|
Beyond Normal: Multiply and Screen Blending Mode
Normally, layers in an image are merged using a blending mode appropriately known as "Normal." But learning what other blending modes do can go a long way towards improving your Photoshop skills. This week we'll go beyond Normal and introduce Multiply and Screen blending modes.
In the Layers palette, each layer that comprises an image file is stacked, one atop another. They get combined together in different ways to create what you see in the combined image. You can see which blending mode each layer uses by looking at the drop-down selector at the top of the Layers palette. It's right there next to the Opacity selector. One controls the method by which a layer is combined with what is underneath, and the other controls how much of each layer goes into that method.
 With the Normal blending mode, each layer directly blocks the next layer down, except where it is either transparent or semi-transparent. Transparency allows you to see what is underneath. If the layer on top is completely transparent over some portion, it's as it's not even there at that point. If partially transparent, you'll see the contents of that layer as a ghost image on top of the underlying layer. This works just like things do in real life. Wave your hand in front of your eyes and you can no longer see what is beyond it. Look through a sheer curtain and you can only partially see outside.
But what on earth could the other blending modes do? The engineers at Adobe have devised quite a few other ways of combining layers, some based on traditional darkroom techniques and other real-world analogs, and others only possible as formulas in the digital world of computers.
Multiply blending mode takes the color at each point in the top layer and multiplies it by the color value at the same point in the layer underneath. Yes, it's math. Doing so always creates a color at least as dark as what we started with. How much darker depends on the blend color. If the top layer is black, the result will be black. If the top layer is white, the underneath color remains unchanged. Any color between black and white creates a proportionally darker color.
Where Multiply comes in extremely handy is in improving image contrast on moderately overexposed images. Take an image and duplicate it as a new layer on top of the original. Change the blending mode of the top copy to Multiply and see what happens. The contrast goes through the roof. You can tone down the effect with the Opacity slider or by adding a Levels adjustment layer on top of the whole thing, but lets look at just why this effect happens. If a given point on the image was white, it will be multiplied by the same white in the top copy. As we know, white does not change the underlying color at all in Multiply blending, so we are left with white, just as we started with. Every other color gets multiplied by itself, creating a darker color. And the darker the color was to start with, the even darker it ends up as.
Think about math for a minute. Two times two equals four, right? But four times four is all the way up at sixteen, so doubling the starting number (2 doubled is 4), we end up with a result that is four times as much. Our results increase exponentially since we are multiplying each number by itself. Multiply blending mode does the same thing when we multiply an image by itself. If you have a moderately overexposed image that lacks contrast, you can work wonders by multiplying it by itself.
Lost Lake reflecting Mt. Hood in Oregon. The image is a bit overexposed. |
|
Duplicating the image layer and changing the blending mode to multiply results in a darker image with better contrast, but it's a bit too dark now. |
Decreasing the opacity on the Multiply blended top layer. The lake reflection looks much better now, but the sky needs more work still. |
|
Final tweaks by using a Levels adjustment layer over the sky. |
Screen blending mode does the opposite of Multiply and essentially divides the base color by the blend color. If we duplicate an image on a new layer and set the blending mode to Screen, it has the effect of lightening medium toned pixels while leaving darker ones relatively unchanged. Thus, an image that was slightly underexposed can be improved by using Screen. Dull dingy snow will get lighter without doing the same to trees and other objects on the snow. As with Multiply, if the effect is too pronounced, you can tone it down with the opacity slider.
Mt. Hood in Oregon. The image is a bit underexposed. |
|
Adding a Screen blended copy on top of the original makes things much brighter. |
|
Toning down the opacity and adding a layer mask over the sky completes the fix. |
Photoshop has a lot of features and most users never come close to tapping the full potential of this program. If you once thought that anything beyond Normal blending mode must be abnormal, hopefully I've convinced you otherwise. Multiply and Screen are as easy as 1-2-3. Well, that and a little arithmetic.
| 
