JP2000023085A - Digital camera and image signal processing storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital camera which can satisfactorily suppress the false colors and moires despite increase of the number of pixels by executing the median processing to the data on a specific pixel area via an image processing circuit in a format processing mode. SOLUTION: A block processing circuit consists of a white balance fine adjustment circuit 210 and an interpolation/outline processing circuit 220 and performs various types of signal processing every (n×m) pixel data, i.e., in every block. The circuit 210 multiplies the R and B signals which undergone the processes up to that of a γ correction circuit and are stored in a buffer memory by the white balance fine adjustment gain that is calculated by a mean value circuit for each of R and B signals of a (20×20)-pixel area respectively to perform fine adjustment of the white balance. Then format processing is applied to the image data for each of block data on the (20×20) pixel-area for the compression of data of a JPEG system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital camera that stores a subject as electronically compressed image data and a storage medium that stores an image signal processing program.

[0002]

2. Description of the Related Art Conventionally, a finder device in which an image of a subject passing through a photographing lens is guided by a quick return mirror, and an imaging device such as a CCD arranged behind the quick return mirror to capture an image of the subject and output image data. Device, an image processing circuit that performs image processing such as white balance and gamma correction on image data output from the imaging device, and a storage medium such as a flash memory that compresses the data after image processing using a method such as JPEG. 2. Description of the Related Art An electronic still camera including a compression circuit for storing image data and a monitor for displaying data after image processing is known. In the image processing circuit, based on image data output from the imaging device,
Parameters such as an R gain and a B gain for white balance adjustment or a gradation curve for γ correction are calculated by a predetermined algorithm. Further, the image data is converted into 8 × 8 luminance data Y and color difference data Cr, Cb for compression by the JPEG method.

[0003]

In such an image pickup apparatus of a conventional electronic still camera, a single primary color CCD,
CCDs (each for G, R / B) or 3 Cs
Use CDs (each for R, G, B). One CCD
Is used, an RGB color filter is arranged in front of each pixel of the CCD, so that the R signal, G
Signal or B signal is missing. Therefore, using the G signal of the actually acquired pixel, the G signal of all pixels is generated by interpolating the pixel having no G signal component, and the (RG) signal and the (BG) signal are similarly generated. Interpolated. The same applies to the case where two CCDs are used.

[0004] However, depending on the characteristics of the captured image and the characteristics of the low-pass filter to be used, a false color or moiré occurs after the interpolation processing, resulting in remarkable deterioration in image quality. Therefore, conventionally, the above-described Y signal, C signal generated from the R, G, B signals is used.
Of the r signal and the Cb signal, the Cr signal and the Cb signal are processed by a low-pass filter to prevent false colors and moire.
A high-quality electronic still camera in which the number of pixels of the CCD exceeds 2 million pixels is insufficient.

It is an object of the present invention to provide an electronic still camera capable of sufficiently suppressing false colors and moiré in a short processing time even when the number of pixels is large. Another object of the present invention is to provide a storage medium storing a program for performing signal processing such that false color and moiré can be sufficiently suppressed in a short processing time even for image data captured by an imaging device having a large number of pixels. It is in.

[0006]

FIG. 1 shows an embodiment of the present invention.
The present invention will be described with reference to FIGS. (1) An image pickup device 73 for picking up an image of a subject passing through a photographing lens 91 and outputting image data.
(26), an image processing circuit 29 that performs image processing on image data output from the imaging device 26, and a compression circuit 3 that compresses image data output from the image processing circuit 29
And the image processing circuit 29 is applied to a digital camera which also performs data format processing suitable for the compression circuit 33. The object described above is achieved by the image processing circuit 29 performing median processing on data in the n × m pixel area during the format processing. (2) The digital camera according to the first aspect of the present invention is the digital camera according to the first aspect, wherein (n-
i) × (m−j) image data is extracted and median processing is performed. (3) The invention according to claim 3 is an imaging device 73 that captures an image of a subject passing through a photographing lens 91 and outputs image data.
The present invention is applied to a digital camera including (26) and an image processing circuit 29 that performs predetermined image processing on image data output from the imaging device 26. Then, the image processing circuit 29 outputs (n-
i) The above-mentioned object is achieved by extracting the image data of (m−j) and performing the median processing. (4) In the storage medium according to the fourth aspect of the invention, there are provided a format process for formatting the image data captured by the imaging device 26 to compress the image data, various signal processes performed prior to the format process, and a format process. A compression process for compressing the processed image data, and a program for performing a median process on the image data in the n × m pixel area during the format process is stored, and the image data is signal-processed and compressed by the program. Thereby, the above-mentioned object is achieved. (5) The image signal processing storage medium according to claim 4, wherein the image data of the n × m pixel area is
It is characterized in that median processing is performed by extracting (ni) × (mj) image data. (6) In the storage medium according to the sixth aspect, when performing predetermined image processing on the image data captured by the imaging device, (ni) of the image data in the n × m pixel area. ×
A program for extracting (mj) image data and performing median processing is stored, and the image data is processed by the program to achieve the above-described object.

