JP2005045483A - Color management by reference region - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop color management which is flexibly adaptive to a different input device (image capturing device) and an output device (image reproduction system) as to the photography field meaning image data representing a photographic image captured by an image capturing device such as a photographic camera, a video camera, a digital camera, and a scanner. <P>SOLUTION: In a color managing process for image data representing color values of an image, image data wherein a 1st color value which represents a 1st position of a 1st color space and is positioned in an input color area are received to convert the 1st position to a reference position through input conversion, and then the conversion is so performed that the reference position is set in a 2nd color space and a 2nd color value is described, and a reference color area prescribes color values which can be reproduced with the reference position, which is converted to a 3rd position through output conversion. Consequently, the output conversion is so performed that the 3rd position is set in a 3rd color space and a 3rd color value included in an output color area of the output device is described. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

上の式で使用されているＷｉは例えばＷ_ＲＧＢ であり、上式のｄｉ は例えばｄ_ＲＧＢ であり、“ｉ”はｉ番目のｓＲＧＢデータを意味している。Ｗｉのコースは図４ではｄｉの関数として示されている。明白に示されているように、中心近辺の“プラスティック変形”はほとんど存在しないか、中心付近で非常に僅かにのみ存在し、その後、最大距離の約３０％から外方向に減少する。したがって大きい距離では、出力基準領域の影響は距離の増加と共に増加し、それによって入力基準領域の影響は距離の増加と共に増加するが、少なくとも小さい距離では優勢である。
【００５５】
以下の条件を満たす他の加重関数も適切である。
Ｗｉ＝表面上で１，０、
Ｗｉ＝キューブの中心で０，０、
Ｗｉは単調に増加、
ｄｉにおけるＷｉの第１の導関数は全て０＜ｄｉ＜１では特異ではなく、特に（予め選択された）数字的処理では適切な予め定められた値の範囲内である。
【００５６】
１例を基準領域がＸＹＺ領域全体をカバーする以下の説明で説明する。
【００５７】
ＸＹＺ領域は全て可能なカラーを含んでいる。変換を３つのステップで説明する。
【００５８】
変換は標準的な公式にしたがってＣＩＥＬＡＢからＸＹＺへ実行される。入力データがＣＩＥＬＡＢ形態で存在していないならば、ＣＩＥＬＡＢからＸＹＺへの変換は例えば前述した先行する例のように実行される。このＬ_{ｓａｍｐｌｅ}値の変換から生じるＸＹＺ値はｘｙｚ_{ｓａｍｐｌｅ}と呼ばれる。
【００５９】
続いて、ｘｙｚ_{ｓａｍｐｌｅ}値はｘｙｚ_{ｍａｐｐｅｄ}値へ変換され、それによってカラーの色相は維持される。ｘ＝０…１を有するグレード軸（ｘ，ｘ，ｘ）を含んでいるＸＹＺの半平面内では、全てのカラーはあるカラーの色相を含んでいることが説明されている。図５はこのグレー軸を含むこのような半平面を示している。グレー軸に位置しない図５で示されている半平面の全てのカラーの値は同一のカラーの色相を有している。
【００６０】
第３のステップとして、ＣＩＥＬＡＢカラースペースへ戻す変換は標準的な公式にしたがって実行される。ｘｙｚ_{ｍａｐｐｅｄ}値はそれによってＬ_{ｍａｐｐｅｄ}値へ変換される。
【００６１】
要約すると、ｘｙｚ_{ｍａｐｐｅｄ}へのｘｙｚ_{ｓａｍｐｌｅ}変換は一定のカラー色相により半平面で記述される。直線は２つの点を通過する位置ｘｙｚ_{ｓａｍｐｌｅ}により各カラー値に対して規定されることができる。１つの点は基準点ｘｙｚ_{ｒｅｆｅｒｅｎｃｅ} （例えば０．５，０．５，０．５）と呼ばれ、他方の点はｘｙｚ_{ｓａｍｐｌｅ}と呼ばれる。この線は点ｘｙｚ_{ＲＧＢ−Ｓｕｒｆａｃｅ} で入力カラー領域（ＲＧＢ領域）と交差し、ｘｙｚ_ｃｕｂｅでＸＹＺキューブと交差する。
【００６２】
マッピング関数ｘｙｚ_{ｍａｐｐｅｄ}＝ｆ（ｘｙｚ_{ｓａｍｐｌｅ}）は直線上の全ての点に対して適用される。この関数は以下の境界条件で規定されることができ、即ちｘｙｚ_{ＲＧＢ−Ｓｕｒｆａｃｅ} はｘｙｚ_ｃｕｂｅにマップされ、ｘｙｚ_{ｒｅｆｅｒｅｎｃｅ} 付近の全ての点は変更されない状態である。さらに前述したように、カラーの色相は変更されないで維持され、これは全てのカラー変換が半平面内で実行されるので演繹性を確実にする。
【００６３】
図６はｆに対する典型的なマッピング関数を示している。連続的なラインはｘｙｚ_{ｓａｍｐｌｅ}に基づいた関数ｆのコースをマークしている。破線は１：１のマッピングのケースをマークしており、それはｘｙｚ_{ｓａｍｐｌｅ}＝ｘｙｚ_{ｍａｐｐｅｄ}を意味し、これはそれぞれの方向で入力ＲＧＢ領域が基準領域に等しいときのケースである。
【図面の簡単な説明】
【図１】本発明のプロセスにしたがってカラースペースプラットフォームを介して異なる入力装置と異なる出力装置の結合を示した図。
【図２】本発明のカラー管理プロセスを示した図。
【図３】第２のカラースペースのｓＲＧＢカラー領域と写真紙領域を示した図。
【図４】基準位置の生成で使用される加重関数のコースを示した図。
【図５】色相が維持される第２のカラースペースのマッピングを示した図。
【図６】基準位置を得るためのさらに別のマッピング関数を示した図。[0001]
BACKGROUND OF THE INVENTION
The present invention processes image data to achieve the best possible color reproduction, in particular image data representing photographic images as captured by image capture devices such as photographic cameras, video cameras, digital cameras, scanners, etc. Is related to the field of photography.
