1 Scope
This document specifies requirements for the characteristics of soft proofing displays for colour images at two levels of compliance, including requirements for uniformity under different drive signals and electro-optical characteristics that vary with the viewing direction.
2 Normative references
The contents of the following documents constitute essential provisions of this document by means of normative references in the text. In particular, the date of the reference document, only the date of the corresponding version applies to this document; not to date of the reference document, the latest version (including all the revision of the list) applies to this document.
ISO 13655 Printing technology-Spectral measure-ment and colourimetric computation for graphic arts images
Note: GB/T 19437-2004 Printing technology: Spectral measurement and colourimetric computation for graphic arts images (ISO 13655-1996, IDT)
3 Terminology and definitions
The following terms and definitions apply to this document.
3.1
Calibration
A set of operational relationships between the value of a quantity displayed by a measuring instrument or measuring system, or expressed as a material measure of a reference material, and the corresponding quantity achieved by a corresponding standard, under given conditions.
[Source: ISO International Glossary of Basic and General Terms for Metrology]
Note: In typical printing production, however, it is positive to adjust the monitor or press to the specified target value, depending on the actual application.
3.2
Colourimeter
An instrument for measuring colour values, such as the tri-stimulus value of a colour. [Source: ISO 12637-2; 2008, 2.18].
3.3
design viewing direction; the direction in which a DVD is optimised for the specific electro-optical characteristics of a display.
Note: Examples of important electro-optical characteristics are maximum brightness and maximum contrast in a given direction.
4 Requirements
4.1 Overview
For all display tests it is advisable to calibrate the display to a gamma value of peal.2, a luminance of 160 cd/m' and a chromaticity coordinate corresponding to a Dso illuminant with a 2° observer function (x = 0.345 7, y = 0.358 5). The display should show a "white" image when the red, green and blue channels are all at their maximum value (255 at 8 bits). If other calibration target values are used, a report should be given.
Note 1: The calibration conditions are typical of the printing industry and ensure that the results are comparable from monitor to monitor, as the consistency depends to some extent on the selected gamma value.
The consistency depends to some extent on the selected gamma, brightness and white point settings.
Calibration can be omitted if the monitor to be tested is only for a specific soft proofing system that does not require monitor calibration and only characterises the monitor state. In this case information on luminance, white point chromaticity (expressed as CIExy) and tone reproduction curves (expressed as a gamma value or a set of list values) should be given.
The monitor test should be carried out in a steady state. To determine the monitor stabilisation time, each monitor to be tested should be operated in a temperature-controlled room in calibration mode for 12 h. The room temperature should not vary by more than 0.5 °C and should be in the range 18 °C to 28 °C.
The monitor's stabilisation time (warm-up time) requires a brightness variation of no more than 2% (compared to the average of the last 9 h of measurements within the 12 h period) and a white point of CIEAx ,4y within 0.005 compared to the calibrated state. If the monitor does not reach a steady state, it should not be used.
The warm-up condition of the monitor should be expressed as a graph of the change in brightness and the measured value of CIEAx ,4y as a percentage of the average value of the last 9 h of the 12 h period.
Note 2: When using the P viewing condition, a luminance of 160 cd/m is equivalent to 500 lx of illuminance projected onto a completely diffuse reflector according to ISO 3664.
4.2 Luminance and chromaticity uniformity
4.2.1 Overview
The uniformity of the soft proofing system is very important and the screen should be checked for field colour and colour gradation uniformity. If the recommended requirements of 4.2.2 and 4.2.3 are not met, an explanation should be given. The following method is a normative requirement in ISO 14861. As some soft proofing solutions can be corrected for spatial uniformity. Therefore, this document is only used as an informative recommendation in the uniformity evaluation.
If the hardware-based look-up table shows that the correction is switched on (if available), this should be stated.
