5.3.1 HOW TO PERFORM A COLOUR DIFFERENCE CHECK ANALYSIS
1. Select the Colour Difference Check function from the Operating Mode selector
2. Set the Acceptance Thresholds
3. Acquire a desired Reference sample. Either select an existing sample from the References list or let the
software detect the closest to Measure, belonging to the selected group of the Reference list.
4. Acquire the data of the Measure sample under evaluation. If acquisition has already been performed, any
colour in the Measure list can be selected by double-clicking on it.
5. The software performs the colour difference calculation and shows the results of acceptance threshold
validation and plots the (L*; a*; b*) Measure coordinates against the Reference ones.
5.3.2 USING THE INTERFACE
The acquired colour is displayed on the monitor as a guide only. It is very likely that it will appear
to be different from the actual colour of the sample. This is due to several factors (such as the
ambient light, monitor calibration, gamma settings) which must be controlled and fine tuned in
order to for the colours to match.
The Reference can be selected in two different ways, using the Reference Mode selector .
Manual mode. Manual mode is enabled by selecting the MANUAL option in the Reference Mode selector
In Manual mode, the user selects a colour from the Reference List by double-clicking on it, by dragging it to the
Reference colour display area , or by acquiring a new Reference colour. Manual mode allows the colour
difference of the current Measure (either that just acquired or selected from the Measure list) to be evaluated
with respect to a Reference which is fixed and does not change during operations.
Automatic mode In automatic mode the software automatically chooses the Reference colour selecting the
most similar (lower E*
ab
) to the current Measure. If the ALL option is selected in the Reference Mode selector
, the colour will be chosen among all colors in the Reference list. If the corresponding group name is
selected, a colour group will be chosen. Automatic mode allows the user to highly speed up the Colour
Difference Check when a large set of samples comprised of a subset of various colours is to be checked. The
user does not need to select the right Reference when a new sample is being acquired since the software
automatically detects it. The automatic selection process is effective even on very similar colors if a group of
Reference colours to be selected is specifically built and the E*
ab
difference between these colors is larger
than the highest Acceptance Threshold.
The software displays the colour difference between Measure and Reference in terms of CIE 1976 a,b (CIELAB) E*
ab
colour difference . The CIELAB lightness difference L*, CIELAB chroma difference C*
ab
, a* and b* difference
are also provided .
;
;
being (L*
1
; a*
1
; b*
1
) the Measure coordinates and (L*
0
; a*
0
; b*
0
) the Reference coordinates.
The colour difference E*
ab
is then compared to the user-defined Acceptance Thresholds and if the corresponding
threshold is not exceeded, the Measure is ranked to one of the three acceptance classes (1, 2, 3). If the largest
threshold is exceeded, the Measure is ranked to the "void" (x) class.
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