Using Blend Modes in Photoshop-- Part I

Article and Photography by Ron Bigelow

www.ronbigelow.com

Photoshop CS or Photoshop CS2 Used in this Tutorial

One of the most important features of image editing programs is the ability to use layers. Layers allow a photographer to perform separate editing steps on individual layers. An overall brightness change can be done on one layer, a contrast enhancement on another layer, and a saturation increase on yet another. The use of selections and masks can further increase the power of layers as the editing done on any one layer can be restricted to a specific area of an image. Some photographers increase the power and versatility of layers even further by using the Opacity, Fill, and Blend If controls.

Figure 1: Layers Palette

Yet, there is one aspect of layers that is often overlooked, the Blend modes. The Blend modes can be found on the Layers Palette as shown in Figure 1. Clicking on the Blend mode pop-up reveals a list of Blend mode options (see Figure 2). The Blend modes determine how a particular layer blends with the layers below it. The Blend modes are very useful because they determine how a layer will affect the look of an image. Changing a layer to a different Blend mode can have a very dramatic effect on the appearance of an image. This is demonstrated in Figures 3 to 8. In each of these images, the Background layer was duplicated. Then, the Background Copy layer was assigned a different Blend mode to produce the images in these figures.

Figure 2: Blend Mode Options

Figure 3: Normal Blend Mode

Figure 4: Multiply Blend Mode

Figure 5: Screen Blend Mode

Figure 6: Vivid Light Blend Mode

Figure 7: Exclusion Blend Mode

Figure 8: Difference Blend Mode

A first reaction might be that only the Normal Blend mode produced a usable image, so why bother with the rest? The reality is that each Blend mode has its own uses and can be of great value to a photographer when used appropriately.

This article will review the Blend modes and some of their uses.

Some Background

Figure 9: Base and Blend Colors

When using layers and Blend modes, a new layer is blended with the layers below it. The color that is being displayed by all the layers below the new layer is referred to as the base color. The color of the new layer is referred to as the blend color. The result color is the color that is created from the bending of the base and blend colors. Figure 9 demonstrates the base, blend, and result colors related to the Layers palette.

Normal Blend Mode

The Normal Blend mode is probably the most commonly used. This is most likely because it is the easiest to understand, and it is also the default Blend mode.

The Normal Blend mode creates the result color by simply replacing the base color with the blend color. Mathematically, the Normal Blend mode is defined as:

Result Color = Blend Color.

If the Opacity is set to 100%, the base color simply disappears. If the Opacity is set to something less than 100%, the blend color will be somewhat transparent, and the base color will bleed through. The normal mode is used for many purposes. Graphics artists use it to blend different images to create graphics or photographic art. Photographers commonly use it as the Blend mode for adjustment layers (e.g., Hue/Saturation and Brightness/Contrast). It is also commonly used for blending different exposures of the same scene in order to deal with tonality and dynamic range issues.

Figures 10 to 12 show the use of the Normal Blend mode to blend two exposures of the same scene in order to deal with the wide dynamic range of the image. Figure 10 was exposed to open up the shadows on the side of the building in order improve the detail, but this exposure blew out the detail in the much of the cloud mass. Figure 11 was exposed to keep the detail in the clouds, but this caused the shadows to be too dark. Figure 12 shows the two images blended together with the Normal Blend mode and the use of a mask. The final image was able to keep good detail in both the shadows and the highlights. Figure 13 shows the Layers Palette with the two exposures set to the Normal Blend mode.

Figure 10: Exposure for Shadows of Building

Figure 11: Exposure for the Cloud Highlights

Figure 12: Exposures Blended with Normal Blend mode

Figure 13: Layers Palette with Normal Blend Mode on 2nd Exposure Layer

Table 1 summarizes the Normal Blend mode.

