Image analysis – Color image processing
Reexamination Certificate
1999-09-07
2004-03-23
Johns, Andrew W. (Department: 2621)
Image analysis
Color image processing
C382S167000, C382S272000, C358S518000
Reexamination Certificate
active
06711285
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image correcting method, an image correcting apparatus and a storage medium. In particular, the present invention relates to an image correcting method for correcting the density and color of an image, an image correcting apparatus capable of applying the image correcting method, and a storage medium in which a program for executing the image correcting method in a computer is stored.
2. Description of the Related Art
Color correction such as white balance adjustment or density correction for normalizing the density of the entire image need be performed on analog image signals or image data obtained by photography using a video camera or a digital still camera. In general, the color correction and density correction of an image are performed as follows: an image signal or image data is sampled for each of a plurality of channels (for example, red, green and blue), and then, an average value is calculated for each channel based on the data for each channel obtained by the sampling. Based on the calculated average values, a correction value for the color correction and a correction value for the density correction are then determined such that the average value relating to chromaticity becomes a neutral color (gray) in the color correction and the average value relating to luminance becomes an intermediate value (a numeral such as “0.75” issued in the case of reflection density, and “118” issued in the case of image data representing the density of each pixel in 8 bits) in the density correction, thus adjusting (converting) the image signal or image data.
In this specification, besides a simple average, the term “an average” also generally signifies various evaluation values similar to an average value such as a value obtained by dividing the entire screen into a plurality of regions, as is the case with division photometry or evaluation photometry, calculating the average value of each region, and synthesizing the average values of each region by the use of weighting coefficients which are different for each region.
As for the color correction and density correction of the image, an improvement in correction accuracy has been demanded, and further, for example, an improvement in operational stability has been demanded, that is, that images representing similar scenes can be corrected with similar correction values or that the malfunction rate be reduced. In order to improve the operational stability and achieve stable correction results by correcting the color and density of images representing similar scenes, it is necessary to stabilize an average to be used for the calculation of the correction values for the color correction and the density correction.
In view of this, the average has been conventionally stabilized by devising an algorithm exclusively for determining the average (as disclosed, for example, in Japanese Patent Application Laid-open (JP-A) No. 3-160891). However, as for both the color correction and the density correction, it has not been easy to achieve both an improvement in correction accuracy and an improvement in operational stability at the same time. Moreover, problems, such as variations existing in the accuracy of the color correction and the density correction for each image, have also arisen.
SUMMARY OF THE INVENTION
The present invention has been accomplished in an attempt to solve the above problems experienced in the prior art. Therefore, an object of the present invention is to provide an image correcting method, an image correcting apparatus and a storage medium which enable color correction and density correction to be performed with high accuracy all the time.
Desired color correction of an image is to correct, to a neutral color, portions which were to be originally in a neutral color in an original image. As the ratio of data of the portion which should be in a neutral color included in data for obtaining the correction value for the color correction increases, the accuracy of the color correction based on the obtained correction value can be improved. Although most high luminance points or low luminance points in an original image are likely to be neutral color portions, the high luminance points or low luminance points in the original image are frequently a minute portion of the area of the original image, and therefore, the portions where high luminance points or low luminance points exist on the original image include high spatial frequency components. In contrast, the density correction of the image is to correct the average value relating to the luminance of the original image to an intermediate value. Consequently, if data indicative of the high luminance points or low luminance points in the original image is included in data for obtaining the correction value for the density correction, the average value relating to the luminance of the original image is liable to fluctuate, thereby inducing deterioration in the accuracy and stability of the density correction.
In an image correcting method according to a first aspect of the present invention, color correction of a original color image is performed by using first image data including higher spatial frequency components of the original color image, and density correction of the original color image is performed by using second image data in which the high frequency component is removed or reduced.
In the first aspect, the color correction is performed on the original color image by using the first image data including the high frequency component of the original color image. Since the first image data includes the high frequency component of the original color image, data of high luminance points or low luminance points of a small area in the original color image, in which a number of data of portions to be a neutral color are included is also stored. Consequently, it is possible to perform the color correction with high accuracy.
Furthermore, in the first aspect, the density correction is performed on the original color image by using the second image data. Since the high frequency component of the original color image is removed from or reduced in the second image data, the variations of the luminance at the portions where the high luminance points or low luminance points exist in the original color image become dull (averaged) in the second image data, thereby preventing or alleviating any adverse effect of the high luminance points or low luminance points in the original color image on the accuracy and stability of the density correction. Consequently, in the first aspect, it is possible to perform the color correction and the density correction with high accuracy all the time.
Some apparatuses for producing image data (for example, a digital still camera for photographing an object so as to produce image data, a scanner for scanning an image recorded on a storage medium such as a photographic film so as to produce image data, or the like) are so constructed as to produce the image data corresponding to the first image data according to the present invention and the image data corresponding to the second image data according to the present invention. Some apparatuses for processing input image data to output it (for example, various image processors, various interface circuits, or the like) are so constructed as to produce the image data corresponding to the second image data according to the present invention upon inputting of the image data corresponding to the first image data according to the present invention so as to output data for each image. According to the present invention claimed in claim
1
, there may be used the first image data and the second image data produced by the above-described apparatuses or obtained from the original color image, as described below.
In an image correcting method according to a second aspect, first image data including higher spatial frequency components of the original color image and second image data, in which the high frequency component is rem
Alavi Amir
Fuji Photo Film Co. , Ltd.
Johns Andrew W.
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