[0007] In the section of the means for solving the above-mentioned problems, which explains the configuration of the present invention, the drawings of the embodiments are used to facilitate understanding of the present invention. However, the present invention is not limited to this.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, a single-lens reflex electronic still camera according to this embodiment
0 and a finder device 80 that is attached to and detached from the camera body 70
And a camera body 7 having a photographic lens 91 and an aperture 92 built therein.
0 and an interchangeable lens 90 which is attached to and detached from the camera. The subject light enters the camera body 70 through the interchangeable lens 90, and is guided to the finder device 80 by the quick return mirror 71 located at the position shown by the dotted line before the release, and forms an image on the finder mat 81. The subject image is further guided to an eyepiece 83 by a pentaprism 82. After the release, the quick return mirror 71 rotates to the position shown by the solid line, and the subject light forms an image on the imaging device 73 via the shutter 72. Before the release, the subject image enters the white balance sensor 86 through the prism 84 and the imaging lens 85 to detect the color temperature of the subject image.

FIG. 2 is a circuit block diagram of the embodiment. The CPU 21 receives a half-press signal and a full-press signal from a half-press switch 22 and a full-press switch 23 linked to the release button, respectively. In response to a command from the CPU 21, the driving of the CCD 26 of the imaging device 73 is controlled via the timing generator 24 and the driver 25. Also,
Analog processing circuit 2 by timing generator 24
7 and the operation timing of the A / D conversion circuit 28 are controlled. Further, the white balance detection processing circuit 35 starts driving according to a signal from the CPU 21.

When the full-press switch 23 is turned on after the half-press switch 22 is turned on, the quick return mirror 71 rotates upward, and subject light from the interchangeable lens 90 is condensed on the light receiving surface of the CCD 26. The CCD 26 accumulates signal charges corresponding to the brightness of the subject image. C
The signal charges stored in the CD 26 are discharged by the driver 25 and input to an analog signal processing circuit 27 including an AGC circuit, a CDS circuit, and the like. Gain control for the analog image signal by the analog signal processing circuit 27,
After analog processing such as noise removal is performed, the signal is converted into a digital signal by the A / D conversion circuit 28. The digitally converted signal is guided to an image processing circuit 29 configured as, for example, an ASIC, where white balance adjustment,
Image pre-processing such as contour compensation and gamma correction is performed.

The white balance detection processing circuit 35 has a white balance sensor 35A (FIG. 1) which is a color temperature sensor.
White balance sensor 86), an A / D conversion circuit 35B that converts an analog signal from the white balance sensor 35A into a digital signal, and a CPU 35C that generates a white balance adjustment signal based on the digital color temperature signal. The white balance sensor 35A includes, for example, a plurality of photoelectric conversion elements having sensitivity to red R, blue B, and green G, respectively, and receives a light image of the entire object field. C
PU35C outputs R based on the outputs of the plurality of photoelectric conversion elements.
Calculate the gain and B gain. These gains are
The data is transferred to a predetermined register 21 and stored. Also,
The white balance sensor 86 shown in FIG. 1 can be constituted by a two-dimensional CCD having 24 columns × 20 rows.
D is divided into 16 regions, and a plurality of elements having sensitivity to RGB are arranged in each region.

The image data on which the image pre-processing has been performed is further subjected to a format processing (image post-processing) for JPEG compression, and thereafter the image data is temporarily stored in the buffer memory 30. .

The image data stored in the buffer memory 30 is processed by the display image creation circuit 31 into image data for display, and displayed on an external monitor 32 such as an LCD as a photographing result. The image data stored in the buffer memory 30 is subjected to data compression by a compression circuit 33 at a predetermined ratio according to the JPEG method, and is recorded on a storage medium (PC card) 34 such as a flash memory.

