Figure 1 lists the information on this server:
For example Part A includes on the pages with the names A(G/E)(A..Z)(I/S/0..9).HTM
about 4000 figures with english and german text.

Therefore the Server1 and the Server2 with approximately the same content seem
to be important for the scientific basis and applications of the above topics.

The development of this web site is connected with the author Klaus Richter.
His PhD thesis was published in 1969 by the University of Basel (Switzerland):
"Antagonistic signals in colour vision and relation to the perceived colour order".
This PhD paper (in German) is available under "publications", see XY91FEN

In 2024 the following new TUB project was completed:
Content and application of the TUB text_image_vocabulary (tubtiv) for colour education and standardization.
This vocabulary of the Technical University of Berlin (TUB) combines text (three lines) with colour images. Therefore any search text within the three lines is connected by links to a special colour image. This colour image of the size A4 may consist of 16 sub images.

The same search text usually appears in many other of the about 36.000 lines of 6.000 pdf-colour images. For example there are 283 hits for the search text: hue circle.

One may start the tubtiv with a browser click on the following link.
This link opens a new window, see http://color.li.tu-berlin.de/index.html.
Then one may replace this window by a click to tubtiv_2he.htm.

The tubtiv output of Section 2 (2019-2024) appears. Links to more information are at the beginning. All (a) Sections include the time period 1998-2024.

In 2019 the following TUB-project title was decided:
Colour and colour vision with Ostwald device and elementary colours -
Antagonistic colour-vision model and properties for many applications.

This TUB project consist of 5 parts:
A. Colour Image Technology and Colour Management (2019),
Summary: AEA_S in English or AGA_S in German.

B. Colour Vision and Colorimetry (2020),
Summary: BEA_S in English or BGA_S in German.

C. Colour Spaces, Colour Differences, and Line Elements (2021),
Summary: CEA_S in English or CGA_S in German.

D. Colour Appearance, Elementary Colours, and Metrics (2022),
Summary: DEA_S in English or DGA_S in German.

E. Colour Metrics, Differences, and Appearance (2023, under work),
Summary: eea_s in English or ega_s in German.

Links of resent papers about the antagonistic TUB-relativity model of colour vision:
At the meeting of the German Society for Colour Science and Application in Potsdam, October 5&6, 2023 a presentation will be given,
Deductive and inductive antagonistic TUB colorimetry to extend the CIE colorimetry for a wide range of luminance and chromatic adaptation, see a summary
dfwg_23e.pdf in English or dfwg_23d.pdf in German.

In 2022 a paper about the TUB model appeared on this web site:
TUB-relativity model of colour vision for light and surface colours.
see: farbe2207.pdf in English or farbg2207.pdf in German.

1. Antagonistic TUB-relativity model of colour vision
The TUB-project title includes the term "antagonistic" of the Greek language. This term is well known in medicine for muscles. The muscles may work in "antagonistic" (or opponent) directions.

Colours may have "antagonistic" properties, which for example can be described by "opponent", "complementary", "compensatory", "shadow effect", "after image effect", "successive contrast", and "simultan contrast".

The "antagonistic" colour appearance attributes can be described for example by
"lightness - darkness", "blackness - brilliantness", "whiteness - deepness", "chromaticness - achromaticness".

These attributes change for example with the reflection of the ambient light on the display, compare the properties for eight reflections:
OE73/OE73F1P0.PDF.

The question arises, if an "antagonistic" colorimetry is able to describe many colour effects and colour appearance attributes. These affects and attributes are applied in the area of design, architecture, and art, and for example in the Swedish "Natural Colour System NCS".

It is believed that the visual system of man constantly adapts to a "medium" achromatic stimulus with a "medium" luminance of the visual scene. Based on the TUB colour vision modell, all light and surface colour sensations are calculated relative to these "average" measurable data of colour and light.

For example the TUB-relativity model of colour vision calculates equal hue thresholds for complementary optimal and display colours in agreement with experimental results of Holtsmark and Valberg (1969). For properties of this model see the papers marked with a *) under XY91FEN

In applications a ISO-colour loop plays an increasing roll. Effective information is possible from a pdf file with a pdf reader. The links in the image are only working from the downloaded pdf file with vector graphic.

