Overlaying Two Exposures

Most digital cameras are capable of handling up to 5 stops of brightness differential. Therefore, when one wants to shoot a scene that has a difference of 6 or more stops then the result is either a blown sky (in order to capture the foreground) or an underexposed foreground (in order to capture the sky). Sometimes this is fine. Other times you want to get both foreground and sky properly exposed. Many photographers use split neutral density filters. However, many people have no clue what those are or how to use them. So - what to do? The answer is simple - two exposures (one right after the other). In order to do an image overlay properly your camera must not move. Get a good, solid tripod and a good, solid camera mount. You will never be sorry for this gear acquisition. Learn your camera and know how to make quick adjustments. Not all cameras will be able to be used with the following technique. A big thanks to Marc Muench for the teaching me this technique.

The first image (Image 01 below) was taken at sunrise along Skyline Drive in the Shenandoah National Park. I used my Canon 20D with a 17-40L wide angle lens. The settings were ISO 200, manual control, center-point focus, f/11, and 21mm. The meter showed 1/30 sec. for proper exposure of the sky. Look at the histogram. The brightness (right side) shows a nice exposure. The blacks (left side) are severely clipped.

Image 01

Want to see where the blacks are clipped? Easy, in the histogram at the upper right there are two triangles. Place your mouse over the left one and see what happens. If the blacks are clipped then they will show as bright blue in the main image. See Image 02 below. Also, in this example, the recovery icon is shown. Put you mouse over that and see what highlights are being clipped. Highlights that are being clipped are shown in bright red. See Image 03 below.

Image 02

Image 03

The next image (Image 04 below) was taken a few seconds later. The settings were ISO 200, manual, center-point focus, f/11, and 21mm. My 20D is set to be adjustable by 1/3rd stop increments. So opened up the exposure by 2 stops (going from 1/30 sec, to 1/25 sec. is 1/3, to 1/20 sec. is 2/3, to 1/15 sec. is 3/3, to 1/13 sec. is 4/3, to 1/10 sec. is 5/3, and finally to 1/8 sec. is 6/3 = 2 stops). Knowing that 6 clicks on my camera’s dial is the equivalent of 2 stops (1/3 stop for each click) I extended the second shot’s exposure to 1/8 sec.

Image 04

Look at the image’s histogram. The brightness (right side) is severely clipped. However, the blacks (left side) are better exposed. Because this is a sunrise I expect to have some areas in the foreground that are very dark. You can see the clipped blacks in Image 05 and the clipped highlights in Image 06 below.

Image 05

Image 06

Now, it’s not always the case that two stops are sufficient to get a good exposure on the darks and the highlights. Sometimes it’s more - sometimes it’s less. How will you know? It’s easy!!! Read and understand the histogram if your camera has it. Once you get a good exposure on the highlights then go two stops and see what the foreground shows. If the blacks are still clipped then go one more stop (or 1/3, 2/3, or 1/2 if your camera is set for 1/2 stop increments). Go less (-1/3, -2/3, or -1/2, etc.) if needed.

Once you get your two exposures it’s time to head inside, get some coffee, and fire-up the ol’ computer. I use Lightroom and Photoshop CS2. Others that use Elements (which doesn’t support layers from what I understand) may have difficulty with the following technique.

I will refer to the shot exposed for the foreground (the one which increased the exposure) as the Shadow Exposure. The other image is the Highlight Exposure. The following settings are merely recommendations. You may want (and probably should) use different setting for each image, particular if you are trying to get a specific artistic feel.

LIGHTROOM (Shadow Exposure)

Adjust the blacks by ALT-clicking on the slider and moving left or right. You want the clipped blacks to drop out some. I typically have a setting of 2 or 3. Image 07 below shows what you see when you ALT-click the slider to see where the blacks are being clipped.

Image 07

Adjust the fill-light. I typically use a setting of 10-15.

Adjust vibrancy. I typically use a setting of around 30.

Adjust the temperature as needed to warm or cool the image.

Adjust sharpening to add some contrast. Maybe I will use around 30-50 for the 20D. Play with this for your camera.

Adjust luminance. I typically use a setting of 25-35.

Adjust lens correction. Red/cyan will be -20 or so. This depends on the camera. I defringe all edges.

LIGHTROOM (Highlight Exposure)

Adjust exposure. ALT-click on the slider to reduce the clipped highlights. In this example you will not want to completely eliminate the clipped highlights. It’s a sunrise after all. Image 08 below shows what you see when you ALT-click the slider to see where the highlights are being clipped.

Image 08

Adjust recovery. I typically use a setting of 10-13.

Adjust vibrancy. I typically use a setting of around 10-20.

Adjust the temperature as needed to warm or cool the image.

Adjust sharpening to add some contrast. Maybe I will use around 30-50 for the 20D. Play with this for your camera.

