Minolta CR-400 - Principles of Measuring

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Description
Principles of Measuring
Principles of Measuring
The measuring head measures a specimen, gets the color information from the specimen, converts it to
one of the various display modes in the measuring head, and displays it. Also the data processor
converts data to one of the various color space modes, displays it, and prints it.
The measuring head is divided into the specimen measuring part which measures the reflected light
from the specimen and the monitoring illumination part which directly measures the light from the
illumination light source. Each measuring part is equipped with sensors with equal color function
_
x2λ
(
_
xλ long wavelength side),
_
yλ, and
_
zλ sensitivities, which are the spectral response for a standard
observer and (this instrument uses a spectral response for a CIE 1931 2° observer).
By measuring the illumination light source with the monitoring illumination part, it is possible to get
data unaffected by subtle changes in the illumination light source.
The circuit offset influence is eliminated by applying the following formulas to the specimen measur-
ing part measurement data (X2s’, Ys’, Zs’) and the monitoring illumination part measurement data
(X2r’, Yr’, Zr’) gotten when illuminating, and the specimen measuring part measurement data (X2s’’,
Ys’’, Zs’’) and the monitoring illumination part measurement data (X2r’’, Yr’’, Zr’’) gotten when not
illuminating.
The following formulas eliminate the influence of subtle changes in the illuminant.
_
x1λ data is calculated by multiplying Zm by the constant.
The tristimulus value (X, Y, Z) are calculated by multiplying the data achieved from the above (Xm,
Ym, Zm) by the calibration constant (α, β, γ).
These tristimulus value (X, Y, Z) can be converted to various different color spaces.
X2m = Ym =
Ys
Yr
Zm =
Zs
Zr
{
X2s=X2s’ - X2s’’
Ys= Ys’ - Ys’’
Zs= Zs’ - Zs’’
{
X2r=X2r’ - X2r’’
Yr= Yr’ - Yr’’
Zr= Zr’ - Zr’’
X1m = 0.1672
•
Zm
∴Xm= X1m+X2m
{
X = α
•
Xm
Y = β
•
Ym
Z = γ
•
Zm
X2s
X2r