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onOne / Tone Enhancer and the Tone Curve

I've been quiet recently. Quiet on the blog, quiet on social media. Yet I'm busy. I've been working lots of stuff. I've been writing, writing, writing. I'm about half way done with a new eBook on post-processing with onOne. Processing photos as part of and in between writing.

Also, I'm right smack dab in the middle of a series of videos on the Tone Enhancer filter in Perfect Effects 8. As a companion to the upcoming videos, here's a more in-depth explanation of the tone curve in the Tone Enhancer. 

The Histogram

In case you’re not familiar with what a histogram is, here's a brief description. The histogram shows the spread of brightness levels in your scene. It's a distribution of the dark and light tones in your image. The far left edge is pure black — the shadows. And the far right edge is pure white — the highlights. Blown highlights fall off the right edge of the histogram and and underexposed areas fall off the left edge.

Perfect Effects presents both the luminance and RGB values in the histogram. White is overall luminance and the colors are the RGB values — the red, green and blue channels. Other colors that are displayed, such as yellow, cyan and magenta, are where the primary colors mix. There’s no “correct” or “perfect” histogram shape… it’s all relative to the mix of tones in your scene.

Reading the Tone Curve

Let’s start with the basics — how do we read the tone curve? The lower left corner is pure blacks — the shadows. And the upper right corner is the pure whites — the highlights. And the axes emphasize this, too. The gradient bars start at black in the lower left corner and progressing to white along both axes. Up and/or right makes tones brighter, down and/or left makes tones darker.

When I am working with the tone curve, I like to relate the curve to the histogram. Shadows on the left, highlights on the right, and everything else in between. When I read the tone curve, I mentally divide it into 4 columns — from left to right there’s the shadows, the low-midtones, the high-midtones, and the highlights. You might like 5 regions. Or 3. It really doesn't matter. It's still shadows on the left and highlights on the right.

Adjusting the Tone Curve

Let’s start with a classic S-curve adjustment. I’ll click in the darker tones about 1/4 of the way up the curve, and bring the curve down slightly. Then, another click and drag at about 3/4ths of the way up the curve and boost the highlights. And there’s a gentle S-shaped curve. 

The classic S-curve

The histogram with the S-curve adjustment

Notice how the S-curve affects the histogram. There is more of a valley in the center. The midtones drop, as the darker midtones push more towards black (left) and the lighter midtones push more toward white (right).

The Perfect Photo Suite Histogram

Tone Curve in the Tone Enhancer Filter

How I mentally look at the Tone Curve

For very granular control of the tones, you can set points on the curve. Click on the curve to set a point. You can set as many points as you like, although only a few are usually necessary. Points on the curve serve two purposes. One is a point of control to alter the tones in the image and the other is an anchor to protect tones in the image.

A tighter S-curve, protecting the highlight and shadows

The histogram with a tighter S-curve

Here I’ve set four points. I first set the two points toward the edges of the curve to act as anchors. I call these control points (I have no idea if they have an official name). I usually set these first. I generally know what tonal range of the image I want to remain unadjusted.

Then,  I adjust the middle of the curve into the S-shape. The deepest shadows and brightest highlights are not changed. The midtones undergo a more radical separation, as exhibited in the histogram – the valley in the center is much more pronounced.

Control points give you the ability to protect very specific tonal regions of your image.

The Color Channels

There are also individual curves for the red, green, and blue channels. Each channel can be manipulated uniquely. The color channels are useful to address overall color issues in your photo or for artistic styling, such as vintage effects. Knowing your color wheel will help you make the most of the color channels. Each channel controls its namesake color and what's opposite it on the color wheel.

  • Red channel: control the reds vs. cyans
  • Blue channel: control the blues vs. yellows
  • Green channel: control the greens vs. magentas

Raising the curve of a color channel boosts that color in the photo and de-emphasizes the opposite color. For example, raising the blue curve will reduce yellows in the photo. And vice versa. You can do combinations, too. Bump up the red and blue curve, you're amplifying purple.

Combine all of this color power with control points on a color channel tone curve, and you can create very unique looks for your imagery. For example, add more pinks and magentas into just the highlights with this pair of color channel tone curves:

Boosts the reds in the highlights

Boost magenta highlights by decreasing greens

These curves, plus an increase to the detail slider, creates a cross process-y style


The Tone Enhancer filter in Perfect Effects 8 gives you a huge amount of control over your image. Stay tuned to the onOne Software U YouTube channel for some Tone Enhancer videos coming real soon from yours truly.