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Digital Camera Patent Abstract
A solid-state image pickup element is mounted on a digital camera.
The solid-state image pickup element has: first color pixels which
detect an amount of incident light of a first color of the three
primary colors; second color pixels which detect an amount of incident
light of a second color; third color pixels which detect an amount
of incident light of a third color; and luminance detection pixels
which are adjacent to the color pixels, respectively, and which
detect luminance information. In the digital camera, when data of
a reduced image in which the resolution is more reduced than the
resolution of all the pixels of the solid-state image pickup element
are to be produced, data of each of the color pixels (R, G, B),
and data of one or more of the luminance detection pixels (Y) which
are adjacent to the color pixel are added together. A signal processing
is applied to the added data to reproduce a photographed image.
Digital Camera Patent Claims
1. A digital camera comprising a solid-state image pickup element,
the solid-state image pickup element comprising: first color pixels
which detect an amount of incident light of a first color of three
primary colors; second color pixels which detect an amount of incident
light of a second color of the three primary colors; third color
pixels which detect an amount of incident light of a third color
of the three primary colors; and luminance detection pixels which
detect luminance information, each of the luminance detection pixels
being adjacent to each color pixel of the first, second and third
color pixels, wherein the digital camera comprises: a controlling
section that, when data of a reduced image in which a resolution
is more reduced than a resolution of all pixels of the solid-state
image pickup element are to be produced, adds data of each of a
set of color pixels to be selected among color pixel of the first,
second and third color pixels and data of one or more of the luminance
detection pixels which are adjacent to said each of the set of color
pixels to be selected; and a signal processing section that processes
data of the set of color pixels to be selected to which data of
luminance detection pixels have been added, and reproduces a photographed
image.
2. A digital camera according to claim 1, wherein the solid-state
image pickup element is of a CCD type, and the controlling section
comprises an adding and reading section that, when data are to be
read out from each of pixels of the solid-state image pickup element,
adds data of each of the set of color pixels to be selected and
data of one or more of the luminance detection pixels which are
adjacent to said each of the set of color pixels to be selected,
and reads out resulting data.
3. A digital camera according to claim 1, wherein the solid-state
image pickup element is of a MOS type, and the controlling section
comprises a data adding section that, after data of all pixels of
the solid-state image pickup element are read out, adds data of
each of the set of color pixels to be selected and data of one or
more of the luminance detection pixels which are adjacent to said
each of the set of color pixels to be selected.
4. A digital camera comprising a solid-state image pickup element,
the solid-state image pickup element comprising: first color pixels
which detect an amount of incident light of a first color of three
primary colors; second color pixels which detect an amount of incident
light of a second color of the three primary colors; third color
pixels which detect an amount of incident light of a third color
of the three primary colors; and luminance detection pixels which
detect luminance information, each of the luminance detection pixels
being adjacent to each color pixel of the first, second and third
color pixels, wherein the digital camera comprises: controlling
means for, when data of a reduced image in which a resolution is
more reduced than a resolution of all pixels of the solid-state
image pickup element are to be produced, adding data of each of
a set of color pixels to be selected among color pixel of the first,
second and third color pixels and data of one or more of the luminance
detection pixels which are adjacent to said each of the set of color
pixels to be selected; and signal processing means for processing
data of the set of color pixels to be selected to which data of
luminance detection pixels have been added, and reproducing a photographed
image.
5. A digital camera according to claim 4, wherein the solid-state
image pickup element is of a CCD type, and the controlling means
comprises adding and reading means for, when data are to be read
out from each of pixels of the solid-state image pickup element,
adding data of each of the set of color pixels to be selected and
data of one or more of the luminance detection pixels which are
adjacent to said each of the set of color pixels to be selected,
and reading out resulting data.
6. A digital camera according to claim 4, wherein said solid-state
image pickup element is of a MOS type, and the controlling means
comprises data adding means for, after data of all pixels of the
solid-state image pickup element are read out, adding data of each
of the set of color pixels to be selected and data of one or more
of the luminance detection pixels which are adjacent to said each
of the set of color pixels to be selected.
