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Adjust the tonal curve of an image

The Curves adjustment is probably the most versatile of all color adjustments. It can be used for almost everything — adjusting image highlights, shadows, and midtones, increasing or reducing contrast, improving colors, and even creating various artistic effects.

The Curves adjustment represents the image tonality as a diagonal line crossing a square graph. The dark values are represented on the left side and the light values on the right side of the graph. You can add points to the tonal curve and drag them up or down depending on whether you wish to darken or lighten the image. The shape of the diagonal line changes as you add and drag the points and often ends up looking like a curve, hence the name of the adjustment.

With the Curves adjustment, you can edit five different channels — RGB, Luminance, Red, Green, and Blue. Editing these channels affects the image in different ways. RGB let you adjust the colors that make up an image all at the same time. Luminance adds a way to adjust tones without changing the perceived saturation of colors. And if you need to adjust a specific RGB channel in a photo, you can do just that by choosing Red, Green, and Blue individually.

Curves also features the Auto Contrast and Auto Color options, which automatically enhance images to make them more vivid and vibrant. Auto Contrast adjusts the Luminance channel to improve brightness and contrast and Auto Color adjusts each of the Red, Green, and Blue channels to improve colors. The automatic contrast and color adjustments appear right in the Curves graph, so you can always add your own personal twist if you feel like it.

Curves adjustment overview

A — The Curves adjustment pop-up menu. Click it to choose which channels to adjust, apply Auto Contrast and Auto Color, Reset or Remove the Curves adjustments.

B — Histogram. Shows the color distribution in an image.

C — Black point. You can drag this point to the right to add more of the pure black color to your image.

D — Control point. Click the curve to add new points. Drag the points off the graph to remove them.

E — Black, gray, and white color pickers. You can use these color pickers to automatically adjust the curves in different RGB channels.

F — White point. You can drag this point to the left to add more of the pure white color to your image.

G — Tonal curve. Drag the points on the tonal curve to adjust the image colors.

H — Input and output values. You can turn information labels on or off in Pixelmator Pro preferences.

RGB images have 255 different values for each of the three channels, ranging from 0 (completely black) to 255 (completely white). Every new point you add to the tonal curve (and you can add up to 14 of them) will have it's own assigned value. Input and output information label may come in handy if you need to know the exact value you're changing and to which. You can hover the pointer over an added point to see the label.

Put simply, the input value indicates the position of the selected color within the tonal range and the output value shows where this color stands after the Curves adjustment is applied. For instance, if you add a point at an input value of 20 and drag this point directly upward, you'd see the output value change to 21, 23, 24, etc., and moving it down will reduce it to 19, 18, and so on.

The Curves adjustment also features a histogram that lets you know just how much of the highlights, shadows or mid-tones there are in an image so you can adjust the curves accordingly.

Adjust image highlights, midtones, and shadows
  1. Do one of the following:

    • Choose Format > Color Adjustments > Curves (from the Format menu at the top of your screen).
    • In the Tools sidebar, click and choose Curves from the Add menu.
    • Press Command ⌘ + K on your keyboard.
  2. Customize the adjustment:

  • To adjust the highlights, click the top section of the curve to add a new point. Drag the point up to brighten the highlights or down to darken them.
  • To adjust the shadows, click the bottom section of the curve to add a new point. Drag the point up to brighten the shadows or down to darken them.
  • To adjust the midtones, click the middle section of the curve to add a new point. Drag the point up to brighten the midtones or down to darken them.

    You can remove points by dragging them off the Curves graph.

Show Original: Click the Show Original button or press the O key on your keyboard to see what the image looks like without any color adjustments.

To reset your changes, click the Curves pop-up menu in the Tool Options pane and choose Reset.

Tip: A couple of the most common Curves adjustments are known as the S-curve and an inverted S-curve. The S-curve adds more contrast to the image, while the inverted S-curve does the exact opposite — reduces it. Extremely steep or very flat curves usually aren’t recommended unless they’re used for a specific artistic effect, such as posterizing. Otherwise, smooth curves are usually what gives the best results.

Adjust individual RGB channels to change the color and tone of an image

When adjusting Red, Green, and Blue channels individually, dragging the curve points upward adds more of that color to an image, while dragging the points down boosts its complementary color instead. The complementary color pairs are cyan for red, magenta for green, and yellow for blue. So, for instance, for an image that has too much blue in the shadows, adding a point somewhere around the bottom of the curve and dragging it down will bring in more yellow to neutralize the blue. This also works vice versa — you can neutralize a yellow image by dragging the blue channel curve up.

To choose a channel to adjust, do one of the following:

  1. Do one of the following:

    • Choose Format > Color Adjustments > Curves (from the Format menu at the top of your screen).
    • In the Tools sidebar, click and choose Curves from the Add menu.
    • Press Command ⌘ + K on your keyboard.
  2. Click the Curves pop-up menu and choose Red, Green, or Blue.

  3. Click the tonal curve to add a new point and drag it to adjust the colors.

Show Original: Click the Show Original button or press the O key on your keyboard to see what the image looks like without any color adjustments.

To reset your changes, click the Curves pop-up menu in the Tool Options pane and choose Reset.

Automatically enhance image contrast

The Auto Contrast adjustment automatically adjusts the Luminance of an image:

  1. Do one of the following:
    • Choose Format > Color Adjustments > Curves (from the Format menu at the top of your screen).
    • In the Tools sidebar, click and choose Curves from the Add menu.
    • Press Command ⌘ + K on your keyboard.
  2. Click the Curves pop-up menu and choose Auto Contrast.

Show Original: Click the Show Original button or press the O key on your keyboard to see what the image looks like without any color adjustments.

To reset your changes, click the Curves pop-up menu in the Tool Options pane and choose Reset.

Automatically enhance image colors

The Auto Color adjustment automatically adjusts the Red, Green, and Blue channels of an image:

  1. Do one of the following:
    • Choose Format > Color Adjustments > Curves (from the Format menu at the top of your screen).
    • In the Tools sidebar, click and choose Curves from the Add menu.
    • Press Command ⌘ + K on your keyboard.
  2. Click the Curves pop-up menu and choose Auto Color.

Show Original: Click the Show Original button or press the O key on your keyboard to see what the image looks like without any color adjustments.

To reset your changes, click the Curves pop-up menu in the Tool Options pane and choose Reset.

Automatically enhance an image by setting black, gray, and white points

In the top-right corner of the Curves adjustment, you’ll notice three color pickers:

  • Set the black point: Use the color picker on the left to pick an area in an image that should be pure black. The curves in the Red, Green and Blue channels are automatically adjusted.
  • Set the grey point: Use the middle color picker to pick an area in an image that should be midtoned.
  • Set the white point: Use the color picker on the right to pick an area in an image that should be pure white.

Show Original: Click the Show Original button or press the O key on your keyboard to see what the image looks like without any color adjustments.

To reset your changes, click the Curves pop-up menu in the Tool Options pane and choose Reset.

Pixelmator Pro User Guide