Hue, Saturation and Luminance: What Are They?


One of the things that you will want to do when post-processing is manage the colors in your picture.  There are a number of tools that you can use to manage and manipulate color. Three of the most important are hue, saturation, and luminance (or lightness).  Together, they are often abbreviated as HSL.

All three of them can be used to manipulate color in your picture, but each of them controls a different aspect of the color.  

So, what do they do?

Hue represents the actual color itself.  You can choose, red, blue, green, pink, yellow, brown, or any one of the millions of shades in-between.  Whatever color you pick is represented numerically as the hue value. By changing the hue in your photo, you can change red to blue, orange, pink, or any other color that you can see. 

Saturation is a measure of how deep the color is.  The higher the saturation, the less gray is in your color.  If you push the saturation all the way up, your color will be a strong representation of that color.  If you push it all the way down, it will be completely gray. Take a look at the color strip below:

As you can see, this strip is red.  On the left, the saturation has been turned down to 0. As a result, all the color has been drained away, and we’re left with a completely gray color.  As we progress further to the right, more and more saturation is applied, resulting in a progressively stronger shade of red.  

The luminance (or lightness) value represents how much white or black is mixed into your color.  The higher the luminance, the brighter your color will be (until it reaches white at maximum luminance) and as you lower your luminance, the color will appear to be darker (until it reaches black at no luminance at all).  Take a look at the color strip below:

This is the same red strip as above, except that instead of changing the saturation, I changed the luminance.  At the far left, there is no luminance at all, and so the red has completely changed to black. As you proceed further to the right, the red gets brighter and brighter until it starts to fade into white.  When you bump the luminance of an image all the way up, you are left with white.  

OK, I understand how it applies to color strips, but how does this work in real photos?

Well, let’s take a look.  Here’s a basic photo of a flower on a black background in Photoshop.  Feel free to download this picture and follow along with me.

When I went to manipulate the colors in Photoshop (Image > Adjustments > Hue/Saturation), a popup box appeared with the three HSL sliders.

I could easily change the colors of the entire photo just by sliding the hue slider one way or the other.

Move the Hue slider to one side....
... and to the other

As you can see, by moving the hue slider, I changed the colors in the entire picture.  

By moving the saturation slider, I can make the colors deeper, or grayer.

Saturation turned all the way up...
... and ll the way down.

And by changing the luminance, I can change the brightness of the image.;  adding white or black to the image.

Luminance (lightness) turned up....
... and down.

That’s fine if I want to change the whole image. But what if I want to adjust only one part of an image? Can I do that?

Yes, you can.  There are several ways that you can do this.  One is by using masks and selections, which will be the subject of a different post. 

Another way is by targeting specific colors.  For example, let’s look at our picture again. Suppose I like the stem the way it is, but I want the flower to be colored purple.  (Why? Who knows?) Well, one thing I can do is make sure that my changes only target the red pixels in the picture.  

If you pull down the dialog box, you’ll find that you can target specific colors.  So, if I choose red, the changes that I make will only affect the red pixels, leaving the green pixels alone (although note that it also affected the red on the underside of the stem).

In Summary

Hue, saturation, and luminance are three different properties that you can manipulate to change the appearance of colors in Photoshop, Lightroom, or almost any other image editing program.

  • Hue represents the actual color that is shown.
  • Saturation represents how deep the color is, going from grey (completely desaturated) to a very deep shade of the color (oversaturated).
  • Luminance is how much white or black is mixed into the color.  If the luminance is set to 100%, the color will be white. If set to 0%, it will be black.

Do you have any questions or comments about this? If so, please feel free to ask in the comments.

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