7. A digital camera according to claim 1, wherein the first, second
and third color pixels and the luminance detection pixels are arranged
in a surface portion of the solid-state image pickup element so
as to form a square lattice pattern, the square lattice pattern
comprises: a first checkered pattern in which the first, second
and third color pixels are arranged; and a second checkered pattern
in which the luminance detection pixels are arranged.
8. A digital camera according to claim 1, wherein data of each
of the set of color pixels to be selected and data of one or more
of the luminance detection pixels which are vertically adjacent
to said each of the set of color pixel to be selected are added
together.
9. A digital camera according to claim 4, wherein the first, second
and third color pixels and the luminance detection pixels are arranged
in a surface portion of the solid-state image pickup element so
as to form a square lattice pattern, the square lattice pattern
comprises: a first checkered pattern in which the first, second
and third color pixels are arranged; and a second checkered pattern
in which the luminance detection pixels are arranged.
10. A digital camera according to claim 4, wherein data of each
of the set of color pixels to be selected and data of one or more
of the luminance detection pixels which are vertically adjacent
to said each of the set of color pixel to be selected are added
together.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a digital camera on which
a solid-state image pickup element having color detection pixels
for R (red), G (green), and B (blue) and luminance detection pixels
is mounted.
[0003] 2. Description of the Related Art
[0004] A solid-state image pickup element which is mounted on a
digital camera to take a color image has color filters of the three
primary color R, G, and B that are arranged in, for example, the
Bayer pattern. In a configuration in which only R, G, and B color
filters are disposed, when the color of an object is biased, there
is a problem in that the luminance resolution of a photographed
image is impaired.
[0005] In order to solve the problem, JP-A-2003-318375 discloses
a related-art technique in which, among pixels constituting a solid-state
image pickup element, pixels in a checkered pattern position are
used as luminance detection pixels, and R, G, and B color filters
are formed on respective pixels in the other checkered pattern position,
so that the luminance resolution of a photographed image does not
depend on the color of an object.
[0006] In some of digital cameras on which a solid-state color
image pickup element where luminance detection pixels are formed
is mounted, when a motion picture is to be photographed, for example,
reduced image data are read out from the solid-state image pickup
element in order to enhance the frame rate.
[0007] Also JP-A-2003-318375 teaches a technique for reading reduced
image data from the solid-state image pickup element. For example,
image data are not read out from the luminance detection pixels,
image data are read out only from color detection pixels having
respective R, G, and B filters, and the image resolutions in both
the vertical and horizontal directions are accurately reduced to
1/2.
[0008] In the case where reduced image data are read out from a
solid-state image pickup element, when the reading is performed
while pixels are decimated as described above, all photo data of
the decimated pixels are wasted. In recent solid-state image pickup
elements, the number of pixels reaches the limits of the technology,
and the signal charge amount which can be received by one pixel
is very small. When image data are read out from a solid-state image
pickup element while decimating pixels, therefore, there arises
a problem in that the luminance sensitivity is lowered.
SUMMARY OF THE INVENTION
[0009] It is an object of the invention to provide a digital camera
in which data of a reduced image can be read out from a solid-state
image pickup element without lowering the luminance sensitivity.
[0010] The digital camera of the invention is a digital camera
comprising a solid-state image pickup element, the solid-state image
pickup element comprising: first color pixels which detect an amount
of incident light of a first color of three primary colors; second
color pixels which detect an amount of incident light of a second
color of the three primary colors; third color pixels which detect
an amount of incident light of a third color of the three primary
colors; and luminance detection pixels which detect luminance information,
each of the luminance detection pixels being adjacent to each color
pixel of the first, second and third color pixels, wherein the digital
camera comprises: a controlling section that, when data of a reduced
image in which a resolution is more reduced than a resolution of
all pixels of the solid-state image pickup element are to be produced,
adds data of each of a set of color pixels to be selected among
color pixel of the first, second and third color pixels and data
of one or more of the luminance detection pixels which are adjacent
to said each of the set of color pixels to be selected; and a signal
processing section that processes data of the set of color pixels
to be selected to which data of luminance detection pixels have
been added, and reproduces a photographed image.
