Two of the more obvious ways to combine elements from different layers in Photoshop are: A) to erase or use a layer mask to reveal content from the layers beneath and B) to reduce a layer’s opacity and make it translucent. These are powerful and ultimately straightforward techniques. But there’s a third option. Photoshop’s blend modes let you go far beyond what alpha-based transparency alone can do. Blend modes permit layers to transform each other’s appearance.

In Chapter 28, “Blend Modes Revealed,” from the Photoshop CS5 One-on-One: Mastery video course on lynda.com, Deke clearly explains what blend modes do, how they work, which are the go-to modes to try first, and which ones are essentially useless. The chapter is so packed with examples and details that this article can serve only as a condensed introduction. But a rich introduction it is, packed with lots of insights and advice.

You can choose a blend mode from a pop-up menu at the top of the Layers panel to change the way the active layer interacts with those behind it. The menu does not have a label, but it stands out and by default it reads ‘Normal.’

Making sense of the modes

The problem is that there are 27 blending modes, each one representing a distinct mathematical operation. Worse, the names of many of them are about as clear as mud when it comes to understanding when or why you would want to use them.To make the modes a bit more accessible, Adobe has arranged them into the following functional groups:

• Normal
• Darken (shadow)
• Lighten (glow)
• Contrast
• Inversion/Cancellation
• Component (HSL)

A few key points about the blending mode groups:

• Every Darken mode has a complementary Lighten mode, and they’re in the same relative positions in the menu. The ‘honorary’ Darken mode, Subtract,is an exception. It is in the Inversion/Cancellation group instead.
• Linear Dodge (Add) is one of the more useful Lighten modes. It is the complement of Subtract.
• The contrast modes work by burning-in (darkening) the tones below middle gray and dodging (lightening) the tones above middle gray, which increases contrast.
• The Inversion/Cancellation group has become something of a catch-all with the introduction of the Subtract and Divide modes in CS5. It probably makes more sense to consider the Subtract mode as part of the Darken group, and Divide as part of the Lighten group.
• Three of the HSL Component modes combine the hue, saturation, or luminosity of the active layer with the other two tonal components from the underlying layers. FYI, in Photoshop, color-related terminology is very specific. A hue with a particular degree of saturation gives us a color, and a tone is a color at a particular luminosity. The Color mode applies the hue and saturation of the active layer to the luminosity of the underlying layers.

Applying Modes

To apply a blend mode, you can select it from the menu directly or use a keyboard shortcut. Holding the Shift key and tapping the [+] or [-] keys will cycle through the modes. However, two pitfalls can absorb your keyboard shortcuts and prevent them from working:

• On Windows, whenever you select an item by hand from the blend mode menu, the menu switches into data entry mode, and it absorbs all of your subsequent keystrokes until you hit the Esc key.
• On both Mac and Windows, the brush-based tools (brush tool, healing brushes, clone stamp, dodge/burn, etc.) also have blend modes, so Shift[+] and Shift[-] will cycle through the blend modes for the brush instead of the layer. To avoid this, click on a tool such as the Marquee tool to activate it before you try to cycle through the layer’s blend modes with the keys.

There are also some keyboard shortcuts for specific blending modes that are worth memorizing. Hold down the Shift + Alt (Mac: Shift + Option) keys Plus the following letter keys to select specific blending modes; the modes with one or more asterisks are especially useful:

N: Normal
M: Multiply**
A: Linear Burn*
S: Screen**
W: Linear Dodge (Add)
O: Overlay**
H: Hard Light**
J: Linear Light
E: Difference*
C: Color**
Y: Luminosity*

As you experiment with blending modes, it’s worth noting that each blending mode change uses another history state. This can quickly clutter up your History panel. To make it easy to return to your image to its current state, you can save the image or create a snapshot in the History panel before you start playing with blending modes.

Looking at the Darken modes

These modes “cast a shadow” on the underlying layers. 

• Multiply: This is the “when in doubt” darkening effect. Start there. Any white pixels turn transparent, making it a great tool for automatically removing white elements without erasing or masking.
• Color burn: increase saturation and intensify effect
• Linear Burn: Second-best to Multiply. More intense than Color Burn, but with less saturation boost. Careful, though—the mode can clip shadows.

One benefit of the Multiply blend mode is that it renders white pixels transparent even as it burns and integrates darker colors into the layers below. In the example shown here, the bulb and its surrounding rays meld easily into the underlying image by switching the blend mode to Multiply.

By comparison, using the Color Range to select and delete the white pixels shows jagged edges and a white halo around the edges of the bulb and the rays. The inside of the bulb is also more opaque and appears to lie on top of the layer below, rather than integrating with it.

Looking at the Lighten modes

The best Lighten modes are Screen, Linear Dodge (Add), and Color Dodge, in that order.

