JP2004236159A - Image recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for more conveniently recording an image to be expressed in colors belonging to a color space including colors outside a visible region in a prescribed recording medium when the colors belong to the color space including the colors outside the visible region and can be expressed in colors belonging to a color space with a smaller number of colors which can be expressed by the color space. <P>SOLUTION: In the case of recording image data to be expressed by using colors belonging to a first color space in the prescribed recording medium, a color area of the colors used by the image data is judged and when the colors used by the image data are judged that the number of colors which can be expressed is less than that of the first color space and the colors can also be expressed in a second color space to which visible colors belong, information indicating that the color space in which the colors used by the image data belong is the second color space is recorded in the recording medium with the image data. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for recording image data, particularly image data captured by a digital still camera, a digital video camera, or the like, and image data of each frame constituting a moving image on a predetermined recording medium.
[0002]
[Prior art]
At present, image data captured by a digital camera is mainly converted into sRGB format inside the camera, compressed by JPEG format, and stored in Exif / DCF format. FIG. 2 shows a functional configuration of a conventional digital camera. FIG. 2 is a block diagram showing a functional configuration of a conventional digital camera.
[0003]
Reference numeral 201 denotes an imaging unit, an imaging lens, an imaging device such as a CCD, a gain adjustment circuit for adjusting the gain of an output signal from the imaging device, and an A / D conversion circuit for converting an output signal of the imaging device after the gain adjustment into a digital signal. The imaging unit 201 outputs a captured image as digital image data to a pixel interpolating unit 203 at a subsequent stage by the above units.
[0004]
Reference numeral 202 denotes an exposure adjustment unit which refers to image data output from the imaging unit 201, and performs shutter control according to a predetermined program diagram so that the image has an appropriate brightness based on the luminance of a predetermined portion in the image. The speed and the aperture value are determined, and the exposure time of the image sensor included in the imaging unit 201 and the aperture of the photographing lens are controlled. Reference numeral 203 denotes a pixel interpolation unit that adjusts the white balance of the image data output from the imaging unit 201 and adjusts the values of R, G, and B, which are the pixel values of each pixel of the image, according to the color filter array of the imaging device. To interpolate and output color image data.
[0005]
A color correction unit 204 performs color correction on the color image data output from the pixel interpolation unit 203 so that the color reproduction characteristics have desired characteristics. An image compression unit 205 performs a compression encoding process on the color image data color-corrected by the color correction unit 204.
[0006]
Reference numeral 206 denotes a recording unit which adds predetermined supplementary information to the image data compressed by the image compression unit 205 and records the image data on the recording medium 207 as image data in a predetermined format. The Exif / DCF format is generally used as the predetermined format at present.
[0007]
[Problems to be solved by the invention]
In the Exif / DCF format, not only the image data (main image data) compressed by the JPEG method but also a reduced image (of the main image) for displaying a list and the shooting conditions, and the image data are expressed in any color space. Information indicating whether or not the information has been written is also written. However, the current DCF rules do not permit the use of a color space other than sRGB as described below.
[0008]
(JEIDA standard, camera file system standard) DCF Version 1.0
The ColorSpace tag in Exif IFD defined by the color space Exif standard is declared as sRGB as follows.
[0009]
Color space colorSpace (ExifIFD required)
Declare sRGB.
[0010]
Tag = 40961 (A001.H)
Type = Short
Value = 1 (sRGB)
Count = 1
However, in the future, it is possible to handle an image represented by a color space other than sRGB as long as a value representing another color space, for example, AdobeRGB or scRGB is defined.
[0011]
Adobe RGB is a color space for printing. Although the color space that can be expressed with respect to sRGB is slightly wide, it does not exceed the human visible region. On the other hand, scRGB is a color space that can be expressed in a wider color space than the visible region of human beings, and can handle colors synthesized by computer graphics. scRGB is defined by 16 bits for each color, and the number of colors that can be represented in the scRGB color space exceeds 216 × 216 × 216 colors, that is, more than 280 trillion colors.
