ISL29125_14 Datasheet, PDF (13/17 Pages) Intersil Corporation – Digital Red, Green and Blue Color Light Sensor with IR Blocking Filter

ISL29125
Data Register (Address: 0x09,0x0A,0xB,0xC,0xD and 0xE)
NAME
REGISTER
ADDRESS
DEC
HEX
GREEN data-Low 9
byte
0x09
GREEN data-High 10
byte
0x0A
RED data-Low
byte
11
0x0B
RED data-High
12
0x0C
byte
RED data-Low
byte
13
0x0D
RED data-High
14
0x0E
byte
TABLE 20. CONFIGURATION-3
REGISTER BITS
DEFAULT ACCESS
B7
B6
B5
B4
B3
B2
B1
B0
GREEN[7] GREEN[6] GREEN[5] GREEN[4] GREEN[3] GREEN[2] GREEN[1] GREEN[0] 0x00 RW
GREEN[15] GREEN[14] GREEN[13] GREEN[12] GREEN[11] GREEN[10] GREEN[9] GREEN[8] 0x00 RW
RED[7] RED[6] RED[5] RED[4] RED[3] RED[2] RED[1] RED[0] 0x00 RW
RED15] RED[14] RED[13] RED[12] RED[11] RED[10] RED[9] RED[8] 0x00 RW
BLUE[7] BLUE[6] BLUE[5] BLUE[4] BLUE[3] BLUE[2] BLUE[1] RED[0] 0x00 RW
BLUE[15] BLUE[14] BLUE[13] BLUE[12] BLUE[11] BLUE[10] BLUE[9] RED[8] 0x00 RW
The ISL29125 has two 8-bit read-only registers to hold the higher and lower byte of the ADC value. The lower byte and higher bytes are
accessed at address respectively. For 16-bit resolution, the data is from D0 to D15; for 12-bit resolution, the data is from D0 to D11.
The registers are refreshed after every conversion cycle. The default register value is 0x00 at power-on. Because all the register are
double buffered the data is always valid on the data registers.
Applications Information
Below is a plot of the 1931 standard normalized spectral
response of various types of light sources for reference.
2.0
1.8
NORMALIZED TO GREEN
1.6
1.4
RED
1.2
GREEN
BLUE
1.0
1931 STD RED
0.8
1931 STD GREEN
0.6
1931 STD BLUE
0.4
0.2
0.0
350 380 410 440 470 500 530 560 590 620 650 680 710 740 770 800 830
WAVELENGTH
FIGURE 13. 1931 STANDARD NORMALIZED SPECTRAL RESPONSE
OF LIGHT SOURCES
System Compensation and RGB to XYZ
Transform (Chroma Meter)
The accuracy of the RGB sensor is extremely sensitive to the
opto-mechanical design of the system in which it resides. The
compensation setting and calculation of RGB to XYZ transform
should be characterized within that environment with as many
standard illuminants as possible. A minimal recommended set
would include A, F2 and D65 illuminants (see Notes 11, 12, 13
and “References” on page 15 about IEC 1931, Planckian locus
and standard illuminants). The two most important
opto-mechnical features are FOV (field of view FWHM) and
optical filters as example of tinted cell phone glass through
which the sensor will detect the ambient lighting. With the
combination of the FOV and a large sample for the filter
(30x30mm) it is possible to determine the best compensation
and XYZ transform coefficients. It is also possible to project the
accuracy of the measurement system.
RGB → XYZ TRANSFORM
Once the proper compensation setting is determined measure
the RGB values of the various illuminates at this value. Calculate
the RGB to XYZ transform coefficients based on the measured
result against appropriate Chroma Meter Standard (using x and y
values) as shown in Equation 1.
X
C_XR C_XG C_{XB R}
Y ^{= C}_YR ^C_YG ^C_YB ^x G
Z
C_ZR C_ZG C_ZB ^B
(EQ. 1)
X, Y and Z are in the IEC system which specifies the color and
brightness of a particular homogeneous visual stimulus.
R, G and B are digital output from the sensor.
Cs are coefficents. These coefficients will be changed
respectively depending on the system setup.
COMPENSATION
The compensation adjustment is used to balance the various
illuminates of interest (A, F2 and D65 recommended) such that
the value measured at the same power level (measured with a
Lux meter) is the closed value. Since the compensation
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FN8424.2
January 24, 2014