Learn the basics of Photoshop with simple exposure blending - Part #1

Photoshop is synonymous with two things, unbridled and near-limitless pixel‑pushing power as well as a certain gratuitous complexity that often leaves aspirant novices staring at the user interface bewildered. Regrettably, in 28 years since Photoshop first shipped, Adobe's relentless quest for digital image-editing supremacy has not been matched, in any meaningful way, by efforts to make the controls more user-friendly. With more buttons and menu options than a Soyuz, the reluctance of some photography enthusiasts to engage with the suite is entirely understandable.

However, as the de facto standard in photo editing software, Photoshop honestly does afford those with the gumption to look past the convoluted menu bars and side panels, near-boundless creative opportunity. In fact, even a rudimentary knowledge of the program is likely to see one equipped with the skills necessary to complete editing tasks that might otherwise be impossible.

While it would be difficult for me to argue that learning to use Photoshop is an ‘easy' undertaking, I can assure you that getting to the point where you can complete useful landscape photography tasks is not difficult at all. Indeed, Photoshop is built upon one fundamental concept, the idea of layers and masks, and there is no better way to learn about this crucial concept than with a staple of landscape photography photo editing, a simple exposure blend.

An exaggerated example of two exposures ready for exposure blending.

As you might remember from previous articles, exposure blending requires taking the highlight detail from one photo and combining it with the shadow detail from another to create a final composite image that contains the best of both photos. Sunrises and sunsets are always prime candidates for this sort of approach, and in our example image (below), the underexposed photo is set to donate the highlights for the sky and the overexposed the foreground detail.

Creating the layers

As previously indicated, the objective of any blending exercise is to create a single output file, and to this end, the first step is to incorporate the two individual photos into one single Photoshop file or PSD. There are several ways to achieve this rather trivial objective, but the most reliable approach is to use the Photomerge facility.

To execute this technique, both the donor photos should be simultaneously open within Photoshop, something that is indicated by an individual tab for each picture at the top of the workspace.

With the images open, selecting the File->Automate->Photomerge menu option will reveal the Photomerge dialogue box, and a subsequent click on the Add Open Files button will load the open files into the dialogue box as Source Files.

By default, no further action is required at this stage but if you're in any doubt as to whether or not the Photomerge will work properly, it is worth checking that Auto is selected in the left corner of the screen and that Blend Images Together is unchecked at the foot of the box. If everything is in order, click the OK button and the two photos will be combined into one new PSD file.

Just like the original images, the newly created PSD file is signified by a new (third) tab at the top of the workspace. By all accounts, the new file is the same as the originals, except that each of the donor images now constitutes an individual layer within it. The appearance of these layers offers crucial insight for those in pursuit of Photoshop enlightenment. It shows that in Photoshop, the essential ‘layer' is little more than a wholly independent image that happens to share a space in a file with some other entirely independent image.

The individual layers are stacked, one on top of another, in much the same way as you might stack physical prints and, just as with a pile of photographs, only the very top layer is visible to the viewer in the workspace at any one point in time. If you wish to see the layers below that topmost image, the top layer must be hidden by clicking on the Layer Visibility icon or ‘eye' located immediately to the left of the layer itself.

All the layers that happen to constitute a given PSD file can be hidden and revealed independently, which can be altogether baffling if the layer you are clicking on is not the topmost image. At the risk of sounding like a stuck record, it's worth me repeating that only the highest visible layer will be shown in Photoshop's primary workspace. Hiding and revealing layers that are not the topmost layer will have no impact whatsoever.

The Layers panel showing both the over- and underexposed images.

The Mask

On its own, the existence of layers and the ability to show and hide them is of little benefit in the world of photo manipulation. However, if there were a way to show and hide only selected parts of an image or to vary the degree to which layers are visible or invisible, then we'd be in business. If you haven't guessed it already, the modest ‘mask' provides this very piece of functionality.

To understand how a mask is implemented, let's consider our example again. The objective of our simple exposure blend is to combine the sky from the underexposed image with the foreground of the overexposed image. A look at the Layers panel reveals that the underexposed photo is (by chance) on the top of the pile, which means that to realise the effect we are after, we need to selectively hide the foreground portion of the image to reveal the overexposed image below.

To do this, we need first to select the layer that we wish to operate on (in this case, the underexposed layer) by single-clicking on the name of that layer in the Layers panel. If done correctly, the underexposed layer should then be highlighted.

The Layers panel showing the Underexposed layer highlighted.

The next step is to use the Rectangular Marque tool to select the portion of the underexposed layer that we wish to retain (for more on the Rectangular Marque tool, please read here). In this instance, it's the sky that we need in the final image; thus, a selection-rectangle needs to be dragged across the workspace accordingly.

The underexposed image, with the sky selected using the Rectangular Marque tool.

Having selected the sky, all that remains is to add the mask, and this is done by clicking on the Add Layer Mask button at the bottom of the Layers panel. Photoshop will automatically understand, based on the selection, where to place the mask and indicate that it has done so by adding a layer mask to the Layers panel.

A closer look at the layer mask reveals how the area initially selected with the Marque tool is shown in white and the area that was left unselected is black.

In the world of layer masks, black and white are hugely important colours since they translate directly into which areas and to what degree the layer below is visible. For example, if a layer mask were created that featured only white, nothing of the layer below would be visible and if it were entirely black, only the layer below would be visible.

It's the black and white that give users the opportunity to reveal and conceal selected parts of the various layers to create composite images. In fact, the idea of black and white is so vital to layers within Photoshop that there is a short maxim used to help one remember which colour does what: "black reveals, and white conceals".

“black reveals, and white conceals”

But, despite the fundamental nature of black and white, there is one decidedly unsightly drawback to the monochromatic layer mask (as I have described it), hard transitions. As we can see in our example, the layer mask's sudden change from black to white has resulted in an awful exposure step mid-way through the frame.

A close-up of the step change in exposure.

To prevent this offensive line from appearing, we need a way to fade the mask from black to white or, in other words, we require a gradient. In part two of this series, we'll have a close look at how to add just such gradient and consider how one might tailor the final layer masks to get the most out of the scene.

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