GB/T 18721.4-2024Graphic technology - Prepress digital data exchange - Part 4: Wide gamut display-referred standard colour image data[Adobe RGB (1998)/SCID] (English PDF)

0.1 Standard digital test image requires

The standard test images provide a set of data that can be used for any of the following tasks.

--- Evaluate the color reproduction of the imaging system;

--- Evaluate color image output devices;

--- Evaluate the effectiveness of image processing algorithms applied to images;

---Evaluate the coding technologies required for storing and transmitting high-definition image data, etc.

As a standard well-defined dataset containing high-definition images with typical common image content, standard test images can make users confident that If the mapping is done properly, the image will produce a high-quality replica and provide a reasonable test of the evaluation task.

Any system, but the image set provided in this document can be expected to obtain reasonable testing with a limited image set. In addition, the existence of a standard set makes it possible to Users in the same region can compare images without exchanging images before copying.

However, different applications require standard image data to use different image encodings in different image states (see ISO 22028-1).

The user needs to select the encoded image data that is suitable for the evaluation task. Although it is always possible to transform the image data into another image state, Generally speaking, there is no consensus among experts on how to best accomplish this task. Therefore, in the various parts of GB/T 18721, Consider providing data for different image states.

GB/T 18721 "Printing Technology Prepress Data Exchange" is divided into 5 parts.

--- Part 1: CMYK standard color image data (CMYK/SCID);

--- Part 2: XYZ/sRGB coded standard color image data (XYZ/SCID);

--- Part 3: CIELAB standard color image data (CIELAB/SCID);

--- Part 4: Wide color gamut standard color image data for display [AdobeRGB (1998)/SCID];

--- Part 5: Scene-related standard colour image data (RIMM/SCID).

GB/T 18721.1 provides a set of 8-bit data per channel defined by CMYK dot percentage.

The colors are strictly defined only when printed, so these data are only suitable for evaluation of CMYK printing applications and cannot be transferred to other image states.

In fact, because in traditional printing applications, these image data are defined in the use of "Typical" ink systems and "typical" tone value mappings produce "satisfactory" images, while CMYK printing differs from this.

Printing systems that use inks of significantly different colors or produce very different tonal value mappings may not be useful without clear Without a defined color conversion, the data cannot be reproduced as a satisfactory image. Furthermore, with a bit depth of only 8 bits per channel, any any color changes may be affected by human intervention.

GB/T 18721.2 provides a set of test image data, which are encoded with XYZ values ranging from 0 to 65535 per channel, and Encoded in sRGB (defined in IEC 61966-2-1) with a bit depth of 8 bits per channel. (Due to the perceptual non-uniformity of linear color spaces the two sets of data are tested for the reference sRGB viewing environment and the reference sRGB CRT display.

The images are optimized and the XYZ tristimulus values are calculated relative to the CIE standard illuminant D65 before scaling.

It is based on a system that uses sRGB as a reference encoding and is therefore primarily suitable for the consumer market and for those whose color displays are used as "distributed" devices.

Although these systems have some applications in the printing industry, sRGB is definitely not the most common image encoding.

A significant disadvantage is that the gamut shape is very different from the typical offset gamut. This difference may require more vivid colors to be remapped to this will produce the best printing results for sRGB image data.

GB/T 18721.3 provides a set of test image data for a wide color gamut of reflective media, using D50 illumination.

The color depth is 16 bits per channel, while the color table and gradient map are 8 bits per channel.

In applications where the output color gamut plays a role, it is considered desirable to generate an image set that allows the entire color range close to the surface color gamut boundary to be in addition, from the perspective of color management, if the image uses D50, the main reference illuminant in printing and photography, the image it is beneficial for both image observation and measurement. For this reason, this illuminant has become the main reference illuminant for most color management applications.

This document provides a set of wide color gamut test image data encoded in AdobeRGB with a bit depth of 16 bits per channel.

Optimized for viewing in the AdobeRGB reference viewing environment and on an AdobeRGB reference monitor [in AdobeRGB (1998) Color Image Coding Specification]. In addition to the reference AdobeRGB display in the reference AdobeRGB viewing environment Furthermore, the preferred mapping of these images on any medium depends on the medium used and the viewing environment. Therefore, no mapping is provided for any other medium.

