High-Speed Drop Outs

by Dave Montizambert

Dave Montizambert

Christiane against the sea, mountains and sky.

September 01, 2011
My clients are always making crazy requests, especially since the introduction of digital. They frequently ask for summer fashion catalogues with outdoor themes shot in the dead of winter in the Northern Hemisphere, and they always pick the rainiest or snowiest days to shoot on. To deal with this common request, I create the image indoors using a technique called simulated sunlight, and marry it with a simple background drop out technique in Photoshop to drop in a suitable outdoor scene.

The image used in this article is from a lighting demo I did at a convention presentation in the U.K. during a howling January snowstorm. Once you get this technique down, it is really easy to do quickly. But while cutting around flesh and most garments is easy and can be somewhat automated, cutting out hair can be a tedious, time-consuming task because of the size and translucent quality of hair.

Simply put, the background will partially show through any given strand of hair and will be viewed as a contaminant once a different colored/toned background scene is added. To make things even more challenging, the smooth surface of a strand of hair is highly reflective and picks up original background color and tone. Strands of hair are also very thin, and the edge pixels of these strands can mush together with the original background when imaged if the lens and/or imaging sensor’s resolving power is not adequate. This looks perfectly fine and natural against the original background but does not against a new background.  

After being frustrated with these challenges, I found a wonderful, fast solution using blending modes to blend the hair into a new background, which works beautifully most of the time if you light the edges of the hair correctly and carefully choose an appropriate background for the original shot. An appropriate background can only be determined once you know what the final background tone around the subject’s hair will be.

Fast Blend Mode Knockout recipe for dark background scenes: 
Let’s take a look at one of my Hair Knock Out recipes by applying it to an image I shot using my simulated sunlight lighting technique on model Christiane (www.ulorinvex.com) during a masterclass at the SWPP 2010 Convention (see Images 3 and 4).
Disclaimer: This Fast Blend Mode Knockout technique works really well if the replacement background is either dark in tone or light in tone; mid-tones can be tricky.

Recipe:
Open the subject image.

Double click background layer and rename it to make it a true layer.
Open the background scene image.

Drag the background scene image into the subject image file; hold down the shift key as you click and drag the background layer from background scene into the open window of the subject image file.

Drag the background subject scene layer to the bottom of the layer stack so that is sits underneath the subject layer.

Select the subject layer and then duplicate it: Layer > Duplicate Layer > Okay (keystroke short cut—Cmd/Ctrl J).

Hide this new layer’s visibility by clicking on its visibility eyeball icon.

Select the middle layer (the original subject layer).

Near the top of the Layer palette, switch the layer blend mode from its default setting of “Normal” to “Lighten.” In some instances, “Screen” may work better.

Select the top subject layer and turn its visibility back on.
Create a Hide All (Black) Layer Mask—Layer > Layer Mask > Hide All for this top layer.

From the tool palette select the brush tool.

Near the bottom of the tool palette, set foreground color to white, then paint over image where subject is ghosted (where the background shows through). Make sure that the layer mask thumbnail on the subject layer is selected before you start painting.

If you make a mistake painting on the layer mask, select black as the foreground color and paint over this area to correct it.

If the rest of the body is hidden or partially hidden, you can paint white over the layer mask to reveal it. Alternatively, you can create selections using color range or the pen or lasso tool, and then fill these selections on the black hide-all layer mask with white.

In conclusion, there were three elements that made the above background swap successful: 1) selecting a background as dark as, or darker than the final background, 2) lighting Christiane so that there was good separation from the dark background, and 3) using lighten blend mode to meld the two images. Lighten blend mode blends layers by favoring the lighter pixels. That’s what made this blend so easy: the edges of her hair, due to the rim lighting are lighter than the background, and so they dominate. Imagine a pixel on a layer that is lighter than the pixel directly underneath it—Photoshop will display the top pixel and not the lower pixel.  

If a pixel on the bottom layer is lighter than the pixel directly above it, the bottom pixel, not the top pixel, will be displayed. When using the Lighten blend mode, think “lighter pixels rule,” and when opting for a “canned” background scene, plan your shot. A few minutes of planning can save you hours of postproduction in Photoshop.

Sidebar - Indoor simulated sunlight setup
While planning the image for my lecture demo, I chose a couple of outdoor background scenes from Hawaii that I thought would work nicely (see Images 1 and 2). In both instances, Christiane’s hair would fall against a dark area of the land/seascape and so a black backdrop was selected for the lighting demo (see Image 3). Also for a realistic-looking background match up, make sure to light the subject from the same direction as the sunlight in the chosen background scene.

With this in mind, Christiane was illuminated by light reflecting off a 4.3  x  6.6-foot white nylon fabric stretched over a panel frame placed in front of her on the camera left side of the image frame (see lighting diagram in Image 4). A shutter-speed of 1/125 was selected to overpower the room lights and the aperture was set to f/8 to correctly expose Christiane with the aforementioned panel main light source.  

The origin of the light energy for this main light source was a studio strobe placed behind her on the camera left side of the image frame. This light origin also provides heavy dramatic backlighting for Chris, separating her from the dark background. Reflective meter readings were taken off the black backdrop to make sure that any light spilling onto the background was minimized through light origin placement, goboing, and feathering, to ensure a minus 41/3 stop reflective reading.

To fill in the subject shadows, a second reflector panel was placed on the camera right side of Christiane, as shown in Image 4. This fill light source caught stray light from the backlight origin and redirected it onto her dark side. An incident meter reading showed that the fill panel reflected 2 stops less light onto Christiane than did the main light panel.

Dave Montizambert lectures internationally on lighting, digital photography and Adobe Photoshop. He is also a published author, having written two books on lighting and digital photography, plus numerous magazine articles on these topics in North America, Europe, Russia and Asia. Dave also creates Photoshop tutorial CDs and DVDs for www.software-cinema.com. Dave is available for lectures and workshops in your area. He can be reached at montizambert@telus.net or www.montizambert.com.

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