BAM Federal Institute for Materials Research and Testing
Prof. Dr. Klaus
contact point :
+49 30 8104-1917
|Visual Methods and Image Reproduction|
|Colour management and colour workflow|
Colour management and colour workflow with transformations between CIELAB and device coordinates and vice versa
Different colour workflow for ISO/IEC-test charts
The reproduction of an ISO/IEC-test chart may be influenced by a lot of parameters and some of them are shown in the above flow chart. The diagram shows different colour workflow possibilities. The output is changed here by the MTL (Measurement, Transfer and Linearisation) PostScript code.
This PS code may be included (from left to right) in the file, the PostScript printer memory, the PS printer driver or the startup directory of the Software Adobe Acrobat Distiller. The MTL PS code uses different PS operators and may change, e. g. a PS operator www* setrgbcolor to another PS operator w* setgray. The real output devices and the real application software includes different company specific software and setttings, e. g. in the printer driver code which changes the output.
Because of the different colour workflow (which include different company specific changes) a systematic colour management of the output gets very difficult. But colorimetry can tell many basic principles for this output. There are achromatic and chromatic test files which test the agreement with the basic models of colorimetry.
Problem of different output for CIELAB corresponding colour
The figure include four 16 step grey scales from black to white. The third scale looks very brownish with the software Adobe Acrobat Reader. With other software the third scale looks neutral, e. g. the software Macintosh OS X and GostVIEW on Windows.
On the operating system Macintosh OS X it is possible to produce both the PDF file output of the 16 step gray series by the software Adobe Acrobat Reader 5.0 and by the software Macintosh OS X. Large differences appear on the monitor. It is even more surprising that with the software Adobe Acrobat Reader the output of the PDF file is different on the monitor and equal with some PostScript printers, e. g. Xerox Phaser 740.
The four top figures include 16 step colour scales from white to the colours cyan blue, magenta red, yellow, and black (CMYN, N = french Noir). The left two are defined in "image graphic" by pixels and the right two in "vector graphic". In the files for all four figures colour definitions are used in corresponding device colour spaces and therefore the output should appear equal according to the standards. But the output appears different on most device systems. A device system is a software and hardware combination used for the output.
The lower four figures which show the series between white and orange red, leaf green, violett blue and black (OLVN) according to ISO/IEC 15775 should appear equal as well.
There is e. g. a monitor system, the PDF viewer on Macintosh OS X, which produces equal output for the above PDF file for both the four colour series at the top and at the bottom. The spacing of corresponding colour series appears the same on this monitor system. In general the monitor output is not equally spaced.
For most applications the output is different but there are at least methods on this web site to make the output equal for every device system for the two figures on the right side. The output may be additionally equal compared to the second figure on the left side in many cases. And additionally the output can be made approximately equally spaced in CIELAB.
The output differences for CIELAB colours defined in corresponding device colour spaces are an unsolved and basic problem for the different colour management methods which are required to correct e. g. the different output of coresponding colours in the above files.
Colour management using the PS operator settransfer
Transform between CIELAB and olv*, cmy* and sRGB
Colour Workflow (CW) and Output Linearization (OL)
Output colour management with digital PostScript pictures