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.