adjustments, we need to understand what it is we’re looking at. There’s no better tool to do that with than the dreaded histogram. It may look complicated, but we can unravel its mysteries. 

Open any image, then open the Histogram panel (Window>Histogram). To set it up, click on the four small lines in the top-right corner of the panel to open its options, and choose the Expanded View. Make sure everything else in that menu is unchecked. The last thing you need to do is choose RGB from the Channel drop-down menu so you can start analyzing the image. 

The “mountain range” in the Histogram panel is a graph that represents all the tonal values in the image. The x values (horizontal) go from total black to total white, and the y values (vertical) go from 0 to 100%. If the graph has taller bumps to the right, it’s a high-key or brighter image. If there’s a huge spike at the right end of the horizontal scale, the image has highlight areas that are blown out; but if the spike is on the left, then you have crushed blacks. 

Throughout this article, we’re going to move around this histogram mountain range using adjustment layers. This will help us better comprehend what each slider in the adjustment layers does to the tonal values, and you’ll be able to use that to your advantage later when we create our own looks. 

Brightness/Contrast 

We’re going to start with the Brightness/Contrast adjustment, as that’s the one that can be found in most image-processing applications. It lets you make simple adjustments to the tonal range of an image. 

According to the Adobe Photoshop User Guide, moving the Brightness slider “to the right increases tonal values and expands image highlights, to the left decreases values and expands shadows.” So through a complicated algorithm, the image gets either brighter or darker, mostly by moving the midtones (the values around the vertical centerline of the histogram). 

On the other hand, the Contrast slider “expands or shrinks the overall range of tonal values in the image.” This translates (again, through a complicated algorithm) to either making the histogram mountains more prominent and spread out—hence resulting in more contrast—or reducing the height and width of the mountain range, making the entire image flatter with less contrast. 

This might all seem a bit complicated, so let’s see how this looks in practice. Go to Layer>New Adjustment Layer>Brightness/Contrast to create a new Brightness/Contrast adjustment layer on top of the Background layer. Now, while looking at both the histogram and the image, drag the Brightness slider in the Properties panel to one side and then the other, and note the changes on the histogram. When you move the slider to the right, it moves certain bumps in the histogram to the right side, toward the brighter values, making the image brighter without brightening the darker values. Moving it to the left results in the opposite: more bumps move toward the darker values, and the image becomes darker overall without darkening the extreme highlights. 

Next, let’s take a look at the Contrast slider. Move it to the right, and you’ll see the highlights and shadows getting taller in the Histogram panel. This means you have more contrast in your image; more contrast means a larger difference between dark and bright values. Moving the slider to the left makes the shadow and highlight bumps shorter, and slightly elevates the midtones. This results in a flatter image because there’s less difference between the darker and brighter values. 

Checking the Use Legacy box simply takes away those algorithms, and you can see what the tool does in its raw form. Moving the Brightness slider moves all the values to either side, and moving the Contrast slider expands or shrinks all the values along the x axis (horizontal). This nonlinear method is undesirable for photographs but can be very useful when dealing with masks.

Levels 

Levels is an extremely powerful tool. With it, you can adjust the tonal values and color balance of an image; however, in this article, we’re only going to talk about its basic tonal applications, but even that’s a lot in itself. 

Create a new Levels adjustment layer by going to Layer>New Adjustment Layer>Levels. This automatically opens the Properties panel, where you’ll see a big histogram in the middle. This is what you’re going to work with visually. Before you do anything, make sure that the Channels drop-down in the Properties panel is set to RGB, because we only want to work with tones, and not individual color channels. 

You’ll find the main controls for Levels below the histogram: three input levels sliders directly below the graph, and two output levels sliders below the gradient strip. The input levels sliders are blacks, grays (midtones), and whites; and the output levels sliders are blacks and whites. Both sets of sliders range from 0–255 levels. 

Let’s start with the three-slider group. The sliders on the outer edges (blacks on the left and whites on the right) control the cutoff points of the image values. Observe the histogram (the actual histogram in the Histogram panel) after you drag the blacks slider closer to the middle. It shows that anything to the left of this slider is now cut off (or set to 0 levels, which is pure black), and the whole range will be extended to accommodate the space created by the cutoff. 

