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Hue/Saturation, Levels and Curves Comparison

Levels, Curves and Hue/Saturation adjustment layers can be used to manage tone, contrast and color.  Which adjustment is better?  There is no direct answer.  Each one has their strengths.  Let's explore these strengths.


Tone Management

 

Color Ranges and Color Channels

A color range is a series of one or more colors that are contiguously located on the color wheel.  A color channel is the color and tonal information for one of the colors in a color model.  More information on color ranges and color channels can be found on the Color Ranges and Color Channels page.

Hue/Saturation allows us to edit individual or all color ranges.  The Hue/Saturation color ranges are red, green and blue and their complementary opposites of cyan, magenta, yellow and Master.  The Master color range is all colors.  When working with color ranges, we are working only with those pixels whose dominant color is in the selected range.

Levels and Curves allow us to edit individual or all color channels.  When working with color channels, we are working with any pixel that has information in that channel.

With a Hue/Saturation adjustment layer, when we pick a specific color range, the sliders affect only those pixels whose dominant color matches the color range being edited.  In both Levels and Curves adjustment layers, if we edit a color channel, the adjustment we make will affect every pixel that has any information in the specified color channel, even if that color is not the dominant color.
 

Hue/Saturation

In Figure 1A, there are three color chips.  Each color chip has some red, green and blue in them.  But each has a different dominant color.  The single dominant RGB color channel for each chip is as follows: chip 1 is Green, chip 2 is Red, chip 3 is Blue.

Assume we wish to darken the green color chip.  Using a Hue/Saturation adjustment layer with a blending mode of Normal, I used the eyedropper tool Eyedropper tool to click the green chip and then moved the Lightness slider to -100 (negative 100) as in Figure 2.  The result is Figure 1B.  The green chip has been darkened and notice that chips 2 and 3 have been unaffected.  Likewise, if we move the Lightness slider to +100, we get the light green as seen in Figure 1C.

 

Color chips Figure 1A.  Three Color Chips

Dark green Figure 1B.  Dark Green

Light green Figure 1C.  Light Green

Dialog box

Figure 2.  Dialog Box

Levels

Now, lets make the same adjustments using Levels.  I created a Levels adjustment layer with a blending mode of Luminosity.  I then changed the Channel drop down box to Green and moved the middle slider until the gamma Input Level read 0.29.  The result is in Figure 3A.  As we can see, the green chip has been darkened the same amount as in Figure 1B, but chips 2 and 3 have been darkened also.  This is because Levels and Curves affects all the pixels that have green information.  And since color chips 2 and 3 have green in them, they were affected.  Color chips 2 and 3 were not affected by Hue/Saturation because green is not their dominant color.  I then moved the middle slider until the gamma Input Level read 3.65.  The result is in Figure 3B.  As we can see, the green chip has been lightened the same amount as in Figure 1C.  However, once again, chips 2 and 3 were modified also.

Dark green Figure 3A.  Dark Green

Light green Figure 3B.  Light Green

Levels Figure 3C.  Levels for Dark Green


Using color ranges with Levels and Curves

Color ranges can be used with Levels and Curves, but it requires a two step process. Step one creates a selection by color range.  Step two creates a Levels or Curves adjustment layer using the selection as a layer mask.  The details of using color ranges with Levels or Curves is discussed on the Using Levels and Curves with Color Ranges page.
 

Hue/Saturation or Levels/Curves

Since it requires additional steps to use Levels or Curves to edit by color range, why not use Hue/Saturation all the time?  There are two reasons why Levels or Curves could be the better choice.

First, we can darken or lighten a color using Levels or Curves more than we can with Hue/Saturation.  In Figure 4A below, the green color chip is the darkest green we can get with this particular green using the Hue/Saturation Lightness slider.  With Levels and Curves, I can make it even darker, as seen in Figure 4B.  In fact, with Levels or Curves, we can darken it to the point it is solid black.  Likewise, we can lighten a color further with Levels or Curves.  In Figure 4C below, the green color chip is the lightest green we can get with this particular green using the Hue/Saturation Lightness slider.  With Levels and Curves, I can make it even lighter, as seen in Figure 4D.  We can even lighten it to the point it is solid white.  (For Figures 4B and 4D, a layer mask was used to prevent color chips 2 and 3 from being modified and the blending mode was Luminosity.)

 

Dark green Figure 4A.  Hue/Saturation Dark Green

Curves Figure 4B.  Curves Dark Green

Light green Figure 4C.  Hue/Saturation Light Green

Light green Figure 4D.  Curves Light Green


The second reason is the Lightness control on Hue/Saturation is linear.  This means if the color range includes both dark and light colors, Hue/Saturation will adjust both equally.  With Levels or Curves, we have the additional ability of adjusting either the dark or light versions of the color, but not the other.  This gives us increased control over our adjustments.  Figure 5A is of two color chips.  Chip 1 is dark cyan.  Chip 2 is light cyan.  In Figure 5B, a Hue/Saturation adjustment layer was used to lighten the dark cyan.  However, it also lightened the light cyan, which is not what we wanted.  In Figure 5C, a Curves adjustment layer was used to lighten the dark cyan without affecting the light cyan.  The Curves adjustment used to create Figure 5C can be seen in Figure 5D.

 

Original Figure 5A.  Original

Hue/Saturation Figure 5B.  Hue/Saturation

Curves Figure 5C.  Curves

Curves dialog box Figure 5D.  Curves Dialog Box

Summary

With Levels and Curves, we can modify the tonal range to a greater extent than we can with Hue/Saturation.  We can use either Hue/Saturation, Levels or Curves to adjust by color range.  However, using Levels or Curves to adjust by color range is more involved.  We cannot use Hue/Saturation to adjust by color channel.  We can easily use Levels or Curves to adjust by color channel.  Hue/Saturation is a linear control and will affect all tones equally.  Levels and Curves gives us the ability to narrow the tonal range we wish to change.

Tip

When using Levels or Curves to adjust tone, I usually change blending mode to Luminosity.  If left to Normal, we run the risk of adjusting color as well as tone.