230201 1L2L0X0A_(I), http://farbe.li.tu-berlin.de/AEHI.HTM or http://color.li.tu-berlin.de/AEHI.HTM

For this main page with general information and special images
of the corresponding image page with 10 colour series, see AEHI in English, AGHI in German.
For the previous main page, see AEGI in English, AGGI in German.
For the next main page, see AEII in English, AGII in German.

For links to the chapter A Colour Image TechnoloGL and Colour Management (2019), see
Content list of chapter A: AEA_I in English or AGA_I in German.
Summary of chapter A: AEA_S in English or AGA_S in German.
Example image part of 26 parts AEAS to AEZS: AEAS in English or AGAS in German.

Chapter A: Colour Image Technology and Colour Management (2019), Main part AEHI

1. Introduction and goals.

There are different devices und reflections of the ambient light on the display in the area of image reproduction. The colour of any display system are different, for example the display system sRGB according to IEC 61966-2-1, and the display system WCGa (Wide Colour Gamut) according to ETU-R BT.2020-2.

ISO 9241-306:2018 defines eight contrast steps for the standard sRGB display. For example:
1. eight lower contrast steps between black and white n the Low Dynamic Range (LDR), and
2. eight higher contrast steps between black and white in the High Dynamic Range (HDR).

ISO-test charts for these applications are available, see for example
http://standards.iso.org/iso/9241/306/ed-2/AE49/AE49F0PX.PDF for LDR and
http://standards.iso.org/iso/9241/306/ed-2/AE49/AE49F0NX.PDF for HDR.

According to the output questions for the page with 1080 colours any user can determine one of the eight pages by the visual criteria approximately equal spacing of the grey and colour scales.

Usually this is a page of the LDR (Low Dynamic Range) series. However, in a dark room with no or very low ambient reflection (<1% compared to white 100%) on the display, then a page of the HDR (High Dynamic Range) series may produce the best output by the above visual spacing criteria.

For an ergonomic output on displays it is required to reduce the fatique of users. Equal colours steps without clipping are often essential for many applications.

The colours and the output on page 1 of the above two ISO files is equal. The output shall be equally spaced at least at standard work places. If this is not the case, then section AEGI shows solutions.

The reflection on any matte surface is about 3,6% compared to white 90%. The standard ambient reflection in standard offices is 2,5% and equal as a standard semi glossy offset paper according to ISO/IEC 15775.

Allready the standard reflection 2,5% with the contrast range YW : YN = 90 : 2,5 = 36 : 1 reduces the CIELAB lightness range between L*=0 and 95 (Delta L*=95) to L*=18 and 95 (delta L*=77).

The CIELAB chroma range decrease similar. Both reductions reduces the colour gamut by about a factor 0,81 times 0,81 or from 100% to 65%. This reduced gamut for the contrast step 36:1 is the standard gamut according to ISO 9241-306. Therefore this contrast step produces the least fatique in standard offices on a standard sRGB and WCGa display.

Usually the output of the whole display of page 1 of the above ISO files for the LDR or HDR range can be changed by a gamma slider, see the possibilities in section AEXI.

2. rgb* input and CIELAB-LabC*h output for offset colours with YN=2,5 and YW=88,6.

In the following colours of two hue planes are given. They are described by rgb* and CIELAB-L*C*h data.

Fig. 1 - Equally spaced colour steps in hue planes for offset with rgb* and CIELAB LCh* values
For the download of this Figure in the VG-PDF format, see
AEG91-7N.PDF.

The figure includes colour samples in hue planes with the coordinates L*C*ab. The elementary hue planes Yellow Ye and Green Ge for standard offset are shown.

If an LCh*-value set is given, then for example the four most adjacent LCh* values can be determined, see top right. Then the rgb* values for the intended LCh* output values can be calculated by interpolation. Fast calculation methods were described by Witt (2007), see
http://farbe.li.tu-berlin.de/A/WITT07.PDF.
They were used by Richter (2016) in CIE R8-09:2015, see with the same technical content
http://farbe.li.tu-berlin.de/OUTLIN16_01.PDF.