Similarly, if you move the slider that controls the whites, it cuts off anything to its right by making everything to the right of it pure white (level 255). 

If you move the middle slider (grays) to the right, it will darken the image by compressing the shadows and expanding the highlights; if you move it to the left, it will brighten the image by compressing the highlights and expanding the shadows. 

The output levels sliders below the gradient strip control the negative starting point. As you move either of them, it creates a gap on the sides of the histogram, based on the position of the slider. This way you can tell Photoshop to make the darkest values lighter and the lightest values darker. 

Curves 

The Curves adjustment layer might seem complicated at first, but it works similarly to Levels, only with a slightly different visual representation. In capable hands, it’s one of the best retouching tools to use for tonal and color manipulations. 

Go to Layer>New Adjustment Layer>Curves. As we did with the Levels, we need to make sure that RGB is selected in the channels drop-down menu in the Properties panel because we need to adjust the overall tones and not the color channels. 

We have another histogram, but this time it has a diagonal line going through it, and we only have two sliders below it. If you move those two sliders closer to each other, they’ll behave just like the blacks and whites input levels sliders in Levels; they represent cutoff points. As you move them, they cut off parts of the graph in the Histogram panel to the left or right, depending on which one you move. The rest of the mountain range in the Histogram panel expands to fill the space. 

The diagonal represents the image’s tonality, going from smaller values (darker) on the left to higher values (brighter) on the right. By clicking on the line, you can add any number of points that allow you to adjust the tonal values to make the image darker or brighter. Moving the points higher or lower will make the image brighter or darker, respectively. 

Adding a point in the middle works just like the grays input levels slider in the Levels adjustment: It shifts the midtones. When you have multiple points on the curve, they’ll lock that part of the curve when you move another point. 

The endpoints on the line control the output levels, or the “gap” at both ends of the histogram. By grabbing the bottom-left point and dragging it up vertically, you can create lighter black values; dragging the upper-right point down creates darker white values. 

Essentially, Curves can achieve the same results as Levels. The only difference is that you can add a point anywhere along the curve and shift its value in any direction, giving you immense control. 

Exposure 

The last adjustment we’ll look at is Exposure. It was mainly designed to be used on 32-bit HDR images (this is actual high-dynamic range images, not the tone-mapped ones). It still works on 16- and 8-bit images, but with less control. In a 32-bit environment, its sliders do exactly what they say: The Exposure controls the exposure, Gamma controls gamma, and the Offset can offset everything but the highlight values. On a 16- or 8-bit image, it works more like the Levels adjustment with set limits. 

It’s better to jump into Photoshop and see what the sliders do both visually and on the histogram. So go to Layer>New Adjustment Layer>Exposure. Since most of us only use images up to 16 bits, let’s explore what each of the sliders does to our tonal values. 

Usually, Exposure adjusts mostly the midtones and lower highlights, and one might think that the first slider in the Properties panel does the same, but that’s not the case. If you start adjusting the slider, you’ll notice that it shifts the highlights with minimal effect to the extreme shadows. It can even start creating gaps on the whites side of the histogram, which means that it can darken the absolute whites in the image. Not exactly what one might expect from a slider called “Exposure,” so don’t let the name fool you. 

The next slider is Offset. Sliding this around affects the shadows and midtones with some effect on the highlights. This can also create gaps (lighter blacks, or darker whites) on both sides of the graph. Usually, adding a bit of Offset can wash out an image nicely. 

The last slider is the Gamma Correction, which is hard to understand if you don’t know what gamma means (unfortunately, I don’t have the space to explain gamma here, so you’ll need to look it up on your own). According to the Adobe Photoshop User Guide, this slider “adjusts the image gamma, using a simple power function. Negative values are mirrored around zero (that is, they remain negative, but still get adjusted as if they’re positive).” Translating this to histogram “language,” it can either lighten or darken the absolute darks. 

The Crushed-Blacks Look 

Now that we know more about our tonal manipulation tools, we’re going to use them to create two completely different looks. The main tool we’re going to focus on is the histogram, which is going to tell us how to get to the desired outcome using the tools we’ve just learned about. Both looks can be applied to any type of photo, especially since you can determine their characteristics by looking at the histogram. So, let’s get to work. 

