Site Links
|
 |
 |
 |
Lesson Of The Month Understanding Digital White Balance
By Ben Clay/Web Photo School August, 2002
| |
|
1
Photos
© 2002, Ben Clay, All Rights Reserved
|
|
Color temperature refers to
the frequency of color that can be measured from any particular light
source. The efficiency of our own visual experience, however, can make
the idea of color temperature somewhat confusing. This is because our
eyes have the intrinsic ability to adjust to color shifts such that a
white piece of paper will appear white no matter what type of light is
being cast on it. Many people only become conscious of color shifts when
witnessing a scene lit with light sources of differing color temperatures,
like yellow light emanating through the windows of a house contrasted
against the blue light of dusk.
Color temperature is measured
in degrees Kelvin. The most important thing to remember in color temperature
is that the higher the Kelvin number, the cooler (more blue) the light source.
The following chart illustrates an approximate color temperature scale (#1).
|
|
Color Balance
Color balance is achieved when a color recording device (like a camera)
renders an image close to how the human eye perceives it. White balance
settings, film type, colored filters and gels can all help to assist the
device in achieving "accurate" color. Alternately, you can also throw
the color balance off to render a different mood or effect to an image.
White Balance
If you shoot with a film camera and want to achieve color balance in a
daylight setting, you would use daylight film to match the color temperature
of daylight. If you shoot with a film camera indoors with incandescent
lighting, you would either choose tungsten film or place a tungsten filter
over the lens to balance the color temperature. If you are shooting digitally,
however, achieving color balance in any lighting situation is just a matter
of setting the white balance in the camera. To illustrate how the white
balance function works, I took a series of portraits (both inside and
outside) using different color temperature settings. I first started indoors
using the built-in flash of an Olympus E-20N digital camera.
|
|
Since the built-in flash of
any camera (film or digital) is balanced to the color temperature of daylight
(5500Þ Kelvin), I set the white balance accordingly. The E-20N has white
balance controls external to the main menu navigation that allow for a
faster change in settings. To set the white balance to 5500, I first pressed
and held down the small WB button on the top of the camera and jogged
the main dial until 5500 appeared in the control panel (#2).
I then pressed the button to
pop-up the flash, set the camera to Program (automatic) and took a shot
of my assistant/model, Jarred, in front of a sweep of white seamless paper
(#3).
|
|
I decided to light Jarred with
a large diffused light source for a more natural-looking effect. I deactivated
the flash and set up a Photoflex Large Starlite Kit and positioned it
to the right of him at approximately a 45Þ angle. The Large Starlite Kit
uses a 1000w tungsten lamp that's color balanced to about 3200Þ Kelvin,
about 2300Þ warmer than daylight or flash. For demonstration purposes,
however, I left the white balance on 5500.
I then set the camera to manual
to achieve a custom exposure. Since I wanted Jarred's eyes to be in sharp
focus and for the background to be relatively soft, I opened the aperture
up to f/4 (the wider the aperture, the more selective the focus). I then
set the shutter speed to 1/60 sec to render the proper exposure, focused
and shot (#4).
|
|
The result shows a tremendous
difference in the look of the shot. The SilverDome softbox from the Starlite
Kit had diffused the light to render a soft, wraparound light on Jarred's
face. The effect is that of a window light. And since the lamp in the
Starlite Kit is continuously on, it forces Jarred's pupils to close down
to reveal more color in his irises. Notice the natural-looking catchlight
in his eyes.
The color of the shot, however,
is much warmer than in #3 because the camera recorded the relatively warm
light from the Starlite (3200) at a cooler daylight/flash setting (5500).
Remember the lower the color temperature, the warmer (more yellow) the
light. To balance the color, I changed the white balance preset from 5500
to 3000 (the closest preset to 3200 in the E-20N) and took another shot
(#5).
|
|
In the result, notice how Jarred's
skin tone looks more natural and that the blue in his eyes is truer in
color.
The next morning at about 11:00am,
we decided to shoot a similar portrait outside. I wanted to shoot against
a background that was neutral in color (as we did with the white background
paper inside) to illustrate clearly the shifts in color, so we went up
to the roof of the studio and set up against the shadow side of a neutral
gray wall.
Jarred stood with the sunlight
raking across the side of his face and I set the camera on a tripod and
framed up the shot. I left the aperture on f/4, set the shutter speed
to 1/500 sec to compensate for exposure, set the white balance back to
3000 (the neutral white balance point for tungsten) and shot (#6).
|
|
Now our color shift has flopped
to the blue side! With the white balance dialed to 3000, the camera was
set to record our subject illuminated with tungsten light. But again,
shooting at an "incorrect" color setting can sometimes render an interesting
look.
At this point, I had a couple
of options for achieving color balance. I could either dial the white
balance to the 5500 preset or I could create a custom white balance setting.
Here's how to set the white balance to neutralize any single light source.
|
|
Listed among the white balance
presets is the option -0-. Once that is selected, you will want to find
something neutral, like a white sheet of paper or cardboard, from which
to take an exposure. The E-20N has a One Touch White Balance button placed
on the front of the camera. Fill the frame with the white sheet of paper
or neutral gray card and press this button. After the exposure is taken,
the LCD will present one of two windows. If the exposure is either too
dark or too light, the window will read "NO GOOD" and you will have to
take another shot of the paper in either more or less light. If the window
reads "GOOD," press the OK button and you are ready to shoot. After I
recorded my custom setting, I shot (#7 and #8).
Now our result is much more
natural looking. However, similar to the on-camera flash shot indoors,
the shot is very high in contrast. The major difference between these
shots is the positioning of the light. Here, the sun rakes across Jarred's
face, whereas inside, the flash was hitting him straight on.
|
|
We went about softening the
sunlight similar to the way we softened the Starlite with the softbox
indoors. We attached a Photoflex 42" Trans-lucent LiteDisc to a Photoflex
LiteDisc Holder, secured it to a Photoflex LiteStand, and positioned it
in between Jarred and the sun. To create a negative fill (similar to the
look in the studio), we set up a Photoflex 42" Black LiteDisc and positioned
it to the right of Jarred to both block the ambient light of the sky and
to absorb the light passing through the Translucent LiteDisc. Once it
was in place, I took another shot with the same settings (Final Image).
It's good to keep in mind,
however, that there is no definitive way to light a headshot. The architecture
of each person's face is unique and as such may require a very different
lighting approach. It will only help you to experiment and develop different
lighting techniques and white balance settings for different situations.
|
|
This lesson will be posted
in the free public section of the Web Photo School at: www.webphotoschool.com.
You will be able to enlarge the photos from thumbnails. If you would like
to continue your digital step by step education lessons on editing, printing,
and e-mailing your photos it will be on the private section of the Web
Photo School. To enroll for WPS just go to www.shutterbug.net
and click on WPS Free Lessons.
Technical Equipment
Camera/Media: Olympus E-20N digital camera; Olympus Telephoto Conversion
Lens; Olympus lithium Polymer battery pack; Olympus 4040 digital camera
(for setup shots); Lexar 160MB CompactFlash card; Lexar 64MB SmartMedia
card; Olympus USB Dual Slot Smart-Media/CompactFlash Reader; Manfrotto
3443 Carbon Fiber tripod
Lighting: Photoflex Large Starlite Kit; Photoflex 42" White Translucent
LiteDisc; Photoflex 42" Black/Silver LiteDisc; 2 Photoflex LiteDisc Holders;
2 Photoflex LS-2322 Litestands
|
 |
|
 |
|
|
 |
 |
 |
|