Adjust luminance. I typically use a setting of 25-35.

Adjust lens correction. Red/cyan will be -20 or so. This depends on the camera. I defringe all edges.

My final Lightroom-adjusted images are shown in Image 09 and Image 10

Image 09

Image 10

Now, open your adjusted images in Photoshop. In the bottom of Lightroom select both images. Right-click on either one then chose “Edit in Adobe Photoshop. See Image 11 below. Choose to Edit a Copy with Lightroom Adjustments. See Image 12 below. In Lightroom I export to 16 bit tif in Adobe RGB space. However, you can export to 8 bit psd file in sRGB.

Image 11

Image 12

You can close Lightroom if you want.

In Image 13 below you can see the Highlight Exposure and the Shadow Exposure are both open. I will be overlaying the Shadow Exposure on top of the Highlight Exposure. The order does not matter, though you will have to modify some of the steps that follow.

Image 13

First, the following Image 14 below shows the common tools we will be using in this tutorial.

Image 14

With the Shadow Exposure active (see Image 13 above) choose move (press V). Then press and hold the SHIFT key and click on the background icon under the layers palette (on the right side of the image). See Image 15 below. While still pressing and holding the SHIFT key drag the background icon over the Highlight Exposure and release. By using the SHIFT key Photoshop will automatically align the Shadow Exposure over the Highlight Exposure. Close the Shadow Exposure file.

Image 15

In Image 16 below notice that the Highlight Exposure now has two layers (Background and Layer 1) under the layers palette. Notice also that your histogram is from the Highlight Exposure.

Image 16

Make sure your foreground color is black and your background color is white in your Tools. With Layer 1 active (highlighted) click on the Add Layer Mask (rectangle with the white circle) at the bottom of the layers palette. This will add a layer mask to Layer 1. Select the Gradient Tool from the Tools and make sure Foreground to Background is selected. It is the icon that shows a transition from black to white. You will draw a gradient from a start point to an end point.

Your particular start and end points for the gradient will vary depending on your particular image. Since you working on layer 1’s mask what is “black” (the start point) and everything before the start point will be erased to show the background layer. That is, the mask is deleted in order to reveal what is underneath (which is the Highlight Exposure). What is white (the end point and everything after it) will retain the mask and only show Layer 1 (the Shadow Exposure).

It is important to note that the start and stop points are not to be equated with 100% erased (100% black) and 100% kept (100% white). Since you are using gradient the start and stop points are actually the equivalent of 50%. Therefore you don’t necessarily want to position your start point right at the mountain/sky interface. Somewhere lower would be better in this example in order to provide a nicer transition to the sky. As you will see later you can and should adjust the mask a bit later on in order to make it better.

My start point was somewhere near the top of the mountain ridge in the middle of the image. I drew downward and released. See Image 17 for an idea on where I drew my gradient. The exact location of my end-point didn’t really matter in this case since everything afterwards will be kept as Layer 1.

Image 17

With the gradient applied to the layer mask the Highlight Exposure’s sky now shows. However, we still have some problems with the foreground on the right and the mountains near the sky. See Image 18.

Image 18

So, let us clean up the remaining mountains. You need to use a large, soft brush from the tools. For this example I used a soft brush with a radius of 400px. I set the opacity to 50%. IMPORTANT: Set your foreground color to white and start painting back-in Layer 1. You do this by clicking once on the mask icon in Layer 1 and then painting back-in over the left and right sides of the mountains to obtain more from the Layer 1 (Shadow Exposure). The large, soft brush @ 50% opacity applies the strokes nicely so that there are no hard edges. See the Image 19.

Image 19

Let us work that sky a bit more. Control-click the layer mask on Layer 1. This will add a selection to your image (at the bottom in this case). Note that the selection line (the dashed line) really represents the 50% region since we used a gradient mask to define were the mask is removed. Let’s invert this selection to get the sky. To do this choose Select - Inverse from the Photoshop menu. At the bottom of the layers palette choose Create New Fill or Adjustment Layer (the half black - half white circle) and then Curves. Adjust the curves to suite your taste. See Image 20 below. Once you are done with the curves click OK.

Image 20

This curve adjustment caused some of the mountains to become slightly darkened. Click once on that layer mask icon in Layer 1. Make sure you still have a large, soft brush, and drop the opacity down to 20%. This time we can paint back in the background some more, and with the opacity at 20% we don’t affect the sky too much. We can also switch our foreground color to black and paint away that dark blue on the top. There are a lot of things that can still be done such as minor tweaks (using a smaller brush diameter) where the sky meets the mountains. We can also create a curve layer for the foreground to give it more contrast. You can do a lot with this to finesse the colors and shading. However, the above steps are should get you started. See Image 21.

Image 21