Basler A640F, User Manual

Page: 48 / 188

Basic Operation & Standard Features
3-26
BASLER A640
f
DRAFT
3.5.1 White Balance
White balance capability has been implemented on the
A641
fc
camera. With white balancing,
correction factors are applied to the interpolated RGB values for each pixel. The correction factors
can be used to adjust the color balance of the images transmitted from the camera.
The white balancing scheme outlined in the IIDC specification dictates that blue and red are
adjustable and that green is not. On
A641
fc
cameras, green has a fixed value of 64 (0x40) which
corresponds to a correction factor of 1.0.
The Blue Value field of the White Balance control register (see page 4-29 ) can be used to change
the blue correction factor. The usable range of settings for this field is from 64 (0x40) to 255
(0xFF). If the field is set to 64 (0x40), blue will have the same 1.0 correction factor as green. If the
field is set to a higher value, blue will have a higher correction factor and the image will be more
blue. The default setting for the Blue Value is 89 (0x59).
To determine the correction factor for blue, use this formula:
The Red Value field of the White Balance control register can be used to change the red correction
factor. The usable range of settings for the this field is from 64 (0x40) to 255 (0xFF). If the field is
set to 64 (0x40), red will have the same 1.0 correction factor as green. If the field is set to a higher
value, red will have a higher correction factor and the image will be more red. The default setting
for the Red Value is 104 (0x68).
To determine the correction factor for red, use this formula:
To make your images appear less green, raise the correction factors for blue and red. To make
your images appear more green, lower the correction factors for blue and red.
L
The values for U and for V normally range from -128 to +127. Because the 1394 Dig-
ital Camera specification requires that U values and V values be transmitted with un-
signed integers, 128 is added to each U value and to each V value before the values
are transmitted from the camera. This process allows the values to be transmitted on
a scale that ranges from 0 to 255 (see Section
5.4.2 ).
When an
A641
fc
is operating in a YUV (4:2:2) mode, the average number of bits per
pixel is 16. This means that the camera will require twice the bandwidth of a camera
operating in an 8 bit monochrome mode.
The
A641
fc
can operate in several YUV (4:2:2) color modes and can also operate in
several monochrome 8 bit modes (see Section 3.10 ).
Blue Correction Factor
Blue Value Setting
64
------------------------------------------------- =
Red Correction Factor
Red Value Setting
64
------------------------------------------------ =