JP2000278598A - Digital camera and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct inclination of an image signal toward a high luminance side and to obtain an appropriate output picture by allowing the signal conversion means to have conversion characteristics for a high luminance image where a rising part shifts toward the high luminance side of an input level rather than reference conversion characteristics for ordinary photographing at the time of flash photographing at a short distance. SOLUTION: In a signal processing circuit 313, prescribed signal processing is applied to an image signal obtained from a CCD 303 and level adjustment of the image signal is performed by gain adjustment of an AGC circuit inside. In an A/D converter 205, each pixel signal of the image signal to be obtained from the signal processing circuit 313 is converted into a digital signal. In a γcorrection circuit 208, there are plural γ correction tables of different characteristics and γ characteristics of the image signal are corrected. In the case of short distance flash photographing mode, the γ correction table for high luminance image is selected. When a bit length of an output signal has a γ correction circuit smaller than that of an input signal, it becomes particularly effective to perform high luminance correction in the γcorrection circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital camera, and more particularly to an improvement for obtaining a proper photographed image in flash photography at a short distance.

[0002]

2. Description of the Related Art In a digital camera, after an image signal obtained by an image pickup device such as a CCD is digitized, information of a personal computer or the like is transmitted through a recording medium such as a flash memory, or by cable connection or infrared communication. Transfer to processing unit. The personal computer can display the image on a monitor such as a CRT or a liquid crystal display.

The gradation (luminance) characteristic of such a monitor is not linear with respect to the level of an image signal input to the monitor, and the relationship between the input signal and the luminance level x, y between the monitor is expressed by the following equation. Γ characteristics as shown in FIG.

[0004]

## EQU1 ## Therefore, in order to correctly reproduce the gradation of the photographed image on the monitor, it is necessary to correct the gradation of the input image according to the monitor. Specifically, such correction is performed by performing in advance a process corresponding to the inverse function of Equation 1 (γ correction).

FIG. 19 is a diagram for explaining the γ correction. The horizontal axis x is the luminance level of the input signal, and the vertical axis y
Indicates the luminance level of the output signal. The input / output conversion characteristic curve C0 shown in FIG. 19 corresponds to the inverse function of Expression 1, and the rising portion from the x-axis is x = 0 (black level). The conversion characteristic curve C0 is set so as to correspond to the upper limit value Xmax of the dynamic range of the input signal and the upper limit value Ymax of the dynamic range of the output signal. Then, the gradation of the signal subjected to the image processing by the correction circuit having such a conversion characteristic is correctly reproduced on the monitor.

[0006]

However, when flash photography is performed at a short distance, the brightness of the entire scene greatly depends on the flash light. large. However, emission of flash light is not always performed properly for the following reasons.

(1) In the case of a camera with a flashmatic function: the emission state changes due to variations in the rising characteristics of the flash arc tube and mechanical variations in the aperture diameter, so that the automatically set emission state cannot always be obtained. . In particular, over-exposure occurs when shifting to the side where light emission is excessive.

(2) In the case of a camera with a dimming function: Since the function of the dimming element corresponding to the maximum amount of light is limited, the output of the dimming element is particularly large when the brightness of the scene is particularly large, such as in flash photography at a short distance. It becomes saturated and the brightness of the scene cannot be accurately detected. As a result, it is not possible to actually stop the flash emission even though the scene has high brightness.

If the light emission of the flash becomes inappropriate due to these causes, the captured image is often overexposed.

A photographed image overexposed for the above-mentioned reason is composed of image signals which are biased toward the high luminance side as a whole. When the overexposed photographed image is directly processed by a gamma correction circuit or the like and reproduced on a monitor, the photographed image is reproduced as an image that has no tightness in the shadow portion and gives the impression of flying white as a whole.

This is different from the concept of a high key in which an image is intentionally taken on the high luminance side, and is a result contrary to the intention of the photographer. It is desired to prevent such a situation. However, in the case of flash photography, it is difficult for the photographer to directly check the brightness of the scene at the time of flash emission with the naked eye before flashing, and it is difficult to correct the automatic exposure to the under side in advance. is there.

Also, especially in the case of a compact digital camera, it is required that the digital camera be automated so as to obtain almost satisfactory photographing results without making fine adjustments. It is not appropriate to require a complicated setting from the photographer.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has an object to correct an image signal bias toward a high luminance side even at a short distance and in flash photography to obtain an appropriate output image. It is intended to provide a digital camera technology capable of performing the following.

[0014]

According to a first aspect of the present invention, there is provided a digital camera for converting an input image signal obtained by photographing with a predetermined signal converting unit to obtain an output image signal. In flash shooting at a short distance, a conversion setting for setting a conversion characteristic for a high-brightness image in which the rising portion is shifted to the high-brightness side of the input level as compared with the reference conversion characteristic for normal shooting in the signal conversion unit. Characteristic setting means.

According to a second aspect of the present invention, in the digital camera according to the first aspect, the flash photography at a short distance is flash photography in a macro mode.

According to a third aspect of the present invention, in the digital camera according to the first or second aspect, the conversion characteristic setting means specifies a minimum luminance value included in the input image signal. And characteristic determining means for determining the conversion characteristic for the high luminance image so as to substantially rise from the vicinity of the minimum luminance value.

According to a fourth aspect of the present invention, in the digital camera according to the third aspect of the present invention, the luminance specifying means includes:
The luminance determining unit further specifies a maximum luminance value included in the input image signal together with the minimum luminance value, and the characteristic determining unit substantially rises from around the minimum luminance value and substantially rises near the maximum luminance value. This is a means for determining the conversion characteristic for the high-luminance image so as to be saturated.

According to a fifth aspect of the present invention, in the digital camera according to the third aspect of the present invention, the characteristic determining means includes:
The conversion characteristic for the high luminance image is determined by moving the curve representing the reference conversion characteristic in parallel to the high luminance side of the input level.

According to a sixth aspect of the present invention, in the digital camera according to the fourth aspect of the present invention, the characteristic determining means includes:
The conversion characteristic for the high brightness image is determined by compressing the curve representing the reference conversion characteristic on the input level side while maintaining the dynamic range of the output level.

According to a seventh aspect of the present invention, there is provided a computer-readable recording medium, wherein the digital camera is installed in a microcomputer built in the digital camera. A program for functioning as a digital camera according to the invention is recorded.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <A. First Embodiment><A-1. Configuration of Main Part of Digital Camera> FIGS. 1 to 3 are views showing the main part configuration of a digital camera 1 according to a first embodiment of the present invention, and FIG. FIG. 2 corresponds to a rear view, and FIG. 3 corresponds to a bottom view. These drawings are not necessarily based on the triangular projection, and the main purpose is to conceptually illustrate the configuration of the main part of the digital camera 1.

As shown in these figures, the digital camera 1 has a structure roughly divided into a substantially rectangular parallelepiped camera body 2 and a substantially cylindrical imaging unit 3.
9 to be detachable from the camera body 2 and
The camera is rotatably mounted in a plane parallel to the mounting surface of the camera body 2.

