JP2003299107A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that a black color becomes predominant by misjudgment when compensation is performed by making a judgment on backlight from image information when taking a picture against the sun. <P>SOLUTION: Images of photographic subjects passed through a lens 10 are adjusted in the amount of incident rays by an aperture diaphragm 11 to be converted into electric signals s10 in a solid-state image sensing device 12. The electric signals s10 are subjected to noise reduction and gain adjustment in an analog preprocessing means 13 to be converted into brightness signals and R, G, B in a YRGB converting means 14. Reference numeral 17 detects the frequency of appearance (histogram) in each of levels in the case of separating the brightness signals s15 into each of signal levels, and then reference numeral 18 calculates compensation signals for compensating gradation sequence of the brightness signals and R, G, B based on the histogram, so that the compensation signals are output when a backlight compensation switch 19 is ON, while non-compensation signals are output when it is OFF. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus which corrects gradation of a video signal when it is backlit.

[0002]

2. Description of the Related Art Conventionally, as an image pickup device for correcting the gradation of a video signal at the time of backlighting, the one described in Japanese Patent Laid-Open No. 06-189186 is known.

FIG. 11 shows the structure of a conventional image pickup device. A solid-state image pickup device (CCD) 14 converts an object image passing through a lens 11, an aperture 12 and an IR cut filter 13 into an electric signal, and an amplifier (AMP). ) 15, the photographed image data obtained in the preprocessing 16 is temporarily stored in the frame memory 19. The range of brightness represented by this image data is two stages A and B for darker ones and two stages C for brighter ones.
The backlight brightness determination circuit determines the brightness histogram in each of the four stages of D, and when the frequency of the brightness in the relatively bright segment of the two darker segments is higher than that of the other segments. In 20, it is determined to be backlit photography. Amplify / amplify the image data obtained by actual shooting
The back light correction is performed by the near processing circuit 21.

[0004]

In the conventional image pickup apparatus, the backlight is determined based on the distribution of the brightness histogram, so that it is not the backlight when the background is dark and there is a bright subject in the foreground. However, there is a problem that the background is erroneously determined to be backlit, the black background is floated, and the contrast is lowered.

It is an object of the present invention to suppress the above-mentioned erroneous judgment of backlight, and to perform backlight correction by gradation correction of a captured image at the time of backlight.

[0006]

In order to solve this problem, the present invention provides a lens, an image pickup device, an adjusting means for adjusting the exposure amount of the image pickup device, and a signal output from the image pickup device. Preprocessing means, conversion means for converting the luminance signal of the image captured from the signal output from the preprocessing means and R, G, B signals, and histogram detection means for detecting a histogram of the luminance level of the captured image , A switch for judging back light, a gradation correction means for performing gradation correction on the brightness signal and the R, G, B signals based on the histogram when the switch is turned on, and gradation corrected brightness It is provided with a γ correction means for γ-correcting the information signal and the R, G, B signals, and a matrix means for matrix-calculating the γ-corrected luminance signal and the R, G, B signals and outputting them as a video signal.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. 1 to 10.

(Embodiment 1) FIG. 1 shows an embodiment of an image pickup apparatus of the present invention. In FIG. 1, 10 is a lens, 11 is a diaphragm for adjusting the exposure amount, 12 is a solid-state image pickup device, and 13 is an analog front. A processing means 14 is a signal of the solid-state image pickup device 12 processed by the analog pre-processing means 13 as a luminance signal and R, G,
YRGB conversion means for converting into B, 15 is a luminance signal, R,
A gradation correction means for correcting the gradation of the G and B signals, and 16 is a matrix means for performing a matrix operation on the brightness signal and the R, G and B signals and outputting the brightness signal and the color difference signal. Reference numeral 17 is a histogram detecting means (HIST detection) for detecting the histogram of the luminance signal, and 18 is a correction for calculating and outputting a correction signal for correcting the gradation of the luminance signal and the R, G, B signals based on the histogram. It is a signal generating means. A switch 19 turns on the backlight correction when the user determines that the backlight is on.

The operation of the image pickup apparatus constructed as above will be described below.

The amount of incident light of the subject image passing through the lens 10 is adjusted by the diaphragm 11 and the electric signal s10 by the solid-state image pickup device 12.
Is converted to. The electric signal s10 is the analog preprocessing means 1
Noise reduction, gain adjustment, etc. were made in 3.
The luminance signals s15 and R, G, B are applied by the YRGB conversion means 14.
(Each s12, s13, s14). Reference numeral 17 detects the appearance frequency (histogram) at each level when the luminance signal s15 is divided for each signal level, and reference numeral 18 indicates the luminance signal s15 and R, G, B based on the histogram.
A correction signal for correcting the gradation of each (s12, s13, s14) is calculated, the correction signal is output when the switch 19 is on, and the signal that is not corrected is output when the switch 19 is off.

