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Monday, September 2, 2013

Multi-Image Compositing Tips - Part Two

How to combine multiple exposures in the computer

This Article Features Photo Zoom


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Last week we covered my favorite in-camera tips for making multiple image composites. Assuming you've followed that great advice and created separate individual images that are all nicely aligned and ready to make the merge into a single composite, you'll have an easier time compositing those exposures in the computer. But still, you'll want to utilize these computer compositing tips to make your results as perfect as possible.

1. When I combine multiple exposures in the computer, I start with the selected images in Lightroom and make sure to apply any adjustments to color, contrast, brightness and sharpness across each image I'm going to use. I wait to make crops until the finished composite is complete, but for adjustments to white balance and exposure (common changes that I like to make in Lightroom) I simply apply the exact same changes to every exposure so that the changes to pixels in one image are applied in the same way to the corresponding pixels in another image. This will make the blending process easier all the way through.

2. Opening those separate images in Photoshop, I start with the overall base image as the background layer, choosing the image that is the most ideal in terms of overall look and feel. Then any subtle adjustments can be made to the scene by adding each additional exposure into its own separate layer, and masking away the parts I don't want to see. (Quick masking tip: Simply create the mask by clicking the Add A Layer Mask icon in the bottom of the Layers palette. This defaults to a clear mask—one that isn't hiding anything on that layer. Option-clicking when you create the mask will make the mask opaque so that you paint away the transparent parts, or you can simply create the clear mask and then use Command-I to invert the color—turning the clear/white mask into an opaque/black one. Choosing between the two is simple: if you only want a little bit of the layer to show, start with an opaque mask and paint in to reveal that little part. If you want most of the layer to show, start with a clear mask and paint away the parts you'd like to hide. When I say paint away, it's that simple: a paint brush and black, white or gray color. Just remember that black is opaque and white is clear when it comes to layers, and everything in between is… well… in between.) When I started using Photoshop many moons ago, I wasn't familiar with layers and instead I simply erased away the elements on a layer that I didn't want in the composite. This technique is a bit too primitive, and sacrifices the subtlety and ability to undo changes that layer masks afford. The moral of the story being if you're not familiar with layer masks, start getting familiar with them if you want to be happier with your compositing results.

3. When it comes to blending those layers together via masking, feathering is key. A large-diameter soft-edged paint brush is a great way to make subtle blends from layer to layer, and I use this as my tool of choice by default. But for certain things, a hard-edged brush with a smaller diameter, or a selection defining an edge between two scene elements, will be important. This is often necessary when trying to blend areas that contain textures or patterns. Sometimes a moire-like pattern or blurry effect emerges from the competing blends of textured areas (often found in places such as wallpaper or carpet, for instance). Finding a place in the scene to make a hard-edged cut from one layer to another is necessary in situations like this, and it's easies to hide those cuts along the edges of scene elements. Hard-edged brushes can be used here, or creating selections with the lasso tool can work as well. Just remember to activate the content layer, rather than the mask (done by clicking on the layer thumbnail in the layer palette). Sometimes a subtly feathered selection of just a pixel or two can help to hide these hard-edged transitions a little more easily.

4. No matter how careful you were when making the separate exposures in the camera, and no matter how well the layers generally align when they're piled up in Photoshop, there always seems to be at least one exposure that's out of sync with the rest. The best way to manually align layers containing matching scene elements is to change the layer mode of the top layer to Difference. You can find this option at the top of the Layers palette. This will show an inverted view of the pixels (light is dark, warm is cool, etc) and when the difference layer matches up with the pixels below, the visible pixels turn black—meaning that a perfectly aligned layer will be incredibly easy to see. Subtle arrow-key movements adjust the layer until it disappears into the pixels below, at which time you can switch the layer mode back to Normal and proceed knowing that the layer is perfectly matched to the rest of the scene.

Digital Photo Tip Of The Week
5. When you've got all your different layers together, and you've masked away all the bits and pieces that you don't want to see, a simple key combination will deliver a new layer on top of all the others, and it will be comprised of all the others, too. It's Command-Shift-Option-E (or Ctrl-Alt-Shift-E on Windows) and it will create a new layer made of the merged layers below, while maintaining the original layers separately. This layer is perfect for retouching without having to click back and forth among a bunch of different layers and masks, trying to find the element you want to fix, and yet it maintains the integrity of the original layered file so that you can always undo changes and blends later on down the road.

6. When you're happy with the overall appearance of the scene, an adjustment layer with an overall color adjustment can help unify the scene and bring the composited elements seamlessly together. I like to add a bit of warmth with the Photo Filter adjustment, by using a fairly transparent (say, 10 percent opacity) layer with the Warming Filter (85) filter enabled. (You can easily mask adjustment layers if you'd like, but for this unifying approach that would defeat the purpose.) That warmth is almost always great for people pictures, but I also use it in many other situations as well. Another great way to unify the layers is to add a bit of grain across the whole scene via the Texture filter; how much grain is a matter of personal preference, but remember that less is often more. Lastly, I will often add a bit of dodging and burning by hand for the very same reason, as anything that masks the multiple exposures and makes them appear as one is worth its weight in gold. Ultimately only you, not the viewer, should know that you've composited several separate pictures into one.


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