The first look we’re going to create is a crushed-blacks look. It creates a sharp, high-contrast image that’s especially flattering when you want to emphasize shapes. It has many variations, but one thing is always the same: the blacks are shifted off the graph, or in other words, cut off. This means that we need to choose a tool that can cut off certain parts of our tonal values. This limits us to using Levels, Curves, or Exposure; however, the Exposure adjustment would be a bit clunky for this, so let’s use Levels because it will be the easiest to use to give us the style we want. 

Step One: Since we’re dealing with tones and not colors, turn your image to black and white so the hue and saturation don’t distract you from your goal (of course, this is completely optional). I like to do this by creating a new Solid Color fill layer on top of my image layer by going to Layer>New Fill Layer>Solid Color. After giving the layer a proper name in the New Layer dialog, like “Black and White,” and clicking OK, choose a color in the Color Picker that has 0% saturation, like white or black, and click OK. After that, set the layer blending mode (near the top-left of the Layers panel) to Color. This results in a pure black-and-white image. 

Step Two: When that’s done, you can start adjusting. Create a new Levels adjustment layer by going to Layer>New Adjustment Layer>Levels, and make sure the Histogram panel is still open (Window>Histogram). What we want to do is shift the black values way off the scale, or cut them off. As we learned previously, we can do that by using the first slider (blacks) in the three-slider group directly below the histogram in the Levels Properties panel. Drag that slider to a point where some of the image’s blacks have lost their detail. Make sure to leave enough so that shapes are visible in the image. 

Step Three: In this example, our image has become a bit too dark and flat, so we grabbed the middle slider (midtones), and moved it closer to the black point to lighten the image. This counteracts the effect of the crushed-blacks darkening on the whole expanded range of tones. 

Step Four: Now let’s take a look at the white values. We wanted to achieve a high-contrast image, right? For that to happen, we have to make sure that we have enough white values in the image. Take a look at the histogram, and if you have a gap on the right side before values start to appear, then you need to adjust the highlights. Grab the slider on the right (whites) in the Properties panel and drag it to the point where values first appear in the histogram in the Properties panel. This will result in harsh contrast and might blow out some of the detail in the highlights. The amount really depends on taste; these are just guidelines. Now you can click the Eye icon next to the Black and White fill layer in the Layers panel to hide it and reveal the color image. That’s it, we have our crushed-blacks look, created by using our knowledge of the histogram. 

The Airy Film Look 

The next look we’re going to create is a more high-key, flat, and airy look that’s often associated with the “Instagram look.” For this, we need to create a gap on the left side of the histogram, which will make the blacks look more washed out and lighter. 

Again, we could use Levels, Curves, or Exposure for this, but to make it more interesting, let’s use the Exposure adjustment, which I personally use whenever I want to achieve a similar look. 

Step One: Start by either opening a new image, or turn off the visibility of your previous Levels adjustment layer, and turn the Black and White fill layer back on. Then, create an Exposure adjustment on top of the layer stack by going to Layer>New Adjustment Layer>Exposure. Click OK. 

Step Two: Here, we’re going to work with the Offset slider first. Start moving it to the right and a slight gap will show up on the left side of the histogram. This indicates that the blacks are getting brighter. Move it to a position where it feels nice and airy, and a bit flat—something that feels pleasing. 

Step Three: Then, you can flatten this a bit more by lowering the Exposure slightly. This creates a small gap on the right side of the histogram, as well, which means that the whites are getting darker. These two sliders almost introduce a foggy, but detailed atmosphere to the image.

Step Four: Lastly, to tie it all up, we need to use the Gamma Correction slider. Moving it to the right moves all the values slightly to the left. Continue shifting them until you find something pleasing, probably when the histogram values are centered in the Histogram panel. This balances it all out. 

Done! This style can be used to emphasize open spaces, and to give a filmic vibe to photos without going overboard. 

As you can see, knowing more about the histogram can help you make educated decisions about your stylistic contrast choices. With what you’ve learned in this article, you can dream up or re-create any style that you like with the power of the tonal adjustments and histogram. Now go and move mountains!

ALL IMAGES BY VIKTOR FEJES