• Screen is analogous to Multiply. Black pixels are made invisible, and everything lightens the pixels in the layers below.
• Linear Dodge (Add) is the second best lightening effect, and analogous to Linear Burn.

Looking at the Contrast modes

The big 3 Contrast modes are Overlay, Hard Light, and Linear Light.

• Overlay: The best of the bunch. To temper the effect, reduce the opacity of the layer or downshift the blend mode to Soft Light.
• Soft light: Though it uses completely different math, it is is often viewed as a diluted version of Overlay.
• Hard light: Stronger, still, than Overlay.
• Vivid light: intensify and boost saturation (Color Burn + Color Dodge)
• Linear light*: Good mode to use. Linear Burn for shadows + Linear Dodge for highlights. less sat than Vivid Light. It can be over the top at times, but visit it when you’re perusing the contrast modes.
• Hard mix essentially boils your image down to 8 colors, creating a highly posterized effect, but can be tempered with Fill Opacity value. It is the poster child of the Fill Opacity 8.

A significant difference between Overlay, Soft light, and other contrast modes is that the Overlay effect is driven by the underlying layers, while Soft light and all other contrast modes use the luminance of the active layer to drive the effect. Overlay multiplies dark colors and screens light colors, based on the brightness of the background layer, ignoring medium gray pixels.

With regard to the contrast modes, Deke likes to say “Everything that’s gray is gonna go away,” because gray pixels are rendered invisible by these modes. Techniques like High Pass sharpening take advantage of this fact, because the High Pass filter renders edges in high contrast while reducing other image areas to gray.

Looking at the Inversion/Cancelation modes

Adobe refers to these as the comparison modes.These modes compare the pixels in the active layer to the pixels in the underlying layers. By that logic,Linear Dodge (Add) and Multiply would also fit into this group.

• Difference: Matching pixels become black
• Exclusion: Works like Difference, except matching pixels become gray
• Subtract works by subtracting the luminance of the active layer from the luminance of the underlying layers.
• Divide often ends up making your entire image look white. It divides the luminance of the underlying layers by the luminance of the active layer.

Difference mode extraction technique

One extremely useful application of the Difference blend mode is in isolating just the parts of two screen shots that are different. In the example shown,the mesh points in the original screen shot weren’t distinct enough, so Deke used the technique outlined below to recreate the mesh in its own layer with a different color.

1. Capture screenshots of the two variations and load them into Photoshop layers. Registration is key—all of the matching pixels should line up perfectly for this technique to work. In this example, the layer containing the mesh was set on top.

   

2. Select the top layer and set the blend mode to Difference. This will pop out the unique elements.
3. Stamp a layer: Use Shift+Alt+Ctrl+E (Mac: Shift+Option+Command+E) or Hold down the Alt (Option) key and select Merge Visible from the fly-out menu in the upper right corner of the Layers panel. Name the layer ‘merged’. This will serve as a snapshot of the blending effect.
4. Now, apply a Threshold adjustment to the merged layer to force the brighter elements to white: Select Image>Adjustments>Threshold from the menu bar and move the slider at the bottom of the dialog to the left until the entire mesh and points appear white.

   

5. Activate the Channels Panel and load the RGB channel as a selection: Control-click (Mac: Command-click) on the RGB channel to select the white elements. “Marching ants” will appear on your screen to indicate that a selection is active.
6. Switch back to the Layers panel and add a new layer: Use Ctrl+Shift+N (Mac: Command+Shift+N). When the dialog appears, name the layer ‘points’ and click OK.
7. Click the visibility eyeballs to turn off the merged and difference layers.
8. Use Ctrl+H (Mac: Command+H) to hide marching ants.
9. Fill the selection with a color. You can use Edit>Fill or Ctrl+Backspace (Mac: Command+Delete) to fill with the background color.
10. The marching ants selection is still active. It’s just hidden so that you can see what’s going on more clearly. Use Ctrl+D (Mac: Command+D) to deselect.

Now, your details are separated. From here, you can edit them in a number of ways, e.g. adding a drop shadow or other layer style to further distinguish them from the background.

Refining a Blending Effect

In many cases, the effect of blend modes can be tweaked by reducing the active layer’s Opacity, however there are eight modes that produce dramatically different results when you adjust the Fill value, instead of the Opacity. These are known as “the Fill Opacity 8.”  If you want to moderate the effect of these modes, you should experiment with the Fill value before you even bother with Opacity:

1. Color Burn
2. Linear Burn
3. Color Dodge
4. Linear Dodge
5. Vivid Light
6. Linear Light
7. Hard Mix
8. Difference

Even a slight reduction of the Fill value for Hard Mix turns it into a completely different adjustment—one that’s actually useful!