4.2.2 Evaluation of tonal uniformity
The screen is divided equally into 5 x 5 grids and the CIELAB value is calculated for each of the 5 x 5 grids, using the measured value of the central grid colour block at the maximum drive value as the light source reference white. Note that this method results in some CIEL's greater than 100. The AEoo colour difference formula was used to compare the colour difference between the 24 measured values and the central colour block value for each of the three different drive levels, i.e. white for the maximum drive level (8-bit display R=G=B=255); grey for approximately 1/2 of the maximum drive level (8-bit display R=G=B=127); and grey for approximately 1/4 of the maximum drive level (8-bit display R=G=B=127). Grey for approx. 1/4 maximum drive level (8-bit display R=G=B I 63); dark grey for approx. 1/4 maximum drive level (8-bit display R=G=B I 63). The ΔEo colour difference between the drive level white and the two greys should be less than or equal to 4.
4.2.3 Colour gradation evaluation (uniformity)
In 25 areas, calculate the grey/white ratio of the luminance measurements (cd/m') for 1/2 the maximum drive level (8-bit display R÷G=B=127) of grey and the maximum drive level (8-bit display R=G=B=255) of white. For non-central areas, the ratio T,(i=1,...,24) should be calculated, i.e. the individual grey/white ratio R,(i=1,...,24) divided by the reassuring grey/white ratio R,,minus 1, and then calculated by taking the absolute value, see equation (1). The measured value of the deviation of the colour gradation uniformity should be less than 10%, (i=1,...,24) the maximum value should be less than 0.10.
4.3 Cone characteristics
The instrument set-up and measurement geometry for cone of vision measurements should be in accordance with 5.4.2.
The cone of vision is based on a given viewing distance (default: 500 mm), calculated for the observer with a monocular view of the centre of the display, horizontal, vertical, diagonal direction of the maximum viewing angle (0.m.. , ... .m... . . n..s). In addition, the four 45° angles should be calculated for 0... .x (starting at 45° and 90° apart from each other), see equations (2) to (5). Maximum tilt angle (0...) depends on the screen size, the screen aspect ratio (display width to height ratio) and the viewing distance.
4.4 Reflective properties
The reflective properties of the display surface should be judged by visual observation with a point light source in the glare room when the power is switched off. The reflection of the screen to the point light source should feel blurred, and when deviating from the direction of the mirror reflection, the reflection should gradually and evenly diminish.
5 Test methods
5.1 Overview
For each display colour block (displayed in the centre of the image in turn), the measured spectral radiation value and (or) CIEXYZ value should be recorded. If required, the CIELAB value (calculated according to ISO 13655) can be calculated and the white point used should be given.
The display is calibrated and characterised to the target value specified for the particular application.
Note: If possible, the measuring instrument should be calibrated, by the equipment manufacturer. If this is not possible, use the interstage difference between the two instruments or the measured value of a field reference (e.g. a calibration) to make a calibration.
A visual comparison of the measured values with a field reference (e.g. calibration sample) can help to determine whether the measuring equipment is working correctly.
5.2 Preparation conditions and monitor settings
Prior to calibration and any measurements, the display should be switched on and warmed up as specified in 4.1. All measurements should be performed on a monitor that has been calibrated and stabilised in accordance with 4.1. Information describing and repeating the measurements (e.g. calibration procedure, software used, ICC characteristics file) shall be given together with the measurement data.
If not otherwise required, all measurements shall be made in the design viewing direction and in contact with the display panel. If the supplier does not specify the design viewing direction, measurements shall be taken in the direction normal to the display surface.
5.3 Colour gradation evaluation ("Ay") in relation to the viewing angle
In order to ensure a stable image appearance, it is essential that the change in colour gradation within the viewing angle and display area is as small as possible. The evaluation of the gamma difference (tonal reproduction) starts with the calculation of the normalised "relative" "luminance value at the centre of the display, which is then compared to the normalised luminance value at each viewing direction or viewing point.
Bibliography
1 Scope
2 Normative references
3 Terminology and definitions
4 Requirements
5 Test methods
Bibliography
Standard
GB/T 41598-2022 Graphic technology—Displays for colour proofing—Characteristics (English Version)
Standard No.
GB/T 41598-2022
Status
valid
Language
English
File Format
PDF
Word Count
7500 words
Price(USD)
225.0
Implemented on
2022-10-12
Delivery
via email in 1~3 business day
Detail of GB/T 41598-2022
Standard No.
