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The device output of ISO/IEC-test chart files which include colours defined in the CIELAB colour space and the
corresponding device dependent colour spaces shows a lot of problems. The correponding colours produce very
different output or no output difference on monitors and printers. Sometimes for the present standard software
the monitor output is very different and there are no output differences on printers or vice versa. If a PostScript
MTL code (Measurement, Transfer and Linearization) is added to the code of an ISO/IEC-test chart (the NP file)
then the output of the new FP file produces the same output as expected by users and CIE colorimetry if CIELAB
colours and related device dependent colours are used for input. For this intended output property the definition of
the Colour Workflow (CW) and the Output Linearization (OL) is included in all ISO/IEC-test charts of the FP form.
- Remark: The output of this paper produces large color differences (often 20 CIELAB) for the NP files on most
printers and monitors. The large colour differences for corresponding colours of different colour spaces are not
intended by users and CIE colorimetry. The output of the FP files produces no colour differences as intended.
A reflective and transparent ISO/IEC-test charts no. 3 according to ISO/IEC 15775 and DIS ISO/IEC 19839-1
to -4 is used for different tests of colour reproduction on printers and monitors in the office which is illuminated by
daylight D65. The reflective ISO/IEC-test chart produced by DIN and JBMA in offset printing has a contrast range of
1:35. The calculation and production of a transparent ISO/IEC-test chart is described which produces the same
contrast range for a standard 2.5% reflection condition. The transparent ISO/IEC-test chart has a contrast range of
1:10.000 and on top of the "white" monitor screen with the standard illumination of 500 lux the office lighting reduces
to the standard contrast range between black and white to 1:35. The office illumination changes additionally the 16
step spacing and the appearance of the 16 grey samples on the monitor of both the tranparent test chart on top and
of a digital test chart output. The contrast range and the spacing of the 16 grey steps for the printer and the monitor
output and the transparent ISO/IEC-test chart which is fixed on a "white" monitor screen can be made equal. The
reflective or transparent ISO/IEC-test chart allow to test many properties of the working place in the office, e. i. by
recognition of Landolt-rings, line screens, Siemens stars, 16-step spacing etc. The recognition and spacing is
highly influenced by the office illumination, the luminance and surface reflection properties of the monitor and the
imaging software.
The procedure to produce equidistant 16 step grey spacing for the printer and monitor output is described. The
digital ISO/IEC-test chart no. 3 which includes CIELAB L* lightness input data is used to produce a linear input -
output relationship. It is only necessary to replace the 16 linear (ideal) L* data in the ISO/IEC-test chart file (in
PostScript file format at the beginning) by the 16 L* output data of the printer or monitor output to produce the
intended equally spaced 16 step grey output. In the standard test chart file the L* lightness input data vary within the
standard range between L*=18.0 and L*=95.4. In the digital NP-file the L* data are used by the PostScript (PS)
operator L* setcolor for the standard CIELAB colour space. In the digital CP-file the L* data are transferred to
relative lightness w* which is zero for black N and 1 for white W and the PS operator w* setgray is used. The digital
FP-file includes a PostScript MTL code (Measurement, Transfer and Linearisation) which produces a linear
relationship between the w* input data (between 0 and 1) and the L* lightness output on any printer or monitor. It is
described how to use the reflective or transparent ISO/IEC-test charts to produce this linear relationship by visual
comparison (or CIELAB or XYZ measurement) with the reference. If the transparent BAM-test chart as refererence
is NOT available a training method with a digital test chart as reference is described which leads to the linear input -
output relationship. At present often monitors (and printers) show for the 16 grey steps of the achromatic ISO/IECtest
chart no. 3 mean differences of 10 in lightness L* (between 0 and 25). The method of this paper often allows to
reduce the lightness differences from 10 to less then 3 (by a factor 3 to 5). This is then below the tolerance of 3 which
is intended in ISO/IEC 15775 for colour copiers. So the output on different printers and monitors will be made very
similar.