[0011] According to the configuration, a reduced image can be obtained
without impairing the luminance.
[0012] In the digital camera of the invention, the solid-state
image pickup element is of a CCD type, and the controlling section
comprises an adding and reading section that, when data are to be
read out from each of pixels of the solid-state image pickup element,
adds data of each of the set of color pixels to be selected and
data of one or more of the luminance detection pixels which are
adjacent to said each of the set of color pixels to be selected,
and reads out resulting data.
[0013] According to the configuration, as compared to a CMOS solid-state
image pickup element, an image which is brighter, and which has
a higher color reproducibility can be photographed. Furthermore,
the addition of pixel data can be facilitated, and the frame rate
can be made higher.
[0014] In the digital camera of the invention, the solid-state
image pickup element is of a MOS type, and the controlling section
comprises a data adding section that, after data of all pixels of
the solid-state image pickup element are read out, adds data of
each of the set of color pixels to be selected and data of one or
more of the luminance detection pixels which are adjacent to said
each of the set of color pixels to be selected.
[0015] According to the configuration, even a MOS solid-state image
pickup element can obtain a bright reduced image.
[0016] In the digital camera of the invention, the first, second
and third color pixels and the luminance detection pixels are arranged
in a surface portion of the solid-state image pickup element so
as to form a square lattice pattern, the square lattice pattern
comprises: a first checkered pattern in which the first, second
and third color pixels are arranged; and a second checkered pattern
in which the luminance detection pixels are arranged.
[0017] According to the configuration, in the case where data are
read out from pixels of the solid-state image pickup element and
a photographed image is reproduced at a resolution of all pixels,
even when the color of an object is biased, it is possible to avoid
a situation where the luminance resolution depends on the color.
[0018] In the digital camera of the invention, data of each of
the set of color pixels to be selected and data of one or more of
the luminance detection pixels which are vertically adjacent to
said each of the set of color pixel to be selected are added together.
[0019] According to the configuration, in the case of a CCD solid-state
image pickup element, pixel addition in a vertical transfer path
is facilitated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a functional block diagram of a digital still
camera of an embodiment of the invention;
[0021] FIG. 2 is a diagram showing in detail the configuration
of a digital signal processing section shown in FIG. 1;
[0022] FIG. 3 is a surface diagram of 5.times.5 pixels of a solid-state
image pickup element shown in FIG. 1;
[0023] FIG. 4 is a diagram illustrating an example in which a reduced
image where the resolution is reduced to 1/2 is read out from the
solid-state image pickup element shown in FIG. 3; and
[0024] FIG. 5 is a diagram illustrating an example in which a reduced
image where the resolution is reduced to 1/4 is read out from the
solid-state image pickup element shown in FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Hereinafter, an embodiment of the invention will be described
with reference to the accompanying drawings.
[0026] FIG. 1 is a diagram of a digital still camera of the embodiment
of the invention. Although a digital still camera will be exemplarily
described as the embodiment, the invention can be applied also to
digital cameras of other kinds such as a digital video camera, and
a camera mounted on a portable telephone or a like small electronic
apparatus.
[0027] The digital still camera shown in FIG. 1 comprises: an imaging
lens 10; a CCD solid-state image pickup element 11; an aperture
12 disposed between them; an IR cut filter 13; and an optical low-pass
filter 14. A CPU 15 which controls the whole digital still camera
controls a light emitting section 16 for a flash, and a light receiving
section 17, controls a lens driving section 18 to adjust the position
of the imaging lens 10 to the focus position, and controls the opening
amount of the aperture via an aperture driving section 19 to adjust
the exposure to an adequate value.
[0028] In the embodiment, the solid-state image pickup element
11 has: color pixels which detect a signal corresponding to the
amount of incident light of red (R); color pixels which detect a
signal corresponding to the amount of incident light of green (G);
color pixels which detect a signal corresponding to the amount of
incident light of blue (B); and in addition luminance detection
pixels which detect luminance information (Y). The solid-state image
pickup element 11 may not be of the CCD type, and may be of other
types such as the CMOS type.