[0002]
[Prior art]
The image data is used to control an image reproduction system such as a photographic printer, a photo lab, a mini lab, a color laser printer, an ink jet printer, a monitor (liquid crystal display and CRT monitor), and the like. The present invention is used, for example, to improve the color impression of an image reproduced by an image reproduction system on a medium (paper, photographic paper, foil, etc.) or a screen (monitor). In particular, the present invention provides a color space (input region) and image reproduction that can be captured and / or output by an input device (image capture device such as a scanner, digital camera, etc.) when the input region does not match the output region. This is related to the color space (output area) that can be reproduced by the system. The present invention also relates to the processing of images captured by an input device and residing in a device dependent color space so that they can be output as optimally as possible by an image reproduction system that defines the device dependent color space.
[0003]
The processing of sRGB image data represents an example of the field of use of the present invention described above, for example, image data is output by a digital camera, processed by an image reproduction system (eg, a photographic printer or minilab), and thereby represented by the image data. The image can be generated by photographic paper.
[0004]
The connection between the sRGB color space and, for example, the XYZ color space is described in, for example, the literature (“The Creation of the sRGB ICC Profile”, Mary Neilson, Michael Stokes, Hewlett Packard Company No. 5, Boise Id. Page, 1998). The sRGB color space is particularly popular for the following reasons.
a) The main phosphorescent color transfer function and chromaticity of a cathode ray tube (CRT monitor) is very similar to the sRGB color space. Thus, the image can be shown with reasonable quality on the monitor without the need for color mapping by profile. Since the sRGB color space is now very common, image data input via the sRGB interface is supported even in technical fields with transfer functions that deviate significantly from sRGB, such as LCD monitors or plasma monitors. Yes.
b) Manufacturers of digital scanners, monitors and digital cameras often give them as an additional feature of devices that output sRGB image data.
c) Almost all computer programs available on the market support color spaces such as sRGB.
[0005]
[Problems to be solved by the invention]
Unfortunately, the sRGB color space and the photographic paper color space (eg, silver halide paper) are very different (see FIG. 1). The wide area of sRGB color space, especially bright pure colors, is also outside the area of photographic paper. Conversely, monitors usually cannot reproduce the dark color of photographic paper. The color space of inkjet and color laser printers is also very different from the sRGB color space.
[0006]
The purpose is color management to match the device-dependent color spaces with each other. Each device typically has its own color profile. The connection between the input and output profiles is preferably made in color management by a color space independent of the input and output devices. This color space is also called profile connection or PCS. Input and output devices typically have different areas. The final mental concept of color management is described, for example, in the literature ("Color Management: Current Practice and the New Standard", Michael Has, Todd Newman), which can be found at the Internet address www. color. org / wpapaer1. It can be called with html. In a basic concept called colorimetric matching, the colors in both areas are transferred while maintaining the color values as much as possible. Colors that cannot be generated by certain output devices are mapped to region boundaries. The term “absolute rendering purpose” is used in this process. The compromise on colorimetric matching is usually done to match the white point of the two devices (“relative rendering purposes”). Yet another matching can also be performed by matching the darkest gray tones of the two devices ("Perceptual rendering purposes"). Such color management systems and their standardization (ICC) are used in the printing industry. However, the adoption of this objective in the development industry creates several drawbacks.
a) Some components of the development system are not stable enough for accurate color reproduction. For example, in the case of a photographic paper processor, its stability often does not meet the requirements of previous color management systems. Or, for example, information about the color profile of an input device for film is not known with sufficient accuracy, or much changes.
b) The output device uses only these colors, which are common to the output device and the input device. The full potential of the output device is therefore not used. However, the present inventor, particularly in the field of photography, allows the customer to perceive the color impression of the image more comfortably and positively when the image reproduction is performed in a larger number of colors, i.e. to improve the color potential of the output device. Recognized to use. This comfortable impression is even more important for the customer than the accurate reproduction of the colorimetry in the image data, as in the printing industry.
