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The curve tool is one of the basic tools for color grading. This tutorial will show you just how powerful this tool really is.

While we are using DaVinci Resolve in this particular tutorial, the information can be implemented from Final Cut Pro to Photoshop because the way the curves work is universal – even if their appearance and functionality differ from software to software.

They allow you to make precise luminance and color adjustments to an image – from slightly increasing a specific area of ​​the midtones to making drastic changes to the highlights. At their core, they are a fundamental tool for bringing your images to life.

In the following video tutorial, I will walk you through the core functions of the custom curve and the HSL curve.

* Although we always provide a written transcript of the tutorial, it is recommended that you watch the video to see how the image reacts to the curve adjustments in real time.

Custom curves

This is a typical representation of the curve diagram for all software. The default neutral position of the curve is a diagonal line running from the lower left black point of the graph, through the upper right, to the white point.

A typical representation of a curve diagram.

The graph itself is divided into two axes. The horizontal axis shows the range of image tonality, while the vertical axis shows the range of adjustment that you can make. The custom curves and HSL curves all show a histogram representing the input of the selected correction node that you can use to control your adjustments.

Curve diagram with tonality

The curve diagram is divided into two axes.

What are the tone regions? Although not visible, the graph is broken down into three tone areas: the shadows, the midtones, and the highlights. They are usually divided like this:

Sound regions

The diagram is divided into three tone areas.

To add a control point, left-click anywhere on the curve. Pressing the right mouse button removes the control point. You can also click the ellipses in "Dissolve" in the upper right corner of the curve window. There is also a setting that adds default anchor points.

Moving these control points up or down increases or decreases the tone of the region. If you add just one control point, the entire curve will move with the adjustment, resulting in an overall change in the image. However, once you've added multiple control points, they'll be anchored in the tone area, making it easy to change the luminance of the entire image without changing your previous adjustments.

Curve fit points

Edit the luminance of the image.

In practice

As mentioned earlier, we have two standard control points: the black control point and the white control point. Dragging the black control point up makes a lift adjustment to raise the shadow, and then dragging it makes a right adjustment to lower the shadow. For the highlights, dragging the white point to the left will raise the highlights, while dragging it down will decrease the white point.

If we wanted to make the overall picture darker I could add a control point to the center and drag the curve down.

Dark curve

To make the image darker, add a control point to the center and drag the curve down.

If I wanted to remap the white and black dots to either compress or expand the signal, I could bring standard black and white dots inside.

Compressed curve

Bring the standard black and white dots inside to remap the dots.

If I wanted to raise the highlights and midtones without adjusting the shadows, I could create a control point on the shadows and raise the highlights by increasing the midtones organically, but the shadows would remain untouched.

Curve black point

Create a control point on the shadows, then raise the lights.

And we can see the difference if I remove the checkpoint.

Control point removed

The checkpoint has been removed here.

RGB curves

Although the custom curve appears to be a single curve, the custom curve editor is often displayed as a series of curves overlaid. The YRGB curves are all displayed in a single editor. Y for luma and RGB for red, green and blue. You can use the RGB curves to make tone adjustments to the individual color channels.

YRGB curves

Use the RGB curves to make tone adjustments to individual color channels.

To do this, select the corresponding color channel. The link that combines all four curves is broken so that you can customize the red, blue or green color curve.

The functioning of these curves corresponds to the luminance curve. The bottom of the red curve increases or decreases the presence of red – you press up to add and down to subtract. Likewise, the top of the curve increases or decreases the presence of red in the markings.

Red curve

Press up to add more red to your picture. Drag down to subtract.

However, it should be noted that the individual RGB curves work additively and subtractively. What do I mean by that? If you think this shot is too warm and you look at the scopes and find that the red value has a greater presence than the blue, you might think, well, let's add blue to cool it down. In fact, you better pull the red out of the shadows by lowering the red curve down.

HSL curves

The custom curve is just one of six overall curve adjustments available in Resolve. The other five are the HSL curves – an acronym for hue, saturation, and luminance. Let's quickly go over these curves and how they differ from the custom curves. In total there are:

  • Hue against hue
  • Shade against Sat.
  • Shade against Lum
  • Lum vs. Sat.
  • Lum vs. Lum

Fortunately, I don't need to explain how each function works because while they all work differently from the custom curve, they all work identically. However, the operating results will vary from curve to curve.

To understand the practice, let's take a look at hue and saturation. As with the custom curve, we have a histogram in the curve graph. However, you will find that this curve is displayed differently. We have a more elongated graph with a horizontal curve and the spectrum of hues present.

Hue against hue

An example of hue versus hue.

The information in the histogram directly represents what is present in the viewer. There is an abundance of red-green and blue in that particular shot described in the curve diagram. So if I wanted to adjust the blue saturation, I could put two control points around the tip and then increase or decrease that hue. Alternatively, you can go through the preview monitor and a qualification tool will appear. When you select a hue in the image, the corresponding control point is displayed in the curve diagram for a more precise setting.

We could increase the green saturation and decrease the blue saturation at the same time, all in one curve, all in one knot.

Shade against Sat.

With just one curve, you can simultaneously increase the saturation of green and decrease the saturation of blue at the same time.

This works in the same way with the other four HSL curves. Although the luminance vs. Sat and Sat vs. Sat are slightly different and maybe more niche in their use. For example, if we pull the LUM-Sat curve up, the graph is now monochromatic and represents the saturation levels from black to white of the image. By adding more control points to the shadow area, we can decrease the saturation of the darker areas of the image.

Lum. Sat

Reduce the saturation of the darker areas by adding multiple control points to the shadow area.

So, on just one node, you can adjust the tonality of the image, increase the saturation of a particular hue, and decrease the luminance of another hue. It's a powerful tool.

Some of the fun with curves comes when you make extravagant adjustments but decrease the intensity of the knot – much like decreasing the layer's opacity in Photoshop. You can see this is used for color correction in this time-lapse.

For more information on color correction, see the following handy resources:

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