FIG. 2 is an image of a subject under backlight,
(A) is an image at the time of normal exposure, and (b) is an image at the time of exposure correction. In the case of a normal exposure when the subject is backlit, the exposure is often matched with the background, and a person or the like appears dark. When the user judges that this state is backlight, and the backlight correction is turned on by the switch 19, the correction signal generating means 18 adjusts s115 to open the diaphragm 11 in order to make a person or the like appear bright, and the correction signal generating means 18 opens the diaphragm 11. Exposure compensation is performed by increasing the amount of incident light. As a result of the exposure correction, the subject becomes brighter than that in (a) as shown in (b), but the background becomes too bright, resulting in overexposure.

FIG. 3 shows a histogram of the luminance signal of the subject at the time of exposure compensation detected by the histogram detecting means 17, and FIG. 3 (a) is an image of the subject.
It is the same as (b). (B) is a histogram of the brightness signal s15 of the exposure-corrected image (a), where the horizontal axis represents the brightness level and the vertical axis represents the histogram.
1 to I16 are divided into 16 steps, and the respective histograms are H1 to H16. In the histogram in which the backlight is corrected for exposure, the histograms near the low luminance part (I1 to I6) and the high luminance part (I12 to I16) are large, and the histograms near the intermediate luminance (I7 to I11) are small.

FIG. 4 is a graph showing the calculation process of the correction signal generating means 18, in which (a) is the histograms H1 to H16.
Is a gradation characteristic 1 generated from the above, (b) is a gradation characteristic 2 obtained by converting the gradation characteristic 1, and (c) is a gain characteristic for realizing the gradation characteristic 2. The gradation characteristic 1 is obtained by the following calculation.

Hn (n = 1 to
16) As a result, Hn is normalized by the sum of histograms and N
n.

Nn = Hn / ΣHn (Equation 1) The gradation characteristic Tn (n =
1 to 16) are obtained by stacking Nn.

Tn = ΣNn (Equation 2) The characteristic obtained by this Equation 2 is the graph of FIG.
The graph of FIG. 4B is obtained by plotting Tn on the dividing point In. Next, the gain characteristic that realizes FIG. 4B is obtained by the following calculation. The gain gn (n = 1 to 16) at 16 accurate signal levels is gn = Tn / (In / I16) (Equation 3) The characteristic obtained by this Equation 3 is shown in FIG. When the correction is on, that is, when s114 is on, this In and gn are output as the correction signal s113, and when the backlight correction is off, that is, when s114 is off, gn is all The value is multiplied by 1 and output.

FIG. 5A is a block diagram of the gradation correction means 15. In the figure, 50 is a tone correction gain table, 51, 52, 53, 54 are multipliers, and 55 is γ.
It is a correction means.

The gradation correction gain table 50 is a correction signal s.
The gradation correction gain characteristic is calculated from 113.

FIG. 5B shows the characteristics of the gradation correction gain table. Since the correction signal s113 is 16 discrete signals, the signals are interpolated and converted into continuous gradation correction gain characteristics. It is obtained as a gradation correction gain s50 corresponding to the luminance signal s15. Luminance signal s1
The 5, R, G, and B signals (each s12, s13, and s14) are multiplied by the gradation correction gain s50, and are then γ-corrected to be output as gradation-corrected signals s19, s16, s17, and s18.

The matrix means 16 calculates and outputs a luminance signal and a color difference signal by the following calculation.

Luminance signal s110 = 0.3 × s16 + 0.59 × s17 + 0.11 × s18 (Equation 4) Color difference vibration s111 = s16-s110 (Equation 5-1) and s111 = s18-s110 (Equation 5-2) As the luminance signal s110, the gradation-corrected luminance signal s19 may be output as it is. Gradation correction gain s50 to s1
By multiplying by 2, s13, s14, and s15, the gradation characteristic of the video signal becomes as shown in FIG. 6A. Compared with the histogram in FIG. The gradient of gradation is large in a large luminance area, and the gradient of gradation is small in a luminance area having a small histogram of intermediate luminance. 6B and 6C are images before and after gradation correction, respectively. By gradation correction, the person corresponding to the low-luminance portion becomes bright and the background corresponding to the high-luminance portion. Reduces the overall brightness level without degrading the contrast, and suppresses color saturation.

(Second Embodiment) FIG. 7 shows an embodiment of the image pickup apparatus of the present invention.

