INTRODUCTION
It is possible to convert an Adjustment Layer into a Layer Mask.  A black mask hides it’s linked layer from the layers below and white reveals.  A black/white gradient tool can be used to progressively change intensity of the masked layer.  For this lesson, select Image + Resize + Image Size for each picture and make all the same Width (14”) and Resolution (72).

OPEN A PICTURE AND REMOVE THE SKY
Open Photoshop Elements in the Full Edit mode.  Click File + Open (or hold the Ctrl key and tap the O key) > select a picture such as a landscape with a bland sky > click Open (becomes Background on the Layers palette) > double-click the palette icon (becomes Layer 0) > select the Magic Wand selection tool > click around in the sky to select only the sky > press the Del Key (makes selection the color of the set background color) > select the Magic Eraser Tool > click in the selected area (erases the sky) > click the blue bar above the picture and drag it halfway behind the palettes.

OPEN A SKY PICTURE
Open a picture of a sky > select the Move Tool > drag the sky onto Layer 0 > close the sky picture > drag the combined pictures back to center > on the Layers Palette, drag Sky (Layer 1) below Layer 0.

CREATE A BLANK LAYER
(On the Tools Bar) change the background color to a darker blue than Layer 1 > press the X key (move selected color to background) > hold the Ctrl key and tap the N key (new layer) > set background contents: background color, Width (14”) Height (11”) and Resolution (72) > click OK (becomes Layer 2) > if necessary, drag Layer 2 above Layer 1.

CREATE A LAYER MASK ON THE LAYERS PALETTE
Select Layer 2 > click the adjustment layer icon (black/white ball on the Layers Palette) + Hugh/Saturation > click OK > if necessary, drag Layer 2 above the adjustment layer > hold the Alt key and click the horizontal line between the Layer 2 and the adjustment layer (links the layers and tricks PE6 into thinking the Adjustment layer is a Layer Mask).

USE THE GRADIENT TOOL
In real life, usually the sky is lighter near the horizon and darker above.  Select the Gradient Tool > on the Options Bar, select the Black to White Gradient, the Linear Gradient, Normal Mode and 100% Opacity > uncheck Reverse, check Dither & Transparency >  double click the Gradient picture in the Options Bar > double-click the lower left slider > set B=20 (lightens the background) > click OK > click OK > select the Layer Mask > hold the Shift key and drag a vertical line from the low point in the sky to the top (black hides Layer 2 and white reveals) > select Layer 2 and reduce the Opacity to about 50% > turn visibility eyes on and off to see the effects of the gradient.

CONCLUSION
This lesson included procedures for replacing the sky and applying a gradient tool to a layer mask.  The result is a lightening of the sky at the horizon.  Other filters and adjustments can be applied to further improve a photo.