3. Eight device colours RYGCBMNW of the Television Luminous Systems TLS00 to TLS70 for eight reflections of the ambient light according to ISO 9241-306; ISO-rgb*, CIE-XYZxy, CIELAB-LabC*h, and LABJND-L*ABCh-output data of sRGB colours.

The CIE-XYZ data of the sRGB-display device according to IEC 61966-2-1 are changed by the ambient light. The refection of the ambient light can be described by the percentage compared to the white screen. This percentage increases form cero in a dark room via the standard case 2,5% in offices according to ISO 9241-306 up to 40%, if the luminance of the daylight and of the projector white is equal on the projector sreen.

Fig. 2 - TLS00 Reflection geometry with 0% reflection on the sRGB device
For the download of this Figure in the VG-PDF format, see
AEL60-1N.PDF.


Fig. 3 - TLS18 Reflection geometry with 2,52% reflection on the sRGB device
For the download of this Figure in the VG-PDF format, see
AEL60-7N.PDF.


Fig. 4 - TLS070 Reflection geometry with 40,32% reflection on the sRGB device
For the download of this Figure in the VG-PDF format, see
AEL61-7N.PDF.

The figures 2 to 4 show the changes of XYZ for the basic and mixture colors of the sRGB device. It must be mentioned that the tristimulus value of white increases by the reflected light. The new XYZ data are then normalized as before for white to Y=88,59.
The mathematics of this reflection colorimetry will be described separately. This is done in the linear chromatic value space CIE-LABJND of CIE 230:2019. The letters JND indicates that this space is used to describe the Just Noticeable Difference of colours by a colour difference formula.

The next figures 5 to 7 show the LabC*h data of CIELAB.
The following figures 8 to 10 show the L*ABCh data of LABJND.

Fig. 5 - TLS00 Reflection geometry with 0% reflection on the sRGB device
For the download of this Figure in the VG-PDF format, see
AEL80-1N.PDF.


Fig. 6 - TLS18 Reflection geometry with 2,5% reflection on the sRGB device
For the download of this Figure in the VG-PDF format, see
AEL80-5N.PDF.


Fig. 7 - TLS70 Reflection geometry with 40% reflection on the sRGB device
For the download of this Figure in the VG-PDF format, see
AEL80-7N.PDF.

The figures 5 to 7 show the new CIE-XYZ and CIELAB-LabC*h data for the basic and mixture colors of the sRGB device. For example the CIELAB-C*ab data decrease by a factor three and similar for the L* range.


Fig. 8 - TLS00-reflection geometry with 0% reflection on the sRGB device
For the download of this Figure in the VG-PDF format, see
AEL81-1N.PDF.


Fig. 9 - TLS18-reflection geometry with 2,5% reflection on the sRGB device
For the download of this Figure in the VG-PDF format, see
AEL81-5N.PDF.


Fig. 10 - TLS70-reflection geometry with 40% reflection on the sRGB device
For the download of this Figure in the VG-PDF format, see
AEL81-7N.PDF.

The figures 8 to 10 show the LABJND-L*ABCh data. The chromatic value C decreases by a factor three for the case with no reflection via 2,5% to 40% reflection.

4. Ostwald-hue circle with 16 steps; Calculation of elementary colours according to CIE R1-57:2015 with relative hue scaling.

The Ostwald-optimal colours are the most chromatic surface colours. They have the reflection 1 between two complementary wavelenght. The Ostwald colours and the antagonistic Ostwald colour mix to white.


Fig. 11 - Ostwald-hue circle in the LABJND-AB chromatic-value diagram according to CIE 230.
For the download of this Figure in the VG-PDF format, see
AEK30-2N.PDF.

