Luminosity-Based Masks

Selections based on the luminosity values contained in an image can be created from the composite or default color channels. They can be used to protect a range of levels from highlight to shadow when you apply adjustments and, with a bit of work, clamped to mask changes to extreme highlights, shadows, or midtones when you use them in adjustment layer masks.

You can base the mask on the composite channel by pressing Ctrl+Alt+Tilde (Windows), ^+Opt+Tilde (Mac OS), or on the individual channels, including the composite, by Ctrl-clicking (Windows), ^-clicking (Mac OS).

You can also convert a duplicate to Grayscale mode and use its single channel to load the selection, or to Lab mode and use the L channel, or to CMYK mode and use the K channel (each produces a slightly different mask).

After the selection is loaded, you can import it into the parent document. To do so, choose a selection tool, click in the selected area (the icon should change to a white arrow with an accompanying rectangular selection outline when you are over the selected area), and then drag the selection into the parent document. Hold down the Shift key when the mask is over the target window to center the selection.

Having loaded the selection, you can use the adjustment commands, such as Curves or Hue/Saturation, directly on a layer or create an adjustment layer and have the mask applied automatically.

By default, the highlights are selected and the shadows masked. You can easily inverse the selection by choosing Select^ Inverse, or Ctrl+Shift+I (Windows), 8€ + Shift+I (Mac OS).

To clamp or restrict the luminosity mask, save it as an alpha channel and then apply a curve that basically clips the highlight, midtone, or shadow values Likewise, if the luminosity mask was loaded in an adjustment layer mask, target the mask and then use Curves to restrict the adjustment's influence on the layer content (Figure 9-2).

Figure 9-2: A luminosity mask loaded in a layer mask and then a curve used to restrict the mask to (A) midtones, (B) highlights, and shadows.

Figure 9-2: A luminosity mask loaded in a layer mask and then a curve used to restrict the mask to (A) midtones, (B) highlights, and shadows.

0 0

Post a comment