In the figure, 10, 11, 12, 13, 1
Since 4, 17, 18, and 19 have the same configurations as those in FIG. 1, the description thereof is omitted here. The difference from FIG. 1 lies in the gradation correction means 75 and the matrix means 76. FIG. 8 is a block diagram of the gradation correction means 75. In the figure, 50 is a gradation correction gain table, 51, 52 and 53 are multipliers,
Reference numeral 5 is a γ correction means, and in FIG.
2, 53 are equivalent to the configuration of FIG. What is different from FIG. 5 is a part that multiplies the gradation correction gain s50 only on s12, s13, and s14 to perform γ correction, and outputs s16, s17, and s18.

The matrix means 16 calculates and outputs a luminance signal and a color difference signal by the following calculation.

Luminance signal s110 = 0.3 × s16 + 0.59 × s17 + 0.11 × s18 (Equation 6) Color difference vibration s111 = s16-s110 (Equation 7-1) and s111 = s18-s110 (Equation 7-2) By multiplying s12, s13, and s14 by the gradation correction gain s50, the gradation characteristic of the video signal becomes as shown in FIG. 6A, which is compared with the histogram of FIG. 3B. The gradient of gradation is large in a luminance area having a large histogram such as a low luminance portion or a high luminance portion, and the gradient of gradation is small in a luminance area having a small histogram of intermediate luminance. 6 (b) and 6 (c)
Is the image before gradation correction and the image after gradation correction.By gradation correction, the person corresponding to the low brightness part becomes brighter and the background corresponding to the high brightness part does not lose the contrast and the whole brightness level is It is possible to suppress the fall and color skip.

(Third Embodiment) FIG. 9 shows an embodiment of the image pickup apparatus of the present invention.

In the figure, 10, 11, 12, 13, 1
Since 4, 15, 16, and 17 have the same configurations as those in FIG. 1, the description thereof is omitted here. The difference from FIG. 1 is that a correction signal generating means 98 and a flash detecting means 99 are provided,
The operation will be described below. Correction signal generating means 98
1 is the same as the correction signal generating means 18 of FIG. 1, except that the input signal is from s114 to s914. s914 is a signal output from the flash detection means 99, and the flash detection means 99 turns on the signal s914 at the time of flash emission. When s914 is turned on, the correction signal generating means 18 outputs In and gn to the correction signal s11 similarly to the correction signal generating means 18 of FIG.
Output as 3 and s914 is off gn
Are all multiplied by 1 and output. According to the present invention, by performing gradation correction according to the histogram during flash emission with the above-described configuration, it is possible to suppress color jump due to flash emission and black sinking due to insufficient flash light.

(Embodiment 4) FIG. 10 shows an embodiment of the image pickup apparatus of the present invention.

In the figure, 10, 11, 12, 13, 1
Nos. 4, 75, 76 and 17 have the same configurations as those in FIG. 7 is different from FIG. 7 in that a correction signal generating means 98 and a flash detecting means 99 are provided.
The operation will be described below. Correction signal generating means 98
1 is the same as the correction signal generating means 18 of FIG. 1, except that the input signal is from s114 to s914. s914 is a signal output from the flash detection means 99, and the flash detection means 99 turns on the signal s914 at the time of flash emission. When s914 is turned on, the correction signal generating means 18 outputs In and gn to the correction signal s11 similarly to the correction signal generating means 18 of FIG.
Output as 3 and s914 is off gn
Are all multiplied by 1 and output. According to the present invention, by performing gradation correction according to the histogram during flash emission with the above-described configuration, it is possible to suppress color jump due to flash emission and black sinking due to insufficient flash light.

In the above description, the solid-state image sensor is referred to as 1
Although an example in which the image pickup device is composed of a single image is shown, the present invention can be similarly implemented for an image pickup device having a plurality of images.

[0031]

As described above, according to the present invention, the lens, the image sensor, the adjusting means for adjusting the exposure amount of the image sensor, the pre-processing means for the signal output from the image sensor, A conversion means for converting the signal output from the pre-processing means into a luminance signal of an imaged image and R, G, B signals;
Histogram detection means for detecting a histogram of the brightness level of the imaged image, a switch for judging back light, and if the switch is on, the brightness signal and the R, G, B signals are gradation based on the histogram. Gradation correction means for performing correction, gradation corrected luminance information signal, R, G,
A person corresponding to a low-brightness portion is formed by forming matrix means for matrix-calculating the B signal and outputting it as a video signal, without making an error in determining the backlight, and performing backlight adjustment by aperture adjustment and gradation correction during backlighting. It is possible to obtain a remarkable effect that a background that is bright and has high brightness can be realized without lowering the contrast and lowering the entire brightness level and suppressing the color skip.