The chromaticity values associated with the reproduction on.

These images are designed primarily for systems that use AdobeRGB as the reference encoding and are therefore primarily suitable for the professional market and for broadband A system where the color gamut of a color display is a "distributed" device. This workflow is popular among professional photographers and is increasingly used.

In printing technology. The AdobeRGB reference display color gamut is closer to the typical offset printing color gamut than the sRGB reference display color gamut.

The difference may require color remapping between AdobeRGB images and sRGB images. AdobeRGB -encoded images are often used in print.

Images encoded in sRGB require less vivid color remapping when rendered. Therefore, the purpose of this document is to provide a wider range of colors than sRGB.

The bit depth of natural and synthetic images is 16 bits per channel.

Possible wide gamut color encoding options include AdobeRGB, opRGB (IEC 61966-2-5), and ROMM RGB.

(ISO 22028-2). This document is intended to allow images to be perfectly mapped onto a carefully defined wide gamut reference display. Therefore, compared to other the two options are more inclined to AdobeRGB. Because the color mapping integrity of opRGB is somewhat fuzzy, that is, it is not enough in output ROMMRGB (ISO 22028-2) is clear in output, but the reference media and viewing conditions are slightly different.

The medium is a virtual reflective print (ICC-perceptual reference medium).

GB/T 18721.5 provides a set of scene-related test image data encoded as RIMMRGB with a bit depth of 16 bits per channel.

These data are obtained by capturing natural scenes with various digital cameras and converting the captured camera's original RGB signals to obtain scene chromaticity estimates.

The accuracy of these estimates is affected by several factors, including how closely the camera's spectral sensitivity approximates the color matching functions of the human visual system.

the adequacy of the conversion from the camera raw RGB signal to the colorimetric estimate, optical effects such as off-axis signal attenuation, aberrations, and glare, and the noise in the camera signal. The transformation used to obtain the chromaticity estimate is a general transformation and is not optimized for the spectral characteristics of each scene.

Therefore, in some cases, the color estimation may be significantly biased. The image state of these data is scene-dependent because no the only processing of this data is based on visual evaluation.

This is done by applying gain to the camera channels individually to achieve the desired white balance, converting to scene-dependent, and then the overall gain is then adjusted in a linear, scene-dependent workspace, using the Color mapping transforms the example to view the image. For aesthetic reasons, a different white balance may be desirable in some cases.

The images provided in GB/T 18721.5 are mainly suitable for evaluating different output media.

Quality color mapping.

0.2 Characteristics of test images

The performance of any color reproduction system is usually measured both subjectively (by observing the final output image) and objectively (by measuring the control elements).

The requirement stipulates that the test images include natural scenes (pictures) and synthetic images (color charts and color gradient maps).

The results of image evaluation are greatly affected by the image content, so it is very important to ensure that natural images are of high quality and contain a variety of subjects.

However, it is difficult to generate natural scene elements containing the slight color variations required for test images in a single, relatively small sample set, as well as Therefore, although most images contain colors that extend to the boundaries of the gamut, this is usually only present in each the full reference color gamut can only be achieved by using composite images.

A survey was conducted of all TC130 member countries to determine the ideal image content and to request submission of appropriate images for consideration.

The resulting image set consists of 14 natural images, a color table, and a series of color gradient maps.

images with extreme highlight or shadow detail, neutral grays, brown and wood tones that are usually difficult to reproduce, memory colors, complex geometric shapes, the color chart and color gradients show the color gamut of the display using a wide color space.

0.3 File formats for digital test images

All images are composed of alternating pixel data (first R, then G, then B), with the origin of the data located at the upper left corner of the image.

The data are arranged in rows. These data are included in this document as a separate file. The image file format is in accordance with the specifications of GB/T 22113-2008.

If needed, images can be imported and manipulated through various image processing software tools and platforms commonly used in the industry.

See Appendix C for detailed information on the header.

Graphic technology Prepress data exchange Part 4.

Wide color gamut standard color image data for display [AdobeRGB (1998)/SCID] Important note. The electronic version of this document contains color information that is helpful for the correct understanding of this document. Therefore, users should consider using Print this document using a color printer. If you want to print in non-color, you can refer to the electronic version of this document.