FIGS. 3 and 4 are block diagrams showing details of the image processing circuit 29. FIG. FIG. 3 shows a line processing circuit 100 that performs signal processing on image data from the CCD 26 line by line, and performs the above-described image preprocessing. FIG.
The image data processed by the line processing circuit 100 is
A block processing circuit 200 that performs signal processing in block units of a 0 × 20 pixel area, a 16 × 16 pixel area, a 12 × 12 pixel area, or an 8 × 8 pixel area, and performs the above-described image post-processing. Note that the image processing circuit 29 is realized as software using a plurality of processors, but in this specification, it is described as hardware for convenience.

The line processing circuit 100 shown in FIG. 3 performs various kinds of signal processing described later on the 12-bit R, G, and B signals output from the A / D conversion circuit 28.
Defect correction circuit 101 and digital clamp circuit 102
, Gain circuit 103, white balance circuit 104
, A black level circuit 105, a γ correction circuit 106, and an average value and histogram calculation circuit 107.

The defect correction circuit 101 corrects data from defective pixels (specified in advance and the addresses thereof are set in registers) in a dot-sequential manner for each output of the CCD 26. is there. The digital clamp circuit 102 subtracts a weighted average of a plurality of pixel data used as so-called optical black from each pixel data of the line in a dot-sequential manner for each output line of the CCD 26. Gain circuit 103
Applies a predetermined gain uniformly to each of the R, G, and B signals output from the CCD 26 in a dot-sequential manner for each line with respect to the output of the CCD 26, and
6 is performed on the G signal, and the sensitivity ratio of the CCD 26 is corrected on the R and B signals.

The white balance circuit 104 includes a CCD 2
The R and B signals are multiplied by the R gain and the B gain, which are the white balance adjustment coefficients determined in advance and stored in the register of the CPU 21 as described above, in a dot-sequential manner for each output of the output No. 6. In the present invention, as will be described later, based on the image data corrected by the white balance circuit 104, a white balance fine adjustment gain is further calculated to finely adjust the white balance.
The black level circuit 105 determines the output of the CCD 26 dot-sequentially for each line,
Are added to the R, G, B signals. The gamma correction circuit 106 performs gamma correction on the output of the CCD 26 in a dot-sequential manner for each line using a gradation look-up table. The 12-bit R, G, and B signals are converted into 8-bit data by the γ correction.

Average value and histogram calculation circuit 107
Extracts, for example, image data of a 512 × 512 area centered on the center of the focus detection area from the image data after the γ correction, obtains a white balance fine adjustment gain RFgain for the R signal and a B signal BFgain for fine adjustment of white balance is calculated by the following equations (1) and (2), for example. The gains RFgain and BFgain are stored in registers. For example, when a color filter is arranged on a 512 × 512 pixel area as shown in FIG. 5, the average values of the R, G, and B signals are calculated by equations (3) to (5), and (1) , (2), the white balance fine adjustment gain is obtained from the ratio of the average value Gave of the G signal to the average value Rave of the R signal and the ratio of the average value Gave of the G signal and the average value Bave of the B signal. Calculate RFgain and BFgain.

[0019]

RFgain = Gave / Rave (1) BFgain = Gave / Bave (2) where Rave = Rsum / Rpixel number (3) Gave = Gsum / Gpixel number (4) Bave = Bsum / Bpixel number (5) According to such an average value method, the average value of the gradation of each of the RGB signals of the image data is obtained, and the white balance adjustment result (overall white balance) is empirically improved.

Average value and histogram calculation circuit 107
The white balance fine adjustment RFgain and BFgain may be calculated as follows based on the histograms of the luminance levels of the R, G, and B signals calculated in the above. The average value and histogram calculation circuit 107 calculates a histogram of the luminance level of each of the R, G, and B signals. That is, the number of each color for each luminance level is calculated, and FIG.
A histogram as shown in (c) is calculated. here,
The 95% level value of each color of R, G, B is, for example, R = 1
80, B = 200 and G = 190, RFgain and B
Fgain can be calculated as RFgain = 190/180, and white balance fine adjustment BFgain = 190/200. The 95% level value is a luminance level value of 95% of the largest number of dots. According to such a histogram method, the histogram has a shape including the variance of the gradation distribution of each of the RGB signals of the image data. If the white balance fine adjustment gain is obtained from the shape, the histogram is concentrated on a predetermined portion (white point portion). And the white balance can be adjusted, and the adjustment result of the white balance is empirically improved. Note that the average value method and the histogram method may be combined.

