Photoshop Blend Modes Explained (part 2)

Brush Tool-Specific Keyboard Shortcuts

The Brush Tool has some additional blend modes and associated keyboard shortcuts. These blend modes, which aren’t found in the Layer panel’s blend mode list, are “Behind” and “Clear.” There is also an Airbrush option that, while it’s not really a blend mode, it does have a keyboard shortcut that’s worth mentioning. The behind blend mode will apply paint only on transparent pixels in a layer, and will leave the opaque pixels intact. The Clear blend mode basically turns your brush into an eraser by making the pixels you paint on transparent.

Pass Through Mode

The default blend mode for a layer group is “Pass Through.” The Pass Through mode tells Photoshop to act as if there isn’t a group—it’s like temporarily taking the layers out of the group to perform the blending in the usual order. If Pass Through is changed to a different mode, you’re basically changing the order in which the layers are processed—all layers within the group are blended first, and then the resulting composite is blended with the layers below using the blend mode selected for the group (the layers within the group are acted on first).

Luminance Blending

The luminance blending options can be accessed by double-clicking on a layer near (but not on) the layer name, or by clicking on the “Add a Layer Style” icon in the layers panel, and selecting “Blending Options…” In this dialog box, you will see 2 sliders, the “This Layer” slider, and the “Underlying Layer” slider.

The “This Layer” slider controls which luminance levels are visible in the active layer. The “Underlying Layer” slider controls which luminance levels are visible in the composite view of all of the layers below the active layer (it forces the lower pixels through to the active layer).

When the “Blend If” option is set to Gray (the default), these 2 sliders will work based on the luminance levels of all RGB color channels. To make luminance blending modifications to just one color channel, select the color of the channel you want to work with (Red, Green or Blue).

When adjusting the “This Layer” slider, if you slide the white triangle to the left, any luminance levels to the right of the triangle will become transparent, and the composite pixels from the layers below will show through. If you slide the black triangle to the right, any luminance levels to the left of the triangle will become transparent, so the composite pixels from the layers below will show through. Any luminance levels between the 2 triangles will be opaque. If you look closely at the black and white triangles, you will notice that there is a cleft running down their centers. This cleft indicates that the triangles can be split. To split the triangles, hold down the Option key (Windows: Alt) while dragging one half of a triangle away from the other half. When you split a triangle, any luminance levels between the 2 halves will gradually range from transparency to opacity. This useful technique is often used to introduce smoother transitions between transparency and opacity.

The “Underlying Layer” adjustments work the same as the “This Layer” adjustments. The only difference is that this slider will determine which luminance levels are visible in the composite view of all of the layers below the active layer—it forces the lower pixels through (up) to the active layer.

You will also notice that the Blending Options dialog box has a Blend Mode list and Opacity slider. These options mirror the options found in the Layers Panel, so you can make your adjustments in either location. There is also an “Advanced Blending” section in this dialog box that I’ll discuss in a future article.

Default Settings for Luminance Blending

Luminance Blending Example

Luminance Blending – Simple Underlying Layers Adjustment

The illustration below shows the use of the “Underlying Layers” slider with both of the triangles split.

• All luminance levels below 30 will be transparent
• Luminance levels between 30 and 57 will gradually be transitioned from transparent to opaque for a smoother effect
• All luminance levels between 57 and 200 will be opaque
• Luminance levels between 200 and 227 will gradually be transitioned from opaque to transparent for a smoother effect
• All luminance levels above 227 will be transparent
  
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