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AssigneeSony Corporation
InventorsSeiji Kobayashi, Tomoo Mitsunaga, Hiroaki Ono, Ken Nakajima, Chikako Sano, Nobuyuki Sato
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An image processing apparatus and method and a recording medium therefor control the occurrence of a change in a hue. The histogram of a luminance signal Y is generated in a first step S1. In a second step S2, the histograms of the luminance signals Y are accumulated to generate a cumulative histogram, and the cumulative histogram is subjected to logarithmic approximation thereby to generate a lookup table (LUT) for correcting luminance signals. In a third step S3, a color-difference signal correction parameter LUT is generated by referring to the LUT for correcting luminance signals. In a fourth step S4, an input luminance signal Y is applied to the LUT for correcting luminance signals thereby to acquire a corrected luminance signal Y0. In a fifth step S5, the input luminance signal Y is applied to a color-difference signal correction parameter LUT so as to acquire a correction parameter k. In a sixth step S6, input color-difference signals Cr and Cb are multiplied by the correction parameter k to acquire corrected color-difference signals Cr0 and Cb0.
An image processing apparatus for correcting the gray level of an image signal, comprising:
An image processing method for an image processing apparatus for correcting the gray level of an image signal, the image processing method comprising:
A recording medium in which a computer-readable image processing program for correcting the gray level of an image signal has been recorded, the program comprising:
Dependencies are inferred from the claim text.
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Corrections within particular colour systems: with luminance or chrominance signals, e.g. LC1C2, HSL or YUV
Image enhancement or restoration: using histogram techniques
Image enhancement or restoration: using two or more images, e.g. averaging or subtraction
Dynamic range modification of images or parts thereof: based on global image properties
Term end not estimated
1. Field of the Invention
The present invention relates to an image processing apparatus and a method and a recording medium therefor. More particularly, the image processing apparatus and method and a recording medium of the present invention are ideally adapted for correcting the gray level of an image according to the dynamic range of an image output apparatus, such as a display or a printer.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating a configuration example of a conventional gray level correction processor for individually correcting the gray levels of the three primary color signals R, G, and B;
FIG. 2 is a block diagram illustrating a configuration example of a conventional gray level correction processor for performing gray level correction only on a luminance signal Y in an image signal;
FIG. 3 is a diagram illustrating the gray level correction characteristic of the luminance signal;
The following will describe a digital camera that is an embodiment of the present invention. First, the principle of operation for correcting the gray levels of image signals in the digital camera will be explained with reference to FIGS. 4 and 5.
FIG. 4 illustrates an example of the LUT for correcting the gray level of luminance signal Y. The axis of abscissa of the chart shown in FIG. 4 indicates an input luminance level Y, while the axis of ordinates indicates an output luminance level Y0. The processing for generating the LUT for correcting the gray levels of the luminance signals Y will now be described.
First, a histogram of the luminance signals Y of an image, which indicates the distribution of the frequency of the luminance signals Y at each signal level, is generated. Then, the frequency at each signal level in the histogram is accumulated to generate a cumulative histogram (curve A in the chart), and the dynamic ranges of output luminance signals Y0 are applied to the axis of ordinates. Subsequently, considering Weber-Fechner law regarding human visual characteristics (the sensory amount of humans is proportional to the logarithm of stimulation intensity), the curve A is subjected to logarithmic approximation to acquire a curve B. The curve B is obtained by expression (3) given below: