Digital Camera Patent

Digital camera

Digital Camera Patent Abstract

A digital camera includes a CCD imager. When a display-use UYV signal is generated on the basis of an RGB signal of an object image photographed by the CCD imager, a CPU detects a color saturation degree of the RGB signal and reduces dynamic range of a U signal and a V signal on the basis of the detected color saturation degree. Thus, a color on the basis of the U signal and the V signal is aboundingly included within a color reproducing range of a monitor.

Digital Camera Patent Claims

What is claimed is:

1. A digital camera which generates a color relating signal for display on the basis of a color information signal corresponding to a photographed object image, comprising: a color saturation degree detector for detecting a color saturation degree of the color information signal, said color saturation degree being indicative of a degree that the number of pixels in each of which the color out of the color and the luminance is saturated is large or small; a reducer for reducing dynamic range of the color relating signal on the basis of the color saturation degree; an operator for performing an operation according to a predetermined coefficient on the color information signal so as to generate the color relating signal, wherein said reducer includes an adjuster for adjusting the predetermined coefficient on the basis of the color saturation degree, and wherein said color saturation degree detector detects a first number of pixels in which a level of the color information signal exceeds a threshold value as the color saturation degree; a generator for generating a luminance signal on the basis of the color information signal; and a luminance saturation degree detector for detecting a second number of pixels in which the level of the luminance signal exceeds a threshold value as the luminance saturation degree, wherein said adjuster includes a subtracter for subtracting said second number of pixels from said first number of pixels, and a determiner for determining the predetermined coefficient on the basis of a subtraction result by said subtracter.

2. A digital camera according to claim 1, wherein the operation by said operator includes multiplication of the color information signal by the predetermined coefficient, and said adjuster reduces the predetermined coefficient on the basis of the color saturation degree.

3. A digital camera which calculates an optimal exposure amount on the basis of an image signal of an object photographed with a predetermined exposure amount, comprising: a detector for respectively detecting saturation degrees of luminance at a plurality of portions forming a screen on the basis of the image signal; a determiner for determining a correction coefficient of the predetermined exposure amount on the basis of the saturation degrees detected by said detector, wherein the determiner compares the saturation degrees of luminance detected at respective portions of the screen with different threshold values corresponding to the respective portions of the screen to determine the correction coefficient; and a corrector for correcting the predetermined exposure amount on the basis of the correction coefficient determined by the determiner so as to obtain the optimal exposure amount, wherein said plurality of portions includes a first portion in which a main object exists and a second portion in which a back ground exists, and said determiner includes a first correction coefficient determiner for determining a first value as the correction coefficient when the saturation degree of the first portion is more than a first threshold value and less than a second threshold value and the saturation degree of the second portion is less than a third threshold value, and a second correction coefficient determiner for determining a second value smaller than the first value as the correction coefficient when the saturation degree of the first portion is more than the second threshold value and the saturation degree of the second portion is less than the third threshold value.

4. A digital camera according to claim 3, wherein said determiner further includes a third correction coefficient determiner for determining a third value smaller than the first value and larger than the second value as the correction coefficient when the saturation degree of the first portion is more than the second threshold value and the saturation degree of the second portion is more than the third threshold value.

5. A digital camera, comprising: an imaging device for outputting an image signal which represents an object scene; a first creator for creating a color relating signal for display based on the image signal output from said imaging device; a first detector for detecting the number of pixels producing a color saturation based on the image signal output from said imaging device; a second detector for detecting the number of pixels producing a luminance saturation based on the image signal output from said imaging device; a subtractor for subtracting the number detected by said second detector from the number detected by said first detector; and a changer for changing dynamic range of the color relating signal created by said first creator based on a subtraction result of said subtractor.

6. A digital camera according to claim 5, further comprising a second creator for creating a color information signal based on the image signal output from said imaging device, wherein said first creator includes a calculator for subjecting the color information signal created by said second creator to a calculation referring to a coefficient, and said changer includes an adjuster for adjusting the coefficient depending upon the subtraction result.

7. A digital camera according to claim 6, wherein a calculating operation of said calculator includes multiplication of the color information signal by the coefficient, and said adjuster greatly reduces the coefficient as a numerical value indicated by the subtraction result is increased.

