Part of the joy of landscape photography for me is standing around and waiting for the light to change. You put your camera on its tripod, compose a shot and wait, taking photos every few minutes, whenever the sky or light or whatever looks interesting.
I caught the tail end of a storm in Santorini, Greece, with heavy clouds blowing over right at sunset. An hour or so later and it was blue hour, with streetlights and buildings lit up. Both photos are below, after being edited in Lightroom using the Lightroom Develop System.
They are both individually pretty good, but what if we could combine them?
A stormy sunset over Santorini.
Blue hour and streetlights in Santorini.
Creating & Using Color Channel Luminosity Masks
I would like to be able to take the illuminated buildings and streetlights from the blue hour photo and add it to the stormy sunset. As with shooting into the sun, the best way to do this is through luminosity masks, but with a slight twist.
- Open both photos into the same workspace in Photoshop, making sure that the blue hour photo is the topmost layer.
- Move to the ‘Channels’ tab, but rather than making a luminosity selection for the RGB channel, instead Ctrl-Click on the Red channel thumbnail.
Make a luminosity selection of the red channel to select streetlights.
Add this selection as a layer mask to the blue hour exposure:
- Once you have made the luminosity selection, return to the ‘Layers’ tab, make sure the blue hour layer is active, and click on the add layer mask symbol.
Add the luminosity mask as a layer mask to the blue hour exposure.
You should get a result like the one below. All of the streetlights and other building lights have come through exactly as expected, but there are obvious problems in the sky. This is easy to fix.
A luminosity mask blend of the stormy sky photo and the blue hour photo.
Fixing the Luminosity Mask
- Use the ‘Quick Selection’ tool to easily select the sky, by painting the tool over the areas you want to select, until you have a selection like the one below. Make sure you have the layer selected, rather than the layer mask. You may also need to turn the ‘Sample All Layers’ checkbox on or off, depending on your photo.
- Tip: This tool should automatically snap to the boundaries between your sky and ground. If you have a more complex sky, you can zoom in and lower the size of the ‘Quick Selection’ brush. Also, you can add or subtract areas from the selection by holding down Ctrl (for add), or Alt (for subtract), while you paint with the brush.
Use the ‘Quick Selection’ tool to select the sky.
- Then, make sure the layer mask on the blue hour layer is active by clicking on it’s thumbnail, and use the ‘Brush’ tool, with color set to black, to paint over the sky.
Use the ‘Brush’ tool (set to black) to paint out the sky in the blue hour photo.
You may also want to paint a few small changes into the rest of the mask if some parts just don’t look right. Below, you can see the original luminosity mask created from the red channel, and the modified mask after the sky and other areas were painted out.
The original Red channel luminosity mask.
The modified Red channel luminosity mask, with the sky painted out.
And this leaves you with one finished blend of a stormy sunset in Santorini, with streetlights turned on. To fully bring out the colors and tone, I would now run this photo through the Landscapes Masterclass process.
The final blended version of the Santorini photo.
It’s possible to go even further than this and to combine colour channel luminosity masks with blending modes. For more on this powerful technique, see this video:
About the author: Tim Daniels is a photographer photographerm, photo trainer, and founder of the website Lapse of the Shutter. You can find more of his work and tutorials on Lapse of the Shutter, or by following him on YouTube and 500px. This article was also published here and is being republished with permission.