Hidden in the Layer Style dialog box are several options that are useful both on their own and with “Layer Styles & Effects” (page 193). So, you may wish to return to this topic after using Layer Styles a bit.
To access all the Blending Options, double-click near (not on) a layer’s name; click on the fx menu at the bottom of the Layers panel and choose Blending Options…; or choose Layer > Layer Style > Blending Options…. After settings from the Advanced Blending section are applied, an icon appears to the right of the layer’s name to alert you: .
Simply put, Fill Opacity is identical to ordinary Opacity, except Fill does not affect Layer Styles. That is, if the Fill setting is lowered, the layer’s “native” content disappears, but any effects do not. So you may have a Drop Shadow (page 195) that seems to be cast by nothing! More usefully, we can create styles without regard to the layer’s original appearance and know that the style’s appearance will be consistent.
This is an odd little option! For a layer with no layer under it, disabling a channel here is identical to disabling the visibility of a channel in the Channels panel—but for that layer alone. So, if you uncheck the blue (B) channel, an image will become rather yellow.
Interestingly, if there is a layer below, a disabled channel’s data is replaced with the same channel’s data from the layer(s) below. If there is a lot of blue data, for example, then the result will look rather blue!
Knockout is as much a masking technique as it is a way to blend layers. It’s also tricky in that choosing a setting alone does nothing at all. You must choose Shallow or Deep from the Knockout menu, and also adjust the Fill Opacity. If the Fill is set to 0, then the layer’s native content disappears and acts as a mask on layers below it. Since it’s using Fill Opacity, Layer Styles like overlays and shadows remain.
If Knockout is set to Deep, the layer will knock out all the layers below it except for a Background, if there is one. If it’s set to Shallow, then the layer masks, or “knocks out,” layers below it in the same layer group. If no groups exist, Shallow and Deep have the same result. Hovering over the Knockout menu summons a reminder tooltip. Knockout is great for masking many layers at once, and can be limited by simply grouping layers.
This option is subtle and difficult to use effectively. It impacts only some of the effects that act within a layer’s interior: Inner Glow, Satin, and the Overlay effects. Inner Shadow is not included. Enabling this option causes these effects to blend with each other as a unit (“as group”), and to be treated as part of the layer’s native content when the layer blends with the rest of the document.
The upshot is that Fill Opacity, which normally has no impact on any effects, will impact these “interior” effects when this feature is enabled.
This option, enabled by default, treats layers that are clipped to another as part of that other layer’s native content. See “Clipping Masks” (page 292) to know how layers are masked in this way. So, those clipped layers will vanish if the base layer of that clipping mask has its Fill Opacity set to 0.
If you want clipped layers to retain their own blending, disable this option in the base layer’s Blending Options.
Ordinarily, a mask works with layer content to form the shape of a layer to which effects are applied. This Advanced Blending Option, enabled by default, uses the layer’s inherently nontransparent content to exhibit effects. This does not take into account transparency produced by masking. When this option is disabled, only a mask’s shape forms the layer, and gaps or holes in the layer’s content are ignored. Sadly, this option has no effect on vector shape layers.
As mentioned above, a mask usually collaborates with layer content to form the shape of a layer to which effects are applied. When either Layer or Vector Mask Hides Effects is enabled, however, a mask will no longer be a factor in determining where effects are applied, but will instead mask both content and effects.
These sliders in a layer’s Blending Options control a layer’s visibility based on its own tones or the tones of the layer(s) visible below. You can also use the shades of gray of each color channel. That’s why, when I teach this feature, I call it “visible if.” As usual, you may use the fx menu at the bottom of the Layers panel to access the Blending Options.