The image pickup section 3 has a component of an image pickup system including a macro zoom lens 301 as an image pickup lens and a photoelectric conversion element such as a CCD (Charge Coupled Device), and an optical image of a subject is photoelectrically converted by each pixel of the CCD. This is a component for converting the image into an image composed of the charged signals and capturing the image.

A macro zoom lens 301 is provided inside the image pickup section 3, and a CCD color area sensor (hereinafter simply referred to as a “CCD”) is provided at an appropriate position behind the macro zoom lens 301. An imaging circuit is provided, which is hidden on the back side and is not shown in FIGS. Then, a dimming sensor 3 that receives the reflected light of the flash light from the subject in an appropriate position of the imaging unit 3
05 is provided.

On the other hand, the camera body 2 includes an LCD display section 10 comprising a backlit LCD (Liquid Crystal Display) and a mounting section 17 for a memory card 8 as a recording medium.
And a connection terminal 13 to which a personal computer is externally connected. After subjecting the image signal captured by the imaging section 3 to predetermined signal processing, display on the LCD display section 10 and recording on the memory card 8 And processing such as transfer to a personal computer.

Hereinafter, the camera body 2 will be described in detail.
As shown in FIG. 3, the camera main unit 2 includes a card loading unit 17 for loading a memory card 8 for storing a captured image as a recorded image, and a battery loading unit for loading, for example, four AA batteries so as to be connected in series. 18 are built in. The digital camera 1 is driven by a power battery formed by serially connecting four dry batteries loaded in the battery loading unit 18, except for an RTC 219 described later. When the memory card 8 and the power supply battery are attached and detached, the clamshell type lid 15 provided on the bottom face is opened and closed. In addition, O
N / OFF is performed by a power switch PS provided on the back surface of the camera body 2.

As shown in FIG. 1, on the front surface of the camera body 2, a grip 4 is provided at an appropriate position on the left side, and a built-in flash 5 is provided at an appropriate position on the upper right. A connection terminal 13 is provided on the right side of the camera body so that a computer can be connected from outside the digital camera 1.

Also, as shown in FIG.
An LCD display unit 10 is provided at an appropriate position on the left side of the rear surface of the LCD, and an FL mode (flash) setting switch 11 is provided above the LCD display unit 10 on the left side. As the mode, for example, “automatic light emission mode” in which light emission / non-light emission of the built-in flash 5 is automatically controlled in accordance with the luminance of the subject.
Or built-in flash 5 forcibly regardless of subject brightness
There is a "forced light emission mode" in which the flash is emitted, and a "light emission inhibition mode" in which the built-in flash 5 is not forcibly emitted regardless of the brightness of the subject. It is set by switching automatically.

Further, a two-contact slide type photographing / reproduction mode setting switch 14 is provided above the LCD display unit 10 on the right side, and switches between a "photographing mode" and a "reproduction mode". The shooting mode is a mode for shooting a subject, and the LCD display unit 10 performs monitor display of the subject (corresponding to a viewfinder function). The reproduction mode is a mode in which an image recorded on the memory card 8 is reproduced and displayed on the LCD display unit 10. For example, sliding to the right sets the playback mode, and sliding to the left sets the shooting mode.

Further, a slide-type compression ratio changeover switch 12 is provided below the LCD display unit 10 on the left side, and selects a compression ratio K of image data to be stored in the memory card 8. Compression rate setting slide switch 12
Thus, two types of compression ratios K of 1/8 and 1/20 can be selected and set. For example, sliding the compression ratio setting slide switch 12 to the right sets the compression ratio K = 1/8, and sliding to the left sets the compression ratio K = 1/20. In the present embodiment, two types of compression ratios K
Can be selectively set, but three or more types of compression ratios K may be selectively set.

Further, the compression ratio setting slide switch 12
A liquid crystal display slide switch 16 for turning on / off the display of the LCD display unit 10 is provided on the right side of FIG. By turning off the liquid crystal display slide switch 16, the display on the LCD display section 10 is stopped, and the consumption of the battery can be minimized.

A macro button 20 for setting a macro mode is provided to the right of the liquid crystal display slide switch 16. Pressing the macro button 20 enables macro photography. For example, a business card size subject can be photographed to the size of the entire screen.

In addition, an UP switch 6 and a DOWN switch 7 for frame advance are provided substantially at the center of the upper surface of the camera body 2, and these switches are used to convert a recorded image already stored in the memory card 8 into a recorded image. Playback is performed in the order of the frame numbers assigned to each. Each time the UP switch 6 is pressed, the recorded images are sequentially updated in the order of increasing frame numbers (in the order of shooting), and
It is reproduced on the CD display unit 10. Also, DOWN switch 7
Each time is pressed, the recorded images are sequentially updated in the order of decreasing frame numbers and reproduced on the LCD display unit 10. A shutter button 9 is provided on the upper surface of the camera body 2 on the right side, and an erase switch D for erasing a recorded image stored in the memory card 8 is provided on the left side.
Further, an optical finder 21 used in a silver halide shutter camera is provided below the UP switch 6 and the DOWN switch 7.

<A-2. Functional Blocks of Digital Camera><A-2-1. Functional Blocks of Imaging Unit 3> FIG. 4 is a functional block diagram of the digital camera 1. In FIG.
Reference numeral 303 denotes a light image of a subject formed by the macro zoom lens 301, which is converted into image signals of R (red), G (green), and B (blue) color components (signal train of pixel signals received by each pixel) ) And outputs the signal.

The signal processing circuit 313 performs predetermined analog signal processing on the analog image signal obtained from the CCD 303. For example, CDS (correlated double sampling) processing and AGC (auto gain control) processing are performed. The former process reduces the noise of the image signal, and the latter process adjusts the level of the image signal.

The level adjustment of the image signal is performed in relation to the shutter speed. Since the aperture of the imaging unit 3 is fixed, exposure control is performed by adjusting the exposure amount of the CCD 303, that is, the charge accumulation time by the timing generator 314. However, if the subject brightness is low and the shutter speed is high, the exposure will be insufficient. To correct this, the signal processing circuit 313 adjusts the level of the image signal.

That is, when the luminance is low, the exposure control is performed by combining the shutter speed and the gain adjustment.
The level adjustment of the image signal is performed by the AG in the signal processing circuit 313.
This is performed in gain adjustment of the C circuit.

The timing generator 314 generates a drive control signal for the CCD 303 based on the reference clock transmitted from the timing control circuit 202.
As the drive control signal, for example, a timing signal of integration start / end (exposure start / end), a read control signal of a light receiving signal of each pixel (horizontal synchronization signal, vertical synchronization signal, transfer signal, etc.)
And so on.

