Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
2001-10-22
2004-08-24
Bella, Matthew C. (Department: 2676)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S597000, C345S600000, C345S601000, C345S215000
Reexamination Certificate
active
06781595
ABSTRACT:
BACKGROUND OF THE INVENTION
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
Recent developments in image signal acquiring equipment incorporating a solid-state image sensing device or a charge-coupled device (CCD), such as a digital camera or a scanner, have led to the improved performance of the solid-state image sensing device, permitting multi-stage exposures. This has made it possible to acquire image signals in a wider gray level dynamic range (hereinafter referred to as “the wide dynamic range image signals”).
Meanwhile, the recording formats of media for recording image signals, the formats of signals output to displays or printers, broadcast signal formats, and the like are still limited to the conventional dynamic ranges of 8-bit width or 10-bit width (hereinafter referred to as “the narrow dynamic range”.
Accordingly, to output image signals from electronic equipment capable of acquiring image signals of a wide dynamic range to other electronic equipment of the conventional narrow dynamic range, it is necessary to correct the gray levels of the image signals of the wide dynamic range, that is, to narrow the dynamic range.
Japanese Unexamined Patent Application Publication No. 9-331539 discloses a technique for correcting the dynamic range of image signals by individually correcting the gray levels of the signals of the three primary colors, Red, Green, and Blue (R, G, and B,) in a broadcasting video camera.
FIG. 1
illustrates an example of the configuration of a gray level correction processor in such a broadcasting video camera. In the gray level correction processor, the three primary color signals R, G, and B are supplied to a correction parameter arithmetic circuit 1, and also to their corresponding gray level correction circuits
2
R,
2
G, and
2
B, respectively.
The correction parameter arithmetic circuit
1
uses the received three primary color signals R, G, and B to generate luminance signals, and computes correction parameters on the basis of the luminance signals, then outputs the computed correction parameters to the gray level correction circuits
2
R,
2
G, and
2
B.
The gray level correction circuit
2
R includes a lookup table (hereinafter referred to as “LUT”) for correcting the gray level of a red signal R. The circuit
2
R checks the correction parameter and the red signal R, which have been received from the correction parameter arithmetic circuit
1
, against the built-in LUT, and outputs the associated value to a gamma correction circuit
3
as a correction value. The gray level correction circuit
2
G includes a LUT for correcting the gray level of a green signal G. The circuit
2
G checks the correction parameter and the green signal G, which have been received from the correction parameter arithmetic circuit
1
, against the built-in LUT, and outputs the associated value to the gamma correction circuit
3
as a correction value. The gray level correction circuit
2
B includes a LUT for correcting the gray level of a blue signal B. The circuit
2
B checks the correction parameter and the blue signal B, which have been received from the correction parameter arithmetic circuit
1
, against the built-in LUT, and outputs the associated value to the gamma correction circuit
3
as a correction value.
A gamma correction circuit
3
R carries out a gamma correction on the corrected red signal R received from the gray level correction circuit
2
R, and outputs the result to a matrix circuit
4
. A gamma correction circuit
3
G carries out a gamma correction on the corrected green signal G received from the gray level correction circuit
2
G, and outputs the result to the matrix circuit
4
. A gamma correction circuit
3
B carries out a gamma correction on the corrected blue signal B received from the gray level correction circuit
2
B, and outputs the result to the matrix circuit
4
. The matrix circuit
4
coverts the gamma-corrected three primary color signals R, G, and B into a luminance signal Y
0
and color-difference signals Cr
0
and Cb
0
.
The gray level correction processor shown in
FIG. 1
performs the gray level correction on the three primary color signals R, G, and B, respectively, at the same ratio. Hence, it is possible to compress the dynamic range of image signals to a desired width without causing a change in hue.
The gray level correction processor, however, requires the gray level correction circuits
2
and the gamma correction circuits
3
for the three primary color signals R, G, and B, respectively. This leads to a problem in that using the gray level correction processor in a consumer appliance, such as a digital camera, a video camera, or a television receiver, inevitably results in higher cost and a greater circuit scale.
Japanese Unexamined Patent Application Publication No. 11-55598 has disclosed a technique for correcting the dynamic range of image signals by performing gray level corrections only on the luminance signal Y among the image signals in a television receiver.
FIG. 2
illustrates an example of the configuration of a gray level correction processor for such a television receiver.
In the gray level correction processor, a received luminance signal Y is supplied to a correction parameter arithmetic circuit
11
, a luminance correction circuit
12
, and a color-difference correction circuit
13
, while received color-difference signals Cr and Cb are supplied to the color-difference correction circuit
13
.
Based on a received luminance signal Y, the correction parameter arithmetic circuit
11
computes a correction parameter with which an optimum gray level correction will be made in the luminance correction circuit
12
, and outputs the computed correction parameter to the luminance correction circuit
12
. The luminance correction circuit
12
, which includes a LUT for correcting the gray level of the luminance signal Y, checks the correction parameter and the luminance signal Y received from the correction parameter arithmetic circuit
11
against the built-in LUT, and outputs an associated value as a correction value Y
0
. The correction value Y
0
is also supplied to the color-difference correction circuit
13
.
The color-difference correction circuit
13
performs normalization by multiplying the color-difference signals Cr and Cb by Y
0
/Y, which is a ratio of the luminance signal Y before gray level correction to the luminance signal Y
0
after the correction, and generates color-difference signals Cr
0
and Cb
0
so as to maintain the ratio of the color-difference signals Cr and Cb to the input luminance signal Y.
The gray level correction processor shown in
FIG. 2
requires fewer constituent parts since it is adapted to carry out gray level corrections only on the luminance signal Y, thus controlling an increase in cost and circuit scale. The gray level correction processor of
FIG. 2
, however, presents the problems described below.
First, an error occurs in correcting the luminance of a pixel having a larger color-difference signal value. The relationship between three primary color signals R, G and B, and the luminance signal Y or the color-difference signals Cr and Cb is represented by expressions (1) and (2) shown below:
Y=
0.30
R+
0.59
G+
0.11
B
(1)
Cr=R-Y
Cb=B-Y
(2)
In correcting the gray level of the luminance signal Y, the information regarding the color-difference signals Cr and Cb is not taken into account. The information indicating the balance among the three primary color signals R, G, and B is missing in the luminance signal Y. For this reason, the gray level correction of the luminance signal Y is not properly made on a pixel in which the three primary
Kobayashi Seiji
Mitsunaga Tomoo
Nakajima Ken
Ono Hiroaki
Sano Chikako
Bell Boyd & Lloyd LLC
Bella Matthew C.
Sony Corporation
Tran Tam
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