This
is where Photoshop shines, you can delete the original backdrop then drop in
the perfect background after the fact. Easy, or so everyone thinks, but the
reality is, a seamless job is quite time consuming and therefore expensive
for the client. Cutting around flesh and most garments is easy and can be
somewhat automated, the real challenge is hair, cutting around it is a very
tedious time consuming task because of its size and its translucent quality.
Simply put, the background will partially show through any given strand of
hair and will be viewed as a contaminant once a different coloured/ toned
background scene is added. To make things even more challenging, a strand of
hair’s smooth surface creates a very efficient reflecting surface which
picks up original background colour and tone. Strands of hair are also very
thin, 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.
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 (see sidebar
entitled Indoor simulated sunlight set-up) on model Christiane
www.ulorinvex.com during a masterclass at the Societies' 2010 Convention,
see Image 003 & 004.
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.
Indoor
simulated sunlight setup
Whilst planning the image for my lecture demo, I chose a couple of outdoor
background scenes from Hawaii that I thought would work nicely, see Image
001 & 002. In both instances, Christiane’s hair would fall against a dark
area of the Hawaiian land/seascapes and so a black backdrop was selected to
shoot her against for the lighting demo, see Image 003. Also for a realistic
looking background match up, make sure to light the subject from same
direction as sunlight direction in background scene. With this in mind,
Christiane was illuminated by light reflecting off a 1.3 x 2m, 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 Image 004. 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
came from a studio strobe placed behind her on the camera-left side of the
image frame. This light origin also provides heavy, dramatic back-lighting
for Chris giving her separation 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 4 1/3 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 004. 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.
Here's my Fast Blend Mode Knockout recipe for dark background scenes:
• 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 – 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 colour 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 colour 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, or instead of painting, create selections
using colour range, or the pen or lasso tool and then fill these
In
conclusion there were three elements that made the above background swap
successful:
1) selecting a background as dark or darker than the final background,
2) lighting Christiane so that there was good separation from the dark
background,
3) using lighten blend mode to meld the two images.
Lighten blend mode blends layers by favouring 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 will be displayed and the top pixel not. 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 post-production work in Photoshop.
Dave Montizambert
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