The light control circuit 304 is a circuit for controlling the light emission amount of the built-in flash 5 in flash photography to a predetermined light emission amount set by the overall control unit 211.
In flash photography, the reflected light of the flash light from the subject is detected as the amount of light received by the light control sensor 305 at the same time as the exposure starts, and when the amount of received light reaches a predetermined light emission amount, the light control circuit 304 emits light from the FL control circuit. Stop signal STP
Is output to the flash control circuit 214 described later, and the light emission amount of the built-in flash 5 is controlled to be equal to or less than a predetermined light emission amount.

<A-2-2. Functional Blocks of the Imaging Unit 3> The camera main body 2 includes a built-in flash 5, an LCD display unit 10, a connection terminal 13, a card loading room 17, and a CPU. Overall control unit 211 for integrally controlling the driving of each unit in association with each other, the timing control circuit 2
02, an A / D converter 205 is provided. The overall control unit 211 includes a CPU 211A, a rewritable flash memory 211B storing a control program and the like, and a RAM 211 used as a working memory.
And a microcomputer provided with C.
Further, the black level correction circuit 206 and the white balance (W
B) Circuit 207, γ correction circuit 208, image memory 209
-1 to 209-6, a VRAM 210, and an operation unit 250. Further, a card interface 212, a communication interface 213, a flash control circuit 214 and an R
A TC (Real Time Clock) 219 is provided. Details of each of the above units will be described below.

The A / D converter 205 is provided for the signal processing circuit 31
3 is to convert each pixel signal of the image signal obtained from 3 into a 10-bit digital signal (captured image information). A
The / D converter 205 converts each pixel signal (analog signal) into a 10-bit digital signal based on a clock for analog-to-digital conversion from the timing control circuit 202.

The timing control circuit 202 is controlled by the general control unit 211 and generates a clock for the signal processing circuit 313, the timing generator 314, and the A / D converter 205.

The black level correction circuit 206 corrects the black level of the digital pixel signal (hereinafter simply referred to as “pixel data”) A / D converted by the A / D converter 205 to a reference black level.

The WB circuit 207 uses a level conversion table, which is a set value of a correction condition for white balance, input from the overall control unit 211, and uses a level conversion table for a black level correction circuit 206.
For the black level corrected pixel data obtained from
The white balance correction processing is performed by converting the levels of the G and B color components. The conversion coefficient (gradient of the characteristic) of each color component in the level conversion table is set by the overall control unit 211 for each captured image.

The gamma correction circuit corrects the gamma characteristics of the image signal. The γ correction circuit 208 has a plurality of γ correction tables having different γ characteristics, and performs γ correction of pixel data using a predetermined γ correction table according to a shooting scene and shooting conditions. The details of the γ correction table will be described later.

The image memory 209 (209-1 to 209-
6) is a memory for storing pixel data output from the gamma correction circuit 208. Image memories 209-1 to 209
-6 each have a storage capacity for one frame.
That is, each of the image memories 209-1 to 209-6 has a configuration in which the CCD 303 has n rows and m columns of pixels.
It has a storage capacity for pixel data of n × m pixels, and each pixel data is stored at a corresponding pixel position.

The VRAM 210 is a buffer memory for image signals reproduced and displayed on the LCD display unit 10. VRA
M210 has a storage capacity of an image signal corresponding to the number of pixels of the LCD display unit 10.

In the photographing standby state, each image signal of the image picked up by the image pickup unit 3 every 1/30 (second) is A / A
After being subjected to predetermined signal processing by the D converters 205 to γ correction circuit 208, the signal is stored in the image memory 209 and transferred to the VRAM 210 via the overall control unit 211, based on the image signal stored in the VRAM 210. The image is displayed on the LCD display unit 10. Therefore, the photographer can visually recognize the subject image from the image displayed on the LCD display unit 10. In the playback mode,
The image read from the memory card 8 is transferred to the overall control unit 21.
After predetermined signal processing is performed in step 1, the signal is transferred to the VRAM 210 and reproduced and displayed on the LCD display unit 10.

The card I / F 212 is an interface for writing image signals to the memory card 8 and reading image signals. Also, the communication I / F 213
Is an interface compliant with, for example, the USB standard for externally connecting the personal computer 40 so that communication is possible.

The software for each control executed by the microcomputer in the overall control unit 211 may be fixedly recorded in advance in the flash memory 211B in the overall control unit 211. At the time of uploading, the program may be installed in the microcomputer via an external recording medium. For installation, the program recorded on the recording medium is stored in the flash memory 21 in the overall control unit 211.
1B and stored. When the program stored in the flash memory 211B is operated, the program is loaded on the RAM 211C in the overall control unit 211, and the routine corresponding thereto is executed by the CPU.
It is executed at 211A.

As such a recording medium, a memory card having the same specifications as that of the memory card 8 for recording images and having an installation program recorded in advance may be used. The recording medium 41 such as a CD-ROM may be used.

In the latter case, the personal computer 40 and the digital camera 1 are made communicable by cable connection or infrared communication.
The installation program is transferred to the microcomputer in the digital camera 1 via the “0”. Also, the version upgrade program is loaded into the personal computer 40 via online communication such as a network,
It can be further transferred to a microcomputer in the digital camera 1 and installed. In this case, a hard disk in a server connected to the network or a hard disk in the personal computer 40 can be considered as a recording medium for the upgrade program.

The flash control circuit 214 is a circuit for controlling light emission of the built-in flash 5.

The flash control circuit 214 controls the presence / absence of light emission of the built-in flash 5, the amount of light emission, the light emission timing, and the like based on the control signal of the overall control unit 211.
The light emission amount of the built-in flash 5 is controlled based on the light emission stop signal STP input from the CPU 04.

The RTC 219 is a clock circuit for managing the shooting date and time. It is driven by another power source not shown in FIGS.

The operation unit 250 includes the UP switch 6, DOWN switch 7, shutter button 9, FL mode setting switch 11, and compression ratio setting slide switch 1 described above.
2. A switch corresponding to the photographing / playback mode setting switch 14 is provided, and a request for control of each unit of the digital camera 1 is made to the overall control unit 211.

The overall control unit 211 is composed of a microcomputer, and controls the driving of each member in the image pickup unit 3 and the camera main body unit 2 in an organic manner to control the photographing operation of the digital camera 1 overall. is there.

FIG. 5 shows the CPU 21 in the overall control unit 211.
FIG. 2 is a block diagram showing internal functions realized by the entirety of 1A and memories 211B and 211C. As shown in the figure, the overall control unit 211 includes a luminance determination unit 211a for setting an exposure control value (shutter speed (SS)) and a shutter speed setting unit 211b. In the photographing standby state, the luminance determination unit 211a
In step 03, luminance data is calculated using an image captured every 1/30 (second) to determine the luminance of the subject.

That is, the luminance determining unit 211a divides the storage area of the image memory 209 into nine blocks by using the image data stored renewably in the image memory 209, and G (green) included in each block. The luminance data representing each block is calculated by using the pixel data of the color component of (1) to determine the luminance of the subject.