[0012]
However, even when the scRGB color space is used, a color that can actually exist in a color gamut that can be expressed by the scRGB color space, that is, a color included in the human visible region is converted into a volume of the color space. There is only about 40%. For this reason, if a processing system that receives and processes data using colors belonging to the scRGB color space is designed on the basis of a 16-bit color space for each color, there are actually many useless parts. For example, when performing color conversion using a look-up table, if all 16 bits of each color are tabulated, a huge table of 248 entries is required, which is not practical.
[0013]
In addition, wasteful image data also has a waste in its size, so that even when recording on a storage medium, there is waste in the recording area.
[0014]
The present invention has been made in view of the above problems, and is a color belonging to a color space including a color outside the visible region, and the color belongs to a color space in which the number of colors that can be expressed is smaller than this color space. An object of the present invention is to provide a technique for more easily recording an image represented by a color on a predetermined recording medium when the image can be represented by a color.
[0015]
[Means for Solving the Problems]
In order to achieve the object of the present invention, for example, an image recording method of the present invention has the following configuration.
[0016]
That is, an image recording method for recording image data expressed using a color belonging to the first color space on a predetermined recording medium,
A determining step of determining a color gamut of a color used by the image data;
In the determination step, it is determined that the color used by the image data is a color that can be expressed in the second color space to which the number of representable colors is smaller than that of the first color space and to which visible colors belong. When the image data is recorded on the recording medium, information indicating that the color space to which the color used by the image data belongs is the second color space is recorded on the recording medium together with the image data. Recording step.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail according to preferred embodiments with reference to the accompanying drawings.
[0018]
[First Embodiment]
FIG. 1 is a block diagram illustrating a functional configuration of the image recording apparatus according to the present embodiment. The same parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. Each part shown in the figure may be constituted by hardware, or each part may be represented by a program, read by a computer, and executed by the CPU of the computer, thereby realizing the functions of the image recording apparatus of the figure. May be realized.
[0019]
A color correction unit 104 performs color correction on the color image data output from the pixel interpolation unit 203 so that the color characteristics become desired characteristics. The color correction unit 104 according to the present embodiment performs a matrix operation on each pixel value forming the color image data so that each of the RGB pixel values of the color image data has a predetermined characteristic value. Perform gamma correction. In the present embodiment, each color used in the color image data belongs to the scRGB color space, and each of R, G, and B is represented by 16 bits. An image compression unit 105 performs a compression encoding process on the color image data color-corrected by the color correction unit 204 according to a method such as a JPEG extension system.
[0020]
Reference numeral 106 denotes a recording unit that adds predetermined supplementary information to the image data compressed by the image compression unit 105 and records the image data on the recording medium 207 as image data in a predetermined format (Exif / DCF format). The additional information may also include additional information according to the determination result by the color gamut determining unit 108. The additional information according to the determination result by the color gamut determination unit 108 will be described later in detail.
[0021]
Reference numeral 108 denotes a color gamut determining unit that determines the color gamut of the color used in the color image data with reference to the color image data output from the color correcting unit 104. As a result, the color space to which the color used in the color image data belongs is determined, and the determination result is notified to the image recording unit 106.
[0022]
Next, the additional information will be described. As described above, when an image is compressed and recorded on the recording medium 207, information indicating which color space the image data belongs to in the compressed image data includes the additional information. Is added. In the present embodiment, since the colors used in the color image data belong to the scRGB color space, the image recording unit 106 first converts the following information into the compressed image data as one of the supplementary information. Add.
[0023]
Color space colorSpace (ExifIFD required)
Tag = 40961 (A001.H)
Type = Short
Value = 2 (scRGB)
Count = 1
A value (for example, 2) indicating scRGB is set in Value, which is a variable representing the type of color space.
