1. Field of the Invention
The present invention relates to an information processing device and method, program, and information processing system, and particularly relates to an information processing device and method, program, and information processing system whereby color gamut conversion is performed appropriately in various conditions.
2. Description of the Related Art
In recent years, various types of digital image displays of which the color expression regions differ have been increased. In particular, color gamut enlargement of image display devices is remarkable, and a color gamut has been markedly enlarged with a process from a CRT (Cathode Ray Tube) display, plasma display, LCD (Liquid Crystal Display), and further to organic Electro Luminescence Display (OELD). Also, a great number of imaging apparatuses, such as digital cameras, video cameras, and so forth, which can image-capture colors other than SRGB (standard RGB), have appeared, and there has been demanded a method for outputting wide color gamut image data smoothly to various color gamut devices including a wide color gamut display by suppressing out of color registration, and high-luminance/high-saturation hue shift.
The following three methods can be exemplified as a principal color matching method for solving a problem of out of color registration between devices.
First, there is a method employing an ICC (International Color Consortium) profile. The ICC profile is a file wherein the properties of an image device defined by an organization called ICC are described, and usually, when outputting a single image file, there are employed two profiles of an input device ICC profile, and an output device ICC profile. There are many cases wherein an input device ICC profile is embedded in an image file, and when outputting the image thereof to another device through a PC (Personal Computer), an application which supports an ICC profile on the PC employs the ICC profile to perform color gamut matching appropriately, and outputs the image. With this method, it is a premise to perform image processing conversion employing a PC, or to support an ICC profile at an output device side.
Also, there is a method employing SRGB space as a system for matching colors without having a consciousness of a color gamut difference between devices. The sRGB is International Standard of color space which the IEC (International Electrotechnical Commission) devised in October, 1998, wherein the color space was devised to ensure color reproducibility between different environments such as difference in devices such as displays, printers, and so forth based on the color gamut of a CRT display. For example, if all of a digital camera, personal computer, display, and printer are compatible with SRGB, when displaying a shot image on the display or printing this, color appearances can be matched without subjecting this to any particular processing. With regard to the SRGB, passing through a PC is not indispensable, and the processing is markedly simple and convenient as compared to a workflow based on an ICC profile, but the color range which can be expressed is narrower than that of other space, so emerald green, dark cyan, orange, bright red, yellow, and so forth are difficult to be expressed. Therefore, the SRGB is unsuitable for professional use wherein a photo and graphic design are handled professionally.
Further, there has been a tendency wherein the Exif (Exchangeable image file format) standard is employed to realize color matching with the printer industry as the center. The Exif, which the JEITA (Japan Electronics and Information Technology Industries Association) proposed and devised, is a format standard for recording an image file. Most digital camera makers employs this format along with the DCF (Design rule for Camera file system) which is a file system standard. Specifically, color space can be described as the header information of an image file, so the printer side can perform color conversion into a printer color gamut more suitably by reading this header information. Particularly, with the Exif ver. 2.21, in addition to the SRGB supported by the former versions, the Adobe RGB of which the color gamut is wider than that of the sRGB, which has been employed normally with the business field such as printing industry, can be employed as supported color space, whereby printable emerald green and dark cyan, which have not been able to express with SRGB according to the related art, can be expressed. The workflow to perform printing employing the Exif standard is called as ExifPrint. This can be realized if the printer side includes a function for reading an Exif header, thereby enabling printing by inserting a memory card into a printer without passing through a PC. There is the PIM (PRINT Image Matching) standard similar to this Exif.
However, for example, in the case of employing an ICC profile, the ICC profile has to be embedded in an image file, and accordingly, there is a possibility that the size of the image file becomes unnecessarily great. Also, a PC application or output device side has to generate a CMM (Color Matching Module) for reading the ICC profile to subject this to suitable processing, but this CMM is generated according to each company's own concept, so even though color matching of the color gamut of the common portion of input and output devices is ensured, colors other than the mutual color gamut are not taken into consideration so much, and accordingly, with regard to high/low luminance and high-saturation colors, hue shift frequently occurs according to natural clip.
The natural clip means a phenomenon wherein colors other than the color gamut of image data externally supplied are represented forcibly with a color within the color gamut of the device. For example, in a case wherein only the R component of a certain color represented with RGB is greater than the maximum value of the R component of the color gamut, the R component of the color thereof is represented with the maximum value of the R component of the color gamut (natural clip). At this time, the balance the RGB of the original color is disrupted according to this natural clip, and the hue is changed. Such change in hue is referred to as hue shift. That is to say, the original color is expressed with a color different from the original color, so occurrence of such hue shift is unfavorable.
Also, for example, in the case of employing the sRGB, an assumed color gamut is a CRT monitor for standard PC, so the color gamut is narrow. There is provided no processing for performing color gamut compression between devices with the workflow of the sRGB, so natural clip occurs regarding colors other than the color gamut of the SRGB, and hue shift occurs regarding high/low luminance and high-saturation colors. Therefore, employing the SRGB may prevent dark cyan and green colors which can be printed with a common printer, or red or the like which can be displayed with an LCD of which the color gamut has been expanded remarkably in recent years from being expressed appropriately.
Further, in the case of a method employing the PIM or Exif, an output device has to perform processing according to the image header information defined by the Exif or PIM, and accordingly, there is a possibility that the processing load at the output device side gets greater. Also, the content of the processing depends on the output device, and accordingly, there is a possibility that color reproducibility intended with the input device is not ensured.
Also, all of the above-mentioned methods are methods for processing still images principally, and are not suitable for color matching of a movement image employing real time processing.
Therefore, in order to realize a substantial color reproducibility technique which does not depend on devices, there has been conceived a method for performing color matching appropriately between devices.
For example, with a method disclosed in Japanese Unexamined Patent Application Publication No. 09-098298 (U.S. Pat. No. 5,933,253), the color reproducibility region of an input system are divided into four regions by employing two straight lines on a two-dimensional plane, and the compression direction is changed for each of the regions, thereby performing color gamut compression.
Also, for example, with a method disclosed in Japanese Unexamined Patent Application Publication No. 07-236069, only the chromaticity coordinates of eight points of representative colors red (R), green (G), magenta (M), yellow (Y), black (K), and white (W) are exchanged, and the conversion of intermediate colors are performed according to the conversion results of the representative eight colors.
There has been conceived such a color gamut conversion algorithm variously other than the abovementioned methods.