8. A digital camera according to claim 6, wherein the color information signal is a signal having color information of red and blue.

9. A digital camera, comprising: an imaging device for outputting an image signal which represents an object scene; a first creator for creating a color information signal based on the image signal output from said imaging device; a second creator for creating a luminance relating signal based on the image signal output from said imaging device; a third creator for creating a color relating signal for display based on the image signal output from said imaging device; a determiner for determining a ratio of a color saturation pixel which is saturated only in color out of the color and luminance based on the color information signal created by said first creator and the luminance relating signal created by said second creator; and a reducer for greatly reducing dynamic range of the color relating signal created by said third creator as the ratio of the color saturation pixel is increased based on a determination result of said determiner.

10. A digital camera according to claim 9, wherein said third creator includes a calculator for subjecting the color information signal to a calculation referring to a coefficient, and said reducer includes an adjuster for adjusting the coefficient depending upon the ratio of the color saturation pixel.

11. A digital camera according to claim 10, wherein a calculating operation of said calculator includes multiplication of the color information signal by the coefficient, and said adjuster greatly reduces the coefficient as the ratio of the color saturation pixel is increased.

12. A digital camera according to claim 9, further comprising: a first detector for detecting the number of pixels producing a color saturation based on the color information signal created by said first creator; a second detector for detecting the number of pixels producing a luminance saturation based on the luminance relating signal created by said second creator; and a subtractor for subtracting the number detected by said second detector from the number detected by said first detector, wherein said determiner includes a comparer for comparing a subtraction result of said subtractor with a plurality of threshold values which are different from each other.

13. A digital camera according to claim 9, wherein the color information signal is a signal having color information of red and blue, and the luminance relating signal is a signal having color information of green.

Digital Camera Patent Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a digital camera, and more specifically to a digital camera for displaying an image of a photographed object on a monitor.

The present invention relates to a digital camera, and more specifically to a digital camera for determining optimal exposure amount on the basis of an image signal of the photographed object.

2. Description of the Prior Art

In a digital camera, when a shutter button is pressed, a YUV signal is generated on the basis of an RGB signal obtained by pre-exposure of an image sensor, and an optimal exposure amount is determined such that an integration value of the Y signal (a luminance evaluation value) satisfies a predetermined condition. Main exposure of the image sensor is performed according to the optimal exposure amount, and the YUV signal based on the RGB signal obtained by the main exposure is recorded on a recording medium. When a reproducing mode is set, the YUV signal is reproduced from the recording medium, and an image based on the YUV signal is displayed on the monitor.

However, even if an object is photographed with the optimal exposure amount, if color reproducing range of a monitor is narrower than dynamic range of a U signal or a V signal, color saturation may occur on a display image. This problem becomes prominent when there is deviation in a color of the object. Paying attention to a ratio of the RGB signal indicating a red flower photographed in a macro-mode, for example, an R level becomes extremely high, and a G level and a B level become equal to 0. Since the Y signal used for luminance evaluation is generated on the basis of the RGB signal, when the ratio of the RGB signal is extremely distorted, even if the optimal exposure amount is determined such that the luminance evaluation value satisfies the predetermined condition, the level of the R signal obtained by the main exposure becomes still high. Thereupon, the U signal and the V signal based on the main exposure are also out of the color reproducing range of the monitor, and therefore, the color saturation occurs on the display image.

Furthermore, in a prior art in which the optimal exposure amount is calculated such that the luminance evaluation value satisfies the predetermined condition, brightness of a main object image may be short depending on a background. That is, the background of high-luminance (e.g., blue sky in summer) makes the luminance evaluation value high, and the low optimal exposure amount makes the main object image located at the center of the screen dark.

SUMMARY OF THE INVENTION

Therefore, it is a primary object of the present invention to provide a novel digital camera.

Another object of the present invention is to provide a digital camera capable of finely reproducing a color of a photographed image even if a color reproducing range of the display device is narrow.

The other object of the present invention is to provide a digital camera capable of properly adjusting exposure amount.