[0024]
Here, when the color gamut determination unit 108 determines the color gamut of the color used in the color image data, and determines that the color gamut can be expressed in a color space having a smaller number of expression colors than scRGB, for example, If the image recording unit 106 determines that the image data can be expressed also in sRGB, the image recording unit 106 further adds the following information to the compressed image data as one of the accompanying information.
[0025]
Color gamut information Gammut (Exif IFD option)
The color gamut information of the image data is recorded.
[0026]
Tag = 40XXX (AXXX.H)
Type = Short
Value = 1 (sRGB)
Count = 1
This additional information indicates that the color space used by the color belonging to the color image data is scRGB, but this color gamut is within the range of sRGB. As a result, the color image data can use colors in the scRGB color space, so that consistency with a device that handles a larger color space can be obtained. In addition, since it is possible to notify the image processing apparatus that the color image data can be handled in sRGB, a heavy load processing corresponding to scRGB is unnecessary for this apparatus. Can be avoided.
[0027]
[Second embodiment]
In the first embodiment, the color gamut determination unit 108 determines whether or not the color gamut used for the color image data can be represented by sRGB. It may be determined whether or not.
[0028]
FIG. 3 shows a flowchart of a process performed by the image recording apparatus according to the present embodiment. The flowchart shown in the figure is a process for one image, and the processes from step S401 to step S406 are for all the pixels constituting one image.
[0029]
First, the color correction unit 104 converts the RGB values of the first pixel (for example, the pixel at the upper left corner of the image) in the color image data into XYZ values (step S401). Next, the color gamut determining unit 108 determines whether or not the pixel is in the sRGB color gamut with reference to the XYZ values of the pixel (step S402).
[0030]
If the color gamut is sRGB, the process proceeds to step S404, and the image recording unit 106 sets a flag for this pixel as a flag indicating that the color gamut of the color used by this pixel belongs to sRGB. (Step S404). Note that the set flag is held by the image recording unit 106.
[0031]
On the other hand, if the color gamut of the color used by this pixel belongs to Adobe RGB, the process proceeds from step S403 to step S405 if the color gamut of this pixel belongs to Adobe RGB instead of sRGB. (Step S405). Note that the set flag is held by the image recording unit 106.
[0032]
On the other hand, if the color gamut is neither sRGB nor AdobeRGB, the process proceeds from step S403 to step S406, and the image recording unit 106 sets a flag for this pixel to indicate that the color gamut used by this pixel belongs to the entire horseshoe shape. It is set as a flag indicating that the object is the one (step S406). Note that the set flag is held by the image recording unit 106.
[0033]
Then, the above processing is performed on all the pixels constituting the image. If it is determined that the processing has been performed for all pixels (step S407), the image recording unit 106 refers to the flags set for all pixels. If at least one flag of the entire horseshoe shape exists among the flags, additional information indicating that the color gamut of the color used by the image data belongs to the entire horseshoe shape is added to the compressed image data. To the recording medium 207.
[0034]
If there is no flag for the entire horseshoe shape and there is an AdobeRGB flag, additional information indicating that the color gamut of the color used by this image data belongs to AdobeRGB is added to the compressed image data. Then, it is recorded on the recording medium 207.
[0035]
In cases other than the above, that is, when there is no flag for the entire horseshoe shape, no flag for AdobeRGB, and a flag for sRGB, the color gamut of the color used by this image data is Additional information indicating that the image data belongs to sRGB is added to the compressed image data and recorded on the recording medium 207.
[0036]
In addition, at the stage of setting the flag for each pixel, if the set flag is a flag of the entire horseshoe shape, it can be determined that the color gamut of the color used by this image data belongs to the entire horseshoe shape. At this point, the processing according to the flowchart shown in FIG. 3 is interrupted, and additional information indicating that the color gamut of the color used by the image data belongs to the entire horseshoe shape is added to the compressed image data. May be transferred to the process of recording on the recording medium 207.
[0037]
The processing according to each embodiment described above can be individually applied to a plurality of images. In this case, a large space is used to represent the image data, such that one image needs an sRGB area, another image needs Adobe RGB, and another image needs a horseshoe shape (that is, the entire visible area). However, it is possible to describe the actually required color space for each image.