The shutter speed setting section 211b sets a shutter speed (integration time of the CCD 303) based on the result of the luminance determination of the subject by the luminance determining section 211a. The shutter speed setting unit 211b has a table of shutter speed SS in which brightness and shutter speed SS are associated in advance.

The shutter speed SS is initially set to 1/128 (second) (the shutter speed having the highest luminance) when the camera is started, and in a photographing standby state, the shutter speed setting unit 211b operates the shutter speed setting unit 211b by the luminance judgment unit 211a. The initial value is changed and set one step at a time from the initial value to the high-speed side or the low-speed side according to the determination result of the luminance.

The general control unit 211 also uses a normal photographed image of a landscape, a person, or the like (hereinafter, this kind of captured image is referred to as a “natural image”), but the image is drawn on a board. It further includes an image determination unit 211e that determines whether an image such as a character or a chart is an image similar to a binary image of this type (hereinafter, an image similar to a "character image").

The image judging section 211e includes an image memory 209
A histogram of the luminance data at each pixel position is created based on the image data constituting the captured image stored in the storage device, and the content of the captured image is determined based on the histogram. Generally, in the case of a natural image, a histogram of luminance data of a captured image is a so-called one-peak distribution having a small deviation in luminance distribution and having one peak value. On the other hand, in the case of a character image such as a character drawn on a whiteboard, a luminance distribution is biased in a white background portion and a black character portion, and a two-peak distribution is obtained.

Therefore, the image determination unit 211e determines whether the histogram of the luminance data of the captured image has a single peak distribution,
It is determined whether the captured image is a natural image or a character image by determining whether the image has a two-peak distribution. Then, this determination result is stored in the memory 211d.

The overall control unit 211 performs “low-brightness scene”, “medium-brightness normal scene”, “medium-brightness scene” in order to set appropriate shutter speed SS, perform γ correction and filtering correction (described later) according to the shooting scene. It further includes a scene determination unit 211c that determines four types of shooting scenes of a “luminance backlight scene” and a “high-luminance scene”. A “low-brightness scene” is a scene that normally requires auxiliary light using a flash, such as indoor shooting or nighttime shooting, and a “medium-brightness normal scene” is illumination light (including natural light and artificial light) for a main subject. ) Is a scene that can be photographed without auxiliary light because it is normal light and its brightness is appropriate. Also, the “medium brightness backlight scene” has an appropriate overall brightness,
Since the illumination light for the main subject is backlight, flash emission is a preferable scene, and the “high-brightness scene” is a very bright scene as a whole, for example, photographing in a sunny sea or a ski resort. The low-luminance, medium-luminance, and high-luminance scene determination is performed based on the set value of the shutter speed SS. In the middle-luminance scene, when the peripheral portion is brighter than the central portion by a predetermined value or more, it is determined to be a “medium-luminance backlight scene”. The determination result of the scene determination unit 211c is also stored in the memory 2
11d.

The overall control unit 211 includes a filter unit 211f for performing a filtering process, a recorded image generating unit 211g for generating a thumbnail image and a compressed image, and a memory card 8 for recording the captured image. And a reproduced image generation unit 211h for generating a reproduced image signal for reproducing the reproduced image signal on the LCD display unit 10.

The filter unit 211f includes an image memory 209
Is to correct the image quality of the outline by correcting the high-frequency component of the image to be recorded by the digital filter with respect to the image signal from. The filter unit 211f calculates the compression ratio K =
For each of 1/8 and 1/20, a digital filter that performs standard contour correction, and two types of digital filters that strengthen the contour and two types of digital filters that weaken the contour are used for the standard contour correction. A total of five digital filters are provided.

The recording image generation unit 211g is provided in the image memory 2
The image signal is read from the image data 09 through the filter unit 211f to generate a thumbnail image and a compressed image to be recorded on the memory card 8. The recording image generation unit 211g reads an image signal every eight pixels in both the horizontal direction and the vertical direction while scanning from the image memory 209 in the raster scanning direction, and sequentially connects the memory connected via the card I / F 212. By transferring the thumbnail image to the card 8, the thumbnail image is generated and recorded on the memory card 8.

Further, the recording image generation unit 211g reads out all pixel data from the image memory 209 via the filter unit 211f, and performs predetermined compression processing by JPEG such as two-dimensional DCT conversion and Huffman coding on the pixel data. To generate an image signal of a compressed image, and record the compressed image signal in the main image area of the memory card 8.

As shown in FIG. 6, the memory card 8 converts the image stored by the digital camera into a compression ratio of 1/2.
0, 40 frames of images can be stored. Each frame includes a tag information portion, a high-resolution image signal (640 × 480 pixels) compressed in the JPEG format, and an image signal for thumbnail display (80 × 60 pixels). Pixel) is recorded. For example, each frame can be handled as an image file in the EXIF format.

<A-3. Outline of γ Correction> According to the features of the present invention, the γ correction circuit 208 is used in a short distance and in a flash mode.
Will be described below.

FIG. 7 is a diagram showing an example in which a histogram is generated from an input image signal. In FIG. 7, the horizontal axis represents the luminance level x and the vertical axis represents the number n of pixels, and the larger the x, the higher the luminance. Xmax on the x-axis indicates the upper limit of the dynamic range in the image signal, and Pmin is the minimum brightness level in the histogram HS, Pma
x indicates the maximum brightness level in the histogram HS.

When flash photography is performed in the macro mode which is a typical mode of short-range photography, an image signal having a histogram as shown in the example of FIG. 7 is obtained.
That is, the minimum luminance value Pmin does not coincide with the luminance level 0, and the image signal is entirely biased toward the high luminance side, which is an overexposed image. In the case of such an image signal,
The effective contrast range PW as data is Pmin
ＰPmax.

Therefore, the effective contrast range PW
In order to make effective use in association with almost the entire dynamic range on the output side, in the case of close-range shooting and flash shooting (hereinafter referred to as “short-range flash mode”) represented by the macro mode, FIG. Instead of a normal gamma correction table, a gamma correction table for a high-brightness image described below is used.

FIG. 8 is a diagram showing, as a γ-conversion characteristic curve Cm, the conversion characteristics of the γ-correction table TA for a high-luminance image set in the γ-correction table 208 in the short-range flash mode. In FIG. 8, the horizontal axis represents the input luminance level x, and the vertical axis represents the output luminance level y. The larger the value, the higher the luminance. Xmax on the x-axis indicates the upper limit of the input luminance level. Also, Ymax on the y-axis
Indicates the upper limit of the output luminance level.

This conversion characteristic curve Cm (hereinafter referred to as “high-brightness conversion characteristic curve”) is the conversion characteristic curve C for normal photographing.
0 (hereinafter referred to as a “reference conversion characteristic curve”) is shifted in the x-axis direction toward the high luminance side by a predetermined offset value X0 (X0> 0), thereby shifting the rising portion PS to the high luminance side, thereby reducing the zero. Is substantially raised from the value X0 which is not.