c) In these regions of the input device color space where the color values are subject to more intense changes to fit the region of the output device, the details of color transition and color nuance are lost.
d) If digital data is obtained from a film negative or by scanning a color photograph and outputting in digital form such as a CD, the negative or printout or print of the film usually does not correspond to the area of the scanner. Information is lost. Therefore, the output format of the scanner is usually sRGB. In the following steps, if a reprint or new printout is performed based on the digital data, the result obtained is not the same as if the printout is performed directly, for example based on a film negative.
e) Common implementations of color processing modules used in color management, for example using a three-dimensional reference table (3D-LUT), often have problems with accuracy near area boundaries and number stability. This is because the region mapping performed there produces a single first deviation at the region limit.
[0007]
An object of the present invention is to perform color management that can be flexibly adapted to different input devices (image capture devices) and output devices (image reproduction systems). Furthermore, a preferred object of the present invention is to at least partially overcome one of the aforementioned disadvantages of the prior art.
[0008]
[Means for Solving the Problems]
The present invention relates to a process for processing image data, and more particularly to a color management process. Image data represents the color values of an image, particularly a photographic image. In particular, color values of photographic images captured by an image capture device are processed according to the present invention to provide output devices, particularly image reproduction systems (photo printers, photo labs, monitors, printers, color laser printers, ink jet printers, etc.). Matched to the possibility of image reproduction. The color space that can be managed by the device is called the color area of the device. The color gamut of an input device (eg, an image capture device) contains all the color values, which can be captured and output by the input device. The image data output by the input device is processed by the process according to the invention and therefore indicates the color area of the input device, which captures and / or processes in particular photographic information. The image data received by the process according to the invention can be received in different ways, in particular by a data carrier such as a CD, a network, the Internet or by a direct connection to an image capturing device such as a scanner or a digital camera. it can. Image data input to the process is processed by the process according to the present invention in a way that the image data output by the process represents color values that are better aligned with the color gamut of the output device than the image data input to the process. Is done. The color area of the output device, i.e. the so-called output color area, preferably contains all color values, which are processed (e.g. reproduced, stored and / or transmitted) by the output device when image data is input to the output device. ).
[0009]
The image data is two-dimensional as usual or three-dimensional (for example, a hologram).
[0010]
The image data received by the process according to the invention represents the so-called first position of the first color space and describes the first color value. These color values have the property of being located in the input color area.
[0011]
According to the process according to the invention, the first position is in a first step which is transformed by input conversion to the second position, these are called reference positions. The input conversion is preferably performed in such a way that the reference position is in the second color space. Therefore, conversion from the first color space to the second color space is performed. The first and second color spaces are preferably different. The first color space is basically a device-dependent color space of the input device, and the second color space is an independent color space of a device such as CIE lab or XYZ.
[0012]
In the second step, the reference position is converted by output conversion to the third position. The conversion is preferably performed such that the third position is in the third color space. Therefore, conversion of the reference color space to the third color space is performed. The second color space and the third color space are preferably different. The third color space is a device-dependent color space that preferably matches the output device (eg, RGB color space). It is preferable that at least the first or third color space is different from the second color space. At least a portion of the first position and / or the first color value is preferably different from the second position and / or the second color value. At least a portion of the third position and / or the third color value is preferably different from the second position and / or the second color value. It is preferable that at least a part of the first position or the third position is different from the second position. Preferably, at least the input or output transformation is not an identity transformation, or most transformations are identity transformations. For example, the output conversion is an identity conversion if the output color area corresponds to the reference color area. If the input color area corresponds to the reference color area, this input conversion is also an identity conversion. For example, the output device may be a data recording device or a network interface capable of recording or transmitting image data including, for example, a reference color area. Correspondingly, the input device may be a data reading device or a network interface for reading or receiving image data spanning a reference color area, for example. In this way, data representing the reference position can be stored / transmitted and / or read / received. However, the reference color area is preferably formed in a manner that does not match the input color area and the output color area.
[0013]
The input conversion according to the present invention includes a conversion from a first color space to a second color space (referred to as “conversion of the first color space”) and a mapping in the second color space (“first mapping”). At least intelligently divided). Thereby, the color values are preferably not changed during the conversion from the first to the second color space. The resulting position resulting from the conversion is hereinafter referred to as the input conversion position. The mapping performed thereafter in the second color space is at least partially guided by color value changes. The decomposition from input conversion to input conversion and mapping will be described below. This is purely illustrative because, for example, the first color space transform and the first mapping in the second color space can be arithmetically combined into a single uniform input transform.