[0038]
[Third Embodiment]
Alternatively, the color gamut of each image may be determined, and R, G, and B points circumscribing the color gamut may be represented by an xy coordinate system.
[0039]
Tag = 40961 (A001.H)
Type = Short
Value = 2 (scRGB)
Count = 1
Color gamut information Gammut (Exif IFD option)
The xy coordinates of the RGB points including the color gamut of the image data are recorded. The tag format is as follows:
[0040]
Tag = 40XXX (AXXX.H)
Type = RATIONAL
Value = 1 (sRGB)
Count = 6
Examples of values are 0.64, 0.33, 0.3, 0.6, 0.15, 0.06 for sRGB.
0.64, 0.33, 0.21, 0.71, 0.15, 0.06 in the case of AdobeRGB
It becomes.
[0041]
Thereby, the color gamut information occupied by each image can be recorded in more detail.
[0042]
[Other embodiments]
An object of the present invention is to supply a storage medium (or a recording medium) in which program codes of software for realizing the functions of the above-described embodiments are recorded to a system or an apparatus, and to provide a computer (or CPU or MPU) of the system or the apparatus. Can also be achieved by reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention. When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.
[0043]
Further, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function of the program is performed based on the instruction of the program code. It goes without saying that the CPU included in the expansion card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0044]
The storage medium includes a communication medium such as a communication cable used for a network such as the Internet or a LAN. That is, when the program code of the above-described embodiment is stored in a server device on a network, the program can be introduced into the computer by downloading the program code from the server device to the computer via the network. Therefore, the introduced program is executed by a control circuit such as a CPU or an MPU on the computer, and as a result, the computer realizes the functions of the above-described embodiment. It goes without saying that communication media such as communication cables are included.
[0045]
【The invention's effect】
According to the above description, according to the present invention, it is possible to represent a color belonging to a color space including a color outside the visible region and a color belonging to a color space in which the number of colors that can be represented by this color space is small. In this case, it is possible to provide a technique for more easily recording an image represented by the color on a predetermined recording medium.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a functional configuration of an image recording apparatus according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing a functional configuration of a conventional digital camera.
FIG. 3 is a flowchart of a process performed by an image recording apparatus according to a third embodiment of the present invention when a plurality of images to be recorded exist.

Claims (7)

An image recording method for recording image data expressed using a color belonging to a first color space on a predetermined recording medium,
A determining step of determining a color gamut of a color used by the image data;
In the determination step, it is determined that the color used by the image data is a color that can be expressed in the second color space to which the number of representable colors is smaller than that of the first color space and to which visible colors belong When the image data is recorded on the recording medium, information indicating that the color space to which the color used by the image data belongs is the second color space is recorded on the recording medium together with the image data. And an image recording method. 2. The image recording method according to claim 1, wherein the first color space is scRGB, and the second color space is sRGB. The second color space further includes AdobeRGB, the entire horseshoe shape,
In the determining step, it is further determined which color space the color gamut of the color used in the image data belongs to in the second color space,
3. The recording step, wherein information indicating that the color space to which the color used by the image data belongs is the color space determined in the determination step is recorded on the recording medium together with the image data. The image recording method described in 1. An image recording apparatus that records image data expressed using a color belonging to a first color space on a predetermined recording medium,
Determining means for determining a color gamut of a color used by the image data;
The determination unit determines that the color used by the image data is a color that can be represented in the second color space to which the number of representable colors is smaller than that of the first color space and to which the visible color belongs. When the image data is recorded on the recording medium, information indicating that the color space to which the color used by the image data belongs is the second color space is recorded on the recording medium together with the image data. An image recording apparatus comprising: A program for causing a computer to execute the image recording method according to claim 1. A program for causing a computer to function as the image recording device according to claim 4. A computer-readable storage medium storing the program according to claim 5.

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