181212 and 030101: A/DE08/DE08.HTM
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Test intention for Linearization
Method:
A standard image file including 8bit image data in relative
coordinates olv* (rgb*) or absolute coordinates
OLV* (RGB*) is changed by different transfer
functions.
Method:
There are 12 times 16 gray series
on the page. The series no. 1 and 4 on the left side and no. 7
and 10 on the right side are identical and serve as reference.
In the series no. 3, 5 and 7 on the left side and in the series 8 and 10 on the right side a function is used to transfer the image data before the output.
The function {0.5 exp} transfers the image data to the square root of the image data, see the series no. 5.
The function {0.1801 sub 0.7740 mul} transfers the absolute OLV* data to the relative olv* data, see the series no. 3
The standard PS-operator settransfer is modified in the series no. 12 (last series) to produce the original image (No. 1, 4, 7, 10) from the square root hex data in the image file. In this special case the output LAB* data are used to make the inverse transformation.
This last case is the most interesting one for Linearization Method as here the output change of a device (here asumed to be a square root function, Exponent 0.5) can be eliminated by a inverse transformation (Exponent 2.0). The inverse transformation is only based on the output measurement data of the 16 gray steps of the device. The lightness L* data used here are 18.01, 37.99, 46.21, ..., 92.79, 95.41.
For the inverse transformation in a first step the global (g) PS-operator is defined to be identical to the standard PS-operator
/sgtransfer {settransfer} bind def
Then the former standard PS-operator is redefined by the global (g) PS-operator which is modified by the PS-square function {2.0 exp} here in the following example.
%p=positive change with lightness for
olv* (rgb*)
/transp {2.0 exp} bind def
Finally this function is used for the
inverse transformation in the following PS-line
/settransfer
{/ntransfer exch def {ntransfer transp} sgtransfer} def
The effect is very important
for Linearization Method: All
colour data of the 8bit image are modified by the PS-square function
and become darker.
In the series no. 12 the inverse transformation is not based on a function (square function) but only on the L* output of the device (18.01, 37.99, ..., 92.79, 95.41)
| Linearization Method by digital test files including olv* and OLV* data and the settransfer PS-operator | Remarks for use and reproduction | PostScript format File type A.TXT or A.PS |
PostScript and Portable
Document Format (Version 3.0) File type P.PS or P.PDF |
| Gray series output of 3 and 16 standard grey steps | Output used as reference (no.1, 4, 7, 10) Different transformations |
98 kByte |
98 / 44 kByte |
Table 1: The files in Table 1 use
olv* data for the PS-operator settransfer.
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