Given that the
question arises it is clear that many digital camera users are aware of
the importance of correct white balance (WB), but many are unclear of how
best it may be achieved. I don't intend to
go into the subject in any great detail. However, a few simple demonstration
images and an insight as to the different options should help clear up some
of the most obvious misunderstandings.
For most purposes Auto white balance (AWB) is probably
the safest but not necessarily the most accurate. With AWB we don't need to think too long about whether it's
daylight, cloudy, etc. Nevertheless, even with the aid of complex algorithms
for calculating the white balance the use of Auto can compromise colour accuracy under certain
circumstances. Auto white balance will be at its most effective on a
bright sunny day but much less so under heavy cloud cover when it will
tend to bias towards blue. Auto white balance is variable anywhere between
3000K
and 7000K and just as is the case with Custom mode, the Auto white balance is measured directly from a
segment of the image corresponding to the partial metering area indicated by the circle in the
centre of the focusing screen. If the subject in this area of the screen
has a very saturated single colour the balance will probably be thrown
off neutral.
We could choose from one of the presets: "Cloudy"
on a cloudy day or "Daylight" on a sunny day, but again these
settings are equally risky in that they use fixed values for colour
temperature. If the ambient lighting is not at the specified value the
image will have a global colour cast that may render it virtually useless. As
indicated above, the preset white balance settings are all programmed to specific
colour temperatures, these are as follows:
-
Tungsten 3200K - indoor incandescent (filament
lamps)
-
Fluorescent 4000K - indoor fluorescent
-
Daylight 5500K - bright outdoor lighting
-
Flash 5900K - studio flash (not the Canon
SpeedLites)
-
Cloudy 6000K - cloudy, overcast, twilight and sunset
The optimum choice is Custom white balance,
which allows the user to measure the actual ambient lighting colour
temperature. The range for Custom white balance is fairly large, and at
2000K to 10000K should be sufficient for most conditions. Of course this
will mean that we bring a grey card to each shooting session. An
alternative would be to prepare our own set of preset values. This can
be done fairly easily using the procedure described on Pages 70 and 71
of the user manual for Custom white balance. Typically we would capture
a white card under a range of different lighting conditions, white
balancing each in turn and saving them to the Microdrive. Once out in the
field taking our pictures we keep the camera set for Custom white
balance, but toggle through our series of (WB) options and select the most
appropriate using the Custom white balance selection facility from the
LCD Menu on the rear of the camera. An example list of customised
presets might be as follows:
- Preset 1. Open landscape - Bright Sunlight
- Preset 2. Open landscape - Cloudy Bright
- Preset 3. Open landscape - Cloudy
- Preset 4. Open landscape - Overcast
- Preset 5. Shade
This list isn't exhaustive, but do make sure that you bring the list
with you when out in the field using the camera.
If the above procedure seems overcomplicated; then Auto white
balance and set the camera for Raw mode is my recommendation.
Nevertheless, what I think isn't as important as what I can show. The
following section should demonstrate the results of a poor choice along
with the benefits of using Raw mode and Custom white balance.
The Dahlia image used for the following comparison
was captured in my garden. The lighting was what I would describe as diffuse
sunlight, that is to say, it was bright but there was a thin veil of
cloud, and there lies the dilemma many face
- which setting should I choose? In my case the camera was set for RAW
mode and a custom white balance was performed except that I
used the white side of a Kodak 18% grey card in place of Canons prescribed white paper. So
theory says that from the outset the image colours were going to be accurately
rendered - no chance!
Setting the white balance correctly will ensure
the global colour casts that can arise from the wrong choice are
eliminated, but it does nothing for the other D30 foible; rendering reds
(sometimes blues) inaccurately. True to form when the image was imported
into Photoshop using the full range of white balance settings the Dahlia
looked nothing like the real thing. My red going orange Dahlia was pink - YUK!
 |
 |
Canon Linear Raw Image
(Custom White Balance Mode - No Profile Used) |
Default Canon Processed
Image
(Custom White Balance Mode - No Profile Used) |
The processed image above shows that the red Dahlia isn't anywhere near correct
- the Canon software conversion from Linear (left) to
Processed raw mode is introducing a major error. So how do we fix the
problem and ensure the maximum colour accuracy from the EOS D30? See
next page for details - please note that due to the number of embedded
images the page may take up to 2 minutes to load.