The block processing circuit 200 shown in FIG. 4 includes a white balance fine adjustment circuit 210 and an interpolation / contour processing circuit 22.
0, and performs various signal processing for each n × m pixel data, that is, for each block. The white balance fine adjustment circuit 210 compares the R signal and the B signal that have been processed up to the γ correction circuit 106 and are stored in the buffer memory 30 for each of the R and B signals in the 20 × 20 pixel area. The white balance fine adjustment is performed by multiplying each of the white balance fine adjustment gains RFgain and BFgain calculated by the average value circuit 107.

The interpolation / contour processing circuit 220 includes a G interpolation circuit 221, a band pass filter (BPF) 222, a clip circuit 223, a gain circuit 224, a low pass filter (LPF) 225, and a color difference signal generation circuit 226.
And an interpolation / low-pass filter (LPF) circuit 228;
A matrix circuit 229, an adder 230, and a median circuit 232 are provided to perform format processing for JPEG data compression on image data after white balance fine adjustment for each block data of a 20 × 20 pixel area. To generate a Y signal of a 16 × 8 pixel area, and a Cb signal and a Cr signal of an 8 × 8 pixel area. Luminance signal Y
Is a luminance signal Y of a low frequency component of the G signal as described later.
1 and the contour signal Y2 of the high frequency component.

A block signal of a 20 × 20 pixel area is input to the G interpolation circuit 221, and the G component of the data of the central 16 × 16 pixel area is interpolated with respect to the R signal or B signal pixel area. calculate. That is, as shown in FIG. 7, the input data D2 of the 20 × 20 pixel area
For 0, 5 × 5 pixel area data D51 (1 row, 1 column to
A vacancy point at the center of 5 rows and 5 columns (pixels of 3 rows and 3 columns)
B signal is obtained), and this value is calculated as 16 ×
A pixel (B) of 3 rows and 3 columns of the output data D16 of the 16 pixel area
Is replaced by the G component of (circled in ○).

Next, with respect to the input data D20 of the 20 × 20 pixel area, 5 × 5 pixel area data D52 (2 rows 2
The G component of the central vacancy point (columns 6 rows and 6 columns) (a pixel of 4 rows and 4 columns and an R signal is obtained) is calculated, and this value is set to 1
The output data D16 in the 6 × 16 pixel area is replaced with the G component of the pixel in the 4th row and 4th column (R is circled). By repeating such processing, G interpolation processing is performed on all vacancies in the 16 × 16 pixel area, and output data D16 is obtained. And 12 × 12 of them
The output data D12 of the pixel area is converted to a bandpass filter 22.
2 and a low-pass filter 225, respectively.
The output data D16 of the 16 × 16 pixel area is output to the color difference signal generation circuit 226.

The band-pass filter 222 has an intermediate frequency component (a frequency component that is high enough to extract the outline of the subject) of the 12 × 12 pixel area G signal output from the G interpolation circuit 221. (For convenience, called high frequency components). That is, as shown in FIG. 8, for input data D12 of a 12 × 12 pixel area, 5 × 5 pixel area data D5 (5 rows, 5 columns to 9 rows, 9 columns)
Is multiplied by a band-pass filter coefficient to obtain BPF output data.
Replace as data in row 7 column (bold G). By repeating such processing, all the pixel data in the 8 × 8 pixel area is replaced with the G data after the BPF, and the output data D8
Generate

The clip circuit 223 clips and cuts each of the 8.times.8 pixel area data D8 output from the band pass filter 222 at a set level. The gain circuit 224 multiplies the output of the clip circuit 223 by a predetermined gain.

The low-pass filter 225 is a G interpolation circuit 2
A low frequency component is extracted from the G signal in the 12 × 12 pixel area output from 21. That is, as shown in FIG. 9, for input data D12 in a 12 × 12 pixel area,
The LPF output data is obtained by multiplying the 5 × 5 pixel area data D5 (5 rows, 5 columns to 9 rows, 9 columns) by a low-pass filter coefficient, and the value is converted to the 7 × 7 pixel data of the 8 × 8 pixel area.
Replace as column data (hatched area). By repeating such processing, all the pixel data in the 8 × 8 pixel area is replaced with the G data after the LPF, and the output data D8 is generated.