[0029] The CPU 15 drives the solid-state image pickup element 11
via an image pickup element driving section 20 so that an object
image taken through the imaging lens 10 is output as color signals.
The manner of driving the element will be described in detail later.
An instruction signal from the user is supplied to the CPU 15 via
an operating section 21, and the CPU 15 conducts various controls
in accordance with the instructions.
[0030] The operating section 21 includes a shutter button. When
the shutter button is in a half-depressed state (switch S1), the
focus is adjusted, and, when the shutter button is in a fully-depressed
state (switch S2), a photographing operation is performed.
[0031] An electric control system of the digital still camera comprises:
an analog signal processing section 22 which is connected to the
output of the solid-state image pickup element 11; and an A/D converter
circuit 23 which converts the R, G, and B color signals and a luminance
detection signal Y that are output from the analog signal processing
section 22, to digital signals. These sections are controlled by
the CPU 15.
[0032] The electric control system of the digital still camera
further comprises: a memory controlling section 25 which is connected
to a main memory (frame memory) 24; a digital signal processing
section 26 (signal processing section) for performing signal processing
which will be described in detail later; a compression/expansion
processing section 27 which compresses a photographed image to a
JPEG image and expands a compressed image; an integrating section
28 which integrates photometric data to enable the gain of white
balance to be adjusted: an external memory controlling section 30
to which a detachable recording medium 29 is to be connected; and
a display controlling section 32 to which a liquid crystal displaying
section 31 mounted on, for example, the back face of the camera
is connected. These components are connected to one another through
a control bus 33 and a data bus 34, and controlled by instructions
from the CPU 15.
[0033] FIG. 2 is a diagram showing in detail the configuration
of the digital signal processing section 26 shown in FIG. 1. The
digital signal processing section 26 comprises: an offset correcting
circuit 41 which fetches the digital R, G, and B color signals and
luminance detection signal Y output from the A/D converter circuit
23, and which performs the offset processing; a gain correcting
circuit 42 which takes white balance; and a gamma correcting circuit
43 which performs gamma correction on the white balance-corrected
color signals. In the case where the linear matrix process or the
knee correction is to be performed on the offset-corrected signals,
the process or the correction is performed between the gain correcting
circuit 42 and the gamma correcting circuit 43.
[0034] The digital signal processing section 26 further comprises:
an RGB interpolation calculating section 44 which performs an interpolation
calculation on the gamma-corrected R, G, and B color signals to
obtain the three color or R, G, and B signals in respective pixel
positions; an RGB/YC converting section 45 which obtains a luminance
signal Y and color difference signals Cr, Cb from the R, G, and
B color signals and the luminance detection signal Y; a noise filter
46 which reduces the noise level of the luminance signal Y output
from the converting section 45; an contour correcting circuit 47
which performs contour correction on the luminance signal Y after
the noise reduction; and a color difference matrix circuit 48 which
multiplies the color difference signals Cr, Cb by a color difference
matrix to perform hue correction.
[0035] In the case of a triple-type image pickup element, the RGB
interpolation calculating section 44 is not necessary. However,
the solid-state image pickup element 11 used in the embodiment is
a single-type solid-state image pickup element, and each pixel outputs
only one of the R, G, and B color signals or the luminance detection
signal Y. In a pixel which outputs R, therefore, the degrees of
the colors which are not output, i.e., G and B color signals in
the pixel position are obtained by interpolation of the G and B
signals of peripheral pixels.
[0036] FIG. 3 is a surface diagram of the solid-state image pickup
element 11 used in the embodiment. In the solid-state image pickup
element 11, many pixels are arranged in a square lattice pattern.
Among the arranged pixels, a portion of 5.times.5=25 pixels is shown
in FIG. 3.
[0037] Filters Y, and color filters R, G, B are disposed in respective
surface portions of the many pixels (photodiodes) (not shown) which
are arranged vertically and horizontally in the solid-state image
pickup element 11. The filters Y are disposed on the surfaces of
pixels which are arranged in a checkered pattern position, among
the pixels which are arranged vertically and horizontally. The color
filters R, G, B are disposed on the surfaces of pixels which are
arranged in other checkered pattern position.