Here, the offset value X0 is
The manufacturer can perform a large number of close-range flash shootings experimentally for various scenes and conditions, and statistically process and determine the histograms obtained thereby. For example, the lower 5% of the distribution of the values of the minimum luminance level Pmin in FIG.
Is determined as the statistical lower limit, and the offset value X0 can be determined according to the statistical lower limit.

By this parallel movement, the x-axis upper limit value Xmax
In the vicinity, the y-axis upper limit value Ymax does not completely correspond, and a gap G occurs near the y-axis upper limit value Ymax.
Since the conversion characteristic curve is generally in a "sleeping state" in the vicinity of the x-axis upper limit value Xmax, the gap G is considerably small, and there is substantially no problem (third embodiment described later). Has improved on this.)

Note that the 1 converted by the A / D converter 205
In order to process a 0-bit image signal, the input image signal is specifically composed of 10 bits for each of RGB color components.
The output image signal is specifically composed of 8 bits for each of the RGB color components so that recording on the memory card 8 can be performed efficiently. In this case, Xmax = 1023, Xmin
= 0, Ymax = 255, and Ymin = 0. Although the γ-conversion characteristic curve Cm in FIG. 8 can be set in common for each of the RGB color components, a different high-luminance conversion characteristic curve may be set for each color component in accordance with the characteristics of the monitor.

If the shooting is not a short-range shooting (that is, a middle-range shooting or a long-range shooting), and if the flash prohibition mode is selected even in a short-range shooting, the conversion characteristic curve for high luminance is used. The reference conversion characteristic curve C0 is used instead of Cm.

As described above, in the digital camera 1, a plurality of scenes corresponding to a plurality of types of scenes such as "low-luminance scene", "medium-luminance normal scene". Correction curve C0 of
C1, C2... Are prepared. These are all conversion characteristic curves substantially rising from the input lower limit value Xmin, and a predetermined one of them is adopted as the reference conversion characteristic curve C0, and the reference conversion characteristic curve C0 is used.
, The conversion characteristic curve Cm for high luminance can be generated.

<A-4. Outline of Operation of Digital Camera 1> FIG. 9 is a flowchart for explaining the outline of operation of the digital camera 1.

First, before step S1, the photographer sets basic photographing conditions. Note that the standard photographing mode is set by default when the photographing conditions are not particularly set.
Then, in step S1, the photographer presses down the shutter button 9 while visually recognizing the subject on the LCD display unit 10 or the optical viewfinder 21.

In response to this, in the next step S2, the photographing operation is automatically executed. Here, when the flash is in the automatic light emission mode, it is automatically determined whether or not the illuminance of the subject is insufficient. When the illuminance is insufficient, the flash 5 automatically emits light. In the case of the forced light emission mode, the flash 5 is forcibly emitted.

In step S3, it is determined whether the shooting condition is shooting in the macro mode, that is, whether the macro button 20 has been pressed and shooting has been performed. If the shooting is in the macro mode, the process proceeds to step S4. On the other hand, if the mode is not the macro mode, the process proceeds to step S6. If the digital camera has an automatic focusing function,
In step S3, regardless of whether the mode is the macro mode or not, the condition for determining whether or not shooting is performed at a short distance where the distance from the camera to the subject is equal to or less than a predetermined distance (for example, 50 cm) may be used. The determination in this case can be made by referring to a distance signal obtained from a distance measuring unit provided in the digital camera for automatic focusing or the like, and comparing the distance signal with a distance threshold.

In step S4, it is determined whether the shooting condition is flash shooting. In other words, the process proceeds to step S5 in the case of flash photography, but otherwise proceeds to step S6 in the same manner as step S3.

The determination of the photographing conditions in steps S3 and S4 is performed by the overall control unit 211.

Here, the criteria for judging whether the photographing is a close-up photographing and a flash photographing are generally arranged as follows.

(1) Whether or not short-distance shooting is used: When setting short-distance shooting manually, as shown here, when the photographer selects the macro mode (for a digital camera with interchangeable lenses) In some cases, the macro lens is replaced with a macro lens), and when the photographer manually focuses, the set distance is equal to or less than a predetermined threshold distance.

In the former case, the overall control unit 211 determines whether or not the macro mode has been set by a mode selection button or the like. In the latter case, the distance manually set by the photographer as the focusing distance and the above threshold value The overall control unit 2 determines whether or not the photographing is performed at a short distance by comparing the distance with the distance.
11 will know.

Further, in the case of a digital camera having an auto-focus function having a distance measuring unit, as described above, when the subject distance as a result of auto-focusing is equal to or less than a predetermined threshold distance, short-distance shooting is performed. Is determined.

In each of these cases, a macro mode setting button, a manual focusing mechanism,
And the device configuration for the autofocus function each functions as a shooting distance setting unit, and the overall control unit 211 refers to the state of those shooting distance setting units to determine whether or not it corresponds to short distance shooting. Determine the shooting conditions.

(2) Whether or not to use flash photography: If the forced flash mode is set manually, flash photography is performed regardless of the state of the subject.

When the automatic light emission mode is selected, for example, when the shutter button 9 is half-pressed, the output value of the CCD image pickup device in the image pickup section 3 is read to detect the brightness of the object, and the luminance of the object is detected. If the brightness is lower than a predetermined threshold, the flash is set to emit light. For this reason, in the automatic light emission mode, it is determined whether or not flash light emission is to be performed according to the result obtained by the combination of the subject luminance detection means and the threshold value comparison means.
The overall control unit 211 refers to the result.

Therefore, when both the case of the forced light emission mode and the case of light emission in the automatic light emission mode are expressed, the overall control unit 211 refers to the determination result of the flash light emission determination means and performs the flash photography. The photographing condition of whether or not is determined.

Returning to FIG. 9, the process proceeds to step S5 in the case of the short-distance flash photography mode. In this case, an image signal having a histogram as shown in the example of FIG. Therefore, the γ correction circuit 208 performs γ correction based on the γ correction table TA for a high-brightness image as illustrated in FIG.

First, in step S5a, a gamma correction table TA for a high luminance image is selected or set. The selection or setting in the γ correction table TA will be described below with reference to FIG.

A γ correction table T0 for normal photographing having a reference conversion characteristic curve C0 in the γ correction circuit 208.
When the .gamma. Correction table TA for high brightness image is set in parallel in advance, the .gamma. Correction table TA for high brightness image is selected among them. That is, FIG.
As shown in (a), the selector 208a selects the γ correction table TA by the switching signal from the overall control unit 211.

If the gamma correction table for a high-brightness image is set in the gamma correction circuit 208 every time a photograph is taken, the reference conversion stored in the memory of the overall control unit 211 in advance is performed. Characteristic curve table is C
The PU reads and transfers the value of the output image level y corresponding to each value of each input image level x to the address of the output image value corresponding to the input image level (x + X0) shifted by the offset value X0. For the range of 0 ≦ x ≦ X0, y = 0 is forcibly given. The gamma correction table TA for a high-luminance image created in this way is shown in FIG.
As shown in (b), the data is set in the gamma correction circuit 208 in a look-up table format. In this case, it is not necessary to always store the entire γ correction table TA for the high-luminance image, and the entire control unit 211 of the digital camera 1 may hold only the offset value X0.

