Conditions of shooting a white and a black lusterless
sheet of paper: a lens is unfocused, ISO 320.
Light sources:
I - daylight, cloudy,
II - incandescent lamp, 150 W,
III - luminescent lamp LÁ6,
IV - halogen lamp, 150 W 220V,
V - candle.
 |
I |
II |
III |
VI |
V |
| Manual |
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| 7500K |
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| 6500K |
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| 5500K |
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| 4500K |
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| 4000K |
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| 3700K |
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| 3000K |
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| Auto |
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When adjusting a white balance manually one can
obtain a normal balance with actually any source. An auto balance
mode mustn't actually work normally if daylight is not a main source
(you can see it from the table). It is necessary for a fine adjustment
of a white balance if a spectrum of the source doesn't differ much
from that of daylight.
Measurement of signal level and noise level: levels
of a signal and a standard deviation according to "Histogram" option
from Photoshop 5.5 for L 185 and 25 brightness, 15*15 pixels area
(linear dimensions changed with area remaining the same in order
to prevent illumination space discontinuity effect). Noise level
is given in dB; the calculation was implemented according to 20Lg
formula (deviation/signal).
|
signal |
standard deviation |
noise, dB |
R |
standard deviation |
noise, dB |
| I |
186.4
|
0.68
|
-48.8
|
190
|
0.87
|
-46.8
|
|
27.6
|
1.36
|
-26.2
|
30.13
|
2.42
|
-21.9
|
| II |
187.3
|
1.16
|
-44.2
|
192
|
1.93
|
-40
|
|
26.6
|
1.57
|
-24.6
|
26.16
|
2.18
|
-21.6
|
| III |
185
|
1.5
|
-41.8
|
185.6
|
1.9
|
-39.8
|
|
25.6
|
1.46
|
-24.9
|
26.7
|
2.77
|
-19.7
|
| IV |
182
|
1.07
|
-44.6
|
182
|
1.6
|
-41.1
|
|
26.6
|
1.42
|
-25.4
|
27.1
|
2.37
|
-21.2
|
| V |
185
|
2.08
|
-39
|
207.6
|
2.22
|
-39.4
|
|
25.5
|
1.6
|
-24
|
31
|
2.3
|
-22.6
|
|
G |
standard deviation |
noise, dB |
B |
standard deviation |
noise, dB |
| I |
185
|
0.8
|
-47.3
|
182.7
|
1.25
|
-43.3
|
|
26.3
|
1.56
|
-24.5
|
28.13
|
1.6
|
-24.9
|
| II |
187.7
|
1.6
|
-41.4
|
173.7
|
3.17
|
-34.8
|
|
24.8
|
1.99
|
-21.9
|
38
|
4.93
|
-17.7
|
| III |
186
|
1.79
|
-40.3
|
178
|
2.88
|
-35.8
|
|
23.5
|
2.07
|
-21.1
|
33.2
|
4.45
|
-17.5
|
| IV |
182.3
|
1.5
|
-41.7
|
182.2
|
2.7
|
-36.6
|
|
25
|
1.88
|
-22.5
|
33.6
|
5/13
|
-16.3
|
| V |
182
|
2.3
|
-37.9
|
141
|
4
|
-30.9
|
|
20.8
|
2.3
|
-19.1
|
351
|
5/2
|
-16.6
|
When adjusting white balance a signal in every
R G B channel is different. That is why you should note that an
additional light source which will shift the total sensitivity to
a "noisy" channel can spoil an image. In case of a candle (its color
temperature is 1800 K, what is out of a range of manual balancing
of the camera) all channels "make noise". In case of an incandescent
lamp it is a blue channel that makes noise most of all. Indoors
you'd better use a halogen lamp, a luminescent will lose in a red
and a green channel, and an incandescent will lose in a blue channel.
