Understanding Darken and Lighten in Photoshop

Hells Angels Prison Run in Florence Arizona

Sky adjusted in original image using the darken blending mode to apply a second version of the same image, opened in Adobe Camera Raw with a negative exposure value. Masks and blending sliders to limit blend to sky.

I think a lot about color, maybe because I was severely near-sighted as a child, and pools of inditinct color dominated my visual world until I got glasses. I like to play with color contrasts in my choice of subjects and in post-processing effects. A basic understanding of how Photosop works with colors is the first step toward predictable (and desirable) results, even with seemingly the unrelated blending modes darken and lighten.

Drawing from our grade school color mixing experiments, it would stand to reason that lighten means “add white” and darken means “add black.” So how might Photoshop do that? It’s not so simple as it sounds.

A philosophical friend of mine believes that our strengths are our weaknesses, and there’s a bit of truth in that for Photoshop. The program describes colors several ways; here we are interested in the concepts of HSB vs RGB. (That’s eight letters in a row without a vowel, hardly English at all.)

HSB stands for Hue, Saturation and Brightness, each described by a numerical value and the three together create a unique color. Remember the color wheel, a circular rainbow of hues? In the HSB model, if the color wheel has a spinning central arrow, hue is the direction it points: 0° to 360° with red at the top. Saturation means how much of that hue has been contributes to a color: from 0%, which results in greyscale tones from white to black, to the most vivid shades ato 100% saturation. Brightness, also on a 0% to 100% scale, seems the most intuitive, and Photoshop’s help manual describes it as “Relative lightness or darkness of the color, usually measured as a percentage from 0% (black) to 100% (white).” The best way to learn the HSB concepts is to open up Photoshop’s color picker and drag around the sliders in the HSB model.

From that definition it might seem that the blending mode lighten would simply add white to the exisitng color, without changing hue or saturation. However, the assumption fails because, to add brightness, Photoshop has to add white, and to add white, Photoshop adds more hues. Confused? Meet the RGB model.

Remember as a kid when you got REALLY close to the television monitor and looked at the red, green and blue pixels that made up the t.v. picture? And that the visual effect of red+green+blue created white? And that if all three pixels were dark, the effect was black? Computer monitors still work that way, even though the pixels on our screens are much smaller these days.

In my web designing work, I became intimately familiar with the RGB model, because in the language of web pages (html), colors are described as red+green+blue. 100% of red, zero of green and blue results in a red. 50% of red and blue, but no green makes a dark magenta color. The hardest combination for most people to conceptualize is red+green makes yellow. The phrase “additive color,” as in the two colors emanating from the monitor pixels are added on your retina, might help. Again, messing around in Photoshop’s color picker is the best way to get familiar with the RGB model.

In the lighten mode, Photoshop takes the base layer’s red, green and blue (RGB) values, and adds them to the RGB values of the blend layer. In the example below, the blend looks counterintuitive until we inspect the RGB values.

Sadly, RGB values are not described in a percentage scale in the computer-geekdomness that underlies Photoshop. Instead they use a scale from 0 to 255, which is directly related to how computers store data in memory, and this isn’t the place to go on about that! Here’s a quick table of percentages, so we can compare apples to apples, or HSB to RGB.

RGB value Pct value
0 0 %
128 50%
255 100%

grey-llighten.jpg

In the first example, the base layer is a solid blue fill, Hue 240, Saturation 100%, Brightness 50%. In RGB, it has 0% red, 0% green and 50% blue (0,0,128 in the RGB scale). I made a blending layer of black to white. In the HSB model, hue doesn’t matter if saturation is 0%, and the brightness is spans 0 to 100%. In the RGB model, each point along the ramp has equal values of red, green and blue, increasing from 0 to 255 from left to right.

I have shown a strip of the underlying blue color and its RGB value. In the lower part of the image, the greyscale ramp has been blended to the blue base using the lighten mode. Each of the resulting pixels contains the higher value of blend or base’s red, green and blue values. The important fact here is that the calculation considers each red, green or blue pair separately. So not only do the lighter greys brighten the result, they add red and green in the RGB model, and desaturate the blue values.

lighten-yellow.jpg

Here’s a more extreme example, where I replaced the black to white gradient with a black to yellow gradient. In the yellow color I chose has 0 blue in its RGB value (HSB is hue=60, saturation =100, brightness=100). The comparision process for the lighten blend is the same, adding the R,G and B values separately. The result is logical, if not exactly intuitive.

darken.jpg

Lighten takes the larger of the each pair of RGB values; darken does the opposite, creating a new color out of the smaller of each RGB pair. Look at what happens when the same black to yellow ramp is blended in the darken mode with the blue! Again logical, although at first it is hard to envision that bright yellow plus medium blue would create a pure black!

Using lighten and darken for image adjustments.

Harnessing the power of the lighten and darken mode can be tricky, but there are some extraordinarily powerful uses out there. Imagine you have made a complex mask of some trees on a horizon, and you want to soften the blend on the edges. If you use a blur filter, you will soften the blend, but some areas of the mask will become lighter, others darker. Change the blending mode of that filter (in the Fade Filter option immediately after applying the blur) to either lighten or darken, depending on the need.

Other tools, like the spot healing brush, stamp and patch tools, can sometimes be better controlled using lighten and darken, particulary on skin tones. Experiment and undo!

A quick way to soften wrinkles in a portrait is to duplicate the image, blur the duplicate, then blend the blurred layer using lighten. Use a mask to control exactly where the blended layer effects the original portrait, perhaps constraining the blended layer to around the eyes, neck, and forehead.

And if your blends get a little wild, the opacity slider can help tone things down.

Into Practice How do you use Lighten and Darken? I’ve uploaded these same images to our Flickr pool , where you can share your examples for lighten and darken blending Describe what you did (masking, opacity, etc.) and why. I’m looking forward to seeing your pictures.