Photoshop Tutorial: Correcting Tone Using Levels

Take control of the black and white points of your photos with the Levels adjustment in Photoshop.

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What you need

To follow through with this tutorial you need at least Photoshop CS, but the general concept of levels applies to PaintShopPro and many other advanced image editing tools. More recent versions of Photoshop may appear a little different (mostly the interface has added features) as this tutorial is originally from 2006, but the techniques here are sound and work quite well across all versions since its publish.

To follow along with this tutorial you will need to download this image: Correcting-Tone-Levels.jpg (right-click and choose: Save As).

What is Tone?

The first item you should be correcting when you bring a photo into Photoshop is the tone, or the variance of dark and light, of the image. Most people do this with the Brightness/Contrast feature. Brightness increases the overall white in a photo, while contrast increases the difference between black and white. Although they may seem effective, using this old-fashioned tool lacks precision and detail, often doing more harm than good to your photo. To become a better Photoshop user you must forget the Brightness/Contrast feature and begin using the Levels adjustment instead. Master Levels and you will master the tone of your images.

About Exposure

What does it mean when an image is over or under-exposed? When an image is so dark that many areas contain pure black and no detail, that portion of the image is considered to be under-exposed. This means not enough light was getting through the lens to provide enough detail to the film or digital image sensor. If too much light was getting through, portions of the image may become so bright that they lose all detail and become pure white. This is called over-exposure.

Levels Adjustment Basics

Open any image and press Ctrl-L, or better yet, add a Levels Adjustment Layer. This will bring up a graph called a Histogram. It plots the brightness of an image from dark (on the left) to bright (on the right). The curve plotted along the histogram represents the strength of the tone along that scale. The higher the peak at a point along the histogram means the more information of that image resides in that level of brightness. By observing where the peaks and dips are along the histogram graph, you can get a feel for what the tone of your image is.

If your histogram leans to the left, your image has lots of shadows or black and is possibly underexposed. If your histogram leans to the right, your image has lots of highlights or whites and is possibly overexposed. Histograms that are balanced and symmetrical often stem from images that are more pleasing to the eye and are generally considered to be exposed properly. These images are often referred to as having a balanced tone. It’s not wrong to have a histogram that leans to the left or to the right, but generally creating a vivid image requires a more balanced tone.

Underexposed histogram

The above histogram shows an image with lots of shadow information. The very left (dark) end of the histogram is clipped off the chart, and there’s no information on the right (light) end.

Well-exposed histogram

This histogram demonstrates a well exposed image with plentiful information across the whole range of tones. Neither of the ends sre clipped and the graph is spread out across much of the range of light and dark.

Over-exposed histogram

The above histogram shows an image with lots of highlight information. The very right (light) end of the histogram is clipped off the chart, meaning a portion of this image is overexposed and there is no data available for that range of tone. The left (dark) end is empty, meaning there are no shadows.

Using Levels

Open the image (Correcting-Tone-Levels.jpg) in Photoshop. You can adjust Levels in two ways. The best way to make adjustments to images is through the use of Adjustment Layers. Otherwise, the old-fashioned way can be found in the Image menu under Adjustments or by pressing Ctrl-L.

This image of the Genesee Gorge at Letchworth State Park lacks contrast and it is a little under exposed. It was taken in bright sunny conditions and I suspect the camera sensor got confused by reflections. It’s not a great photo. The tone is muted. Let’s take a look at the Histogram in the Levels adjustment.

Histogram Low contrast
The small spikes you see spread out on the histogram are outliers, and can be ignored. This may happen on some JPG images if your camera does certain kinds of processing on images before saving to the memory card.