According to the present invention, a digital camera which generates a color relating signal for display on the basis of a color information signal corresponding to a photographed object image, comprises: a color saturation degree detector for detecting a color saturation degree of the color information signal; and a reducer for reducing dynamic range of the color relating signal on the basis of the color saturation degree.

When the color relating signal for display is generated on the basis of the color information signal corresponding to the photographed object image, the color saturation degree of the color information signal is detected by the color saturation degree detector. The reducer reduces the dynamic range of the color relating signal on the basis of the detected color saturation degree. The color based on the color relating signal can be included within a color reproducing range of the display device by the reduction of the dynamic range. Accordingly, although a width of a tone of the color becomes narrow, the photographed image can be finely displayed.

In a case an operation according to a predetermined coefficient is performed on the color information signal upon generating the color relating signal, it is preferable the predetermined coefficient is adjusted on the basis of the color saturation degree. If the operation is multiplication of the color information signal by the predetermined coefficient, the predetermined coefficient can be reduced on the basis of the color saturation degree.

In a case the number of pixels in which a color level exceeds a threshold value (a first number of pixels) is detected as color saturation degree, the color saturation degree is precisely obtained. Furthermore, in a case a luminance signal is generated on the basis of the color information signal, and the number of pixels in which a level of the generated luminance signal exceeds a threshold value (a second number of pixels) is detected as a luminance saturation degree, the predetermined coefficient may be determined on the basis of a subtraction result subtracting the second number of pixels from the first number of pixels. Thus, the predetermined coefficient may be determined by the number of pixels in which the color saturation only occurs.

According to the present invention, a digital camera which calculates an optimal exposure amount on the basis of an image signal of an object photographed with a predetermined exposure amount, comprises: a detector for respectively detecting saturation degrees of luminance at a plurality of portions forming a screen on the basis of the image signal; a determiner for determining a correction coefficient of the predetermined exposure amount on the basis of the saturation degrees detected by the detector; and a corrector for correcting the predetermined exposure amount on the basis of the correction coefficient determined by the determiner so as to obtain the optimal exposure amount.

When the optimal exposure amount is calculated on the basis of the image signal of the object photographed with a predetermined exposure amount, the detector respectively detects the saturation degrees of the luminance at the plurality of portions forming the screen on the basis of the image signal, and the determiner determines the correction coefficient of the predetermined exposure amount on the basis of detected saturation degrees. The corrector corrects the predetermined exposure amount on the basis of the determined correction coefficient, and whereby, the optimal exposure amount is obtained. That is, the optimal exposure amount is determined respectively taking account of the luminance saturation degrees at the plurality of portions forming the screen. Accordingly, the optimal exposure amount can be suitably obtained.

In a case the plurality of portions includes a first portion in which a main object exists and a second portion in which a background exists, a first value is preferably determined as the correction coefficient when the saturation degree of the first portion is more than a first threshold value and less than a second threshold value and the saturation degree of the second portion is less than a third threshold value. Furthermore, a second value smaller than the first value is determined as the correction coefficient when the saturation degree of the first portion is more than the second threshold value and the saturation degree of the second portion is less than the third threshold value. Thus, the optimal exposure amount for the main object can be obtained.

In addition, when the saturation degree of the first portion is more than the second threshold value and the saturation degree of the second portion is more than the third threshold value, a third value smaller than the first value and larger than the second value may be determined as the correction coefficient. In a case of photographing at a place such as a sandy coast in summer and etc., both of the first portion and the second portion become high-luminance. Herein, if the correction coefficient is set to the third value, a garish air in summer can be expressed.

