What I am going to show you in this tutorial is how to turn these two exposures into one final HDR (High Dynamic Range) image.
What are Luminosity Masks?
Firstly, what are luminosity masks? Well, a luminosity mask allows us to make advanced selections of an image in Photoshop by selecting certain luminance (or brightness) values. Using these advanced selections, we can blend parts of one image with another. In order to use luminosity masks you need to shoot on a tripod and you need to have at least two different exposures. So the thinking behind it is to replace the blown out highlights of an image with correctly exposed areas OR to replace the underexposed areas with correctly exposed areas, depending on how you choose to look at it.
Step 1 – Adjust RAW images and bring into Photoshop
If you are not shooting RAW you can skip this step, but I would highly advise shooting in RAW. RAW images retain more information that will be needed in the merging process and it gives you more room to adjust the properties of the final image.
Once you are happy with your images, click on “Open Images” to open the two images in Photoshop.
Step 2 – Prepare the images for luminosity blending
Select the brighter of the two exposures and right click on the layer. Select “Duplicate Layer” and make sure you duplicate it into the darker image. You should now have both exposures in the same Photoshop file.
Because of the fact that my tripod moved slightly between the two exposures I need to align my images. Generally this is always good to do, even if you are sure that your tripod didn’t move. If you don’t you may notice small ghosting issues in the final image.
To align the two images, make sure that both layers are selected and navigate to Edit > Auto-Align Layers.
One the images have aligned, you will need to slightly crop the edges because there will be areas that only one of the images is visible and there will be some transparent edges too.
Step 3 – Make the luminosity selection and blend layers
In order to make the luminosity selection, you need to find the “Channels” tab above the “Layers” window
Select only the brighter of the two layers and Cmd-click (Mac) or Ctrl-click (Windows) on the RGB channel to make the selection. You will notice the marching ants appear to show you the selection.
Swap back over to the layers tab and click on the “Add layer mask” icon at the bottom.
The next step is very simple but very important. You need to invert your selection by clicking on the “Invert” button under the Layer Masks menu.
The image will look much better at this point but not quite done. If you take a look at the layer mask itself, you will notice that it serves to show more of the light areas of the image from the darker exposure in the layer at the bottom.
In order to add back some of the contrast that one would lose by using this technique, a simple curves adjustment will work well.
And it’s as easy as that! Have a look at the final image below as well as a before and after comparison.
Now it may take a few practice shots to get the results you are looking for. If the difference between the two exposures is more than 2 stops you may start to notice weird grey-coloured areas becoming visible in your image.