Take note of the following controls and how they work:

  • The Black Point slider. By moving the slider you’re telling Photoshop that you want the range of tone within the image to start as black here. Any total information to the left of the slider will be lost. 
  • The White Point slider. By moving the slider you’re telling Photoshop that you want the range of tone within the image to end as white here. Adjusting the Black Point and the White Point sliders is similar to adjusting the contrast of an image, only you have far more control.  
  • The Gray Midpoint slider. By moving the slider you’re telling Photoshop that you want the range of all tones between black and white to center around this point. Moving this control is similar to adjusting the mid-range brightness of an image.  
  • Below, where it says “Output Levels,” is where you can manually clip the highlights and shadows of your image. By moving the black and white sliders along the Clipping Scale, you can force the image to exclude either highlight or shadow information. By shifting the black slider to the right, you are purposely removing some shadow detail in the image. By shifting the white slider to the left you are purposely removing some highlight detail. Essentially this function allows you to remove detail from the tail ends of the histogram if needed.

What does this histogram tell me?

The first thing you need to do when you bring up Levels, is to study the histogram to find out what the issues are, and then adjust your sliders to their optimal positions. In this example the far left side of the histogram is lacking information (no black graph). This means that there are no deep shadows in this photo. It is a daylight photo of an open canyon, so there shouldn’t be overly strong shadows, but there should be some mild shadows within the trees.You can almost tell by looking at it: the darkest points in the image only reach a mild grayish green. They should be darker.

On the far right, a thinning graph shows that there are some highlights, but not many and certainly not approaching pure white. Looking at the image, the frothy water, as well as the reflections from wet surfaces, should be pretty close to pure white on a bright sunny day. They aren’t.

Luckily it appears as though almost no histogram information is being clipped off the far ends of the graph. If too much information was clipped off the far ends, it would be very difficult to fix. Any information that is clipped from the graph, cannot be recovered.

Remapping tone

Essentially what you need to do is tell Photoshop that you want the image’s darkest shades (on the far left of the graph) to be close to the black point, and the image’s lightest shades (the far right)  to become close to pure white. This will re-map all the shades in the image, giving it better contrast, detail, and making the image more vibrant.

Not every scene you capture needs to have pure white and pure black in it. A night scene for example, probably won’t benefit from having pure white remapped in it, because pure white in a dark scene is unnatural.

  • Check the Preview box so you can see your adjustments applied to the image in real-time. 
  • The Black Point slider. You want to position this slider just under where the left side of the histogram data appears or bulges. Because this is a bright daylight scene, we don’t want to make the shadows too predominant  You’ll notice in the preview, the shadows darken as you move the slider to the right. I went with a setting of 24
  • The White Point slider. You want to position this slider just under where the right side of the histogram data appears or bulges. You’ll notice in the preview, the highlights brighten as you move it left. Since there were small bits of information on the highlights end, moving this slider past them has clipped these highlights from the image (nothing can be brighter than pure white). Sometimes clipping highlights or shadow detail is a sacrifice that must be made to gain a more pleasing tonal range. It’s OK in this case since the highlight data that is present is very small (not a large bulge on the graph). I went with a setting of 227
  • The Gray Midpoint slider. You can fine tune the brightness of the image by moving this slider. In most cases this can be left as is. Because this image appeared a little dark, I decided to move this slightly to the left, closer to the middle of the curve. Left brightens the image. Right darkens it. A small adjustment to 110 works well for this image.
Levels adjustment

By re-positioning the white, black and grey points to align better with the Histogram for the image, we can remap tone to make the image more dynamic.

Levels adjusted

Keep an eye on the image, the highlights, shadows, and overall tone as you make slider adjustments.

Final Results

Levels has an AUTO feature. But I highly recommend never using it. It tends to change the color, which is never something you want to do in the Levels Adjustment. More importantly, it does not consider the conditions the photo was taken in. So if you are trying it on a photo of a dark sunset scene, for example, it may brighten the image too much and change the warm colors to a balanced tone. Once you get used to manipulating the sliders, manually adjusting Levels shouldn’t take much more time than hitting the “Auto” button.

Low contrast

Original image

Levels adjusted

Manually adjusted levels

Auto levels

The “Auto” setting resulted in too much shadow information and a pink tint.

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