In the following as example a project application is described. This application is part of the ISO-colour loop for the display output at the ergonomic workplace. Unfortunately in 2022 after more as 20 years the company Apple has deleted the GammaSlider, which is described in ISO 9241-306:2008 and ed-2:2018. This GammaSlider is shown in the following. Application programs for macOS and replace the properties of the GammaSlider.

In 2022 alternatives to the deleted slider applications of macOS have been presented. In addition new possibilities for the display output at the ergonomic workplace are created, see workshops http://www.deutsches-farbenzentrum.de

2. Ergonomic changes of the rgb*-colour output at office work places by power functions depending on the display reflection of the ambient light

The reflections of ambient light in offices change the display-output colours. About 3,6% reflection compared to the white display (90%) reduces the colour gamut to 50%. Often more important is the change of the colour spacing by the reflection of the ambient light. In a worse case the reflection of the ambient light may be 40% compared to the white displays. This happens with projectors in an office with much daylight or for displays with sunlight reflections.

In this worse case four dark of 16 grey steps may appear black and can not be distinguished. The visual equidistant spacing of a 16 step grey series without display reflections is therefore to a high degree destroyed.

If the rgb* values are changed by a power function one can make the 16 steps again visible and equally spaced. Appropriate rgb* changes increase the visibility and reduce visual fatigue at any display-work place.

ISO EN DIN 9241-306:2018 defines 15 contrast steps for luminance between the High Dynamic Range (HDR) and the Low Dynamic Range (LDR). The colour gamut decreases from 100% to about 13% for a change of the contrast step between Cmax=288:1 and Cmin=2:1. Both the lightness and the chroma decreases.

For example for the display-output test, the ISO-test chart AE49 with 1080 colours has been developed. The output questions for the 15 contrast steps are given in English (E), German (G), and French (F).
The ISO-test charts are on the ISO Standards Maintenance Portal in the file formats PDF, and PostScript (PS, TXT), see
http://standards.iso.org/iso/9241/306/ed-2/index.html.


Figure 2: Test chart AE49 according to ISO 9241-306 with 1080 colours for 15 contrast steps
For the download of this figure in the VG-PDF format, see AEW8L0NP.PDF.

Instead of the 15 contrast steps on 15 pages Fig. 2 includes the 15 contrast steps on one page and in addition one reference image (with a red frame). Usually by visual inspection only one of the 15 outputs shows the intended equal spacing of the colour steps. The visual spacing changes with the display reflection of the ambient light.

The test chart is designed for the relative gamma range 0,475 < gp < 2,105. This range corresponds to the (absolute) gamma range 1,20 < ga < 4,8. The gamma value g = 2,4 in the middle of this range is known from the lightness L*IECsRGB of the sRGB colour space according to IEC 61966-2-1.

The above gamma range corresponds to the contrast range 2:1 < C < 4608:1. In offices the contrast C = 36:1 is the standard contrast for the displays and the paper. The standard contrast of the white and black paper is determined by the reflections R=0,90 and R=0,036. The reflection ratio defines the office contrast C = 36:1. The standard luminance of the display is LW=142 cd/m^2 for white and LW=4 cd/m^2 for black. Also the luminance ratio defines the office contrast C = 36:1.

The contrast C=36:1 has the name CP5 in ISO 9241-306 and produces the optimal readability and colour spacing in a standard office.

In ISO 9241-306:2008 and ed2:2018 a GammaSlider is described. The GammaSlider serves for the creation of an equally spaced output of the reference ISO-test chart (with a red frame in Fig. 2). This is then also the recommended ergonomic output for the whole display.

With the "slider technology" the rgb* values are changed by a power function. With a power function the start-rgb* values 0, 0, 0 for Black N and 1, 1, 1 for White W will not change. However, for example the three start-rgb* values 0,5, 0,5, 0,5 change to the values 0,25, 0,25, 0,25 for the exponent k=2 or to the values 0,70, 0,70, 0,70 for exponent k=0,5.

Remarks:
Since 2000 macOS X includes a menu for the GammaSlider. ISO 9241-306 describes the advantages of the GammaSlider as example. The slider has been available under "System Preferences - Display - Color - Calibrate" until 2019.

Since 2020 (macOS 10.15) the slider has been only available, if the "Alt-key" is pressed during the option "Calibrate".

Since 2022 (macOS 12.3) the option "Color" is deleted and the Slider for the ergonomic output is not any more available.