Further, the parallel movement of the reference conversion characteristic curve C0 can be equivalently achieved by level shift of the input image signal. That is, as shown in FIG. 10 (c), the offset value X0 is subtracted from the level V of the input image signal by the subtractor 208b and synthesized, and the synthesized signal Vc = (V-X0)
The combined signal Vc may be converted by the γ correction table T0 corresponding to the reference conversion characteristic curve C0. In this case, the γ correction table TA for the high luminance image is not used, but the “conversion characteristic for the high luminance” in the present invention is equivalently achieved by the shift of the input image signal. Conversion characteristics.

After the γ correction table TA for the high-brightness image is selected or set in the γ correction circuit 208, when the image signals obtained by imaging are transferred for each pixel, those pixel signals are sequentially converted to γ. Γ in the correction circuit 208
It is converted by the correction table TA. (Step S5b).

On the other hand, in step S6, a γ correction table for normal photographing corresponding to the conversion characteristic curve C0 is selected, and image processing is performed based on the table.

Then, in step S7, the image signal processed in step S5 or S6 is stored in one of the image memories 209 in FIG.

The image signal after the γ conversion can be displayed on the LCD display unit 10 of the digital camera 1. By transferring the image signal to a personal computer or the like external to the digital camera 1 using the memory card 8 or the like, It can be displayed on a monitor of a personal computer.

<A-5. Example of Image Processing> Next, a specific image of the improvement of the reproduced image by the image processing based on the gamma correction table TA for a high luminance image will be described with reference to FIG.

FIG. 11 shows an image signal schematically composed of a 5 × 5 pixel matrix, and is a case of image processing in this case. The image signal 51 is transmitted from the CCD 30
3 is an image signal after being converted into a digital signal by the A / D converter 25 and subjected to signal processing by the black level correction circuit 206 and the WB circuit, and indicates data before being subjected to γ correction. ing. The image signal 52 is an image signal after the γ correction by the γ correction circuit 208 and is stored in the image memory 209. The image signal 53 is obtained by converting the image signal stored in the image memory 209 on the monitor of the personal computer 40 or the LC of the digital camera 1.
D10 shows luminance level data of an image reproduced.

The image signal 51 has a luminance level of 1 for each pixel.
The histogram HG1 is generated as shown in FIG. 12, the horizontal axis represents the luminance level x and the vertical axis represents the number n of pixels, as in FIG. Then, the brightness levels x = 0, 1, 2,.
For each value of 3, the number of pixels n = 0, 16,
8 and 1 are taken. That is, the luminance level corresponding to the minimum luminance level Pmin shown in FIG.
It can be seen that 1 in G1 corresponds, and there is no pixel near the luminance level x = 0, that is, the image signal is biased toward the so-called high luminance side. Note that, for convenience of explanation, the luminance level is up to 3, but as described above, the actual image signal is distributed over 10 bits (= 1024).

In the case of the image signal 51, image processing is performed based on a gamma correction table for a high luminance image having the conversion characteristic curve. Here, the rising point of the characteristic curve 54 is the input luminance level value 1. Specifically, the input luminance level value 1,
2, 3 are converted into output luminance level values 0, a, b, respectively. In general, a and b should be integers in a digital signal, but here, for convenience of explanation, it is not limited to integers.

By the above image processing, the image signal 51 is
It is converted into an image signal 52. This image signal 52 is an image signal including the luminance level value 0.

Thereafter, the image signal 52 has the γ characteristic curve 5
5 is output as a reproduced image 53 on a monitor 56 having the same. Here, the input luminance level values 0, a, and b are converted into output luminance level values 0, 1, and 2, respectively, by the γ characteristic curve 55 represented by the function shown in Expression 1. This indicates that the reproduced image 53 includes the luminance level value 0, and the bias of the image signal 51 that has been biased toward the high luminance side is improved.

By the above operation, the bias of the image signal toward the high luminance side can be corrected in the overexposed photographed image.

The image processing for correcting the bias toward the high luminance side can be performed by another signal conversion circuit in the digital camera 1. However, the gamma correction circuit 208
Is a circuit of the last stage in a series of signal processing from image acquisition by the CCD 303 to storage of an image signal in the image memory 209, and the output luminance level upper limit Ymax in the γ correction table TA (FIG. 8) is input. 1 of the brightness level upper limit value Xmax
Since the data is compressed by / 4 (= 8 bits / 10 bits), the accuracy of the digital signal between input and output deteriorates due to the quantization error.

Therefore, rather than converting the 10-bit signal to an 8-bit signal by the normal γ correction and then lowering the overall luminance of the image by another conversion circuit, the dynamic range on the output side is converted into the 8-bit signal. It is better to use as effectively as possible.

For example, in shooting in the short-distance flash mode, if pixels are distributed in a band of 200 to 1000 as an effective contrast range PW of FIG. Of the input 1
Although the output signal is compressed at 256/1024 = 0.25 per bit, if the offset value X0 is, for example, 170, 256 / (1024-17) per input bit
0) = 0.3, and the compression ratio decreases. Therefore,
The deterioration of the precision of the digital signal between input and output can be suppressed.

Since the actual γ correction is a non-linear conversion, the quantization error differs depending on the value of the image level, but the tendency is similar to the above calculation.

For these reasons, when a gamma correction circuit having a bit length of the output signal smaller than the bit length of the input signal is provided, it is particularly effective to perform high luminance correction in the gamma correction circuit. .

<B. Second Embodiment><B-1. Main Configuration> The main configuration of a digital camera according to a second embodiment of the present invention is the same as that of the digital camera 1 according to the first embodiment except for a portion related to the gamma correction circuit 208. Is equal to In the digital camera according to the second embodiment, two types of conversion characteristic curves Cm1 and Cm2 for a high-brightness image as illustrated in FIG. It has corresponding gamma correction tables TA1 and TA2.

The first conversion characteristic curve Cm1 for high luminance has its rising portion PS1 substantially rising from the first offset value X01 larger than zero.
Further, the rising portion PS2 of the second conversion characteristic curve Cm2 for high luminance substantially rises from the second offset value X02 which is larger than the first offset value X01. The second conversion characteristic curve Cm2 corresponds to a value obtained by translating the first conversion characteristic curve Cm1 by a predetermined distance (X02-X01) in the x-axis high luminance direction.

<B-2. Operation> As described above, in the second embodiment, two gamma correction tables TA1 and TA2 for a high-brightness image are prepared, so that the operation of the digital camera 1 of the first embodiment is performed. On the other hand, an operation of selecting an appropriate γ correction table from the two types based on the luminance information of the input image signal is added.

