ISO 22028-4:2023 写真およびグラフィック技術 — デジタル画像の保存、操作、交換のための拡張カラー エンコーディング — Part 4: European Color Initiative RGB カラー画像エンコーディング [eciRGB (2008)] | ページ 6

3.1

adapted white

colour stimulus that an observer who is adapted to the viewing environment would judge to be perfectly achromatic and to have a luminance factor of unity, i.e. absolute colorimetric coordinates that an observer would consider to be a perfect white diffuser

Note 1 to entry: The adapted white can vary within a scene.

3.2

additive RGB colour space

colorimetric colour space having three colour primaries (generally red, green and blue) such that CIE XYZ tristimulus values can be determined from the RGB colour space values by forming a weighted combination of the CIE XYZ tristimulus values for the individual colour primaries ここで, the weights are proportional to the radiometrically linear colour space values for the corresponding colour primaries

Note 1 to entry: A simple linear 3 × 3 matrix transformation can be used to transform between CIE XYZ tristimulus values and the radiometrically linear colour space values for an additive RGB colour space.

Note 2 to entry: Additive RGB colour spaces are defined by specifying the CIE chromaticity values for a set of additive RGB primaries and a colour space white point, together with a colour component transfer function.

3.3

colour component transfer function

single variable, monotonic mathematical function applied individually to one or more colour channels of a colour space

Note 1 to entry: Colour component transfer functions are frequently used to account for the nonlinear response of a reference device and/or to improve the visual uniformity of a colour space.

Note 2 to entry: Generally, colour component transfer functions will be nonlinear functions such as a power-law (i.e. “gamma”) function or a logarithmic function. However, in some cases a linear colour component transfer function can be used.

3.4

colour encoding

generic term for a quantized digital encoding of a colour space, encompassing both colour space encodings and colour image encodings

3.5

colour gamut

solid in a colour space, consisting of all those colours that are either: present in a specific scene, artwork, photograph, photomechanical, or other reproduction; or capable of being created using a particular output device and/or medium

3.6

colour image encoding

digital encoding of the colour values for a digital image, including the specification of a colour space encoding, together with any information necessary to properly interpret the colour values such as the image state, the intended image viewing environment and the reference medium

Note 1 to entry: In some cases, the intended image viewing environment will be explicitly defined for the colour image encoding. In other cases, the intended image viewing environment can be specified on an image-by-image basis using metadata associated with the digital image.

Note 2 to entry: Some colour image encodings will indicate particular reference medium characteristics, such as a reflection print with a specified density range. In other cases, the reference medium will be not applicable, such as with a scene-referred colour image encoding, or will be specified using image metadata.

Note 3 to entry: Colour image encodings are not limited to pictorial digital images that originate from an original scene, but are also applicable to digital images with content such as text, line art, vector graphics and other forms of original artwork.

3.7

colour rendering

mapping of image data representing the colour-space coordinates of the elements of a scene to output-referred image data representing the colour-space coordinates of the elements of a reproduction

Note 1 to entry: Colour rendering generally consists of one or more of the following: compensating for differences in the input and output viewing conditions; tone scale and gamut mapping to map the scene colours onto the dynamic range and colour gamut (3.5) of the reproduction; and applying preference adjustments.

3.8

colour space

geometric representation of colours in space, usually of three dimensions

[SOURCE:CIE Publication 17.4, 845-03-25]

3.9

colour space encoding

digital encoding of a colour space (3.8) , including the specification of a digital encoding method, and a colour space (3.8) value range

Note 1 to entry: Multiple colour space encodings can be defined based on a single colour space where the different colour space encodings have different digital encoding methods and/or colour space value ranges. (For example, 8-bit sRGB and 10-bit e-sRGB are different colour space encodings based on a particular RGB colour space.)

3.10

colour space white point

colour stimulus to which colour space (3.8) values are normalized

Note 1 to entry: It is not necessary that the colour space white point correspond to the assumed adapted white point and/or the reference medium white point for a colour image encoding.

3.11

extended gamut

colour gamut (3.5) extending outside that of the standard sRGB CRT display as defined by IEC 61966-2-1

3.12

gamut mapping

mapping of the colour-space coordinates of the elements of a source image to colour-space coordinates of the elements of a reproduction to compensate for differences in the source and output medium colour gamut (3.5) capability

Note 1 to entry: The term “gamut mapping” is somewhat more restrictive than the term “colour rendering” because gamut mapping is performed on colorimetry that has already been adjusted to compensate for viewing condition differences and viewer preferences, although these processing operations are frequently combined in reproduction and preferred reproduction models.

3.13

ICC profile

International Colour Consortium file format, used to store transforms from one colour encoding (3.4) to another, e.g. from device colour coordinates to profile connection space, as part of a colour management system

Note 1 to entry: See Annex A for more information.

3.14

image state

attribute of a colour image encoding (3.6) indicating the rendering state of the image data

Note 1 to entry: The primary image states defined in this document are the scene-referred image state, the original-referred image state and the output-referred image state. See Annex A for more information.

3.15

luminance factor

ratio of the luminance of the surface element in the given direction to that of a perfect reflecting or transmitting diffuser identically illuminated

[SOURCE:CIE Publication 17.4, 845-04-69]

3.16

medium black point

neutral colour with the lowest luminance that can be produced by an imaging medium in normal use, measured using the specified measurement geometry

Note 1 to entry: It is generally desirable to specify a medium black point that has the same chromaticity as the medium white point.

3.17

medium white point

neutral colour with the highest luminance that can be produced by an imaging medium in normal use, measured using the specified measurement geometry

3.18

output-referred image state

image state (3.14) associated with image data that represents the colour-space coordinates of the elements of an image that has undergone colour rendering (3.7) appropriate for a specified real or virtual output device and viewing conditions

Note 1 to entry: When the phrase “output-referred” is used as a qualifier to an object, it implies that the object is in an output-referred image state. For example, output-referred image data are image data in an output-referred image state.

Note 2 to entry: Output-referred image data are referred to the specified output device and viewing conditions. A single scene can be colour rendered to a variety of output-referred representations depending on the anticipated output viewing conditions, media limitations, and/or artistic intents.

Note 3 to entry: Output-referred image data can become the starting point for a subsequent reproduction process. For example, sRGB output-referred image data are frequently considered to be the starting point for the colour re‑rendering performed by a printer designed to receive sRGB image data.

3.19

tristimulus values

amounts of the three reference colour stimuli, in a given trichromatic system, required to match the colour of the stimulus considered

[SOURCE:CIE Publication 17.4, 845-03-22]

3.20

veiling glare

light, reflected from an imaging medium, that has not been modulated by the means used to produce the image

Note 1 to entry: Veiling glare lightens and reduces the contrast of the darker parts of an image.

Note 2 to entry: In CIE 122, the veiling glare of a CRT display is referred to as ambient flare.

3.21

viewing flare

veiling glare (3.20) that is observed in a viewing environment but not accounted for in radiometric measurements made using a prescribed measurement geometry

Note 1 to entry: The viewing flare is expressed as a percentage of the luminance of adapted white.