Since 2023 under MacOS 11 and later for example the free application program GammaAdjuster can be used. Users with MacOS 11 or earlier can still use the GammaSlider.


3. Example software GammaAdjuster and GraphicConverter for changes of Gamma

Figure 3: Links to Gamma-change software and ISO files with different Gamma
For the download of this figure in the VectorGraphic VG-PDF format, see eei20-7n.pdf.

Recommendation: Download this PDF file and use the software Adobe Reader or Mac Preview. This software does NOT change the capital letters to small letters within the links. This change is done by some web browsers and then an error occurs.

The software company given in Fig. 3 is well known for macOS users. For example the GraphicConverter V.5.2 of this software company has been registered to Apple Bundle Customers according to my Mac of 2010 with macOS V10.6.8. The present GaphicConverter V.12.2 and former versions allow to change still images by the input of gamma values under the option "view". For the link to this software company, see
https://www.lemkesoft.com.

During 2023 the software GammaAdjuster appeared for macOS. The GammaAdjuster has similar and additional properties compared to the 2022 deleted GammaSlider of the operating system macOS.

After start the GammaAdjuster changes the gamma values for the whole display output. The GammaAdjuster is similar compared to the GammaSlider for both still images and the video output on the whole display. It is possible to terminate the GammaAdjuster at any time.

An additional property of the GammaAdjuster is a change of a possible colour-output tint of the whole display by three different gamma values for r, g, and b. The GammaAdjuster output is intended only for the local display output. The storage, the video transmission, and the output of all rgb values which are changed by the GammaAdjuster on the graphic card, is not possible.

The present GaphicConverter V.12.2 and former versions allow to change still images by the input of gamma values. A choosen gamma value changes the colour file and shows the corresponding output in real time by the option "view". The storage, the video transmission, and the output of all rgb values which are changed by the GaphicConverter on the still image, is possible.

The ergonomic equally spaced output is possible under many reflections of the ambient light. If the gamma change is included in the output file then an ergonomic output can be produced for a printed output. Usually for the ergonomic output on a printer only one gamma value may produce the ergonomic output.

For example in the printed version of DIN EN ISO 9241-306/ed-2:2019 four of the 16 grey steps were not distinguishable. However, the print output of the former version ed-1:2009 shows 16 equally spaced grey steps. A determined appropriate gamma has produced an approximately ergonomic equally spaced grey scale using the digital ISO-PDF file of ed-2. This printed ergonomic output is efficient and sustainable. The output saves toner compared to the official print version of DIN. Therefore a gamma change is efficient to increase the output quality. The colourimetric output quality can be specified by a high colour-regularity index R according to ISO/IEC 15775, Annex G.

The example includes two special messages:
- Often only a gamma change leads to the intended ergonomic and sustainable output.

- In general only the printer or display user can determine the appropriate and efficient gamma value. Only the user knows the application contrast which is defined by the printer paper or the reflection of the ambient light on the display.

The above two mesages use the following basis:
- The rgb* values in the ISO-PDF file are equal for any output-contrast, for example for a high contrast output by a photo printer and for a low contrast output on recycled paper.

- No metadata or GainMap data are in the ISO-PDF file. Both the device manufacturer or the user can apply a gamma change for the ergonomic, efficient and sustainable output.

At a work place only the user can usually determine visually the ergonomic, efficient and sustainable output.

Under Windows there are many application programs, which allow to change gamma values, see RUSCHIN22.PDF.

For the download of 9 ICC profiles with the absolute gamma 1,0 <= ga <= 2,6, which can be tested as a further alternative method under macOS and Windows, see (94 KB) LCD_XX.zip.

ICC profiles may change 16 Million rgb data to 16 Million rgb' data by colorimetric criteria. For many display applications a ColourConnectionSpace (CCS) is used for the calculation of the transformation. The transfer rgb to rgb' is possible for single and video images with the graphic card of a desktop computer. This method is more complex compared to the simple and effective gamma change. Again the application contrast is only known by the user. Usually the output specified by the manufacturer or the GainMap is unable to fulfill to the user wish for an ergonomic output. In addition the user contrast of the optical eye media is decreasing with the observer age. The user can consider this application effect by the appropriate gamma.