Table 1: Normal Blend Mode
What it does	Creates the result color by replacing the base color with the blend color.
Formula	Result Color = Blend Color
Uses	Many uses including: adjustment layer blending, blending of images to create graphics, and the blending of separate exposures to deal with tonality and dynamic range issues.

Dissolve Blend mode

The Dissolve Blend mode is a bit unusual. It creates the result color on a pixel-by-pixel basis by pulling the color from either the base color or the blend color in a random manner. In other words, some of the pixels get their color from the base color and some get their color from the blend color -- at the pixel level, there is no blending.

Where each pixel gets its color will depend on the opacity setting. At 100% Opacity, all of the pixels get their result color from the Blend color. At 0% Opacity, all of the pixels get their result color from the base color. At other Opacities, some pixels get the result color from the base color and some pixels get it from the blend color. Mathematically, the Dissolve Blend mode is defined as:

Result Color = Random Selection of Base Color or Blend Color

Figures 14 to 16 demonstrate the Dissolve mode. Each of these figures came from the same image. The image consisted of two layers. The bottom layer (base color) was red, and the top layer (blend Color) was green. Figure 14 shows the image at 0% Opacity. Only the red base color shows. Figure 15 shows the image at 100% Opacity. Only the green blend color shows. Figure 16 shows the image at 50% Opacity. This image has a mixture of red and green pixels.

Figure 14: Dissolve Mode at 0% Opacity (Shows Base Color)

Figure 15: Dissolve Mode at 100% Opacity (Shows Blend Color)

Figure 16: Dissolve Mode at 50% Opacity

Of course, we don't normally look at images by staring at the individual pixels. When an image is seen from a bit farther back, it may appear that there has been some type of blending of colors even when the Dissolve Blend mode has been used. However, this is just an illusion due to the way the eye and brain process information.

Frankly, there is limited use for the Dissolve Blend mode among photographers.

Table 2 summarizes the Dissolve Blend mode.

Table 2: Dissolve Blend Mode
What it does	Creates the result color on a pixel-by-pixel basis by pulling the color from either the base color or the blend color in a random manner.
Formula	Result Color = Random Selection of Base Color or Blend Color
Uses	Limited use for photographers.

Darken Blend mode

The Darken Blend mode is fairly simple. It creates the result color by comparing the base color to the blend color, in each channel, and selecting the darker of the two. As a consequence, in each channel, base colors lighter than the blend color are changed to the blend color; base colors darker than the blend color are unaffected. Mathematically, the Darken Blend mode is defined as:

In Each Channel, Result Color = Base Color if Base Color is Darker than

Blend Color or Blend Color if Base Color is lighter than Blend Color

For photographers, a primary use of the Darken Blend mode is to combine masks that that hide effects (unless you invert them). This is done by using the Darken Blend mode with the Calculations command. The Calculations command combines two channels to create a new channel. Since, every mask has its own channel, this works well for combining masks.

Figure 17 shows an image where the Darken Blend mode and the Calculations command where used to combine masks.

Figure 17: Image Requiring the Combining of Masks

In this image, it was important to not sharpen the sky and the dark blue section of the pond. These areas contain no significant detail, and sharpening them would only sharpen noise and insignificant aspects of the image. One mask had already been made for editing that was done on the sky. The channel for the mask is shown in Figure 18.

Figure 18: Sky Mask Channel

Figure 19: Water Mask Channel

A mask for the blue section of water had also already been created. The channel for that mask is shown in Figure 19. Rather than go to the trouble of creating and fine tuning a new mask to protect the sky and water from sharpening, these two channels were combined to create a new channel. This new channel was used to generate a mask for the sharpening layer.

Figure 20: Calculations Palette

Figure 20 shows the Calculations palette (click Image/Calculations) with the Blend mode set to Darken. This article will not go into the details of using the Calculations command as it is outside the scope of the article. However, the new mask generated by the Calculations command can be seen in Figure 21.

Figure 21: New Mask Generated from Calculations

Table 3 summarizes the Darken Blend mode.