Corresponding colours of the olv* and cmy0* colour spaces (described by the PS image operators "4 colorimage, 3
colorimage and image" and described by the PS vector graphic operators "setcmykcolor, setrgbcolor and setgray")
show in a lot of cases an equal output as required by users and colorimetry. For many software - hardware combinations
the colours defined in the olv* and cmy0* colour spaces appear very different (about 15 CIELAB) in the
output. An example is the software Adobe Reader which produces a brownish output on the monitor for the greys
defined in the cmy0* colour space compared to the achromatic output for greys defined in the olv* colour space.
An ISO/IEC-test chart file uses the 6 different PS operators on one page. This test chart is used for a system test
(combinations of hardware and software) of the device colour output. For this test the 16 step colour scales of Fig.
B4 and D4 of the ISO/IEC-test chart according to ISO/IEC 15775 are used. If unexpected result occur then there are
methods to correct the output. e. g. by the MTL code (Measurement, Transfer and Linearisation).
A local, global or external transfer is used to make the output of raw scan olv*' image data of slide and negative film
very similar. A large variation of exposure has no influence on the output. For slide film this exposure range is
between about -0,5 stops (under exposure) and +1,0 stops (over exposure). For negative film the exposure range is
between about -1,0 stops (under exposure) and +3,0 stops (over exposure). The output appears the same for a local
and external transfer. All the different exposures of two film materials are shown on one page. The global transfer is
applied to an image of the flower motif (Fig. B1 and D1 of ISO/IEC-test chart according to ISO/IEC 15775).
The four analog ISO/IEC-test charts in reflectance mode according to ISO/IEC 15775 are designed for
the test of colour copiers. The test charts include many image elements. e. g. Siemens-stars, Landoltrings
and 16 step equally spaced colour scales according to CIELAB. Most important for image
technology is the ISO/IEC pictorial image B1 which includes a 16 step grey scale and 16 CIE-test
colours.This image comes in 5 resolutions between 128 x 192, 256 x 384, and 2048 x 3096 pixels. For
analog production the digital ISO/IEC-test charts are described in ISO/IEC 15775.
Some applications of the digital and analog ISO/IEC-test charts for printers, monitors and scanners will
be discussed. Recently three methods to optimize the ISO/IEC-test chart output have been developed.
Between the digital input values and the CIELAB colour difference of the 16 step colour series a linear
relationship is produced. This linear property allows new and very simple colour management methods.
The application of these methods for the production of the reference ISO/IEC-test charts and for colour
management of slide and negative film images as function of exposure is shown.
Four analog ISO/IEC-test charts according to ISO/IEC 15775 are designed for the test of colour
copiers. The International Standard ISO/IEC 15775 includes the LAB* (CIELAB) data and many cmy*
data of the colours used in the test charts. The digital ISO/IEC-test chart files include mainly cmy*
colour data but also LAB* data for the CIE-test colours and are available on the recommended web
servers. The files have been used for the production of the ISO/IEC-test charts in Germany and Japan.
This paper uses either LAB* or cmy* data in the digital files and still the colour output is identical.
With additional Output Linearisation (OL) the 16 step colour series are produced with equal spacing in
CIELAB. The 16 step series are produced by linearized devices with an accuracy of less than 3 CIELAB
units intended for the office environment. The CIELAB colour difference is often reduced by a factor
3 to 5 for the 16 step series on the surface of the colour solid. For the CIE-test colours which are mainly
located inside the colour solid the accuracy seems to be similar compared to the accuracy of the ISO/
IEC-test chart productions in offset which is near 10 CIELAB units.
The user requirement for a linear relationship between CIELAB data and cmy* data is realised.