The colour group of the Berlin Technical University (TUB) appreciates information about further application programms which allow to change the gamma for till images and video for the operation systems Mac, Window, and Unix. The TUB colour group will support the distribution of information for ergonomic applications.

At many display work places the GammaSlider is still used. Therefore this software version is described in the following for comparison with the GammaAdjuster, see AEXI.HTM.


Figure 4: The GammaSlider of the computer-operation system macOS X (deleted 2022)
For the download of this figure in the VG-PDF format, see AEX50-7N.PDF.

A gamma range 1,00 < g < 2,6 is used under macOS X to change the whole display output. For the ergonomic output the Yes/No criteria come with the test chart AE49 of ISO 9241-306. For many ambient reflections and different default and real values of the display gamma, one position of the slider leads usually to an ergonomic display output.

Also if the display image for example appears under or over exposed, then the gamma slider can usually produce an ergonomic output. The output values rgb* = 0 0 0 for Black N and rgb* = 1 1 1 for White W are not changed by any gamma value, only all values between 0 and 1.

Section AECI.HTM shows, how to normalise images in the case of under or over exposure.


Figure 5: 16 times the same test chart AE49 according to ISO 9241-306 with 1080 colours
For the download of this figure in the VG-PDF format, see AEW7L0NP.PDF.

The test chart is designed for the relative gamma gp=0,775. This corresponds to the contrast C=36:1. This contrast is called CP5 in ISO 9241-306 and produced the optimal readability and colour spacing in a standard office.

It is intended that users download the VG-PDF file of Fig. 50 for a visual test. Often the ambient reflections are different at the corners and in the middle of the display. Visual inspection can decide, if different readability or different colour spacing is visible. In this case one can look for solutions, for example by a position change of the luminaires or of the display.

Summary and applications
One free available ISO-test chart of AG49 in the file format PDF according to ISO 9241-306:2018 simulates eight contrasts, which are produced in the standard office by display reflections of the ambient light. Eight pages include image data between rgb* = (0 0 0) for Black N, rgb* = (0,5 0,5 0,5) for mean grey U, and rgb* = (1 1 1) for White W. Power functions change the rgb* data between 0 and 1. For example r*=0,5 with the power value k=2 is changed to r*'=0,5^k = 0,25. With this change the image looks darker or with k=0,5 it appears lighter.

For an ergonomic and equally spaced output the variables rgb*, R, Y, or L shall be changed by a power function with the exponent k. Appropriate values are necessary for:
1. the display reflection by the ambient light.
2. the surround, for example White W, Grey U, or Black N,
3. the colour-sample distance, for example adjacent or separate on grey surround, and
4. the colour viewing time, which increase local adaptation with time.

In image technology the rgb* data are often changed with a Gamma change by a power function with the exponent k. This change allows usually to reach the goal of an ergonomic and equally spaced ouput.


Figure 6: The ergonomic, efficient, and sustainable colour reproduction circle
For the download of this figure in the VG-PDF format, see eeb00-3n.pdf.

Fig. 6 shows many possibilities to realize an ergonomic colour reproduction circle:
ISO file -> Analog test chart -> Scanner file -> ISO file output.

It is intended that the rgb* values of the ISO file and of the output file are approximately equal. ISO 15775, Annex G, defines a Regularity Index R in the range between 0 (worse) and 100 (excelant) to specify the output quality by CIELAB-colour differences or the proportional rgb* differences.

4. Examples to improve the output quality by the Regularity Index R
For an ergonomic, efficient and sustainable print output a different gamma change is usually appropriate on photographic paper with high contrast, for example C=50:1 (Y=90:1,8, L=(142:3)cd/m^2), or on standard mate paper with low contrast, for example C=25:1 (Y=90:3,6, L=(142:6)cd/m^2).

For an ergonomic scanner output of analog ISO test charts according to ISO/IEC 15575:2022 an appropriate gamma change may transfer the real device rgb values to the equally spaced rgb* values of the ISO Standard File according to ISO/IEC 15775.

Both a simple gamma change or a professional change, see the CIE method in Fig. 6, will increase the output quality according to the Regularity Index R according to ISO/IEC 15775.

Therefore, there are many possibilities to realize an Ergonomic colour reproduction circle:
ISO Standard file -> Analog test chart -> Scanner file -> ISO intended file = ISO Standard file.