GB/T 41598-2022
English Name
Graphic technology—Displays for colour proofing—Characteristics
1 Scope
This document specifies requirements for the characteristics of soft proofing displays for colour images at two levels of compliance, including requirements for uniformity under different drive signals and electro-optical characteristics that vary with the viewing direction.
2 Normative references
The contents of the following documents constitute essential provisions of this document by means of normative references in the text. In particular, the date of the reference document, only the date of the corresponding version applies to this document; not to date of the reference document, the latest version (including all the revision of the list) applies to this document.
ISO 13655 Printing technology-Spectral measure-ment and colourimetric computation for graphic arts images
Note: GB/T 19437-2004 Printing technology: Spectral measurement and colourimetric computation for graphic arts images (ISO 13655-1996, IDT)
3 Terminology and definitions
The following terms and definitions apply to this document.
3.1
Calibration
A set of operational relationships between the value of a quantity displayed by a measuring instrument or measuring system, or expressed as a material measure of a reference material, and the corresponding quantity achieved by a corresponding standard, under given conditions.
[Source: ISO International Glossary of Basic and General Terms for Metrology]
Note: In typical printing production, however, it is positive to adjust the monitor or press to the specified target value, depending on the actual application.
3.2
Colourimeter
An instrument for measuring colour values, such as the tri-stimulus value of a colour. [Source: ISO 12637-2; 2008, 2.18].
3.3
design viewing direction; the direction in which a DVD is optimised for the specific electro-optical characteristics of a display.
Note: Examples of important electro-optical characteristics are maximum brightness and maximum contrast in a given direction.
4 Requirements
4.1 Overview
For all display tests it is advisable to calibrate the display to a gamma value of peal.2, a luminance of 160 cd/m' and a chromaticity coordinate corresponding to a Dso illuminant with a 2° observer function (x = 0.345 7, y = 0.358 5). The display should show a "white" image when the red, green and blue channels are all at their maximum value (255 at 8 bits). If other calibration target values are used, a report should be given.
Note 1: The calibration conditions are typical of the printing industry and ensure that the results are comparable from monitor to monitor, as the consistency depends to some extent on the selected gamma value.
The consistency depends to some extent on the selected gamma, brightness and white point settings.
Calibration can be omitted if the monitor to be tested is only for a specific soft proofing system that does not require monitor calibration and only characterises the monitor state. In this case information on luminance, white point chromaticity (expressed as CIExy) and tone reproduction curves (expressed as a gamma value or a set of list values) should be given.
The monitor test should be carried out in a steady state. To determine the monitor stabilisation time, each monitor to be tested should be operated in a temperature-controlled room in calibration mode for 12 h. The room temperature should not vary by more than 0.5 °C and should be in the range 18 °C to 28 °C.
The monitor's stabilisation time (warm-up time) requires a brightness variation of no more than 2% (compared to the average of the last 9 h of measurements within the 12 h period) and a white point of CIEAx ,4y within 0.005 compared to the calibrated state. If the monitor does not reach a steady state, it should not be used.
The warm-up condition of the monitor should be expressed as a graph of the change in brightness and the measured value of CIEAx ,4y as a percentage of the average value of the last 9 h of the 12 h period.
Note 2: When using the P viewing condition, a luminance of 160 cd/m is equivalent to 500 lx of illuminance projected onto a completely diffuse reflector according to ISO 3664.
4.2 Luminance and chromaticity uniformity
4.2.1 Overview
The uniformity of the soft proofing system is very important and the screen should be checked for field colour and colour gradation uniformity. If the recommended requirements of 4.2.2 and 4.2.3 are not met, an explanation should be given. The following method is a normative requirement in ISO 14861. As some soft proofing solutions can be corrected for spatial uniformity. Therefore, this document is only used as an informative recommendation in the uniformity evaluation.
If the hardware-based look-up table shows that the correction is switched on (if available), this should be stated.