As shown in FIG. 10, the color difference signal generation circuit 226 outputs the RGB signal input data D16− of the 16 × 16 pixel area which is the output of the white balance fine adjustment circuit 210.
1 and the G signal input data D16-2 of the 16 × 16 pixel area which is the output of the G interpolation circuit 221 (B−
G) intermediate data D16-3 including a signal and an (RG) signal.
Generate Further, the intermediate data D16-3 is changed to (B-
G) Output data D16-4 of the color difference signal and (RG) output data D16-5 of the color difference signal are separated.

The interpolation / LPF circuit 228 outputs an 8-bit (B−B−B) of a 16 × 16 pixel area from the color difference signal generation circuit 226.
G) signal and (RG) signal are input, and 5 × 5
The (BG) signal and the (RG) signal are interpolated for each pixel area, and low-pass filtering processing for simultaneously extracting a low-band signal is also performed. The resulting (BG) signal of the 12 × 12 pixel area is obtained. ) Signal and (RG) signal to the CbCr matrix section of the matrix circuit 229. The (BG) signal and the (RG) signal of the 8 × 8 pixel area are output to the Y matrix section of the matrix circuit 229.

The (RG) data of the 5 × 5 pixel area is shown in FIG.
When represented as 1, the above-mentioned interpolation operation and low-pass filtering operation are expressed by the following equation (6).

(Equation 2)

Generally, an interpolation filter and a band-limited LPF
Are applied at the same time, there are restrictions on filter coefficients as follows. The description will be made in one dimension for simplicity. It is assumed that among the sample points after interpolation, there are real sample points in N cycles. For example, a, a, b, b, a, a, b, b,.
(Where a is an actual sample point and b is a sample point to be interpolated. In this example, there are four periods). When this is interpolated by an odd-order symmetric digital filter of (2n + 1) order (where (2n + 1) is larger than N), if the actual sample points are uniform, the sample points after interpolation must also be uniform. Therefore, there are the following restrictions on filter coefficients.

If C (k) is the k-th filter coefficient, the sum of N sets of coefficients must be equal to each other as follows.

(Equation 3) Where i is an integer of 0 or more whose filter coefficient is less than (2n + 1) k is an integer of 0 or more less than n

In the case of a two-dimensional filter, a two-dimensional filter may be formed by applying filters having similar restrictions in the horizontal and vertical directions. In this embodiment, as shown in FIGS. 5 and 11, sample points having a two-pixel period are interpolated.
And the filter coefficients must be equal in the even-order sum and the odd-order sum. That is, ΣC (2 * i) = ΣC (2 * i + 1) In the case of a two-dimensional, fifth-order × five-order symmetrical filter as in the above equation (6), 4 * kc1 + 2 * kc3 + 4 * kc5 + 2 * kc7 + k
c9 = 4 * kc2 + 4 * kc4 + 2 * kc6 + 2 * kc
8

For example, the interpolation / LPF processing of the (RG) signal will be described with reference to FIG. Regarding the (RG) signal of the input data D16 in the 16 × 16 pixel area,
The 5 × 5 pixel area data D5 (3 rows, 3 columns to 7 rows, 7 columns) is multiplied by an interpolation / LPF filter coefficient, and the center area (5
The (RG) data of (row 5 column) is calculated, and this is calculated as 12 × 1
The output data D12 in the two-pixel area is replaced with data of five rows and five columns. By repeating such processing, (R-
G) Interpolation / LPF processing is performed on all pixel data of the 12 × 12 pixel area for the signal, and output data D12 is obtained. The same process is performed on the (BG) signal to generate output data of a 12 × 12 pixel area.

The matrix circuit 229 includes a Y matrix section, a Cb matrix section, and a Cr matrix section. The Y matrix section outputs the (BG) signal of the 8 × 8 pixel area and the (R−G) signal from the interpolation / LPF circuit 228.
G) A signal is input and the low-pass filter 225
, A G signal of an 8 × 8 pixel area is input, and a luminance signal Y1 of a low frequency component of the 8 × 8 pixel area is generated by the following equation (7).