[0038] In the solid-state image pickup element 11 exemplarily shown
in FIG. 3, the filters are arranged in the sequence of "Y,
G, Y, G, . . . " on the respective surfaces of pixels of even
rows, and rows of "R, Y, B, Y, R, . . . " and "B,
Y, R, Y, B, . . . " are alternately arranged on the surfaces
of pixels of odd rows.
[0039] The filters Y can be said to be filters having spectral
characteristics correlating with luminance information, i.e., luminance
filters. ND filters, transparent filters, white filters, gray filters,
and the like fall under the category of luminance filters. Also
the configuration in which no filter is disposed on the surface
of a pixel and light is incident directly on the pixel surface can
be said to be a configuration in which a luminance filter is disposed.
[0040] In the following description, a pixel having a filter R
is referred to as "R pixel", a pixel having a filter G
as "G pixel", a pixel having a filter B as "B pixel",
and a pixel having a filter Y as "Y pixel".
[0041] When a still image having the maximum resolution is to be
produced with using image data obtained by the solid-state image
pickup element 11 having the above-described configuration, for
example, R, G, B, and Y image data are individually read out from
the respective pixels of the solid-state image pickup element 11
in the same manner as the related art, and then processed by the
digital signal processing section 26.
[0042] By contrast, when a reduced image having a 1/2 resolution
in both the vertical and horizontal directions is to be produced
with using image data obtained by the solid-state image pickup element
11, in the embodiment, the CPU 15 controls the image pickup element
driving section 20 so that image data of two pixels adjacent to
each other in the vertical direction are added together as shown
in FIG. 4 and then read out from the solid-state image pickup element
11. In other words, the CPU 15 functions as a controlling section
(hereinafter sometimes referred to as an adding controlling section)
that, when data of a reduced image in which a resolution is more
reduced than a resolution of all pixels of the solid-state image
pickup element are to be produced, adds data of each of a set of
color pixels to be selected among color pixel of the first, second
and third color pixels and data of one or more of the luminance
detection pixels which are adjacent to said each of the set of color
pixels to be selected. In the case of the solid-state image pickup
element 11 of the CCD type, the image data (signal charge amounts)
may be added together on a vertical transfer path, and, in the case
of the solid-state image pickup element 11 of the CMOS type, signal
amounts read out by readout transistors in accordance with signal
charge amounts of pixels are added together.
[0043] In the related art, when a reduced image having a 1/2 resolution
is to be read out, image data (luminance signals) of Y pixels are
not read out from the solid-state image pickup element 11, and are
discarded. In the embodiment, image data (luminance signals Y) of
the Y pixels are added to R, G, and B image data (color signals),
and therefore the signal (luminance data) amount received by the
Y pixels are not wasted.
[0044] Hereinafter, the manner where color information and luminance
information can be accurately reproduced from R, G, and B color
signals to which luminance data of the Y pixels are added will be
described. The original R signal is indicated as "R",
the original G signal is indicated as "G", the original
B signal is indicated as "B", and the R, G, and B signals
which have been read out from the solid-state image pickup element
11, subjected to gamma correction and the like, and interpolated
in the RGB interpolation calculating section 44 are indicated as
"R'", "G'", and "B'", respectively.
Then, the followings hold: R'=R+Y, G'=G+Y, B'=B+Y. When these expressions
are substituted in the general formula for converting the R, G,
and B signals to the luminance signal: Y=0.299R+0.587G+0.114B, the
following holds (where the luminance calculated from RGB is indicated
by Yrgb): Yrgb = 0.299 .times. ( R ' - Y ) + 0.587 .times. ( G '
- Y ) + 0.114 .times. ( B ' - Y ) = 0.299 .times. R ' + 0.587 .times.
G ' + 0.114 .times. B ' - ( 0.299 + 0.587 + 0.114 ) .times. Y =
Y ' - Y .
[0045] In the above expression, Y'=0.299R'+0.587G'+0.114B' is the
luminance obtained from R', G', and B' on the base of the general
formula.
