Blending Modes

When two or more colors overlap in an image you can get one of two results. The top color can block the lower color or the two colors can interact. Photoshop's blending modes allow us to control the interaction.

While they seem mysterious, the various blending modes are actually predictable and consistent. Once you get a handle on how each works, you'll be able to grab the effect you want quickly. Don't get me wrong I'm a big fan of testing each blending mode to see how they compare, but an understanding of how they do their magic not only saves time, but prevents unexpected results.

The first thing to understand about the various blending modes is that they all work mathematically. They deal with the actual color values for the red, green, and blue or L*a*b color components (or grayscale or CMYK in some cases). As we know, the values for the RGB colors can range from 0 to 255 and you can see the numbers in the Color palette or the Color Picker. In a slight over-simplification, when two colors overlap, the blending modes take the color values of each and adds, subtracts, multiplies, or divides the numbers. As we discuss layer blending modes, we'll work with the assumption that opacity for all layers is set to 100%. Reduced opacity will change the interaction between colors.

To show how the blending modes work, let's look at a test pattern. Remember that the bottom color is the base color the overlying color is the blend color and the product of their interaction is the result color. Here we'll create a pattern to use for the base colors. We'll put together a range of base colors on a single layer.

The Spectrum gradient runs across the top of the image, with a black-to-white gradient immediately below. Solid bars of black, 50% gray, and white are next, with red, green, blue, cyan, magenta, and yellow fading to white. These gradient and color bars will be used as the base colors to show how each blending mode affects the interaction with a range of colors and tints.

The blending colors, on a separate layer, are the Spectrum gradient and a black-to-white gradient.

To see how the two layers look together, let's start with the Normal blending mode. Normal is the default (and most common) blending mode. The colors on the upper layer supercede those below, blocking them completely. (Remember that we are assuming 100% opacity for these demonstrations and explanations.)

The second blending mode in the Layers palette is Dissolve. It has no effect with our test image. (We'll look at it again in a later installment when discussing blending modes for painting tools.)

The Multiply blending mode takes the RGB (or CMYK) color values of the blend color and those of the base color and multiplies them. Because it's multiplication, the result color will always be darker except when blending with white. Notice in the upper-left the larger areas of blue and green formed by the interaction of blue and cyan and green and yellow. The relationships among the RGB and CMY colors is also evident along the lower gradients when using Multiply.

Screen can be considered the opposite of Multiply. The color values are inverted, usually resulting in a lighter color. Black has no effect, white produces white. In particular, look where colors that are opposite in the color wheel overlap. Any place where the opposites are blended using Screen the result is white. (Blue/yellow, green/magenta, red/cyan are the pairs.)

Overlay is somewhat of a cross between Multiply and Screen. Dark colors are multiplied (and get darker), light values are screened (and get lighter). In the right side of the test image the black-to-white gradient tells the tale. Check the upper-right whether the grayscale gradient is blended with the Spectrum gradient. Observe how the black side of the gradient increases the amounts of RGB, while the white side of the gradient emphasizes the CMY colors. Also notice that the neutral gray bar has no impact on colors. Because it is smack-dab in the middle of the brightness values, colors blended with a 50% gray are unchanged, neither multiplied nor screened.

Soft Light uses dodging and burning to blend colors. Dark base colors are darkened, light colors are lightened. Blending with black or white results in black or white. Soft Light can be very subtle in images and can result in hue shifting.

Hard Light also darkens and lightens predictably, with black and white remaining unchanged. Hard Light can be very effective for emphasizing highlights and shadows when used in conjunction with a grayscale gradient.

Color Dodge lightens (except when the blend color is black). The impact of colors opposite each other on the color wheel is extreme. Note in the lower-left that the CMY color gradients retain no trace of the RGB colors from the overlying Spectrum gradient. Also look at the left near the top. Where the Spectrum gradient meets the darker part of the horizontal black-to-white gradient, all CMY colors are eliminated. Conversely, the lighter part of the grayscale gradient shows no RGB.

Color Burn has the opposite effect on brightness, but the impact on hue is similar. When you compare the Color Burn and Color Dodge tests samples, you'll see that in both cases the neutral gray color bar (base color) has produced changes to the blend colors.

In the next installment of this series, we'll continue the look at layer blending modes.