Here's a schematic of the blending layer and the base layer.

Blending Layer Pixels
Base Layer Pixels
Photograph Looks Like This

White (255,255,255) pixels in the blending layer create no change.

Black pixels (0,0,0) in the blending layer or in the base layer result in black.

That's because when you multiply anything by zero (and black is 0,0,0,), the result is zero (0,0,0).

Step Wedges

Step wedges can help you understand what a blending mode is doing.

The top step wedge is the original photograph, and the lower step wedge is with the Multiply blending mode.

Normal
Multiply
	(0,0,0)	(128,128,128)	(255,255,255)

Go to Step Wedge - The Understanding Tool.

Used For

You can use the Multiply blending mode to darken an overexposed photograph.

For example, here's an overexposed photograph of a glass block.

The blending mode of the Background copy was changed to Multiply.

Below, the original is to the left, and the version with the Multiply blending mode is to the right.

Original

With Multiply Blending Mode

What  Happened Above?

Let's answer that with some analogies, and some math.

Analogy

Imagine putting two slides of the same scene in a slide projector together.

The dark areas of the scene will become darker, while the lighter areas remain the same.

Mathematics

You can skip the math if you wish.

Go to Opacity.

Let's look at the math for one pixel, say, one along the bottom edge of the above photograph of a glass block.

Let's call this pixel Egor.

The RGB value for this pixel is 30, 32, 31.

The RGB values for Egor are the same on the blending layer and the base layer.

Blending Layer Pixel	30, 32, 31
Base Layer Pixel	30, 32, 31

That's because the same photograph is on each of the layers.

The RGB values for the blending layer Egor are multiplied by RGB values of the corresponding Egor in the base layer.

30	x	30	÷	255	=	4
32	x	32	÷	255	=	4
31	x	31	÷	255	=	4

The new RGB values for Egor are 4, 4, 4.

Egor is darker.

In RGB values, 4, 4, 4 is darker than 30, 32, 31, the original value of Egor.

Opacity

You can reduce the effect of a blending mode by reducing the opacity of the blending layer.

With Multiply Blending Mode

With Multiply Blending Mode

And Opacity Reduced to 50%

Use More than One

You can add more than one Multiply layer to darken more.

There are brief descriptions of the other Top-Transforms-Lower blending modes in the next section.

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