[0014]
The output conversion according to the invention also includes a mapping in the second color space (referred to as “second mapping”), a conversion from the reference color space to the third color space (“conversion of the second color space”) Called) at least intelligently. Mapping performed in the second color space is at least partially guided by changes in color values. In contrast, the color values are preferably not changed during the conversion from the second to the third color space. The resulting positions from the mapping are hereinafter referred to as output conversion positions, which are then transferred to a third position by conversion to a third color space. The decomposition of the output transform into a mapping and transform is described below, which is a combination of the second mapping in the second color space and the second color space transform, for example, arithmetically into a single uniform output transform. This is a pure illustration.
[0015]
Thus, according to the process according to the invention, the matching of the color value with a preselected color area called the reference color area is performed, for example, after input conversion to the second color space according to the first mapping described above. This color area acts as a “bridge” of “mediation” between the input color area and the output color area. Both reference positions relate to the color space and the area independent of the input and output devices. Therefore, not only the color space platform but also the “regional platform” exists. Preferably, the color value represented by the input conversion position corresponding to the first color value is matched in the reference color space with the color reproduction possibilities indicated by the reference color region. This is preferably performed by a first mapping that maps the input conversion position of the reference color space to another position that is the aforementioned reference position. The reference position indicates a reference color value in the reference color space. The mapping is designed such that the reference color value (also referred to as “second color value”) is on the reference color region or its boundary. The reference color area is preferably designed to include at least all of the considered color values of the input color area and the output color area which are predetermined.
[0016]
The reference color region is preferably in addition to the input color region (or in addition to the number of merge sets or a plurality of predetermined input color regions) and the output color region (or number of merge sets or a plurality of predetermined outputs). Color regions), which are not included in the input color region (or the number of merge sets or multiple input color regions) and / or in addition to the output color region (or merge set) Including at least a portion of the input color region (or the number of merge sets or the plurality of predetermined input color regions) in addition to the number or the plurality of predetermined output color regions. (Or the number of merged sets or a plurality of predetermined output color areas), particularly preferably the output color Includes frequency (or number or more pre-output color area defined merger set) and the input color space (or merged set number or more of input color space predetermined) at least approximately. The reference color gamut preferably includes color values from the output color gamut (or the number of merged sets or a plurality of pre-determined output color gamuts), which are input color gamuts (or the number of merged sets or a plurality of pre-set color areas). Not included in the defined input color gamut) and / or include color values from the input color gamut (or a number of merged sets or a plurality of predetermined input color gamuts), which are output color gamuts (or The number of merge sets or a plurality of predetermined output color areas).
[0017]
The first mapping in the reference color space is preferably designed with full single shots, which means that in particular lost color information has been lost.
[0018]
The third position is preferably used to determine image control data for controlling an output device having an output color area.
[0019]
The reference position then preferably serves as a base for obtaining processed image data, which controls the output device. The output information is designed such that the third color value is within the output color region (or its boundary). Preferably, the second mapping in the reference color space is designed as a full shot, which means that there is no missing color information.
[0020]
Input conversion and output conversion are preferably designed in full single shot. In this way, the processing of the image data is reversible and therefore no color information is lost even in a long processing chain. Full-single-shot conversion is particularly effective when data is output from an input device such as a film scanner and on the other hand from an output device such as a photographic printer and simultaneously stored via a digital medium such as a CD. When the image is later output again from this digital medium on an output device, in particular the same output device, it ensures that no color information is lost. During the period when it is read from the digital medium (in this function, the input device), the conversion must correspond to the inverse conversion of the record (in this function, the output device), which requires a full single copy. Thus, according to the present invention, the same device can be used as an input device and as an output device.
[0021]
According to the invention, the input and output transformations, in particular the first and second mappings in the reference color space, are designed according to predetermined limit states and / or characteristics. Preferably, the first position (first color value) is present in a predetermined region or part of the first color space, and / or the input transformation and / or the reference position (second color position) ) Is located in a predetermined region or partial space of the reference color space, the reference color value is essentially the same as the first color value. In particular, the second color value (also referred to as the second color value) is at least essentially the same as the first color value when the first and / or reference color value represents or is near gray. Also, when the color value (represented by the first position and / or the reference position) is located in the input color area and / or the internal area of the reference color area (especially the subspace located inside including the intermediate gray), There is no change in color value or no significant change. This interior region is particularly remote from the boundary surface of the reference color region and / or the input color region. The distance is for example less than 50, 30 or 10% of the minimum distance with respect to the boundary of the input color area and / or the reference color area.
[0022]
The input conversion is therefore preferably performed position-dependent, meaning that it depends on the position of the first position and / or the reference position.
[0023]
The first color value located at the boundary surface of the input color region is mapped by mapping of the input conversion of the reference color space, preferably to the boundary (boundary surface) of the reference color region.