More specifically, in FIG. 14 showing a process corresponding to step S5 in the flowchart of FIG. 9, first, in step S11, the minimum luminance value Pmin included in the input image signal of the γ correction circuit 208 is specified. This specification is performed by the overall control unit 211 functioning as a luminance specifying unit.
(FIG. 5). Here, the luminance value of the image signal may be specified by sequentially comparing the magnitude of each pixel, or a histogram may be created and specified by analyzing the histogram.

In any case, the image signal obtained by the imaging is temporarily stored in the image memory 209 without being subjected to the correction such as the γ correction, and the minimum luminance value Pmin is specified, and the γ correction is used as described below. After the conversion characteristics are specified, they are read out from the image memory 209 pixel by pixel and subjected to actual gamma correction. The image signal after γ correction is replaced with the image signal before γ correction and stored in the image memory 209.

Next, at step S12, the minimum luminance value Pmin of the image signal is set to the first γ correction table TA1 for high luminance.
Is smaller than the offset value X01. here,
If Pmin <X01, the process proceeds to step S16.
On the other hand, if Pmin <X01 is not satisfied, the process proceeds to step S13.

In step S13, the minimum luminance value Pmin of the image signal is set to the second γ correction table TA2 for high luminance.
Is smaller than the offset value X02 of here,
If Pmin <X02, the process proceeds to step S15. If Pmin <X02, the process proceeds to step S1.
Proceed to 3.

Next, in step S14, signal conversion is performed based on the second γ correction table TA2 for a high luminance image. In step S15, signal conversion is performed based on the first gamma correction table TA1 for a high-luminance image.

In step S16, image processing is performed based on the gamma correction table T0 for normal photographing, as in step S6 in the flowchart of FIG.

By the above operation, the conversion characteristic curve that always includes the effective contrast range PW of the image signal, that is, the γ correction table can be selected, and the minimum luminance value Pmin
Can be selected, the dynamic range on the output side can be efficiently used in correspondence with the effective contrast range P.

By the above operation, as in the case of the first embodiment, the bias of the image signal toward the high luminance side can be corrected in the overexposed photographed image.

<C. Third Embodiment><C-1. Main Configuration> The main configuration of a digital camera according to a third embodiment of the present invention is the same as the digital camera 1 of the first embodiment except for a portion related to the γ correction circuit 208. Is equal to In the digital camera according to the third embodiment, the offset value X0 of the gamma correction table for a high luminance image that can be set in the gamma correction circuit 208 is determined from the luminance information of the input image signal.

<C-2. Operation> FIG. 15 is a flowchart showing the operation of the main part for this, and corresponds to step S5 in the flowchart of FIG.

First, in step S21, the γ correction circuit 2
08 specifies the minimum luminance value Pmin included in the input image signal. This specification is performed by the overall control unit 211. Here, similarly to the second embodiment, the luminance value of the image signal may be specified by sequentially comparing the magnitude of each pixel, or a histogram may be created and specified by analysis. Actual γ
Before receiving the correction, the image signal is temporarily stored in the image memory 209 as in the second embodiment.

Next, in step S22, the reference conversion characteristic curve C0 is translated so that the offset value X0 in the conversion characteristic curve Cm (FIG. 8) coincides with the specified minimum luminance value Pmin. Generate a table TA. Here, as shown in FIG. 16, for example, after the offset value X0 (= Pmin) input from the overall control unit 211 to the subtractor 208c and the image signal are combined, a γ correction table having a reference conversion characteristic curve C0 Converted by T0. The subtracter 208c and the gamma correction table T0
With the above processing, generation of the γ correction table TA can be equivalently achieved.

In step 23, γ correction is performed based on the generated γ correction table TA.

By the above operation, even if the lower limit value Pmin of the luminance distribution in short-range flash photography varies from scene to scene, the offset value X0 is determined in accordance with them.
Since the correction table can be generated, the effective contrast range PW can be more effectively utilized.

As a result, as in the case of the first embodiment,
In the overexposed captured image, the bias of the image signal toward the high luminance side can be corrected.

<D. Fourth Embodiment><D-1. Main Configuration> The main configuration of a digital camera according to a fourth embodiment of the present invention is the same as that of the digital camera 1 according to the first embodiment except for a portion related to the gamma correction circuit 208. Is equal to In the digital camera according to the fourth embodiment, as shown in FIG. 17, not only the low luminance side offset value X1 but also the high luminance side offset value Also set X2.

The high luminance image γ correction table TB thus generated substantially rises from the low luminance side offset value X1, reaches the upper limit value Ymax of the output luminance level at the high luminance side offset value X2, and substantially increases. It is set in accordance with the conversion characteristic curve Cmb that saturates temporarily. That is, the γ conversion characteristic curve Cmb for the high luminance image is obtained by converting the reference conversion characteristic curve C0 to the dynamic range (0
ＹYmax) in the x-axis direction (X2−X1) / (Xma
(x-Xmin). Here, effective processing is performed only in the effective conversion range W whose input luminance level is in the range of X1 to X2.

In this case, based on the luminance information of the input image signal, the effective contrast range PW (FIG. 7) of the input image signal and the effective conversion range W are approximately equal, that is, X1 = Pmin and X2 = Pmax The conversion characteristic curve Cmb is generated so as to satisfy the following conditions. This conversion characteristic curve Cmb
Is generated by the overall control unit 211 for each shooting of each scene.

<D-2. Operation> FIG. 18 shows γ for a high-brightness image.
10 is a flowchart illustrating an operation of generating a correction table TB, and corresponds to step S5 in FIG.

First, steps S31 and S3
In step 2, the minimum luminance value Pmin and the maximum luminance value Pmax included in the input image signal of the γ correction circuit 208 are specified. This specification is performed by the overall control unit 211. The process is
In the third embodiment, the operation of specifying the maximum luminance value Pmax is added to the operation of specifying the minimum luminance value Pmin.

Next, in step S33, the γ correction is performed so that the low luminance side offset value X1 and the high luminance side offset value X2 in the conversion characteristic curve Tmb coincide with the specified luminance minimum value Pmin and luminance maximum value Pmax, respectively. Generate a table TB.

In step 34, γ correction is performed based on the generated γ correction table TB.

By the above operation, the conversion characteristic curve, that is, the γ correction table can be generated based on the information at both ends of the effective contrast range PW of the image signal, so that the effective contrast range PW can be utilized to the maximum.

As a result, as in the case of the first embodiment,
In the overexposed captured image, the bias of the image signal toward the high luminance side can be corrected.

<Modifications> The image processing for improving the high-brightness image acquired by the digital camera is not necessarily performed by the gamma correction circuit.
It may be performed in another signal conversion in the digital camera. However, as described above, it is preferable to perform the conversion at the same time before or after conversion into an image signal having a short bit length, or in conversion involving a change in bit length.

As shown in FIG. 19, the conversion characteristic curve for a high-luminance image gradually increases relatively from the input signal level 0 to the low-luminance region, and reaches around a predetermined luminance level X0 (X0> 0). May be a conversion curve Cmd that rises steeply.