4.2.2 Evaluation of tonal uniformity
The screen is divided equally into 5 x 5 grids and the CIELAB value is calculated for each of the 5 x 5 grids, using the measured value of the central grid colour block at the maximum drive value as the light source reference white. Note that this method results in some CIEL's greater than 100. The AEoo colour difference formula was used to compare the colour difference between the 24 measured values and the central colour block value for each of the three different drive levels, i.e. white for the maximum drive level (8-bit display R=G=B=255); grey for approximately 1/2 of the maximum drive level (8-bit display R=G=B=127); and grey for approximately 1/4 of the maximum drive level (8-bit display R=G=B=127). Grey for approx. 1/4 maximum drive level (8-bit display R=G=B I 63); dark grey for approx. 1/4 maximum drive level (8-bit display R=G=B I 63). The ΔEo colour difference between the drive level white and the two greys should be less than or equal to 4.
4.2.3 Colour gradation evaluation (uniformity)
In 25 areas, calculate the grey/white ratio of the luminance measurements (cd/m') for 1/2 the maximum drive level (8-bit display R÷G=B=127) of grey and the maximum drive level (8-bit display R=G=B=255) of white. For non-central areas, the ratio T,(i=1,...,24) should be calculated, i.e. the individual grey/white ratio R,(i=1,...,24) divided by the reassuring grey/white ratio R,,minus 1, and then calculated by taking the absolute value, see equation (1). The measured value of the deviation of the colour gradation uniformity should be less than 10%, (i=1,...,24) the maximum value should be less than 0.10.
4.3 Cone characteristics
The instrument set-up and measurement geometry for cone of vision measurements should be in accordance with 5.4.2.
The cone of vision is based on a given viewing distance (default: 500 mm), calculated for the observer with a monocular view of the centre of the display, horizontal, vertical, diagonal direction of the maximum viewing angle (0.m.. , ... .m... . . n..s). In addition, the four 45° angles should be calculated for 0... .x (starting at 45° and 90° apart from each other), see equations (2) to (5). Maximum tilt angle (0...) depends on the screen size, the screen aspect ratio (display width to height ratio) and the viewing distance.
4.4 Reflective properties
The reflective properties of the display surface should be judged by visual observation with a point light source in the glare room when the power is switched off. The reflection of the screen to the point light source should feel blurred, and when deviating from the direction of the mirror reflection, the reflection should gradually and evenly diminish.
5 Test methods
5.1 Overview
For each display colour block (displayed in the centre of the image in turn), the measured spectral radiation value and (or) CIEXYZ value should be recorded. If required, the CIELAB value (calculated according to ISO 13655) can be calculated and the white point used should be given.
The display is calibrated and characterised to the target value specified for the particular application.
Note: If possible, the measuring instrument should be calibrated, by the equipment manufacturer. If this is not possible, use the interstage difference between the two instruments or the measured value of a field reference (e.g. a calibration) to make a calibration.
A visual comparison of the measured values with a field reference (e.g. calibration sample) can help to determine whether the measuring equipment is working correctly.
5.2 Preparation conditions and monitor settings
Prior to calibration and any measurements, the display should be switched on and warmed up as specified in 4.1. All measurements should be performed on a monitor that has been calibrated and stabilised in accordance with 4.1. Information describing and repeating the measurements (e.g. calibration procedure, software used, ICC characteristics file) shall be given together with the measurement data.
If not otherwise required, all measurements shall be made in the design viewing direction and in contact with the display panel. If the supplier does not specify the design viewing direction, measurements shall be taken in the direction normal to the display surface.
5.3 Colour gradation evaluation ("Ay") in relation to the viewing angle
In order to ensure a stable image appearance, it is essential that the change in colour gradation within the viewing angle and display area is as small as possible. The evaluation of the gamma difference (tonal reproduction) starts with the calculation of the normalised "relative" "luminance value at the centre of the display, which is then compared to the normalised luminance value at each viewing direction or viewing point.
Bibliography
Contents of GB/T 41598-2022
1 Scope
2 Normative references
3 Terminology and definitions
4 Requirements
5 Test methods
Bibliography