Y1 (i, j) = [Mkg × G (i, j) + Mkr1 × RG (i, j) + Mkb1 × BG (i, j)] (7) where Mkg, Mkr1, and Mkb1 are Matrix coefficient

Each of the Cb matrix portion and the Cr matrix portion has a 12 × 1
The (BG) signal and the (RG) signal of the two-pixel area are input, and the Cb signal and the Cr signal of the 12 × 12-pixel area are generated by the following equations (8) and (9).

[Equation 5] Cr (i, j) = [Mkr2 × RG (i, j) + Mkb2 × BG (i, j)] (8) Cb (i, j) = [Mkr3 × RG (i, j) + Mkb3 × BG (i, j)] (9) where Mkr2, Mkr3, Mkb2, and Mkb3 are matrix coefficients

The adder 230 includes a matrix circuit 229
Is added to the luminance signal Y1 of the low frequency component of the 8 × 8 pixel region output from the pixel circuit and the contour extraction signal Y2 of the high frequency component of the 8 × 8 pixel region output from the gain circuit 224. The contour extraction signal Y2 output from the gain circuit 224 is obtained by extracting a high-frequency component from the G signal of the 16 × 16 pixel area subjected to G interpolation, that is, by extracting a contour.
Accordingly, the luminance / contour extraction signal Y (Y1 + Y2) of the entire image is calculated by adding the luminance signal Y1 calculated by the expression (7) by the adder 230 and the contour extraction signal Y2 calculated by the gain circuit 224. You. The result of this addition is stored in the buffer memory 30.

The median circuit 233 receives the Cb signal and the Cr signal of the 12 × 12 pixel area from the matrix circuit 229 and receives the 9 × 9 pixels of the 3 × 3 pixels included in the 5 × 5 pixel area.
Performs median processing using points, and sets 8 × 8 pixel C
An r signal and a Cb signal are output.

In the median processing of this embodiment, as shown in FIG. 13, of the data D12 of 12 × 12 pixels (data is a black dot), 3 × 5 pixels included in a 5 × 5 pixel area are included.
A median filter process is performed on nine data (x marks) of data D3-5 of three pixels (5 rows, 5 columns to 9 rows, 9 columns). That is, the nine data are sorted in ascending or descending order, and the median value is used as the median processing data. Then, the obtained median processing data is replaced as data of 7 rows and 7 columns of output data D8 of 8 × 8 pixels. By repeatedly performing such calculations, Cb, Cr
Output data D8 of 8 × 8 pixels is generated for each of the signals. The output data D8 of the Cr signal and the Cb signal is stored in the buffer memory 30.

As described above, the JPEG compression circuit 33 applies a 16 × 8 pixel Y signal generated by the addition circuit 230 to the input data of each 20 × 20 pixel area input to the block processing circuit 200, Median circuit 23
Based on the 8 × 8 pixel Cr signal and Cb signal generated in step 2, the YCrCb signal formatted into 8 × 8 pixels of the JPEG compression method is extracted as one unit, and is compressed by a well-known procedure. Repeat to compress all images. The compressed image data is stored in the PC card 34 via the CPU 21.

The operation of the thus constructed electronic still camera will be described. When the full-press switch 23 is operated, the quick return mirror jumps up, and the program of the photographing sequence shown in FIG. 14 is started. In step S21, each pixel of the CCD 26 accumulates the light receiving signal, and after the accumulation is completed, the accumulated charges of all the pixels are sequentially discharged.
In step S22, the discharged image data is processed by the analog signal processing circuit 27, converted into digital image data by the A / D conversion circuit 28, and input to the image processing circuit 29. Next, proceeding to step S23, the image processing circuit 29 performs white balance adjustment, gamma gradation correction, JPEG formatting, and the like. When the image processing is completed, the process proceeds to step S24, and the image data after the image processing is temporarily stored in the buffer memory 30. In step S25, the image data is read from the buffer memory 30, and the data is compressed by the JPEG compression circuit 33. In step S26, the compressed image data is stored in the PC card.