Table 3: Darken Blend Mode
What it does	Creates the result color by comparing the base color to the blend color, in each channel, and selecting the darker of the two.
Formula	In Each Channel, Result Color = Base Color if Base Color is Darker than Blend Color or Blend Color if Base Color is lighter than Blend Color.
Uses	Used for combining masks

Multiply Blend mode

In each channel, the Multiply Blend mode multiplies the base and blend colors to create the result color. As a result, every pixel will get darker (unless one of the colors is white). Any color (base or blend) multiplied by black produces black, and any color (base or blend) multiplied by white remains unchanged. In essence, the Multiply Blend mode builds up image density. Mathematically, the Multiply Blend mode is defined as:

In Each Channel, Result Color = (Base Color)*(Blend Color)/255

The formula is divided by 255 so that the result color will fit in the 0 -- 255 range of values, for each of the three colors, used in the RGB color spaces.

The Multiply Blend mode is often used to darken areas that are too light, especially if more detail is desired in those areas. Often, this is done by duplicating the Background layer and setting the Blend mode of the Background Copy layer to Multiply. This technique is demonstrated in Figures 22 and 23. Figure 22 shows an image with beautiful rich color in the cliffs, but the sky is somewhat washed out due to the large dynamic range of the image. In Figure 23, the Background layer was duplicated and set to Multiply Blend mode with a mask used to protect the already dark cliffs from the new layer. As can be seen, the sky has been significantly improved with respect to both tonality and color. Figure 24 shows the Layers Palette with the Background Copy layer set to the Multiply Blend mode.

Figure 22: Image before Adjustment

Figure 23: Sky Adjusted with Multiply Blend Mode

Figure 24: Layers Palette with Multiply Blend Mode on Background Copy Layer

Table 4 summarizes the Multiply Blend mode.

Table 4: Multiply Blend Mode
What it does	In each channel, multiplies the base and blend colors to create the result color.
Formula	In Each Channel, Result Color = (Base Color)*(Blend Color)/255
Uses	Used for building up detail and density in light areas.

Color Burn Blend Mode

In each channel, the Color Burn Blend mode analyzes the colors and does three things to create the result color:

Darkens the base color in relation to the tonality of the blend color. The darker the blend color, the darker the base color becomes to create the result color.
Increases the contrast of the base color in relation to the tonality of the blend color. The darker the blend color, the greater the contrast of the base color becomes to create the result color.
Adds the blend color to the base color in relation to the tonality of the blend color. The darker the blend color, the greater the amount of the blend color that is added to the base color to create the result color.

In short, in each channel, as the blend color becomes darker, the base color becomes darker, more contrasty, and picks up more of the blend color to create the result color. If the blend color is white, the Color Burn Blend mode does nothing. As the blend color gets darker, the effect of the Color Burn Blend mode becomes more intense.

Of course, there are other ways to add density, contrast, and color to an image. The advantage of the Color Burn Blend mode is that it is dependent on the tonality of the blend color. This is an advantage for images where it is desired to have a greater effect in the darker parts of the image.

Figure 25 and 26 demonstrate the use of the Color Burn Blend mode. In this image, most of the mountain was in shadow. It was necessary to provide a significant amount of exposure to hold the detail in the mountains. This produced a sky that was washed out with little detail. The fix was to duplicate the Background layer. The new Background Copy layer was then set to the Color Burn Blend mode, and the Opacity was adjusted to produce the desired image. A mask was used to protect all of the non-sky areas from the color burn. The result is that the blue parts of the sky, which are darker than the clouds, picked up more density while the clouds were relatively unaffected and retained their original, white color. Figure 25 shows the image before the Color Burn step, Figure 26 shows it afterwards. Figure 27 shows the Layers Palette with the Background Copy layer set to the Color Burn Blend mode.

Figure 25: Image before Adjustment

Figure 26: Sky Adjusted with Color Burn Blend Mode