The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing one embodiment of the present invention;

FIG. 2 is a block diagram showing one example of a signal processing circuit;

FIG. 3 is a block diagram showing one example of a YUV conversion circuit;

FIG. 4 is a flowchart showing a part of operation of a CPU;

FIG. 5 is a flowchart showing another part of the operation of the CPU;

FIG. 6 is a flowchart showing the other part of the operation of the CPU;

FIG. 7 is a flowchart showing a further part of the operation of the CPU;

FIG. 8 is a flowchart showing another part of the operation of the CPU;

FIG. 9 is an illustrative view showing one example of a table storing a RGB signal and a Y signal;

FIG. 10 is an illustrative view showing one example of an upper area and a center area formed on a screen; and

FIG. 11 is an illustrative view showing a part of an operation of a color correction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a digital camera 10 of this embodiment includes an optical lens 12 and an aperture member 13. An optical image of an object is incidented to a light-receiving surface of a CCD imager (an image sensor) 14 through these members. A camera signal (a raw image signal) corresponding to the incidented optical image is generated by photoelectric conversion on the light-receiving surface. It is noted that the light-receiving surface is covered with a primary color filter having a Bayer array (not shown), and each pixel signal forming the camera signal has any one of color information of R, G, and B.

When a photographing mode is selected by a mode change-over switch 38, a CPU 42 respectively sets an aperture amount and an exposure time (shutter speed) in the aperture member 13 and a timing generator (TG) 16, and instructs the TG 16 to make an exposure every 1/15 second. The TG 16 exposes the CCD imager 14 every 1/15 second, and reads out from the CCD imager 14 the camera signal generated by the exposure. A camera signal of each frame read out every 1/15 second is subject to well-known noise removal and level adjustment in a CDS/AGC circuit 18 so as to be converted to a digital signal in an AID converter 20.

A signal processing circuit 22 performs signal processing such as color separation, white balance adjustment, color adjustment (color tone correction), YUV conversion, and etc. on the camera signal outputted from the AID converter 20 so as to generate an image signal including a Y signal (luminance), a U signal (color difference: R-Y) and a V signal (color difference: B-Y). The image signal of each frame thus generated is applied to a memory control circuit 24 and written into an image signal storing area 26a of an SDRAM 26 by the memory control circuit 24.

A video encoder 28 makes the memory control circuit 24 read out the image signal in the image signal storing area 26a. Then, the video encoder 28 encodes the image signal of each frame thus read to a composite image signal of an NTSC format and applies the encoded composite image signal to a monitor (LCD) 30. The monitor 30 is displayed with a real-time motion image (a through image) of the object at a frame rate of 15 fps.

When a shutter button 40 is pressed, the CPU 42 instructs the TG 16 to perform a main exposure after performing the color adjustment described later, and applies a compression instruction to a JPEG codec 32 at a time the image signal based on the main exposure is stored in the image signal storing area 26a of the SDRAM 26. The JPEG codec 32 makes the memory control circuit 24 read out one frame of image signal stored in the image signal storing area 26a so as to perform a compression process on the read image signal in compliance to a JPEG format. When a compressed image signal is obtained, the JPEG codec 32 applies the generated compressed image signal to the memory control circuit 24. The compressed image signal is stored in a compressed signal storing area 26b of the SDRAM 26 by the memory control circuit 24.

After completion of a storing process of the compressed image signal, the CPU 42 reads out the compressed image signal from the compressed signal storing area 26b through the memory control circuit 24, and records the read compressed image signal onto a memory card 36 through an I/F circuit 34. Thus, an image file is created within a memory card 36. It is noted the memory card 36 is a detachable involatile recording medium and when attached to a slot (not shown), can be accessed by the CPU 42.

When a reproducing mode is selected by the mode change-over switch 38, the CPU 42 reads out the compressed image signal from the memory card 36 through the I/F circuit 34 and stores the read compressed image signal in the compressed signal storing area 26b through the memory control circuit 24. After completion of a storing process, the CPU 42 applies an expansion instruction to the JPEG codec 32, and applies a processing instruction to the video encoder 28. The JPEG codec 32 reads out the compressed image signal from the compressed signal storing area 26b through the memory control circuit 24 and performs an expansion process on the read compressed image signal in compliance to the JPEG format. An expanded image signal is written to the image signal storing area 26a by the memory control circuit 24.

The video encoder 28 repeatedly reads out the expanded image signal from the image signal storing area 26a through the memory control circuit 24. Then, the video encoder 28 encodes each expanded image signal thus read to a composite image signal of the NTSC format, and applies the encoded composite image signal to the monitor 30. Thus, a reproduced image is displayed on the monitor 30.

