How can I avoid halos when darkening skies for black-and-white conversions?
Asked 4/19/2017
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When converting photos to black and white, darkening the sky with a Black & White adjustment or by reducing blue luminance can create a bright halo along the horizon where the sky meets the land. Is there a better way to darken skies without introducing this edge halo, either in Photoshop or during RAW processing?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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The easiest way to do this is through single-image exposure blending. It works well for any image where the sky is clearly separated from the other elements of the picture.
You can do it with one original (colour!) photo, but you need to develop two more separate images from it. Image 1 is the unedited original in colour. Image 2 is edited to have a correctly-exposed foreground/rest of the image, Image 3 is edited for the sky only. Note that any canges to exposure must be applied to the whole image. If you want to darken your skies, you must reduce the overall exposure of the image; do not just reduce the luminance of the blue tones in the image, as this is what creates the halos.
Now that you have three versions of the same image, stack them like this (top-to-bottom):
- Layer 3: Black-and-white image exposed for the foreground
- Layer 2: Black-and-white image exposed for the sky
- Layer 1: Original image (colour)
Apply a white layer mask to Layer 3. Go to Layer 1 and select the whole sky, using the colour selection tool. Now increase your selection by 1 to 2 pixels and feather it. Go back to the layer mask you have applied to Layer 3 and fill the entire selection with black colour.
Admittedly this still needs a bit of work to create the two versions of the image, but if done correctly, it will still save you a lot of manual healing brush work.
For more on exposure blending, check out this website.
Originally by user62519. Source · Licensed CC BY-SA 4.0
user62519
9y ago
0
Generated from our catalog & community — verify before relying on it.
Yes. The halo usually appears because you’re selectively darkening only the blue tones, which creates an abrupt tonal mismatch at the horizon.
Better approaches:
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Use a graduated adjustment Apply a graduated filter in Lightroom, Photoshop Camera Raw, Darktable, etc., so the sky is darkened progressively rather than by color only. This often gives a more natural transition and is much faster than brushing the edge manually.
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Blend two versions of the same image Process one version for the foreground and another for the sky, then blend them with a mask. For the sky version, reduce overall exposure rather than just blue luminance. This avoids the color-based edge halo.
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Use B&W color filters during RAW conversion In monochrome conversion, applying a virtual color filter can darken the sky without complex masking. For example, an orange filter often darkens a blue sky relative to the landscape.
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Capture-side option A graduated neutral density filter can reduce sky brightness in-camera and lessen the need for heavy post-processing.
In short: avoid relying only on blue-luminance reduction; use graduated adjustments, masking/blending, or B&W color filters instead.
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AI9y ago
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