How to replace sky with channels
How to do sky replacement using channels

How to replace a Sky in photoshop using Channels

Sky Replacement in Photoshop using channels to combine multiple exposures

For today’s tutorial I’ll show you a quick solution for sky replacement in photoshop using multiple exposures. Often you’ll find to properly expose the foreground would be different than exposing for the sky, especially if you live in a place like Florida – which I do.

This was one photo taken in Raw but we could’ve used multiple photos or even a completely different sky.

HDR stands for High Dynamic Range. It really has nothing to do with multiple exposures but has come to be synonymous with that in the current digital photography world. Using a single image however if shot in raw you can pull a lot of data out of it. When doing this its best to underexpose – you’ll be amazed what you can pull out of shadows, but there’s very little you can do about blown out areas (overexposed white areas).

To conserve space on my server I’m not going to give out the Raw file but here’s two exposures in .jpg form if you want to follow along:

Original Exposed for Foreground
Original Exposed for Foreground (Image 1)
Original exposed for the sky
Original exposed for the sky (Image 2)

 

 

 

 

 

 

 

 

Step 1:

In your Raw Processor (Lightroom, CaptureOne, Darktable, Adobe Camera Raw, etc.) export your base image into Photoshop (image 1 above). Then open it in your Raw Processor again and adjust the exposure for the sky then export into Photoshop (image 2 above).

Step 2:

Start by thinking. Crazy right? But seriously, think. We want to combine these, we have tools for doing that, what would work? A lot of tutorials skip this so I’ll do my best to include a bit of the thought process.

Alright, I know we want to combine these. That means a mask. How might that work for these two exposures?

  • The sky in Image 1 is very white and the rest of the image has little white.
  • The sky in Image 2 is very blue and the rest of the image has almost no blue.

Of those if I glance at the channels I can see exactly what I thought…. the blue channel in Image 2 has great separation (contrast) between the sky and foreground. I’ll roll with that.

Blue channel of the sky exposure
fig 50.1 Blue Channel of the sky exposure has great contrast to work with.

Step 3:

I’ll duplicate this Blue channel. Then just using the lasso tool quickly draw a marquee around the bottom like this:

Marquee around the foreground
fig 50.2 Draw a marquee around the bulk of the foreground

Then fill that with black. Now do the same thing roughly on the sky to get rid of the clouds except fill with white. Then go to Image > Apply Image > Blue Copy then use Vivid Light but lower the opacity as far as you can while still having basically all Black and White. 50% for this image worked pretty well on my marquee. Brings us to here:

Apply image with vivid light
fig 50.3 Apply Image with Vivid Light

Step 6:

Copy and paste Image 1 (the foreground exposure) on top of Image 2 (where we’ve been working). Then in your channel panel hold down Ctrl/Cmd while clicking the new channel (Blue copy if you didn’t rename it) so that it creates a marquee. Go back to RGB then back to your layer panel and Apply Mask. Woops its backwards! Hit Ctrl/Cmd+I with the mask selected to invert it. Congrats! You can then click into the mask properties to refine it as much as you’d like.

Combined Exposures
fig 50.4 After combining the exposures with a mask

I then did some additional post processing that I won’t get into in this tutorial. Some warmth, some sharpening, color work, nothing fancy. Here’s my final before and after.

Original Exposed for ForegroundHow to replace sky with channels

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