The Ostwald-hue circle forms a closed curve. The calculation of the RG and YB chromatic values A and B is given in the figure. In the CIE-(x,y) chromaticity diagram this antichromatic hexagon is approximately a triangle. Among any hue circle there are four elementary colours. Elementary red Re and green Ge are not located on the honrizontal axis, similar is in the CIELAB-chroma diagramm (a*, b*). All Ostwald colours are located on an antichromatic ellipse in the chromatic value diagram (A, B). They are shown in different diagrams in Fig. 58 of the publication Richter (2012) Colour and Colour Vision - Elementary Colours in Colours Information Technology, see
http://standards.iso.org/iso/9241/306/ed-2/GS15.PDF.


Fig. 12 - CIE-table data of the Ostwald-hue circle with the elementary hues
For the download of this Figure in the VG-PDF format, see
AEP61-3N.PDF.

The role of the Ostwald-hue circle for the device-independent hue output in colorimetry and image technology is described in the Reportership Report CIE R1-57 Border between Blackish and Luminous Colours, see (23 pages),
http://web.archive.org/web/20150413002133/http://files.cie.co.at /716_CIE%20R1-57%20Report%20Jul-13%20v.2.pdf.

5. CIE data of eight Offset and BAM-test colours; Output in six hue planes.

The offset colours are colours with a relative high CIELAB chroma C*ab, and a high lightness range between L*N=18 for black and L*W=95 for white W. The standard offset colours White W and Black N according to ISO/IEC 15775 have CIELAB-a*b* data which are slightly different from cero. Therefore some kind of adaptation is necessary for the achromatic colours.

Fig. 13 - CIE-table data of the Offset-hue circle for six device hues
For the download of this Figure in the VG-PDF format, see
AEP71-1N.PDF.

6. CIE data of the display system sRGB according to IEC 61966-2-1 (ITU-R BT.709.3) and of the display system WCGa (Wide Colour Gamut) according to ITU-R BT.2020 for the normalizations Yw=100, and Yw=88,6.

The display system sRGB according to IEC 61966-2-1 (ITU-R BT.709.3) plays a most important role in image technology.

Fig. 14 - CIE-table data of the sRGB-hue circle for six device hues
For the download of this Figure in the VG-PDF format, see
AEP90-3N.PDF.

However, the display system WCGa (Wide Colour Gamut) according to ITU-R BT.2020 will get increasing importance in future.

Fig. 15 - CIE-table data of the sRGB-hue circle for six device hues
For the download of this Figure in the VG-PDF format, see
AEP90-7N.PDF.

7. CIE-XYZxy and CIELAB or LABJND data for the four devices sRGB, WCGa, Offs, and Ostw

The colours change by different reflections of the ambien light. The chnages are studied here for the four devices:
1. sRGB according to IEC 61966-2-1,
2. WCGa (Wide Colour Gamut) according to ITU-R BT 2020-2,
3. Offs (Standard offset print) according to ISO/IEC 15775,
4. Ostw (Ostwald-optimal colours) with a rectangular reflection.

The Ostwald colours of a colour half are anti-chromatic complementary colours and play a special role in colour vision, see as example the table in Figure 12 and diagrams in AEQ8L0NP.PDF. The Ostwald colours form an ellipse in the chromatic value diagram (A, B) of the colour space LABJND used in CIE 230:2019.
The LABJND lightness is a logarithmic function, and the CIELAB lightness is a cube root function of the CIE tristimulus value Y. If the CIELAB lightness is used, then the space of CIE 230:2019 is called L*ABJND.

Only the devices sRGB and WCGa are real display devices. The numbers 3 and 4 are hypothetical display devices. Number 3 may be an offset print on a tranparent material, for example a print of the 1080 colours of the test chart AE49 according to ISO 9241-306, see http://standards.iso.org/iso/9241/306/ed-2/AE49/AE49L0NP.PDF.

Then a D65 background produces the display colours. They are changed by reflections of the ambient light on the transparent material.

