Today’s Question: I’ve used Sky Replacement in Photoshop with some success, but in some images the clouds in the original sky “bleed through” the new sky and faintly appear. Is there an adjustment I am missing?
Tim’s Quick Answer: This type of issue is not uncommon with the Sky Replacement feature in Photoshop. When this happens, I recommend refining the layer masks associated with the new layers created by the Sky Replacement command.
More Detail: The Sky Replacement command attempts to ensure that the new sky blends into the surrounding areas of the image to create a more natural effect. However, this often leads to too much blending, allowing some of the original sky area to remain partially visible. In some cases portions of the sky might not be detected at all, leading to an area where only the original sky is visible.
When using the Sky Replacement command I recommend making sure that the “New Layers” option is selected from the “Output To” popup. This will cause the replacement sky and additional effects layers to be added to a layer group named “Sky Replacement Group” to be added above the image layer you’re replacing the sky for.
Within that layer group you’ll find several layers, with layer masks associated with some of those. In particular you’ll want to evaluate the layer mask for the Sky image layer. You can then paint with white on that layer mask to reveal additional areas of that replacement sky layer, or paint with black to block the sky to reveal portions of the underlying image.
It can also be helpful to perform a little bit of dodging and burning on the mask to reduce the blending along edges between the replacement sky and the underlying image. To do so you can set the blend mode for the Brush tool on the Options bar to Overlay. Then paint with white over the areas of the layer mask where you want to reveal the new sky without blending, and paint with black over areas of the layer mask where you want to reveal the underlying image without blending.
With the Overlay blend mode you can paint with white without affecting any black areas of the layer mask, and you can paint with black without affecting white areas of the layer mask. This provides a helpful way to shift shades of gray on the layer mask to black or white to completely block or reveal pixels, respectively.
