3.6 CMC Difference Operation
CMC is an ellipsoidal tolerancing method which attempts to correlate small
measured color differences with visual assessment.
CMC provides a single numeric value (∆E
CMC
) which describes the color
difference between a sample and a standard. This allows the use of a single
tolerance value for comparing the acceptability of a color match.
∆E
CMC
is derived from the following formula:
∆Ec = [L
C
2
+ C
C
2
+ H
C
2
]
1/2
The CMC reference menu consists of the three factors that can be set: Lightness
factor (ι), Chromaticity factor (c), and Commercial factor.
• The lightness factor is normally set to 2.00 (default) but other values may be
required when surface characteristics differ dramatically.
• The chromaticity factor normally does not require any adjustment from the
default setting of 1.00.
• The commercial factor is the tolerance limit that each sample is not to exceed.
(e.g., if cf= 1.00 then any sample which has a ∆E
CMC
value greater than 1.00
would be commercially unacceptable.)
To Setup CMC Difference:
> CMC Option is only available on L*C*H* difference function.
> CMC option must first be selected in Operation Parameters (Sec. 5.2).
1) Follow Step 1 through 5 in Section 3.5.1 for entering a reference manually or by
measurement.
2) Press [DIF] until the CMC menu is
displayed. The cursor will blink
over the active value that can be
edited. Enter the number for each
value.
•The [DIF] key advances the
cursor to the next value to be
edited.
•The [DIF] key is used in
conjunction with the [t] to
decrease and [s] to increase the
value. NOTE: Hold [DIF]
depressed then press either [t] or
[s] to change values.
L
C
=
∆L
S
L
C
C
=
∆C
cS
L
H
C
=
∆H
S
H
FUNCTION ILLUM
DIF
CAL
CURSOR
+
REFERENCE SPACE
REF 01
DECREMENT
INCREMENT
+
l 2 . 0 0
c 1 . 0 0
cf = 1 . 0 0
CHROMATICITY
FACTOR
LIGHTNESS
FACTOR
FACTOR
ι
19