[0024]
The reference color value is preferably when the third position (third color value) is located in a predetermined area, or is located in a part of the first color space, and / or output conversion and / or When the reference position (second color value) is located in a predetermined area or a partial space of the reference color space, it is at least basically the same as the third color value. In particular, the reference color value is at least essentially the same as the third color value when the reference color value and / or the third color value represents or is near gray. Also, when the color value (represented by the third position and / or reference position) is located in the output color area and / or the interior area of the reference color area (especially the subspace located inside including intermediate gray), There is no change in color value or no significant change. This interior region is particularly remote from the boundary surface of the reference color region and / or the input color region. The distance is for example less than 50, 30 or 10% of the minimum distance with respect to the boundary of the input color area and / or the reference color area.
[0025]
The input conversion is therefore preferably performed position-dependent, meaning that it depends on the position of the first position and / or the reference position.
[0026]
Reference color values located at the boundary surface of the reference color region are mapped by mapping the output transformation of the reference color space, preferably to the output color region boundary (boundary surface).
[0027]
Preferably, plastic deformation of the input color region to the output color region is performed through the reference color region. This deformation in the central area, particularly in the vicinity of the gray axis, that is, the change in the color value, as described above, is the degree of change in the color value in such a way that the input color area and the output color area are different in each color value range. Is preferably formed only in a short period of time when increasing toward the boundary of the input color region. Therefore, the first color value located inside the input color area and in the vicinity of the boundary of the input color area is preferably the second color value located within the boundary of the output color area and again close to the boundary of the output color area. Is mapped to
[0028]
As described above, plastic deformation of the input color region through the reference color region to the output color region is preferable. In other words, the adjacency relationship is preferably maintained, so that preferably the color value is closer to the boundary of the color region and / or the output region is further different from the input region of this color value range, depending on the mapping. The change in the distance between adjacent color values is correspondingly larger or possibly compressed.
[0029]
When standards are made in this application for distances between color values or in the color space, this is defined according to the CIE standard for human color perception, and in particular means color distance.
[0030]
For example, the CIE LAB color space is a color space adapted to the color sensitivity of the human eye. Each color pair separated by a Euclidean distance of 1 in the CIE LAB color space appears to human observers to be equally spaced from one another. A trained observer is under ideal conditions at that position to discriminate the collar to approximately:
[0031]
ΔE = [(ΔL²+ Δa²+ Δb²]]^1/2= 1
The first mapping in the reference color space is preferably designed such that the input transformation including the mapping is preferably constant. The first derivative of the input transformation is also preferably constant and not singular. This applies to the associated values (ie the first color value in the input color area and the second value in the reference area).
[0032]
The second mapping in the reference color space is preferably designed such that the output transformation comprising the second mapping is preferably constant. Preferably, the first derivative of the output transform is also constant and not singular. This preferably applies at least for the associated value space (ie the second color value in the reference area and the third color value in the output color area).
[0033]
The reference color region is preferably designed to include not only one but also input color regions of a plurality of input devices. Image data originating from a plurality of input devices is thereby preferably processed according to the process of the present invention in color management of image data. The reference color region preferably includes output color regions of a plurality of output devices. Flexible color management of multiple output devices can thereby be realized. Thus, the image data of a plurality of input devices having different color gamuts are preferably flexibly adapted to each desired output device of the plurality of output devices by the process of the present invention.
[0034]
The first and second mappings in the reference color space are preferably designed such that the first, second and third color values have the same or at least (very) similar hues. Therefore, the conversion is performed only in the color plane of the reference color space where the hue is constant. The basic characteristics of the color information are thereby maintained, while the output device dynamic with respect to luminance and / or color saturation can be fully utilized.
[0035]
When manipulating color values that affect a part of the image, i.e. locally affecting color values, in particular local operations, these are based on a reference color space, preferably a reference position, preferably a reference region. Is preferably performed in the reference color space. Based on the manipulated reference position, the image control data is then determined according to one of the aforementioned processes. This has the advantage that the operating process can be used independently of the input device and the output device. The manipulation process is basically a process for local darkening and / or lightening of an image, for example a process based on recognition of the image content, such as a process of removing the red-eye effect, for example a “memory color such as skin color It includes a process based on the perception of “ Typically, a process involving local changes in image characteristics within the image, such as local sharpness changes, local color value changes, local brightness changes, and the like, is included.
[0036]
In particular, the present invention relates to a program that causes a computer or data processing apparatus to execute a process when the computer or data processing apparatus executes the process. In particular, the present invention relates to a computer storage medium that stores the aforementioned processing, such as CD, DVD diskette, etc., and includes information corresponding to a program. Furthermore, the present invention relates to a signal wave that contains and / or transfers the above-mentioned program as information, in particular a signal wave that represents the transmission of the program over a network such as the Internet.
[0037]
The present invention further relates to a computer storing the aforementioned program.
