Image analysis – Image enhancement or restoration – Intensity – brightness – contrast – or shading correction
Reexamination Certificate
1998-06-17
2001-06-19
Rogers, Scott (Department: 2624)
Image analysis
Image enhancement or restoration
Intensity, brightness, contrast, or shading correction
C358S461000
Reexamination Certificate
active
06249615
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus and, more particularly, to an image reading apparatus which is applied to a film scanner system for reading color images and has a shading correction function for performing shading correction and the like.
Conventional image reading apparatuses such as a film scanner system for reading color images use a color linear sensor such as a CCD to read color images.
Unfortunately, in image reading apparatuses using a color linear sensor such as a CCD, the sensitivity varies from one pixel to another due to, e.g., an uneven density of RGB filters, an uneven photoelectric conversion efficiency, or an uneven transfer efficiency. This significantly deteriorates the quality of read images.
Such unevenness is generally called shading.
This shading is produced not only by a color linear sensor such as a CCD described above but also by the nonuniformity of luminance of an illuminating light source itself. This nonuniformity results from the shadow of mercury grains of a fluorescent lamp used as a light source for illuminating color images or from uneven coating of a phosphor.
One conventional method (to be referred to as a shading correction hereinafter) of eliminating the influence of this shading is to prestore shading patterns and correct shading by multiplying a sensor output by an inverse coefficient on the basis of the stored shading patterns.
In the shading correction as described above, however, if color originals have substantially different optical characteristics, no equally optimal corrections can be performed for these color originals.
For example, when color originals are a negative film and a positive film, the quality of an image deteriorates upon shading correction of the positive film if shading correction of the negative film is optimized.
Jpn. Pat. Appln. KOKAI Publication No. 61-121667, therefore, has disclosed a method of performing different shading correction processes for a negative film and a positive film by checking whether the color original is a negative film and a positive film.
Unfortunately, the shading correction processes as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 61-121667 require a memory with a very large capacity to store shading parameters.
Accordingly, the method disclosed in Jpn. Pat. Appln. KOKAI Publication No. 61-121667 wastes a very large memory capacity.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image reading apparatus capable of obtaining high-quality images regardless of the types of color originals by performing equal shading correction processes regardless of the types of color originals without wasting memory capacity.
To achieve the above object, according to the first aspect of the present invention, there is provided an image reading apparatus comprising illuminating means for illuminating a color image, an imaging device for reading the color image illuminated by the illuminating means and outputting an image signal, AD-converting means for performing analog-to-digital (AD) conversion for the output image signal from the imaging device, storage means for storing digital data corresponding to a reference voltage of the AD-converting means, converting means for converting an output from the AD-converting means into an equivalent voltage value of the output image signal from the imaging device based on the digital data stored in the storage means, and shading correction means for performing shading correction for an output from the converting means.
According to the second aspect of the present invention, there is provided an image reading apparatus comprising illuminating means for illuminating a color image, an imaging device for reading the color image illuminated by the illuminating means and outputting an image signal, AD-converting means for performing analog-to-digital (AD) conversion for the output image signal from the imaging device, reference voltage setting means for setting a reference voltage of the AD-converting means based on the output image signal from the imaging device, storage means for storing digital data corresponding to the reference voltage set by the reference voltage setting means, converting means for converting an output from the AD-converting means into an equivalent voltage value of the output image signal from the imaging device based on the digital data stored in the storage means, and shading correction means for performing shading correction for an output from the converting means.
According to the third aspect of the present invention, there is provided an image reading apparatus comprising illuminating means for illuminating a color image, an imaging device for reading the color image illuminated by the illuminating means and outputting an image signal, AD-converting means for performing analog-to-digital (AD) conversion for the output image signal from the imaging device, storage means for storing digital data corresponding to a reference voltage of the AD-converting means, converting means for converting an output from the AD-converting means into an equivalent voltage value of the output image signal from the imaging device based on the digital data stored in the storage means, and arithmetic means for performing at least one of a shading correction operation, a color conversion operation, and a gradation conversion operation for an output from the converting means.
Additional object and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The object and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinbefore.
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Frishauf, Holtz Goodman, Langer & Chick, P.C.
Olympus Optical Co,. Ltd.
Rogers Scott
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