That is, the "rising portion" of the conversion characteristic curve in the present invention is not limited to a portion rising from a strict zero level (y = 0) as shown in FIG. It is a concept that includes a part that can be seen.

The gamma correction circuit in each embodiment may be realized by an analog circuit instead of a digital circuit. In this case, before the processing in the A / D converter 205, a gamma correction circuit for a high-brightness image having a conversion characteristic curve TA shown in FIG. 8 is provided separately from the gamma correction circuit for normal photographing. . Then, the signal conversion is performed by the gamma correction circuit for the high brightness image under the shooting conditions (macro mode and flash shooting) that can be determined relatively quickly without analyzing the brightness information of the image. In this case, since a quantization error generated in the digital circuit does not occur, signal conversion can be performed with high accuracy.

In the second embodiment, two types of gamma correction tables for high luminance images are provided, but three or more types may be used.

In the fourth embodiment, the effective contrast range PW (FIG. 8) of the input image signal and the conversion characteristic curve T
It is not essential that the effective conversion range W of B completely match. However, when there is a deviation between these ranges PW and W, it is preferable that the effective conversion range W can include the effective contrast range PW.

Regarding the conversion characteristic curves of the first and second embodiments, the conversion characteristic curves are set at a predetermined magnification in the y-axis direction such that the upper limit value Xmax of the input luminance level corresponds to the upper limit value Ymax of the output luminance level. It may be reduced.

[0151]

As described above, according to the first and seventh aspects of the present invention, when the photographing condition is flash photographing at a short distance, the rising portion is more input than the standard conversion characteristic for normal photographing. The conversion characteristics for the high-luminance image shifted to the high-luminance side of the level are set in the signal conversion means.
As a result, in the overexposed photographed image, the bias of the image signal toward the high luminance side can be corrected.

Further, according to the second and seventh aspects of the present invention, since flash photography at a short distance is flash photography in a macro mode, photography conditions can be specified more easily.

Further, according to the third and seventh aspects of the present invention, the minimum luminance value included in the input image signal is specified, and the conversion for the high luminance image is performed so as to substantially rise from the vicinity of the minimum luminance value. Since the characteristics are determined, the input image signal can be effectively used in reproducing the gradation.

According to the fourth and seventh aspects of the present invention, the minimum luminance value and the maximum luminance value included in the input image signal are specified, and substantially rise from the vicinity of the minimum luminance value.
In addition, the conversion characteristic for a high-luminance image is determined so as to be substantially saturated near the maximum luminance value. Therefore, the effective contrast range of the input signal can be efficiently reflected on the output signal.

According to the fifth and seventh aspects of the present invention, the conversion characteristics for a high-brightness image are determined by moving the reference conversion characteristics in parallel to the high-brightness side of the input level. The conversion characteristics for a high-brightness image can be easily generated.

According to the sixth and seventh aspects of the present invention, the conversion characteristic for a high-luminance image is determined by compressing the reference conversion characteristic on the input level side while maintaining the dynamic range of the output level. In addition, it is possible to generate a conversion characteristic for a high-brightness image that is simple and can efficiently reflect an effective contrast range of an input signal to an output level.

[Brief description of the drawings]

FIG. 1 is a digital camera 1 according to a first embodiment of the present invention.
FIG.

FIG. 2 is a diagram illustrating a back surface of the digital camera 1. FIG.

FIG. 3 is a diagram illustrating a bottom surface of the digital camera 1;

FIG. 4 is a functional block diagram of the digital camera 1.

FIG. 5 is a block diagram showing an internal configuration of the overall control unit 211.

FIG. 6 is a diagram for explaining image storage of a memory card 8;

FIG. 7 is a diagram illustrating an example in which a histogram is generated from an input image signal.

FIG. 8 is a diagram illustrating a gamma correction table TA for a high-brightness image.

FIG. 9 is a flowchart illustrating an outline of an operation of the digital camera 1.

FIG. 10 is a diagram illustrating an example of processing in a γ correction circuit 208.

FIG. 11 is a diagram illustrating an example of image processing based on a γ correction table TA for a high luminance image.

FIG. 12 is a diagram illustrating an example in which a histogram is generated from an input image signal.

FIG. 13 is a diagram showing γ correction tables TA1 and TA2 for a high-luminance image.

FIG. 14 is a flowchart illustrating a selection operation from two types of γ correction tables TA1 and TA2.

FIG. 15 is a flowchart illustrating an operation of generating a γ correction table TA.

FIG. 16 is a diagram illustrating an example of processing in the γ correction circuit 208.

FIG. 17 is a diagram showing a γ correction table TB for a high luminance image.

FIG. 18 is a flowchart illustrating an operation of generating a γ correction table TB.

FIG. 19 is a diagram illustrating a modified example of the gamma correction table for a high-luminance image.

FIG. 20 is a diagram for describing gamma correction during normal shooting.

[Explanation of symbols]

1 Digital camera 5 Built-in flash 20 Macro button Cm, Cm1, Cm2, Cmb Conversion characteristic curve for high-brightness image C0, C1, C2 Conversion characteristic curve for normal use TA, TA1, TA2, TB Gamma correction table for high-brightness image T0 γ correction table for normal shooting 211 Overall control unit 208 γ correction circuit Pmin Minimum luminance value Pmax Maximum luminance value

Claims (7)

[Claims] 1. A digital camera which obtains an output image signal by converting an input image signal obtained by shooting by a predetermined signal converting means, wherein a standard for normal shooting is used in flash shooting at a short distance. A conversion characteristic setting unit configured to set, in the signal conversion unit, conversion characteristics for a high-brightness image in which a rising portion is shifted to a high-brightness side of the input level rather than the conversion characteristics. 2. The digital camera according to claim 1, wherein the flash photography at a short distance is a flash photography in a macro mode. 3. The digital camera according to claim 1, wherein the conversion characteristic setting unit includes: a luminance specifying unit that specifies a minimum luminance value included in the input image signal; and a vicinity of the minimum luminance value. Characteristic determining means for determining the conversion characteristics for the high-luminance image so as to substantially rise from,
A digital camera comprising: 4. The digital camera according to claim 3, wherein the luminance specifying unit is a unit that specifies a maximum luminance value included in the input image signal together with the minimum luminance value. A digital camera, wherein the conversion characteristic for the high-luminance image is determined so as to substantially rise from around the minimum luminance value and substantially saturate near the maximum luminance value. 5. The digital camera according to claim 3, wherein the characteristic determining unit translates the conversion characteristic for the high luminance image by moving a curve representing the reference conversion characteristic in parallel to a high luminance side of an input level. A digital camera characterized in that it is determined. 6. The digital camera according to claim 4, wherein the characteristic determination unit compresses a curve representing the reference conversion characteristic on an input level side while maintaining a dynamic range of an output level, so that the high brightness image is obtained. A digital camera for determining a conversion characteristic for a digital camera. 7. A program for causing a digital camera to function as the digital camera according to claim 1 by being installed in a microcomputer built in the digital camera. Characteristic, a computer-readable recording medium.