A guide to tonal range

As videographers, we live to capture the images we see and create, but we may sometimes struggle to record the full richness of a shot. We may lose details in the bright or dark areas we see with our eyes because our cameras can’t capture the same tonal range. Let’s look at what tonal range is and isn’t, how to know if we’re capturing it properly with the camera in hand and how to adjust it.

What is tonal range?

Tonal range refers to the levels between an image’s darkest and lightest points. In a shot, we see a range of tones and colors from darkest to the brightest, with various shades in between. We can always see and capture the darkest and the brightest tones on either end of the scale. It’s the midrange values that we’re concerned with. The wider the tonal range, the more levels of mid-tones in our image, and the more detail we can see.

Tonal range gives us choices to design a shot using contrast. High-contrast images have a full range of tones, from bright highlights to dark shadows, while low-contrast images have a smaller, shallower range. A bright, low-contrast image of people on a beach looks very different than a high contrast image with dark shadows, bright whites and many shades of gray. One could be a rom-com, and the other could be a movie employing the classic film noir style.

But what you see with your eyes only becomes an image once you record it. Can your camera capture that tonal range?

Dynamic range vs. tonal range

Dynamic range refers to the luminance range your camera sensor can detect and record, while tonal range describes the actual number of tones captured.

Low contrast gray wood of a barn
Image courtesy: Pixabay

You may have a video camera with a wide dynamic range, but your shot consists of faded gray wood on the side of a barn. The shot has almost no blacks or whites, all gray mid-tones. This is a low-contrast shot with a low tonal range.

High contrast image with bright windows
Image courtesy: Pixabay

On the other hand, you may have a bright sunlit room with blown-out windows, bright reflections and dark shadows in the corners. This is a high-contrast shot with a high tonal range.

Measuring tone with the histogram

We measure tonal range in two ways: the histogram and the waveform.

histogram measures the total tonal range of an image and is common on DSLRs. It measures the range of tone within the dynamic range of your sensor — from left, black, to far right, white, with shades of gray tones in between. Any vertical point on the graph represents the total number of pixels of that tone throughout your image.

Image courtesy: Open Window

If we can capture the full tonal range of a shot, then our histogram will look like a bell curve with the black and white ends slopping off to zero.

If the sensor can’t record the full tonal range of the image, you’ll see a peak cutoff on either the black and/or white side of the histogram.

Histogram display on Canon DSLR
Image courtesy: Canon

The image above includes bright white walls and floors with overexposed reflections. The white end of its histogram is vertically cut off. We refer to this as “clipping.” This means there are levels of white tones above this point that may be discernible to our eye but not to a camera’s sensor. Since this range of white tones falls outside of the dynamic range of our camera, it will record as 100 percent white. No detail or texture will be visible in the clipped area. In this case, the hot kicks are just pure white.

The waveform

The histogram — though easy to read — has limitations; it only displays the total tonal value for a whole image. It can’t tell you where those hot or dark areas are in your image. However, a waveform monitor can.

Its vertical axis reads the light level: 0 at the bottom is black, 100 at the top for white. The horizontal axis corresponds with the same axis of the image from left to right and shows the light levels for a vertical section of it.

Waveform example on Canon C100
Image courtesy: Canon

For example, in the image above, we see hot kicks on the floor behind our subject in the middle of the image. We see her shadow on the dark-toned chair at roughly that same vertical point in the image.

On the waveform monitor at that same horizontal point, we can see the reading of the hot floor kick “clipping” above 100. Also, her shadow displays as a line slanting up from about five to 25 as it grades from almost black to the dark red tone of the back of her chair.

A waveform gives you more specific information about the tonal range of specific areas in your image.

Shifting tones in your camera

Our eyes have a wide dynamic range, but we can’t see that range’s extremities simultaneously. For example, when we look at a person silhouetted against a blown-out window, our irises open up and close to adjust to the different light levels. Our eyes are unable to see the detail of the bright environment outside the window while simultaneously seeing the details of the person standing in front of the window.

The same concept applies to camera lenses. When you open your lens’ aperture, you can see the details of the person. However, the window appears blown out. We’ve shifted the tonal range to capture the black side of our camera’s dynamic range. As a result, we’re letting the range’s white end clip. Conversely, as we close the aperture, we shift the tonal range towards the white side of the tonal range. We can’t see many details of the person but the window is no longer blown out. Now we’re allowing the black end to clip.

Affecting the tonal range of your scene

Instead of shifting the tonal range with our camera, we could change it in the scene by adding light to the dark areas of the shot. Lighting the person against the window lowers the tonal range of our image.

We can also bring down bright areas by adding ND gel or nets to the blown-out window. If there’s a bright practical bulb in the shot, put it on a dimmer or use a lower wattage bulb.

We can also change the tonal range of our set, props and costumes. For example, a production can choose between using blue scrubs versus using white ones for a scene at a hospital.

These are all ways of adjusting the contrast on our set, bringing the blacks up and lowering the whites so they fit better within the dynamic range of our camera. We’re lowering the overall tonal range of the scene so that our camera can record that range in our image.

The choice is yours

Whether your shots are from studio sets, locations or run-and-gun videography, you have choices available to you when capturing the tonal range you want. Keep what we discussed in mind and you will have the knowledge you need to capture the best image possible to tell your story.

Frank Dellario is a professional producer, director and videographer with over 20 years of experience. He is also the co-founder of the award-winning creative team, the ILL Clan.

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