2005-06-01 XY04 EN | DE zurück | vor

BAM Federal Institute for Materials Research and Testing

Prof. Dr. Klaus Richter
Visual Methods and Image Reproduction in Non-Destructive Testing (NDT)

contact point :

BAM Division VIII.1
Measurement and Testing Technology; Sensors
Werner Daum
Unter den Eichen 87
12205 Berlin
+49 30 8104-1910


+49 30 8104-1919
+49 30 8104-1919

+49 30 8104-1917


  Visual Methods and Image Reproduction  
  Image reproduction linearisation  

Image reproduction linearisation of 16 step colour scales, see Technical Report ISO/IEC TR 19797:2004

Standards, short title and information about standard test charts
DIN 33866-1 to 5:2000 "Colour Reproduction: Basis, Copiers, Printers, Scanners, Monitors"
ISO/IEC 15775 "Colour reproduction properties of colour copiers"
ISO/IEC TR 19797, 19797 "CIELAB output linearization of 16-step colour scales"
ISO/IEC TR 24705, 24705 "Colour reproduction properties: Basic, printers, scanners, monitors"

Linearisation method for the reproduction
The linearisation method for the output process may be produced by visual or colorimetric colour measurement of a start output, see please publications and standards.

The linearisation method is described for black and white printers and used by students in a competition of colour science during the international colour meeting FARB-INFO '02, see info02/FI02WE.PDF

Linearization data for a reproduction process
The linearisation data may be included at different places for a reproduction process:
1. in the test file
2. in the startup directory of the software Adobe Acrobat Distiller
3. in PostScript printer driver (PPD) file for printers
4. in the memory of PostScript printers.

For an example linearisation file with linearisation data to be used at the four above places, see info02/MTL20000.PS. This file includes PostScript code of about 50 lines with different relative visual data (linear, square root and square) and colorimetric CIELAB lightness data L* of a start output of a printer. The last data may be changed according to the start output of the device system used.

Four 16 step gray scales which appear diffferent in spacing.

In the recommended file for the start output the digital data 0, 1/15, 2/15, ..., 14/15, 1 are equally spaced for the top grey series. According to the standards the output should also appear equally spaced. The four 16 step gray series appear differently spaced and this is based on the different input data used. The exponents 1/2, 1,5 and 2,0 for the data 0, 1/15, ..., 14/15, 1 are used for the three lower grey scales (see figure description)

In the top series often less than 16 steps can be recognized and the steps appear not equally spaced. It is recommended to measure the output of the top 16 step grey colours. If the lightness L* data in the file info02/MTL20000.PS are exchanged then an equally spaced output in CIELAB lightness L* will be produced for the top grey series. If any other series is measured and the output L* lightness data are exchanged then this series will be equally spaced in the second output.

If the linearisation method is used, then the output of the test file is in most cases independent of the the application software, the printer driver and the device.

Therefore it is useful to store the colorimetric measurement data of a reproduction process in the Distiller startup directory and to produce PDF files from PS files, e. g. by the software Adobe Acrobat Distiller. Every PDF file will then produce a linearized output on any corresponding (measured) printer or monitor (not only on PS devices). In the office area then the colour output is very similar for the different device systems.

Problem of different output if different PS operators and with CIELAB corresponding colour data are used.

Requirement for a similar output by the consumers
A similar output is often required by consumers but software and hardware produce for the DIN- and ISO/IEC-test files often different colours. The test file output is often influenced and changed by the computer operating system, the file format, the application software, the printer diver, and the output device. The reproduction differences become visible. The colour differences are sometimes unacceptable, e. g. if the mean colour differences reach about 20 CIELAB. According to ISO/IEC a mean colour difference of 3 CIELAB is intended.

Solution with the Measurement, Transfer and Linearisation (MTL) code
With the MTL PS software code, which includes the output measurement data of 16 (achromatic) or 128 (chromatic) colours in the startup directory of the software Adobe Acrobat Distiller, the linearisation of the output is possible, see the section "Image reproduction linearisation"

Training of the image programming language PostScript (PS)
VE02: 000715: One page with 16 colour figures

DIN 33870: Start and linearized printer output
DE02: 001215: Material and result of start and linearized printer output of DIN-test charts according to DIN 33870:2001-01

Test files and multistep output linearization
DE03: 010102: Test material: digital 2 step test charts to test the variation of reproduction properties by colour measurement

DE04: 001222: Test material: digital 16 step test charts as basis for linearising 16 step black and white and colour series

DE05: 010105: Test material: digital 16 step test charts - Linearising 16 step output of different file formats PS, PDF, BMP, GIF, TIF, etc.

Start and linearized printer output
: XXXXX: Start and linearized printer output of the ISO/IEC-test 8bit image defined in ISO/IEC 15775:1999-12 (in preparation)

DE09: 010301: Start and linearized printer output of the achromatic ISO/IEC-test chart no. 3 according to ISO/IEC 15775:1999-12

DE10: 010415: Start and linearized printer output of the chromatic ISO/IEC-test chart no. 2 according to ISO/IEC 15775:1999-12

DE11: 010415 Start and linearized printer output of the chromatic ISO/IEC-test chart no. 4 according to ISO/IEC 15775:1999-12

Test material for linearization of colour image reproduction
VM03OE: 000715: Test material to linearize colour image reproduction with digital PostScript pictures; Series 8640, 8650, ..., 8690, 8710, 8720, ..., 8990