[0046] Therefore, Y'=Yrgb+Y is attained. It will be seen that the
luminance Y' obtained from R', G', and B' has a value in which the
luminance Y read out from the Y pixels is added to the luminance
Yrgb obtained from R, G, and B, and the luminance sensitivity is
enhanced.
[0047] With respect to the color difference signals Cr, Cb, the
followings hold: Cr=R'-Y'=(R+Y)-(Yrgb+Y)=R-Yrgb, Cb=B'-Y'=(B+Y)-(Yrgb+Y)=B-Yrgb.
It will be seen that the color information is restored.
[0048] FIG. 5 is a diagram illustrating an example in which an
image where the resolution is reduced to 1/4 is read out from the
solid-state image pickup element 11, and showing 50 pixels in total
of 5 columns and 10 rows of the solid-state image pickup element
11. In this example, image data of three pixels arranged in the
vertical direction which are enclosed by an oval in each column
are read out with being added together, and one pixel which is among
the four pixel arranged in the vertical direction, and which is
not enclosed by the oval is decimated so that image data of the
pixel is not read out. In the first column, for example, the image
data of the B pixel, and the image data of the upper and lower Y
pixels are read out with being added together, and the R pixel is
decimated so that the image data of the R pixel is discarded.
[0049] In this readout method, the followings hold: R'=R+2Y, G'=G+2Y,
B'=B+2Y. These expressions are obtained simply by replacing "Y"
in the expressions shown in the description of FIG. 4 with "2Y".
Therefore, it will be seen that, when 1/4 of all the pixels are
not read out, the resolutions can be decimated to 1/4, and color
information and luminance information can be accurately reproduced.
[0050] As seen from FIG. 5, in each column, the arrangements of
three pixels which are to be added are identical with each other
in the vertical direction. Therefore, the pixel addition is further
performed so that six pixels (in the first column, two B pixels
and 4 Y pixels) are added together, whereby a further reduced image
can be read out without lowering luminance.
[0051] In the embodiment described above, it is assumed that the
solid-state image pickup element 11 of the CCD type is used and,
in the readout of image data from the solid-state image pickup element
11, the pixel addition is performed and the readout is then conducted.
In this case, the CPU 15 serving as the adding controlling section
may comprise an adding and reading section that, when data are to
be read out from each of pixels of the solid-state image pickup
element 11, adds data of each of the set of color pixels to be selected
and data of one or more of the luminance detection pixels which
are adjacent to said each of the set of color pixels to be selected,
and reads out resulting data.
[0052] By contrast, in the case where a solid-state image pickup
element of the MOS type such as the CMOS is used, for example, there
is provided the above-mentioned adding controlling section comprising
a data adding circuit (data adding section), the adding circuit
being disposed in front or rear of the offset correcting circuit
41 shown in FIG. 2, and, after image data of all pixels are read
out, addition of image data, i.e., addition of digitized R, G, B,
and Y data is performed. The data adding section has a function
of, after data of all pixels of the solid-state image pickup element
are read out, adding data of each of the set of color pixels to
be selected and data of one or more of the luminance detection pixels
which are adjacent to said each of the set of color pixels to be
selected. In this case, the adding controlling section may not be
the CPU 15, and may be further provided separately from the CPU
15.
[0053] The adding control section comprising the adding and reading
section or the data adding section is primarily constituted of a
processor which operates in accordance with a program. For example,
but not by way of the limitation, these sections each can be a general
purpose computer containing a set of instructions for the foregoing
functions.
[0054] According to the invention, when a reduced image is read
out from the solid-state image pickup element, degradation of a
luminance can be avoided, and hence a bright reduced image can be
obtained.
[0055] In the invention, when a reduced image is read out from
a solid-state image pickup element, the readout can be performed
without lowering luminance, and hence a reduced image of high luminance
can be easily obtained. The invention is suitably used in a digital
camera having a motion picture photographing function or a function
of displaying a reduced image as a through image on a liquid crystal
display device or the like.
[0056] The entire disclosure of each and every foreign patent application
from which the benefit of foreign priority has been claimed in the
present application is incorporated herein by reference, as if fully
set forth. |