The operation and effect of this embodiment will be described in more detail. (1) Regarding signal processing that can be performed in pixel units and line units, the line processing circuit 100 shown in FIG.
Is in charge. That is, the line processing circuit 100 is a CCD
The data is output in a dot-sequential manner for each line along with the data output from. Then, the data after the line processing is temporarily stored in the buffer memory 30, and the subsequent signal processing is performed by the block processing circuit 200 at n × m
(N, m = 20, 16, 12, 8) pixels are performed in units of one block. Therefore, even in the case of an electronic still camera of a high image quality type exceeding 2 million pixels, the line buffer does not increase in size. That is, when signal processing is not performed on a block basis as in this embodiment, as shown in FIG.
Four lines of buffer memories BM1 to BM for each of the BPF processing, the interpolation / LPF processing, and the median processing circuit
Obviously, M4 is required, and the circuit scale becomes large. In addition, since the pipeline operation performed on a pixel basis and on a line basis is not a process for each block but a line process, the pipeline operation time can be reduced as in the conventional case.

(2) On the basis of an image which has been subjected to white balance by using a predetermined white balance adjustment coefficient R gain and B gain, the above equations (1) and (2)
BF gain for fine adjustment of white balance and BF gain for fine adjustment of white balance are calculated, and the RF gain and BF of the image data after white balance are calculated.
Since the fine adjustment of the white balance is performed by the gain, it is possible to prevent the occurrence of a color cast image even if the predetermined white balance adjustment coefficient is poorly adjusted.

(3) By the interpolation / LPF circuit 228,
Since the (BG) signal and the (RG) signal are each subjected to an interpolation operation and a low-pass filtering process for extracting a low-frequency component at the same time, an interpolation process is performed.
The processing time is reduced as compared with a method of processing a signal in the order of the matrix processing and the LPF processing to suppress false colors and color moiré. In addition, the hardware can be omitted, and the total frequency response can be controlled at one place, so that the control is easy.

(4) 8 × 8 before compression by JPEG
Since the median processing is performed on the Cr image data and the Cb image data of the pixels, the false color and the color moiré can be shortened as compared with the conventional case where the false color and the color moiré are suppressed only by the low-pass filtering. The time can be further reduced. When generating 8 × 8 pixel Cr and Cb signals by JPEG compression format processing, interpolation /
For the 12 × 12 pixel data subjected to the LPF processing and the matrix processing, the Cb signal and the Cr signal of the 5 × 5 pixel area are converted into 3 × 3 pixels of 9 × 9 pixels in each of the horizontal and vertical directions.
Since the median processing is performed by extracting the pieces of data, the median processing time can be reduced as compared with the case where the median processing is performed on all 25 data of 5 × 5 pixels.

In the above embodiment, the electronic still camera has been described. However, the line processing circuit 100 or the block processing circuit 200 may be replaced with a CD-ROM in the form of software wafer air.
It can be stored as an image processing program in a storage medium such as a ROM or a floppy disk and used when performing image processing with a personal computer. In this case, the image data digitized by the image pickup by the CCD is stored in a large-capacity image data storage medium, the storage medium is set in a personal computer, the image data is captured, and the image processing program executes The line processing and the block processing as described above are performed. For example, in FIG. 3, output data of the black level circuit 105 is stored as raw data in the PC card 34, and the PC card 34 can be set in a personal computer to perform image processing of the raw data.

In the above description, the single-lens reflex electronic still camera has been described. However, the present invention can be applied to an electronic still camera whose lens cannot be replaced and a digital video camera which can also capture moving images. Although the JPEG compression method has been described above, the present invention can be applied to other compression methods. Other compression methods include TIFF compression, fractal compression, and MPEG compression. Note that the format processing in this specification is not limited to the format processing performed prior to the above-described various types of compression processing, but also includes uncompressed TIFF format processing.

The circuit configuration in the above embodiment is merely an example, and includes, for example, the following aspects. (1) In the G interpolation processing, BPF processing, LPF processing, and interpolation / LPF processing of the block processing circuit 200, 20 × 20
The description has been made assuming that image processing is performed with one of 16 × 16, 12 × 12, and 8 × 8 blocks as one unit. However, in each process, it is sufficient to perform image processing using 5 × 5 image data as one unit. (2) White balance fine adjustment gains RFgain and BF
When calculating the gain, the image data of the 512 × 512 area centered on the center of the focus detection area is extracted. However, the data of all the images may be used, or the center of the shooting area may be used. Data of a predetermined area may be used, or when there are a plurality of focus detection areas, image data of a predetermined area of the selected focus detection area may be used. The white balance fine adjustment area may be set based on the area used as the photometry area.