The signal processing circuit 22 is constituted as shown in FIG. 2. The camera signal outputted from the A/D converter 20 is subjected to the color separation by a color separation circuit 22a. That is, since each pixel forming the camera signal has any one of an R information signal (an R signal), a G information signal (a G signal) and a B information signal (a B signal), two color information signals which each pixel is short of are interpolated by the color separation circuit 22a. The R signal, the G signal and the B signal forming each pixel are simultaneously outputted from the color separation circuit 22a. The R signal, the G signal and the B signal outputted every 1 pixel are applied to a YUV conversion circuit 22c through a white balance adjustment circuit 22b so as to be converted to a Y signal, a U signal and a V signal. Herein, a conversion ratio of Y:U:V is equal to 1:1:1.

The Y signal, the U signal and the V signal outputted from the YUV conversion circuit 22c is converted to an L signal (luminance), a C signal (chroma), and an H signal (hue) in a LCH conversion circuit 22d, and the converted L signal, C signal and H signal are applied to an L adjustment circuit 22e, a C adjustment circuit 22f and an H adjustment circuit 22g, respectively. The L adjustment circuit 22e, the C adjustment circuit 22f and the H adjustment circuit 22g respectively perform predetermined operations on the inputted L signal, C signal and H signal so as to obtain a corrected L signal, C signal and H signal. The corrected H signal, C signal and L signal are then restored to the Y signal, the U signal and the V signal by a YUV conversion circuit 22k. The conversion ratio of Y:U:V at this time is equal to 4:2:2 (or 4:1:1). Accordingly, the Y signal, the U signal and the V signal having a ratio of 4:2:2 (or 4:1:1) are outputted from the signal processing circuit 22.

The H signal outputted from the LCH conversion circuit 22d is also applied to an area determination circuit 22h. The area determination circuit 22h determines an area to which the H signal applied from the LCH conversion circuit 22d belongs with reference to a reference value table 22i. Then, the area determination circuit 22h reads out reference values corresponding to a determination result from the reference value table 22i and target values corresponding to the determination result from a target value table 22j. The predetermined operations performed by the L adjustment circuit 22e, the C adjustment circuit 22f and the H adjustment circuit 22g are executed on the basis of the reference values and the target values thus read.

The YUV conversion circuit 22c is constituted as shown in FIG. 3. An operation circuit 221c performs an operation according to an equation 1 on the R signal, the G signal and the B signal applied from the white balance adjustment circuit 22b so as to generate the Y signal. Y=6G+3R+B [equation 1]

On the other hand, a subtracter 222c generates an R-G signal by subtracting the G signal from the R signal, and a subtracter 223c generates a B-G signal by subtracting the G signal from the B signal. The generated R-G signal and B-G signal are subjected to matrix operation according to an equation 2 in a matrix operation circuit 224c, and whereby, the U signal and the V signal are generated. It is noted that, in the main exposure, matrix coefficients shown in the equation 2 can be reduced in a range of 0% to 40% on the basis of a saturation degree (color saturation degree) of the R signal, the G signal and the B signal at a time of the main exposure.

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When a photographing mode is selected, processes according to flowcharts shown in FIG. 4 to FIG. 8 are executed by the CPU 42. It is noted that a control program corresponding to the flowcharts is stored in a ROM 44. First, a through image display process is performed in a step S1, and it is determined whether or not the shutter button 40 is operated in a step S3. While the shutter button 40 is not operated, an AE process for a monitor is performed in a step S5, and then, the process returns to the step S1. Thus, the aperture amount set to the aperture member 13 and the exposure time set to the TG 16 are repeatedly adjusted, and therefore, the through image having suitable brightness is displayed on the monitor 30. It is noted the processes in steps S1 and S5 are executed in response to a VD pulse generated every 1/15 second from the TG 16.

When the shutter button 40 is operated, an exposure setting for photometry is performed in a step S7. Specifically, the exposure time the same as that of the through image display process is set to the TG 16, and a maximum opening value of the aperture amount is set to the aperture member 13. It is determined whether or not the VD pulse is applied from the TG 16 in a step S9, and if "YES" is determined, the pre-exposure for the photometry is instructed