Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1998-12-21
2004-09-07
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Combined image signal generator and general image signal...
Reexamination Certificate
active
06788339
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image pickup apparatus having an image sensor which is provided with color filters, and more particularly to an image pickup apparatus having an improved signal processing for white-balance adjustment.
2. Description of Related Art
FIG. 10
shows in a block diagram the signal processing system of a conventional single-plate type image pickup apparatus. In this case, the image pickup apparatus is assumed to be provided with complementary color filters having such an arrangement as shown in FIG.
2
.
Referring to
FIG. 10
, an analog image signal outputted from an image sensor
401
is supplied through a preprocessing circuit
402
to an A/D converting circuit
403
, where the analog signal is converted into a digital signal. The black level of the digital signal is uniformalized by an OB circuit
404
and is then temporarily stored in a memory
405
. It is to be noted that the digital signal as mentioned above is composed of signals Wr, Wb, Gr and Gb obtained by performing a generalized addition read-out on the image sensor
401
and adding together respective signals corresponding to color filters Ma, G, Cy and Ye.
The image signal read out from the memory
405
is gain-adjusted by a pixel gain adjusting circuit
406
according to a gain adjustment value obtained from a white balance circuit
420
. The gain-adjusted image signal from the pixel gain adjusting circuit
406
is sent to a color-separation and color-interpolation circuit
407
, where the image signal is then sent out as signals Wr, Wb, Gr and Gb to a color processing part situated at the next stage, and at the same time, the gain-adjusted image signal from the pixel gain adjusting circuit
406
is also sent to a luminance processing part without altering the arrangment of signals read out from the image sensor
401
.
At the color processing part, the output of the color-separation and color-interpolation circuit
407
is sent to a vertical low-pass filter circuit
408
. The output of the vertical low-pass filter circuit
408
is sent to a matrix circuit
409
to be converted into color signals R, G and B. The color signals R, G and B thus obtained are sent to a horizontal low-pass filter circuit
410
to have their frequency band restricted. The output of the horizontal low-pass filter circuit
410
is sent to a gamma converting circuit
411
to be subjected to a gamma correcting process. The output of the gamma converting circuit
411
is sent to a pure-color color-difference converting circuit
412
to be converted into a signal Y and color-difference signals R-Y and B-Y. These color-difference signals R-Y and B-Y are sent to the white balance circuit
420
and a C-SUP circuit
413
. At the C-SUP circuit
413
, the color-difference signals R-Y and B-Y are subjected to a process of killing the color of their saturated areas. The output of the C-SUP circuit
413
is sent to a Y compensating circuit
419
, and is also sent to a color compensating circuit
414
, which then performs fine color adjustment.
On the other hand, at the luminance processing part, the output of the pixel gain adjusting circuit
405
is processed to correct a difference in luminance brought about by the color filters. This process is carried out through a vertical low-pass filter circuit
415
and a horizontal low-pass filter circuit
416
. Then, an edge emphasizing process is performed on the output of the horizontal low-pass filter circuit
416
by a luminance aperture correcting (APC) circuit
417
. The output of the APC circuit
417
is sent to a gamma correcting circuit
418
to be subjected to a gamma correction process. A luminance signal thus obtained is sent from the gamma correcting circuit
418
to the Y compensating circuit
419
to have its luminance finely adjusted by using the color-difference signals sent from the C-SUP circuit
413
.
The color-difference signals processed by the color processing part and the luminance signal processed by the luminance processing part are temporarily stored in a memory
423
. In a case where the image sensor
401
is subjected to the field reading, the field signals are added together into one frame signal by an addition circuit
421
. The frame signal is sent to a compressing circuit
422
to be compressed in accordance with the JPEG system or the like and, after that, is recorded in a flash memory or the like.
The white balance circuit
420
has a clipping circuit for receiving the color-difference signals R-Y and B-Y and for limiting inputs having a large amplitude exceeding a predetermined value with respect to the amplitude of the received color-difference signals R-Y and B-Y. The white balance circuit
420
is controlled by a system control CPU to adjust the gain of output values of the image sensor
401
as follows. While one picture is divided into a plurality of blocks, the color-difference signals and the luminance signal which have passed through the clipping circuit are integrated for each of the divided blocks. Then, in a coordinate system formed by the color-difference signals R-Y and B-Y as shown in
FIG. 11
, a color-temperature varying range of white color is set as a white determining range
501
on the coordinate system. It is determined whether the integrated value obtained at each of the above-stated blocks is within the white determining range
501
on the coordinate system. Then, gains for the R signal and the B signal are decided by using the integrated values which are within the white determining range
501
. From the gains, a gain control value for control over the output of the image sensor
401
is obtained. Thus, the gain of output values of the image sensor
401
is adjusted on the basis of the gain control value.
In an image pickup apparatus using a conventional white balance adjusting method in which a white determining range is set on a coordinate system formed by the color difference signals R-Y and B-Y and an integrated value included within the white determining range is used for white balance adjustment, as mentioned above, if the area of an object of red system of low saturation is large at the time of photography under illumination of high color temperature, the illumination of high color temperature would be misjudged as illumination of low color temperature, because the object of red system of low saturation is included in the same area as that of white of low color temperature in the white determining range. Similarly, if the area of an object of blue system of low saturation is large at the time of photography under illumination of low color temperature, the illumination of low color temperature would be misjudged as illumination of high color temperature, because the object of blue system of low saturation is included in the same area as that of white of high color temperature in the white determining range.
Further, in the conventional white balance adjusting method, any color evaluation value that is not included within the white determining range is not used. Otherwise, the color evaluation value that is not included within the white determining range is replaced with the value of an edge part of the white determining range located nearest to that color evaluation value, and the thus-obtained value is integrated as a new color evaluation value. This arrangement necessitates the image pickup apparatus to be provided with an additional computing circuit.
Further, in a case where the conventional image pickup apparatus uses an image sensor which is provided with complementary color filters, the color reproducibility would degrade unless a matrix arithmetic operation is performed in an optimum manner according to color temperature in converting the image signal after white balance adjustment into a pure color signal through the matrix arithmetic operation.
According to the conventional arrangement, the color evaluation value varies with the method of reading from the image sensor. Therefore, it has been necessary to set the white determining range for one metho
Canon Kabushiki Kaisha
Garber Wendy R.
Robin Blecker & Daley
Rosendale Matthew L
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