Part Three: Combining Images in Photoshop

Now we’re getting to the fun part: blending all your hard work together in Photoshop to make one beautiful image.

Once you’ve captured three or more RAW images of the same scene, open all three files in Photoshop RAW so you can see them all at once.

First I’ll look at the individual images to see if I need to tweak my exposure. I’ll select the shortest exposure (darkest image) and check for blown highlights – since this is the photo I’m using to eliminate any overexposure, this step is very important. You can check your image easily by ticking the blown highlights indicator (Figure 1) which will highlight any overexposed areas in red.

Notice how the sky has great cloud detail and rays of sun poking through – not visible in the longer exposures that were metered for the entire image and/or foreground.

I can see that only the area around the sun is blown out, which is something natural and expected. I’m much more concerned with blown areas AROUND the sun – such as in the sky, in between clouds, and so on. Since I’m okay with that, there’s no need to adjust my exposure any further. If there were blown out areas other than around the sun, I would reduce my exposure right here in RAW.

Repeat the same process for your brightest image – are there any shadows that were not exposed correctly? Turn on the blocked shadows indicator (Figure 2) which will outline in blue if you have any shadow areas that are underexposed.

It seems that the darkest parts of my image (the foreground and the pine trees) were exposed enough to be visible – no need to adjust the exposure here either. If I saw a large amount of blue in the foreground, I would increase my exposure a bit.

When I look at my middle exposure with both indicators turned on – the photo one would normally take just walking by using evaluative metering – it’s easy to see why I need to autobracket this image and blend the exposures (Figure 3). There are blown highlights, blocked shadows, and looks like an exposure nightmare.

If I tried to expose this image more to recover the shadows, I’d overexpose the sky further, and vice versa – the only way to make this kind of image decent is to blend different exposures into one.

From here, you should perform any RAW editing you usually do, such as black and white conversion, white balance adjustments, and so on.  Select all your images to have the same adjustments applied to all three photos instead of just one at a time – except for any adjustments in exposure of course. This helps to cut down on your editing time and keeps all your images uniform.

With all three images still selected, click Open to bring them into Photoshop. You’ll now have three different files (one for each image), but not for long – we’re going to combine them into one file with each image on its own layer.

Select your middle exposure and click CTRL + A so that you see the “marching ants” along the edge of your image. Press CTRL + C to copy the image and switch over to your darkest photo (shortest exposure). Simply press CTRL + V to paste the middle exposure onto your darkest image – Photoshop will automatically place the image on its own layer and align it correctly. If you executed your bracketing properly, you should have no alignment problems.

Repeat this step for your overexposed image so that you have all three photos in one file and on their own separate layers (Figure 4). Your top layer should be your brightest image and the bottom layer should be the darkest.

Since we have all the images in one file, you can go and close any other open files; don’t bother saving them. Now we’re all set up to blend them together.

Combining Exposures Using Layer Masks

Now we’re going to add layer masks to create one image using multiple exposures – much like HDR, only a bit more realistic and completely customizable.

Turn off your top layer (click the eye) so that only the middle and darkest exposures are visible. Add a layer mask to your middle exposure and select your brush tool, with black set as the foreground color. With your new layer mask selected, adjust your brush to a suitable size – for this image, I want to bring forth the lesser exposed sun and sky from my darkest exposure (bottom layer). Start to brush over the area(s) you wish to expose.

What I’m basically doing here is creating an imaginary – and reversible – hole in the middle layer so that I can see the bottom layer. Instead of applying it directly to the layer, I’m using a mask so that I can adjust or reverse this hole later on.

By using your brush tool, you can really customize your image by adjusting your brush hardness and opacity. A brush with 100% hardness will give you a very sharp (or “hard”) transition – good for small areas or sharp lines, but generally doesn’t look too good when you’re trying to blend layers gradually like in this image. I usually start with 0% hardness and readjust as necessary. Try out different brush hardness levels to get an idea of how this works.

Another great tool you can adjust is your brush opacity – or strength. When set at 100%, you’re basically cutting a hole in your layer, allowing the bottom layer to be seen completely. When you reduce the opacity – let’s say to 50% – you’re only allowing 50% of your bottom layer to be seen and 50% of your top layer to remain.

Since we’re working on layers that are lined up perfectly with the only difference being exposure, you can really take advantage of this tool. Often you’ll find that using 100% opacity will cause too sharp of a transition and look rather unlikely…for my lighthouse image here, some of the sky would look a bit too underexposed as the bottom layer is rather dark outside of the sun area. I can use a brush with a lowered opacity to allow the sun of my bottom layer to be 100% visible, but still retain some of the brighter exposure of the middle layer by using a more transparent brush.

What I do is use a brush of a lowered opacity – around 25% to start – but this can change greatly depending on the image. Instead of going over the image once, I brush it several times to create a mask of varying opacity, which will allow you to decide which areas need to have the bottom layer seen fully, and what areas look better when only slightly visible.

