SpectraTrend HT User’s Guide 3.2
108
The illustration shown above uses the L*a*b* color scale. The middle shade block, 555, is where the
standard is located. The first 5 denotes L*, the second 5 denotes a*, and the third 5 denotes b*. The
tolerance values are indicated as
L*,
a*, and
b*. There are five shade blocks on either side of the
standard (including the standard’s block) on the L* axis, five
on either side of the standard on the a*
axis, and five on either side of the standard in the b* direction. Suppose we wish to use five shade
blocks. Not all of the shade blocks shown on the drawing (from 111 to 999) fall within the established
tolerance. Five blocks for each parameter (L*, a*, and b*) do fall within the tolerance range. For the L*
parameter, these will be blocks labeled 3-7 for the L* number. For the a* parameter, these will be blocks
labeled 3-7 for the a* number. For the b* parameter, these will be blocks labeled 3-7 for the b* number.
Thus, the 345 shade block would be within the tolerance range, but the 245 shade block would be too
dark.
Continuing with our example given above, suppose the entered tolerance for each parameter is
1 unit.
That is,
L* = 1,
a* = 1, and
b* = 1. Thus, with five shade blocks, the center (standard) block extends
0.2 units (1 unit divided by 5) in each direction. The size of this block (and,
in fact, each block) is 0.4 units
high, 0.4 units wide, and 0.4 units deep (
0.2 units times 2 directions for each parameter).
Once the
L*,
a*,
b* difference between the sample and the product standard has been established,
a shade number can be assigned to the sample. A sample that is very close to the standard in a* and b*,
but has values that put it one shade block away for L* would be assigned a shade number of 655 (if
lighter than the standard) or 455 (if darker than the standard).
Although this sample’s color is slightly
“off” from the standard, it will be a good
match with any other samples in the same shade block and
may still be used with these samples.
The number of shade blocks used can be varied using ColorFlex XE Plus. If fewer shade blocks are used
with the same tolerance (e.g., 3 blocks rather than 5), fewer blocks will be required to fit into the
tolerance and each block will be bigger. You may wish to lower the number of shade blocks if you find
that your shade block tolerances are too tight. If more shade blocks are used with the same tolerance
(e.g., 7 or 9 blocks rather than 5), more blocks will be required to fit into the tolerance and each block
will be smaller. You may wish to increase the number of shade blocks if you find that your shade block
tolerances are too loose.
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