1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to gamut mapping, and more particularly, to gamut mapping which can allow a reproduction device to properly represent colors that are not within a gamut boundary of the reproduction device but within a gamut boundary of a source device.
2. Description of the Related Art
In general, color input/output devices such as monitors, scanners, cameras, and printers which represent colors use different color spaces or different color models. For example, for reproducing color images, printers use a cyan-magenta-yellow (CMY) or cyan-magenta-yellow-black (CMYK) color space, color cathode ray tube (CRT) monitors or computer graphic devices use a red-green-blue (RGB) color space, and color input/output devices which are required to handle hue, saturation, and brightness all together use a hue-saturation-intensity (HSI) color space. A CIE color space is often used to define colors which can be accurately represented by any types of devices, i.e., device-independent colors. Examples of the CIE color space include a CIEXYZ color space, a CIELab color space, and a CIELuv color space.
A range of colors that can be represented, i.e., a gamut, may differ from one color input/output device to another. Accordingly, color input/output devices having different gamuts may represent the same image differently. Therefore, in a case when a gamut of a source color input/output device which provides an input color signal is different from a gamut of a target color input/output device which represents a color corresponding to the input color signal, gamut mapping is needed to appropriately convert the input color signal such that the gamut of the source color input/output device can match the gamut of the target color input/output device and that the color reproducibility of the input color signal can be enhanced.
FIG. 1 is a diagram for explaining related art gamut mapping. Referring to FIG. 1, reference character S1 represents a gamut of a source device, reference character S2 represents a gamut of a target device, X1 represents an original color provided by the source device, and X2 represents a color obtained by performing gamut mapping on the original color X1.
Since the gamut S1 of the source device is wider than the gamut S2 of the target device, as illustrated in FIG. 1, gamut mapping must be performed on the original color X1 using the Gamut boundary descriptors (GBDs) of the source device and the target device such that the original color X1 can be mapped to the inside of the gamut S2 of the target device. In other words, gamut mapping is a process of enabling the target device to properly represent the color X1, which is provided by the source device and is outside the gamut S1 of the target device, by mapping the color X1 to the color X2 which is located on the boundary of the gamut S2 of the target device.
In general, a related art gamut mapping operation for different color input/output devices may be performed by converting a color space of an input color signal and converting the lightness and chroma of the resulting input color signal while keeping the hue of the resulting input color signal. In detail, a color space of an input color signal may be converted from a device-dependent color space (DDCS) such as an RGB color space or a CMYK color space to a device-independent color space (DICS) such as a CIEXYZ color space or a CIELab color space, and the DICS is converted to an LCH coordinate system representing lightness, hue, and chroma. Thereafter, gamut mapping is performed on the input color signal on a plane where hue is uniform, i.e., a lightness-chroma (LC) plane, such that the lightness and chroma of the input color signal can be appropriately changed.
Related art gamut mapping methods are broadly classified into a gamut mapping method in which gamut mapping is performed such that accuracy, and brightness/contrast can be enhanced and a gamut mapping method in which different gamut mapping techniques are applied to different gamuts. These related art gamut mapping methods, however, simply use an original gamut of a source device (such as a monitor) as it is. No specific methods capable of properly realizing an original gamut of a source device by appropriately adjusting a gamut of a reproduction device such as a printer have been suggested.
A gamut of a monitor includes a gamut of a printer for most hues. However, referring to FIG. 2, there are colors, such as cyan (C), which cannot be properly represented by a source device such as a monitor, but can be represented by a reproduction device such as a printer. Obviously, there is no need for a printer to represent colors which cannot be represented by a monitor. However, a printer may make C, which is generally displayed by a monitor, appear darker than it actually is.
USPTO Backgrounds
USPTO Backgrounds