[0049]

As described above in detail, according to the present invention, in the format processing for compressing image data by the compression circuit and the image processing for performing predetermined image processing on the image data, n × m pixels are required. Since the median processing is performed on the data in the area, even if the number of pixels increases, false colors and moire can be sufficiently suppressed in a short processing time. Also, of the image data in the n × m pixel area, (ni) ×
If the median processing is performed by extracting the image data of (mi), the median processing can be performed more quickly.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an embodiment of a single-lens reflex electronic still camera.

FIG. 2 is a block diagram of an embodiment of a signal processing system of the single-lens reflex electronic still camera;

FIG. 3 is a block diagram illustrating a circuit that performs line processing in the signal processing system illustrated in FIG. 2;

FIG. 4 is a block diagram illustrating a circuit that performs block processing in the signal processing system shown in FIG. 2;

FIG. 5 is a diagram showing an arrangement of color filters.

FIG. 6 is a diagram for explaining R, G, and B histograms;

FIG. 7 is a view for explaining processing contents of a G interpolation circuit;

FIG. 8 is a view for explaining processing contents of a band-pass filter.

FIG. 9 is a view for explaining processing contents of a low-pass filter.

FIG. 10 is a view for explaining processing contents of a color difference signal generation circuit.

FIG. 11 is a diagram showing an example of data processed by an interpolation / LPF circuit;

FIG. 12 is a view for explaining processing contents of an interpolation / LPF circuit;

FIG. 13 is a view for explaining processing contents of a median circuit.

FIG. 14 is a flowchart showing a program started by a full-press switch.

FIG. 15 is a block diagram in a case where JPEG format processing is performed not by block processing but by line processing;

[Explanation of symbols]

21: CPU, 22: Half-press switch, 23: Full-press switch, 26: CCD, 29: Image processing circuit, 33: J
PEG compression circuit, 35: white balance detection processing circuit, 35A: white balance sensor, 73: CCD,
100: line processing circuit, 104: white balance circuit, 107: average value calculation / histogram calculation circuit, 20
0 ... Block processing circuit, 210 ... White balance fine adjustment circuit, 228 ... Interpolation / LPF circuit, 229 ... Matrix circuit, 232 ... Median circuit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Zheng Hong Chen 3-2-2 Marunouchi, Chiyoda-ku, Tokyo Inside Nikon Corporation (72) Inventor Masahiro Juen 3-2-3 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) in Nikon Corporation 5C022 AA13 AC01 AC02 AC03 AC07 AC12 AC32 AC42 AC51 AC69 AC80 CA00 5C053 FA08 FA17 FA27 FA30 GA11 GB15 GB36 HA18 HA33 HB02 KA03 KA12 KA14 KA21 KA22 KA24 KA25 KA30 BA06 CA03 DA00 EA02 EA04 FA03 FA22 GA01 GA29 HA18 HA31 HA36 HA37 5C065 AA03 BB02 BB12 BB13 BB23 CC02 CC03 CC07 CC08 DD02 DD17 DD18 DD19 EE06 FF03 FF11 GG02 GG08 GG13 GG15 GG18 GG20 GG22 GG30 GG32 GG32.

Claims (6)

[Claims] An image pickup apparatus for picking up an image of a subject passing through a photographing lens and outputting image data, and performing image processing including data format processing suitable for data compression on image data output from the image pickup apparatus. A digital camera comprising: an image processing circuit to be applied; and a compression circuit that compresses image data output from the image processing circuit.
A digital camera which performs a median process on image data in a xm pixel area. 2. The digital camera according to claim 1, wherein (ni) ×
A digital camera, which performs median processing by extracting (mj) image data. 3. An image pickup apparatus for picking up an image of a subject passing through a photographing lens and outputting image data, and an image processing circuit for performing predetermined image processing on the image data output from the image pickup apparatus. In the digital camera, the image processing circuit extracts media data of (ni) × (mj) from the image data of the n × m pixel area and performs a median process. camera. 4. A format process for formatting image data picked up by an image pickup device to compress the image data, various signal processes performed prior to the format process, and an image after the format process. And a compression process for compressing data, wherein a program for performing a median process on image data in an n × m pixel area is stored in the format process. 5. A storage medium for image signal processing according to claim 4, wherein (n−i) ×
A storage medium for image signal processing, wherein a median process is performed by extracting (mj) image data. 6. When performing predetermined image processing on image data picked up by an image pickup apparatus, (ni) × (mj) image data of image data in an n × m pixel area is used. A storage medium for image signal processing, wherein a program for extracting and performing median processing is stored.