1. Field of the Invention
The present invention relates to an image processing apparatus and method and, more particularly, to an image processing apparatus and method of performing color matching processing on an input image photographed by a digital still camera or a digital video camera.
2. Description of the Related Art
In multimedia systems centering around host computers, a color matching system (CMS) for performing image data color matching processing between input and output devices is being extensively developed.
ColorSync(trademark) of Apple Computer, Inc. as a representative CMS framework realizes a common CMS on a system by converting an image signal in a color space (Device Dependent Color Space) dependent on an input device into an image signal in a color space (Device Independent Color Space) independent of the device and further converting this image signal in the device independent color space into an image signal in a color space dependent on an output device.
Conversion characteristics for this conversion process are stored in data called a profile having Inter Color Profile Format. Profiles are prepared in a host computer in a one-to-one correspondence with devices. In performing conversion, one profile is automatically or manually selected, and the color space of an image signal is converted in accordance with the conversion characteristics of the selected profile.
In the above system, an image input device such as a flat bed scanner is directly connected to a host computer. If the characteristics of this input device remain unchanged, the effect of the CMS can be expected by using the conversion characteristics of a single profile of the host computer.
Unfortunately, the color characteristics of images such as those photographed by a digital still camera or a digital video camera are largely influenced by the photographing conditions. Therefore, color matching cannot be performed because the photographing conditions cannot be specified. Accordingly, the effect of the CMS cannot be expected when a single profile is prepared for an image input device such as a digital still camera or a digital video camera. In addition, if the photographing conditions and conversion characteristics do not match, unpreferable conversion is performed. As the photographing conditions, it is possible to prepare a plurality of profiles corresponding to the colors, i.e., white balances or exposure amounts of illuminating light during photographing. However, it is impractical to prepare profiles corresponding to all possible photographing conditions.
In an image input device represented by a flat bed scanner, a profile can be formed by the following method. That is, an image input device for forming a profile is used to scan or photograph a color target having a plurality of color chips. Signal values corresponding to these color chips in a device independent color space are compared with the signal values, obtained by scanning or photographing the color target, of the color chips in a color space dependent on the image input device. In this manner, color conversion characteristics or a profile for converting the color signal from the color space dependent on the image input device to the device independent color space is acquired.
In the above method of deriving color conversion characteristics by scanning or photographing a color target, the color target is inexpensive, and any user can easily perform the work. Therefore, the method has a great merit for the user.
In the following description, signal values in a device independent color space will be sometimes referred to as xe2x80x9ccolorimetric valuesxe2x80x9d. Similarly, signal values in a device dependent color space will be simply referred to as xe2x80x9csignal valuesxe2x80x9d in some cases.
The above color conversion characteristics deriving method is based on the assumption that an original has no brighter color than the brightest white of the color target. The object of a device such as a flat bed scanner is to scan a paper original and store or copy the original image. Such devices are originally so designed as to read xe2x80x9cpaper whitexe2x80x9d as the brightest color. Hence, the above assumption is practical in the color reproduction range of paper as a medium.
A cloud contained in scenery sometimes has a brighter color than the brightest white of the color target. Accordingly, image input devices such as a digital still camera and a digital video camera are so designed as to read a color with lightness much higher than that of xe2x80x9cpaper whitexe2x80x9d as the brightest color.
However, even when the color target is photographed by a digital still camera or a digital video camera, it is impossible to obtain a color signal having brightness larger than a certain value. Even if color conversion characteristics are acquired from the colorimetric values of color chips of the color target and signal values obtained by photographing the color target, no accurate color conversion characteristics can be obtained for an object such as a cloud including a high-lightness color.
It is an object of the present invention to provide an image processing apparatus and method suited to performing color matching processing corresponding to the photographing conditions of each individual input image.
To achieve the above object, one preferred embodiment of the present invention discloses an image processing apparatus comprising: input means for inputting a color image and a photographing condition of the color image; selecting means for selecting a profile corresponding to the photographing condition from a plurality of profiles stored in a memory; and processing means for performing color matching processing on the input color image on the basis of the selected profile.
It is another object of the present invention to provide an image processing apparatus and method suited to performing color matching processing on an image photographed by a digital still camera or a digital video camera with accuracy higher than that of the digital still camera or the digital video camera.
To achieve the above object, another preferred embodiment of the present invention discloses an image processing apparatus comprising: input means for inputting a photographed color image and a photographing condition of the color image; selecting means for selecting a profile corresponding to the photographing condition from a plurality of profiles stored in a memory; and processing means for storing the input color image and the selected profile in a medium.
It is still another object of the present invention to provide an image processing apparatus and method capable of easily obtaining accurate color conversion characteristics for an image input device such as a digital still camera or a digital video camera. It is still another object of the present invention to provide an image processing apparatus and method of performing color matching processing on the basis of the color conversion characteristics obtained for the image input device.
To achieve the above objects, other preferred embodiments of the present invention provide an image processing apparatus comprising: a memory for storing reference image data obtained by photographing a reference image including a plurality of color chips, and color data in a device independent color space of the color chips; selecting means for selecting reference image data corresponding to a photographing condition of a color image; and calculating means for calculating, on the basis of photographing data of the color chips obtained from the selected reference image data and color data of the color chips, a conversion characteristic for converting the photographing data into the color data and the image processing apparatus further comprising: input means for inputting a color image and a photographing condition of the color image; and processing means for performing color matching processing on the input color image on the basis of the conversion characteristic calculated by said calculating means.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.