This linear CIELAB - cmy* colour workflow for offices seems to be both simple and effective. The
yellowness data y*=0.5 will produce a yellow in CIELAB space visually in the middle between white W
and yellow Y. This is similar for the other series, e. g. white - black. Therefore there is agreement with
the basic user requirement. The linear relationship between cmy* and CIELAB has many advantages
for colour image technology. Slightly different output colours compared to the intended CIELAB colours
can be corrected in the digital input file by using the linear CIELAB difference of the output and the
intended CIELAB colour. The CIELAB - cmy* workflow is linear which may be compared to the
nonlinear rgb workflow of the International Standards IEC 61966-X. The spacing of the rgb coordinates
of the Standards IEC 61966-X is incompatible with the CIELAB spacing.
Four ISO/IEC-test charts have been defined in ISO/IEC 15775 (1999) to specify image reproduction of
colour copiers. Corresponding test charts have been defined in DIN 33866-1 to 5 (in print) to specify
image reproduction of colour copiers, printers, scanners and monitors. All colours of all test charts are
defined in CIELAB coordinates. In applications the devices including software are used for test chart
input and output in the three different combinations "analog - analog" (copiers), "digital - analog"
(printers, monitors) and "analog - digital" (scanners, Photo-CD-systems).
This paper uses mainly ISO/IEC-test colours of a 16 step grey scale (defined by olv*-coordinates
according to the standard) in the original scene to calibrate the variable (photographic and Photo-CD)
analog-digital process. The relative digital olv*-input data and the digital olv*'-output data are used to
get approximately the same digital output (image file) independent of exposure (e. g. between -1 stop
under to +2 stop over exposure for slide or negative film) and other variables, e. g. the digitizing Photo-
CD-process. This "direct" colour management method adds a new method compared to the ICC colour
management method which fails to handle variable processes and can not manage the variable data of
original scenes taken by the photographic process.
For colorimetric colour management and
communication 8bit colour codes in perceptive
space (*colour space) are described. Two Standard
Gamut Colour codes for Printing (PR) and Television
(TV) and one universal Wide Gamut Colour code
(WGcode) which includes all real colours of both PR
and TV. There are reverse transformations between
the two different SGcodes of PR and TV, the
universal WGcode and the CIELAB colour
coordinates. The SGcodes and the WGcode are
compatible with CIELAB, ISO/IEC 15775 and DIS
ISO/IEC 19839-1 to 4 which specify image
reproduction properties of colour copiers, printers,
scanners and monitors. These standards correspond
to DIN 33866-1 to 5.
The SGcodes and the WGcode can be calculated for
all colours of the four ISO/IEC-test charts which are
all defined in CIELAB coordinates. Main colour
series are equally spaced in CIELAB colour space
both in lightness L* and chroma C*. Up to now there
are productions of DIN (German Standard Institute)
and JBMA (Japan Business Machine Makers
Association) according to ISO/IEC 15775 which can
be used for all applications.
The 8bit SGcode of television is similar compared to
the nonlinear 8bit code of the sRGB colour space
defined in IEC 61966-2-1:1999-10 which is
incompatible to CIELAB and ISO/IEC 15775.
The committees ISO/IEC JTC1/SC28 and DIN-NI-28 "Information technology, Office equipment" have
worked together to develop the International Standard ISO/IEC 15775. The new national standards
DIN 33866-1 to 5 (in print, drafts May to Nov. 1999) and the International Standard ISO/IEC 15775
are based on equivalent colour series. Both use the same colour series both in digital and analog test
charts and approximately the same layout.
New colorimetric technologies of Germany and Japan have been used to produce the four DIN- and
ISO/IEC-test charts in offset printing (3600 dpi) which are in application for colour devices now.
The different productions will be shown, e. g. in halftone and continuous tone and in reflectance and
transmittance mode. Some problems of measurement (e. g. fluorencent photographic material) and the
accuracy of production is important for applications.
A flat area lamp which is shown at the conference has the chromaticity of D65. With transparent ISO/IEC-test chart material on top this equipment defines a reference monitor for comparison with display
output. For additional information see the URL: www.ps.bam.de