[0038]
The present invention also includes, for example, an ink-jet color printer or a laser color printer, or a photolab, in particular a minilab, ie a photographic paper (eg DMD photographic printer) color printer such as a lab or a large lab with a small floor surface of only a few square meters or less than 1 square meter. The present invention relates to a photographic printer that operates according to the above. The aforementioned photographic printers, color printers or so-called photo labs specifically include devices for receiving image data. This device is for example an interface for receiving data from a network, in particular the Internet, for example a memory reading device such as a CD reading device or a memory card reading device, whereby a storage medium on which image data (photographic image) is stored Read. Furthermore, the data processing device is in particular a computer, a motherboard with a CPU or a CPU or ASIC. The data processing device processes image data received by a process according to the present invention to obtain image control data for control of an output device, in particular an image reproduction system, in particular an image recording system. The image recording system is in particular an exposure device for exposing light-sensitive photographic paper according to image control data, a color printer for generating a photographic image on a medium, in particular paper or foil, in particular an ink jet printer or a toner printer.
[0039]
The present invention also relates to an input device such as a film scanner, for example, an output device such as a photographic print that is separated in space and connected by a network (for example, CAN or the Internet). The transmission of the image data is preferably performed as a reference position in the reference color space. The invention also relates to a system of input and output devices, which are connected, for example by a network, whereby the system uses a process according to the invention. In particular, the present invention relates to a device (input device and / or output device) and / or storage and / or reading and / or process of receiving and transmitting data representing a reference position generated by the present invention. This process or device should be specifically configured for use as described above, whereby the input device represents the left half of FIG. 2 and the output device represents the right half of FIG. Communicate with each other by a reference position (or data representing the reference position) (eg, via a network or data carrier). Thus, the input device generates a reference position from the image data according to the process of the present invention, and the output device generates image control data from the reference position according to the process of the present invention. The input device preferably has at least one input device, a data processing device for converting the image data received according to the process of the invention into reference data representing a reference position, the reference data as a data carrier and / or reference data And a data storage device for storage to the transmission interface. An output device includes a reference data reader for reading reference data from a data carrier and / or a reference data receiver interface, and a data processing device for determining image control data from the received reference data according to the process of the present invention. And an output device that can be controlled by image control data.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
Further features and advantages of the present invention will become apparent from the following detailed description. Different features of different embodiments can be combined with each other.
FIG. 1 illustrates the networking of input and output devices through a color space platform. The desired color space or standard space is used as the color space platform described above as the reference color space. The reference color space is preferably selected to be a CIE color space, such as the CIE LAB color space or the CIE XYZ color space, as is common in today's color management systems. The color space is independent of the type of input or output device and has the desired property of including all possible input and output device color spaces. When the received image data is played back in the reference color space, for example by converting them to the reference color space, they are limited in terms of colors that can be captured if they are not already in the reference color space ( It is found that the color value (first color value) represented by the image data, for example a camera or a film scanner, is not completely independent of the type of device. In other words, the first color value describes the characteristics of the input area of the input device. The reference color space is preferably designed such that it assigns each color value to an individual well-defined location or single point in the color space. The defined transformation is preferably present between the first color space and the reference color space, in particular between the reference color space and the third color space. The output device is in particular an image reproduction system such as a coloring system (photographic printer or color printer), a monitor, a storage medium or a network interface.
[0041]
FIG. 2 illustrates the color management of the present invention from a color space perspective. Input devices are defined as device 1 and device 2. The device 1 is a digital camera, for example, which outputs color data in the form of sRGB format. The apparatus 2 is, for example, a scanner that scans a film negative and outputs data as RGB data. The image data output by the device 1 is called RGB1, and the image data output by the device 2 is called RGB2. The RGB1 and RGB2 data exist in their own color space. These are converted to the reference color space by the process of the present invention. This is the example CIE LAB color space shown in FIG. Within this reference color space, the converted image data mirrors the input area of device 1 or device 2. In other words, all possible input conversion positions span the input color area of the input device into the second color space. A particular idea of the process of the present invention is that this limitation present at the input conversion position is overcome by a mapping that maps the space of possible color values to a reference region (first mapping). In this way, the characteristics of the input device (color characteristics) are eliminated or at least attenuated. Similarly, the output conversion position of the output devices 3 and 4 defines the output color area of the devices 3 and 4 in the reference color space. The mapping of the output transformation (second mapping) again forms a rule for mapping the second position to the output color area of the devices 3, 4. The color values are then imaged into device dependent color spaces RGB3 and RGB4. In this method, the characteristics (color characteristics) of the output device are taken into account in a method that is optimal within the range of the possibility of color reproduction. Therefore, the reference color space, the first mapping belonging to each input device, and the second mapping belonging to each output device lead to mediation between the input device and the output device. Since several input devices, hence some color gamuts, and some output devices, hence some output color gamuts, are connected via a color space platform, high flexibility with a high range of use is achieved. Realized.
[0042]
A full-single-shot conversion from the input device color value (first position) to the reference color value (second position), ie a reversible conversion, is preferably defined for each input device.
[0043]
A single shot conversion of the reference color value (second position) to the output color device value (third position), i.e. a reversible conversion at each color value, is preferably defined at each output device.
