GB/T 12823.3-2025Photography and graphic technology - Density measurements - Part 3: Spectral conditions (English PDF)

0.1 Overview

The ISO 5 series consists of four parts that specify the geometric conditions and spectra for optical density determination used in black-and-white and color imaging applications.

The term "ISO 5 standard density" is used in the ISO 5 series to refer to such standards.

When discussing basic optical principles and concepts, "density" is used as a more general term to refer to its traditional meaning.

The complete definition of ISO 5 standard density values requires both the geometrical conditions of the measurement system and its spectral conditions.

ISO 5-4 describes the geometric conditions for ISO 5 standard densities in transmission and ISO 5 standard densities in reflection, respectively. This document specifies the geometric conditions for ISO 5 standard densities in transmission and reflection.

The spectral conditions for density measurements according to ISO 5 are given. For these conditions, the term "state density" is used to distinguish them.

GB/T 12823 "Measurement of density in photographic and graphic techniques" adopts the ISO 5 series and aims to establish a standard applicable to the field of photographic and graphic techniques.

The criteria for medium density measurement are proposed to consist of four parts.

--- Part 1: Geometric and functional symbols. The purpose is to establish the geometric conditions involved in density measurement and the representation of related functions.

--- Part 2: Geometric conditions for transmission density. The purpose is to establish the geometric conditions for transmission density in density measurement.

--- Part 3: Spectral conditions. The purpose is to establish the spectral related conditions for density measurement.

--- Part 4: Geometric conditions for reflection density. The purpose is to establish the geometric conditions for reflection density in density measurement.

0.2 Density measurement

In photographic applications, optical density is a measure of the modulation of light or radiation flux by an area of a recording medium. Density Measurement it is important in many ways, such as evaluating the brightness and darkness of an image, predicting the performance of film or paper in the printing process, and in color processing.

Density measurement is used in all aspects of image color measurement during processing. If visual effects are important, measure the spectrum.

The conditions need to simulate some suitable lighting and the spectral sensitivity of the human eye. For printing operations, it is necessary to simulate the light source used for printing operations.

Spectral power distribution and spectral sensitivity of printing materials. When evaluating the original material used for color separation reference charts, the spectrum of the light source and the color separation medium the sensitivity and spectral transmittance of the trichromatic filters (and other optical components) also need to be simulated.

In order to provide users with such requirements with measurement data that can be correctly interpreted, it is necessary to provide standard specifications for measurement procedures.

This specification is provided in ISO 5.In this document, a variety of spectral conditions are specified, along with a definition of the spectral response for each spectral condition.

NOTE. The spectral response is a function of the spectral corrections of the optics and filters between the sample plane and the photodetector, and the spectral sensitivity of the photodetector.

In some applications, it is desirable to match the spectral response to the spectral sensitivity of the intended receiver (human eye, photographic paper, etc.).

In this paper, the spectral response is somewhat arbitrarily defined (although often related to the spectral properties of the medium being measured) to facilitate process control problems.

The spectral product is therefore arbitrary in these cases.

The various spectral conditions specified in this document have been shown to be suitable for the corresponding applications. For example, to obtain the sensitivities of films and photographic papers the sensitivity curve produced by the performance also requires some kind of density measurement. Density measurement can also be used for tone reproduction analysis and various operations.

Monitoring (such as photoprocessing, lithography, gravure and screen printing). In graphic technology, reflection density measurement is used to control ink thickness.

Film thickness, or more generally, the amount of colorant per unit area, is used to control the hue value or other parameters of the measurement.

In the early days of density measurement, the spectral conditions of the instrument were mainly determined by the type of filter used in the densitometer.

The spectral response of the photoelectric receiver, the spectral power distribution of the light source and the inserted optical elements are completely consistent.

Very difficult. Modern density measurement standards only stipulate that the spectral product of all components is equal to a certain set of publicly published data.

Technical specifications provide flexibility for density meter manufacturers to improve the accuracy and precision of their products.

The production of quasi-reference materials is also conducive to the measurement of standard quantities.

0.3 Density calculation

In this revision of this document, it has been recognized that the use of simple filter instruments is decreasing. The more common "measurement" ISO 5 standard the density method is to calculate the standard density based on the spectral reflectance factor or spectral transmittance measurement value of the sample.

The spectral reflectance factor or spectral transmittance in the wavelength range is multiplied by the spectral product (defined as the spectral product between 10 nm) provided in the previous version of this document.

This calculation is achieved by summing the products after converting the light into the linear domain. However, such a calculation procedure is not strictly accurate.

The spectral product is the physical spectral property of a device obtained by combining spectral data related to its light source and optical components, with an interval of 10nm.

If the results of measurements on a sample made using an apparatus conforming to this document are compared with results calculated from spectral data of the same sample, the calculation results are obtained by multiplying the spectral data and the 10nm spectrum over the entire wavelength range.

Although this error may be very small (perhaps to the third decimal place), but this situation is still undesirable.

Therefore, for computational purposes, the older, coarsely sampled spectral product is supplemented in this revision with the concept of a spectral weighting factor.

To achieve these goals, the 10 nm spectral products defined in this document and previous versions have been re-evaluated using the method specified in Appendix C.