Going back to my image – since I’m only looking to have the sky poke through, I only brush over that particular area (i.e. I don’t brush over the foreground or the tree line). While the area around the sun should be brushed with 100% opacity to let the bottom layer be fully visible, I think that the rest of my sky would look too dark at this strength. Therefore, I brush the entire image using a brush set at 20% opacity, and brush over the sun area more often than I do the rest of the sky. You can always switch your brush color to white if you want to reverse the brush work you previously did.

As you can see by looking at my layer mask (Figure 5), it’s not strictly black and white, but has varying tones of grey indicating the different levels of visibility. A black brush set at an opacity level under 100% will be some shade of grey – the more times you brush over an area with a low opacity brush, the darker the grey will get until it’s completely black (100% opacity).

The layer mask above gives me the “after” image below (Figure 6). The “before” image is what my middle exposure looked like before adding my mask. When I zoom in a bit, you can see a big difference in sky detail.

Turn your top layer back on by clicking on the empty box where the eye once was. Now you’ll see your previous image disappear and instead be looking at only your top layer – don’t worry, we’re going to bring it back in just a second. For this top layer, we’re going to work on an inverted layer mask – instead of brushing to remove our layer, we’re going to brush to bring it back.

Hold down the ALT key when you click your Add Layer Mask icon (Figure 7) – this will make your layer 100% transparent. Instead of using a black brush like we did previously, we’ll instead use a white brush to gently bring back our top layer.

Since we now have a black layer mask, we’ll need to use a white brush to make this layer more visible.

This method (inverse layer mask) works better for shadows since we are trying to increase the exposure – it’s easier to keep brushing until the shadows are bright enough to your liking. Use the same principles of the first layer mask we did – varying your brush size, opacity, and hardness to blend the areas accurately.

Another great benefit to this technique is that it allows you to get artful with your exposure blending and redirect the attention of your image. Like for my photo here – instead of just going 100% opacity on the areas I want to blend, I can use different opacity levels to make certain parts brighter than others, almost like dodging and burning. Depending on your image, you can get some stunning tonal ranges just by using different exposures.

Advice on Brushing

When blending your layers with the brush tool, don’t get sloppy and use too soft or too wide of a brush when blending along the edges of prominent lines or focal points (for example, in my image here, it would be where the sky meets the lighthouse). When you’re not paying attention, you can create an unnatural glow to your image which is a dead giveaway to editing – not to mention just looks bad. Take your time and do it right as seen in the comparison below:

Once you’ve completed the layer mask for your top layer, it should look something similar to Figure 8 below:

After all that exposure blending, let’s finally compare your normal, non-bracketed, single exposure that you would normally take (our middle exposure) to our final product:

The original:

After exposure blending:

Talk about a big improvement – and now you have a great base with a huge tonal range for further editing. With some adjustment layers and other crafty editing, you can take your image above and make it into something more artful, like my final image below:

Exposure Blending vs. ND Grad Filters

For those who know about ND grad filters, you’re probably a bit boggled why one would go through such trouble to bracket off a scene and then edit in Photoshop – after all, it’s always better to capture your image properly with your camera vs. working in post process, right?

For those of you who don’t know about ND grad filters…you can somewhat replicate this effect by purchasing one. The filter underexposes a portion of your photo – basically, the filter will shade one-half of your image (like a pair of sunglasses) and expose the other half regularly. If you have a slot-in filter system, you can adjust it so that it lines up with your horizon line.

Cokin Graduated ND filter by purplemattfish, on Flickr

A Cokin ND grad filter (left) with the filter holder (right) that attaches to the front of your lens.

This is the ideal way to capture a sky/ground exposure with vibrant colors and tones. The downside to using this is that you’ll often find yourself in situations where the sky/ground exposure ratio will not always be the same, making it necessary to blend exposures even with the ND grad filter as it will only reduce your exposure by a certain amount of stops.

For example, let’s say you purchased a filter system to underexpose a sky, which will reduce it by 5 stops, but the scene you come across may be more dramatic and requires 8 stops to get that perfect exposure. You’d still need to bracket your image even with the filter to get the optimal tonal range.

Also – and probably more importantly – the filter system doesn’t do anything for your foreground. As we saw in my example image, the foreground was quite underexposed in my original (middle) exposure. If I was using a filter system, the sky exposure would be reduced, but that would only solve half my problem – the filter can’t magically increase the exposure of my immediate foreground.

Thirdly, if you don’t want to purchase an ND grad filter system, this is a great way to replicate the effect more accurately – and with no additional cost if you already have Photoshop.

So my recommendation would be to utilize an ND grad filter when appropriate, but still autobracket your scenefor the best results.

Other Uses for Exposure Blending

As you can tell, this technique has a wide variety of uses – and not just for landscapes or sunset/sunrise scenes. What if you’re shooting a portrait in RAW and have some unsightly blown highlights in the background? When you drop your exposure to correct this, your subject is cast into shadow – you’ll need to blend two different exposures in order to keep your subject looking good and also eliminate those distracting highlights.

For this instance, you can open up your image normally after RAW editing – exposed for the subject but with your annoying blown highlights. Afterward, you can re-open that same RAW file, drop the exposure down to the point where the highlights are recovered, and open the image in Photoshop to blend as detailed in this tutorial.

This is just a minor example – you can use this exposure blending technique to recover many images without affecting the exposure of your entire photo.