[Brief description of drawings]

FIG. 1 is a block diagram showing an imaging device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an image of a subject when it is backlit.

FIG. 3 is a diagram showing an image in which a backlit subject is exposure-corrected and a histogram thereof.

FIG. 4 is a graph showing a calculation process of the correction signal generating means 18.

FIG. 5 is a block diagram of a gradation correction unit 15.

FIG. 6 is a diagram showing a gradation characteristic and an image at the time of backlight compensation.

FIG. 7 is a block diagram showing an imaging device according to a second embodiment of the present invention.

FIG. 8 is a block diagram of a gradation correction unit 75.

FIG. 9 is a block diagram showing an imaging device according to a third embodiment of the present invention.

FIG. 10 is a block diagram showing an image pickup apparatus according to a fourth embodiment of the present invention.

FIG. 11 is a block diagram showing a conventional imaging device.

[Explanation of symbols]

10 lenses 11 aperture 12 Solid-state image sensor 13 Analog preprocessing means 14 YRGB generation means 15 gradation correction means 16 Matrix means 17 Histogram detection means 18 Correction signal generating means 19 Backlight compensation switch

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takeshi Tochio             22-6 Motomachi, Kadoma-shi, Osaka Matsushita AVC Ma             Within Rutimedia Soft Co., Ltd. F-term (reference) 5C021 XA03                 5C022 AB15 AB19 AC69                 5C065 BB12                 5C066 AA01 CA17 JA01

Claims (6)

[Claims] 1. A lens, an image sensor, an adjusting unit for adjusting an exposure amount of the image sensor, a pre-processing unit for a signal output from the image sensor, and an image capturing from a signal output from the pre-processing unit. The conversion means for converting the brightness signal of the captured image into the R, G, B signals, the histogram detection means for detecting the histogram of the brightness level of the captured image, the switch for judging the backlight, and the case where the switch is turned on, A gradation correction unit that performs gradation correction on the luminance signal and the R, G, B signals based on the histogram, and a γ correction for the gradation corrected luminance information signal and the R, G, B signals. An image pickup apparatus comprising: a correction unit; and a matrix unit for matrix-calculating the γ-corrected luminance signal and R, G, B signals and outputting the resultant as a video signal. 2. A lens, an image pickup device, an adjusting unit for adjusting an exposure amount of the image pickup device, a preprocessing unit for a signal output from the image pickup unit, and an image pickup based on a signal output from the preprocessing unit. The conversion means for converting the brightness signal of the captured image into the R, G, B signals, the histogram detection means for detecting the histogram of the brightness level of the captured image, the switch for judging the backlight, and the case where the switch is turned on, A gradation correction unit that performs gradation correction on the R, G, and B signals based on the histogram, a γ correction unit that performs γ correction on the brightness signal and the R, G, and B signals that have been gradation corrected, and the γ correction. An image pickup apparatus, comprising: matrix means for matrix-calculating the luminance signal and the R, G, B signals and outputting as a video signal. 3. The image pickup apparatus according to claim 1, wherein the user turns on and off a switch for judging the backlight. 4. The image pickup apparatus according to claim 1, wherein the adjusting means adjusts so as to increase the exposure amount of the image pickup device when the switch for judging the backlight is turned on. 5. A flash, a lens, an image sensor,
Adjusting means for adjusting the exposure amount of the image sensor, pre-processing means for the signal output from the image sensor, luminance signal of an image captured from the signal output from the pre-processing means, and R, G, B signals Conversion means for converting to, a histogram detection means for detecting a histogram of the brightness level of the captured image, a switch for judging the flash emission, and if the switch is on, the brightness signal and the brightness signal based on the histogram. A gradation correction unit that performs gradation correction on the R, G, and B signals, a gradation-corrected luminance information signal, and R, G, and
An image pickup apparatus comprising: a γ correction unit that γ-corrects a B signal, and a matrix unit that matrix-calculates the γ-corrected luminance signal and the R, G, and B signals and outputs the video signal. 6. A flash, a lens, an image sensor,
Adjusting means for adjusting the exposure amount of the image sensor, pre-processing means for the signal output from the image sensor, luminance signal of an image captured from the signal output from the pre-processing means, and R, G, B signals Conversion means for converting to, a histogram detection means for detecting a histogram of the brightness level of a captured image, a switch for judging the flash emission, and when the switch is on, the R, G, and Tone correction means for performing tone correction on the B signal,
[Gamma] correction means for [gamma] -correcting the luminance signal and the gradation-corrected R, G, B signals, and the [gamma] -corrected luminance signal R, G, B
An image pickup device, comprising: matrix means for matrix-calculating signals and outputting them as video signals.