The data were expanded to 1 nm intervals in the data domain, converted to linear form, and normalized to a peak value of 1.Additional spectra were then derived from these data.

Weighting factors are used for data with measurement intervals greater than 1 nm, and the method specified in Appendix A is used to calculate from these weighting factors the any density will exactly match the density value measured using an instrument with a filter that fits the spectral product exactly to 10 nm.

In the linear domain, the value of the 10 nm spectral weighting factor is slightly different from the value of the 10 nm spectral product because the calculation of the ISO 5 standard density (with the direct measurement of ISO 5 standard density is in contrast to the spectral weighting factors and spectral reflectance factors measured at discrete intervals within the appropriate wavelength range.

The spectral weighting factor includes the spectral product of the densitometer and the spectral reflectance factor or spectral transmittance.

The coefficients of the polynomial are related to the ratio, so some wavelengths in the table may have small negative values. This does not cause the density of any typical medium to be negative.

The sum of the weighting factors is always positive, and the logarithmic value of the whole spectrum remains at an appropriate level.

It is worth noting that the relative value of the spectral product (normalized to the peak value) does not change. In addition to linear scaling, the interpolation of 1 nm intervals in any case, the 10nm spectral product value will not be changed. These 10nm spectral product data are still considered to be the Therefore, the spectral products that the filter instrument is expected to match are still the same, but they are now also defined as Finer data interval. At a data interval of 1 nm, the spectral product can also be used as a spectral weighting factor to obtain a spectral image with the same spectral resolution.

The calculation is performed based on the measured spectral data (or spectral data interpolated to the same spectral resolution as in Appendix C).

The spectral data are usually sampled more coarsely than this, so the 10nm and 20nm spectral weighting factors are calculated from these 1nm data tables.

This approach is consistent with recent practice in colorimetry and provides a "best" approximation to calculations performed with finer resolution data.

These weighting factors will also provide data consistent with a "filter" instrument that conforms to the 10 nm spectral product defined in this document.

It is recommended to calculate the ISO 5 standard by using the spectral reflectance factor or spectral transmittance data collected at 10nm or 20nm wavelength intervals using the actual instrument.

When using quasi-density, weighting factors are used instead of spectral products.

For the calculation of the spectral weighting factors and further discussion in this document, see Appendices A, B, and C.

0.4 Lighting source

The incident flux for transmission ISO 5 standard density measurements is traditionally specified to have a different spectral power distribution than that used for reflection ISO 5 standard density measurements.

Although both are based on Planckian radiation at a temperature of approximately 2856 K as defined in ISO 11664-2, the spectral power distribution specified in ISO 11664-2 is not the same as that specified in ISO 11664-2.

This is the spectral distribution of the CIE standard illuminant A, recommended by the International Commission on Illumination (CIE) in 1931 and can be used in the spectral distribution used for transmission density measurement is approximated by a gas-filled spiral tungsten filament lamp operating at a distribution temperature of 2856 K.

Correction to protect the sample and optical system from overheating. Providing a spectral power distribution close to the specification is important in a densitometer because Many printing plate materials, especially printing substrates, and some photosensitive materials contain optical brighteners (OBAs) and have obvious fluorescent effects.

If there is no fluorescence effect, the spectral power distribution of the incident flux is not important and can deviate from the specified spectral power distribution as long as the in addition, when there is no fluorescence effect, the same spectral reflectance factor data can be used to calculate the colorimetric and reflectance ISO 5 Standard density.

In this revision of this document, the use of CIE standard illuminant A for reflectance measurements and the use of corrections has been retained for photographic applications.

Requirements for transmission measurements with CIE standard illuminant A. However, in order to maintain consistency with instruments used for colorimetric measurements according to ISO 13655, to ensure compatibility, this revision introduces three additional lighting conditions for graphic technology applications. These are based on the conditions specified in ISO 13655.

The following are the components.

---M1.Standard illuminator D50;

---M2.Requires that the lighting only contains radiant power within the wavelength range above 400nm;

---M3.Add polarization filter to M2 lighting condition.

For materials without optical brightening agents (OBAs), these changes in lighting have no effect, but since the levels of OBAs present are usually it is unknown, so it is important to clarify the lighting conditions used. Some lighting systems use light emitting diodes (LEDs) as lighting sources and meet the M2 lighting requirements.

Comparison of measurements made under different lighting conditions, especially those with Special care should be taken when making process control measurements between colorants with significantly different spectral characteristics.

0.5 Calibration standard

Primarily concerned with reflection density. Many older reflection density standards specified the use of barium sulfate (BaSO4) as the reference standard. However, the pressed the barium sulfate produced is easily broken and varies with the batch number and pressing method. Its reflectance will drift significantly in the first few days after pressing.

In 1969, CIE recommended the ideal diffuse reflectance factor. The corresponding reflection density is based on the ideal diffuse reflector. This is defined as Calibration reference in file.

Commonly used reflection densitometers typically use materials supplied by the instrument manufacturer or certified reference materials (CRMs) available from a variety of sources.

These working standards are calibrated against reference devices, which are calibrated by national laboratories using absolute methods.

Density measurement for photography and graphics Part 3: Spectral conditions