[0044]
The input conversion from the first color space to the reference color space is preferably colorimetrically accurate when the color values are sufficiently far from the region boundaries. Input conversion is preferably performed from RGB to CIE LAB. The color of the region boundary, eg the RGB cube surface, is preferably mapped by an input transformation from the surface of the RGB color cube to the surface of the reference color region. The color near the region boundary is preferably deformed similar to plastic deformation, so that adjacent color values are always in the state of adjacent color values. The first deviation of the transformation should not be singular to realize the full single shot characteristics of the transformation. For numerical reasons, the first deviation should be within a predetermined value range.
[0045]
The reference position is preferably calculated directly by the IGB-CIELab conversion. The image control data representing the third position is preferably calculated in such a way that the subsequently inverted RGB-CIELab conversion is calculated first.
[0046]
An advantage of the present invention is that no or little region mapping needs to be performed which leads to loss of color detail and numerical problems at the region boundaries. Furthermore, the conversion of each color value can be reversed. No color information is ultimately lost.
[0047]
For example, a series of color value changes corresponding to the mapping in the second color space is possible. For example, the size of the inner area of the reference color region where no change in color value occurs can be changed. Different processes are possible with respect to changes in color values, i.e. particularly with respect to color values located at the borders of the region, e.g. the weights are changed to maintain or change the hue component, color saturation component or luminance component of the color. Can.
[0048]
The reference color region can be selected in a number of different ways. For example, the regions can be selected from XYZ, sRGB regions, typical output device regions, or geometrically well defined regions (eg, spherical surfaces). However, the volume of the reference area must be approximately the same size or larger than the volume of the input and output collar areas.
[0049]
During the processing of the image data, the conversion chain (first color space conversion, first mapping, second mapping, second color space conversion) can be steadily performed one after another. The chain of transformations can be performed in the sequence described above and in the opposite direction (reverse sequence) based on desire and goal. Preferably, two, three, or four adjacent transforms are combined into one transform in order to subject the image to a small number of transforms to allow for faster processing. In particular, the input transformation (first color space transformation and first mapping) can be combined with the output transformation (second mapping and second color space transformation) into a single transformation.
[0050]
FIG. 3 shows an sRGB area as an input color area of the second color space and a photographic paper area as an output color area. As clearly shown, the two regions have large overlapping regions. However, the sRGB area portion exists outside the photographic paper area, and vice versa. Therefore, according to the present invention, the reference color area includes an sRGB area and a photographic paper area.
[0051]
Hereinafter, a combination of the photographic paper area and the sRGB area of the reference color area is used as an example. For that purpose, a conversion from the paper RGB color space to the CIELAB color space is preferably defined, which can be performed, for example, by a simple grid or mesh having the dimensions 65 × 65 × 65. The midpoint is defined by linear interpolation. Instead, an arithmetically defined function can be used. For each RGB triplet there is a corresponding CIELAB triplet, which is labeled Lab._pRGBCalled. The calculation of CIELAB triplets from RGB triplets is described as follows.
[0052]
In the example described, sRGB is used as an example representing the color of the input device. Therefore, the standard formula can be used to perform the conversion from sRGB to CIE LAB. RGB color spaces other than the sRGB color space can also be used. However, the conversion from this color space to a second color space (eg CIELAB) is preferably known.
[0053]
The transformation can be defined, for example, as follows, where Lab represents a single value triplet:
Lab_weighted= (1-_WRGB) ・ Lab_sRGB+_WRGB・ Lab_pRGB
Weight W_RGBIs the closest distance d of the sRGB data to the sRGB surface_RGBIt is a function of (first distance). W for the color of the surface of the RGB cube_RGB= 1 and W at the center of the RGB cube_RGB= 0. The distance d is normalized to 1 if this indicates the distance from the cube surface to the center of the cube.
[0054]
A typical weighting function is:
[Expression 1]

The Wi used in the above formula is, for example, W_RGBIn the above equation, di is, for example, d_RGB“I” means i-th sRGB data. The course of Wi is shown as a function of di in FIG. As is clearly shown, there is little or no “plastic deformation” near the center, and very little near the center, and then decreases outward from about 30% of the maximum distance. Thus, at large distances, the influence of the output reference area increases with increasing distance, whereby the influence of the input reference area increases with increasing distance, but at least at a small distance, it is dominant.
[0055]
Other weighting functions that satisfy the following conditions are also appropriate.
Wi = 1,0 on the surface,
Wi = 0,0 at the center of the cube
Wi increases monotonously,
The first derivative of Wi in di is not singular at all 0 <di <1, and is in the range of appropriate predetermined values, especially for numerical processing (preselected).
[0056]
One example will be described in the following description where the reference area covers the entire XYZ area.
[0057]
The XYZ area contains all possible colors. The conversion is described in three steps.
[0058]
The conversion is performed from CIELAB to XYZ according to standard formulas. If the input data does not exist in CIELAB format, the conversion from CIELAB to XYZ is performed, for example, as in the preceding example described above. This L_sampleThe XYZ value resulting from the value conversion is xyz_sampleCalled.