The eight standard reflections according to ISO 9241-306:2018 are used in tables and diagrams. Especially three display reflections I>Yr=0,0, 2,5, and 40,3 of black N are used in diagrams of
1. CIELAB lightness and CIELAB chroma (C*ab, L*) and (a*, b*) or
2. CIELAB lightness and L*ABJND chromatic value (CAB, L*) and (A, B).

The changes of the lightness and the chroma or the chromatic value are shown for two adaptations to
1. white YWa=89 on the pages AEHx, AEIx, AEJx, and AEKx (x=0 to 3) and
2. mean grey YZa=18 on the pages AELx, AEMx, AENx, and AEOx (x=0 to 3).
For example go to the page AEH1 and then go to other pages.

The CIELAB chroma C*ab or the LABJND chromatic value CAB is much larger for the WCGa device compared to the sRGB device. The Offs device has smaller values compared to the Ostw device, see

space and reflection sRGB for adaptation to white YWa=88,6 sRGB for adaptation to grey YZa=18,0
CIELAB 2,5% AEH0L0NP. PS / TXT / PDF AEL0L0NP. PS / TXT / PDF
L*ABJND 2,5% AEH1L0NP. PS / TXT / PDF AEL1L0NP. PS / TXT / PDF
CIELAB 40,3% AEH2L0NP. PS / TXT / PDF AEL2L0NP. PS / TXT / PDF
L*ABJND 40,3% AEH3L0NP. PS / TXT / PDF AEL3L0NP. PS / TXT / PDF
Table 1 - Diagrams and tables for the sRGB device

space and reflection WCGa for adaptation to white YWa=88,6 WCGa for adaptation to grey YZa=18,0
CIELAB 2,5% AEI0L0NP. PS / TXT / PDF AEM0L0NP. PS / TXT / PDF
L*ABJND 2,5% AEI1L0NP. PS / TXT / PDF AEM1L0NP. PS / TXT / PDF
CIELAB 40,3% AEI2L0NP. PS / TXT / PDF AEM2L0NP. PS / TXT / PDF
L*ABJND 40,3% AEI3L0NP. PS / TXT / PDF AEM3L0NP. PS / TXT / PDF
Table 2 - Diagrams and tables for the WCGa device

space and reflection Offs for adaptation to white YWa=88,6 Offs for adaptation to grey YZa=18,0
CIELAB 2,5% AEJ0L0NP. PS / TXT / PDF AEN0L0NP. PS / TXT / PDF
L*ABJND 2,5% AEJ1L0NP. PS / TXT / PDF AEN1L0NP. PS / TXT / PDF
CIELAB 40,3% AEJ2L0NP. PS / TXT / PDF AEN2L0NP. PS / TXT / PDF
L*ABJND 40,3% AEJ3L0NP. PS / TXT / PDF AEN3L0NP. PS / TXT / PDF
Table 3 - Diagrams and tables for the Offs device

space and reflection Ostw for adaptation to white YWa=88,6 Ostw for adaptation to grey YZa=18,0
CIELAB 2,5% AEK0L0NP. PS / TXT / PDF AEO0L0NP. PS / TXT / PDF
L*ABJND 2,5% AEK1L0NP. PS / TXT / PDF AEO1L0NP. PS / TXT / PDF
CIELAB 40,3% AEK2L0NP. PS / TXT / PDF AEO2L0NP. PS / TXT / PDF
L*ABJND 40,3% AEK3L0NP. PS / TXT / PDF AEO3L0NP. PS / TXT / PDF
Table 4 - Diagrams and tables for the Ostw device

The tables 1 to 4 show links to the PDF files of the four devices sRGB, WCGa, Offs, and Ostw.

For additional files of the sRGB device, see AEHI.HTM and AELI.HTM.

For additional files of the WCGa device, see AEII.HTM and AEMI.HTM.

For additional files of the Offs device, see AEJI.HTM and AENI.HTM.

For additional files of the Ostw device, see AEKI.HTM and AEOI.HTM.

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