[0059]
Next, xyz_sampleThe value is xyz_mappedConverted to a value, thereby maintaining the hue of the color. In the XYZ half-plane containing the grade axes (x, x, x) with x = 0... 1, it is described that all colors contain a hue of a certain color. FIG. 5 shows such a half-plane including this gray axis. All color values in the half plane shown in FIG. 5 that are not located on the gray axis have the same color hue.
[0060]
As a third step, conversion back to the CIELAB color space is performed according to standard formulas. xyz_mappedThe value is thereby L_mappedConverted to a value.
[0061]
In summary, xyz_mappedXyz to_sampleThe transformation is described in a half plane with a constant color hue. The line xyz passes through two points_sampleCan be defined for each color value. One point is the reference point xyz_reference(E.g. 0.5, 0.5, 0.5), the other point is xyz_sampleCalled. This line is the point xyz_RGB-SurfaceCrosses the input color area (RGB area) at xyz_cubeCross the XYZ cube.
[0062]
Mapping function xyz_mapped= F (xyz_sample) Applies to all points on a straight line. This function can be defined with the following boundary conditions: xyz_RGB-SurfaceIs xyz_cubeMapped to xyz_referenceAll nearby points are unchanged. As further described above, the hue of the color is maintained unchanged, which ensures a priori because all color conversion is performed in the half-plane.
[0063]
FIG. 6 shows a typical mapping function for f. The continuous line is xyz_sampleThe course of the function f based on is marked. The dashed line marks the 1: 1 mapping case, which is xyz_sample= Xyz_mappedThis is the case when the input RGB area is equal to the reference area in each direction.
[Brief description of the drawings]
FIG. 1 illustrates the coupling of different input devices and different output devices via a color space platform in accordance with the process of the present invention.
FIG. 2 is a diagram showing a color management process of the present invention.
FIG. 3 is a diagram showing an sRGB color area and a photographic paper area in a second color space.
FIG. 4 is a diagram showing a course of a weighting function used in generating a reference position.
FIG. 5 is a diagram illustrating mapping of a second color space in which hue is maintained.
FIG. 6 is a diagram showing still another mapping function for obtaining a reference position.

Claims (10)

A process for color management of image data representing the color values of an image, which allows color values for different preselected color areas, especially for input devices such as film scanners or digital cameras, and especially for output devices such as photographic printers or photolabs In order to obtain the optimum value as a change, the input color area includes all the color values that can be captured by the input device and the output as image data, and the output color area is input image control data to the output device. In a color management process that includes all color values that can be processed by the output device when
a) receiving image data representing a first position of the first color space and describing a first color value located in the input color region;
b) converting the first position to the reference position by input conversion, whereby the conversion is performed such that the reference position is located in the second color space and describes the second color value, and the reference color area is the reference position Specifies the reproducible color value by position,
c) The output conversion converts the reference position to the third position, whereby the output conversion places the third position in the third color space and the third color value included by the output color area of the output device. A color management process that includes steps performed to describe the. In input conversion,
a) when the color value is approximately at or near neutral gray and / or the first and / or second color value is present in an interior area of the input color region and / or the reference color region, And / or when separated from the boundary surface of the reference color region, the second color value is at least essentially the same as the first color value;
b) a first color value located on the boundary surface of the input color region is mapped to a second color value located on the boundary surface of the reference color region, and / or
c) the adjacency relationship between the color values is maintained, whereby the adjacent first color value is also mapped to the adjacent second color value;
The process of claim 1, wherein d) the first deviation of the input transform is not singular and / or the input transform is a full single shot. In output conversion,
a) when the color value is approximately or near gray and / or the second and / or third color value is present in the output color region and / or an internal area of the reference color region, And / or when separated from the boundary surface of the reference color region, the third color value is at least essentially the same as the second color value and / or
b) a second color value located on the boundary surface of the reference color region is mapped to a third color value located on the boundary surface of the output color region and / or
c) the adjacency relationship between the color values is maintained, whereby the adjacent second color value is also mapped to the adjacent third color value;
The process of claim 1, wherein d) the first deviation of the output transform is not singular and / or the input transform is a full single shot. The process of claim 1, wherein the reference color region comprises a plurality of input color regions of a plurality of input devices and / or a plurality of output color regions or a plurality of output devices. The process of claim 1, wherein the input and / or output conversion is performed such that at least a portion of the second color value has the same hue as at least a portion of the first and / or third color value. The process of claim 1, wherein the image data representing the reference position of the second color space is optimized prior to further processing to obtain image control data. The process of claim 1, wherein the input transformation and the output transformation are combined into one transformation. A program that causes a computer to execute a process according to claim 1. A computer storage medium or a computer having the program according to claim 8. A device for receiving image data;
A data processing device for processing received image data in accordance with the process of claim 1 to obtain image control data;
A photographic printer, color printer or photo lab, such as a particularly large lab or mini lab, comprising an image reproduction system for generating a photographic image based on image control data on a recording medium, particularly paper or photographic paper.

Images