JP2002237995A - Electronic camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic camera that changes the gradation of an actually photographed image, depending on the luminance of a scene so as to obtain the image that responds to the visibility of human beings. SOLUTION: The luminance range of a scene is obtained, as a result of AE operation on the basis of an imaging signal of an imaging element 1, the contrast of the image is obtained from a pixel value histogram of the photographed image, a corresponding gradation conversion table is selected, on the basis of the luminance range of the scene, and the contrast of image and gradation conversion processings are carried out, and an image which corresponds to visibility are made to be outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic camera, and more particularly to an electronic camera capable of reproducing, on a recorded image, a gradation characteristic recognized by a photographer at the time of shooting regardless of the luminance of a scene.

[0002]

2. Description of the Related Art In general, in an electronic camera, tone characteristics (brightness characteristics) are set in a preset state depending on the type of camera, and the brightness of the entire image is adjusted by exposure adjustment. The gradation is uniformly determined from to the darkest scene. Some recent electronic cameras allow the user to select and set the contrast.However, continuous shooting is performed at the selected and selected level of contrast, depending on the scene or shooting state. It is not configured to automatically change contrast.

Also, after photographing, software for allowing a user to adjust the contrast of a photographed image on a personal computer or to automatically perform contrast adjustment is known, but the user's adjustment and software are also required. ,
Analyzing the photographed image, increasing the one with low contrast,
The object of high contrast is intended to keep the contrast of the image constant, for example, low, and the contrast is not adjusted according to the state of the scene to be photographed.

[0004]

FIG. 7 is a graph showing the relationship between the scene luminance and the brightness response of the human eye. The horizontal axis shows the scene luminance, that is, the luminance at the time of shooting. Heights indicate bright and dark areas,
The vertical axis shows the brightness response. As can be seen from this figure, the human eye has a wider response of brightness to a change in brightness in a bright scene with high scene brightness, and the contrast is perceived as higher than the actual contrast. The width of the response is narrower, and it feels lower than the actual contrast.

[0005] As described above, the luminosity characteristic that the contrast is recognized higher in a bright environment than in a dark environment is known. On the other hand, in an electronic camera, as described above,
Regardless of the brightness of the scene, the gradation characteristics for the scene are generally fixed, and therefore, a captured image of a bright scene has a lower contrast than the gradation felt by the photographer on the spot, and a dark scene. Then, there is a possibility that the gradation actually sensed by the photographer on the spot is different from the gradation of the photographed image.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem in the conventional electronic camera, and has an electronic camera capable of changing the gradation characteristic (contrast) of an actual photographed image in accordance with the luminance of a scene. The purpose is to provide.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an image pickup means for photoelectrically converting an image of a formed subject to obtain electronic image data, and an image pickup means using the image pickup means. A luminance detecting means for detecting luminance information of a scene at the time, a gradation converting means for performing a gradation converting process on the image data obtained by the image pickup means, and a luminance detecting means for detecting the luminance information detected by the luminance detecting means. The electronic camera is constituted by control means for controlling the gradation conversion means so as to change the gradation conversion characteristics.

In the electronic camera configured as described above, the gradation conversion characteristic of the recorded image is adjusted according to the scene luminance. Therefore, when the scene luminance is high and bright, the photographer can reduce the scene contrast. Since the user should feel "high," the contrast characteristic is set to be higher than usual, and vice versa when the scene luminance is low and dark. As a result, it is possible to obtain an image that matches the human visibility in that case.

[0009]

Next, an embodiment will be described. FIG. 1 is a block diagram showing an embodiment of an electronic camera according to the present invention. In FIG. 1, reference numeral 1 denotes a zoom lens system, 2 denotes an imaging device such as a CCD for photoelectrically converting a subject image formed by the zoom lens system, and 3 denotes an imaging circuit for processing an imaging signal output from the imaging device 2. Reference numeral 4 denotes an A / D conversion circuit, reference numeral 5 denotes a memory I / F for a memory card for recording a captured image, and reference numeral 6 denotes a card slot for mounting a memory card 7 which is detachably mounted. 8 is A
An image processing unit that performs image processing such as JPEG compression / expansion processing and resizing processing of the / D converted image data, 9 is a RAM for temporary storage used when performing image processing in the image processing unit 8, and 10 is a floor. A ROM for storing information for image processing such as a tone conversion table, 11 an external I / F for input / output signals from an external input / output terminal 12, and 13 for an image signal to be displayed on an LCD image display unit 15. Video memory, 14 is a video output circuit,
16 is a video output terminal. Reference numeral 17 denotes a lens driving unit for driving a zoom lens system, 18 denotes a lens driving control circuit, 19 denotes a strobe light emitting unit, 20 denotes an operation unit for inputting various instructions, 21 denotes control processing of each unit, color conversion processing, and A system controller that performs tone conversion processing and the like, 22 is a power supply unit that supplies power to each unit, 23 is a camera battery, and 24 is an external power input terminal.

Next, the operation of the electronic camera configured as described above will be described. The general operation of the entire shooting mode of the electronic camera will be collectively described later.
First, a specific operation different from the conventional one of the present invention will be described.

According to the present invention, according to the luminance value of a shooting scene,
The system controller 21 performs a gradation conversion process on the image pickup signal. This gradation conversion process is performed using a gradation conversion table as shown in FIG. In the illustrated example, a table having three gradation conversion characteristics of,, is shown. This gradation conversion table is stored in the ROM 10, which is read out and the system controller 21 performs a gradation conversion process. It has become. The horizontal axis of the gradation conversion table shown in FIG. 2 is a digital value before gradation conversion, that is, a digital value of an output signal of the image sensor 2 whose exposure is controlled, and the vertical axis is a digital value after gradation conversion. ing. In the three gradation conversion tables of,,,
Assuming that the gradation conversion table is a standard, the table having the gradation conversion characteristic indicated by is a gradation conversion table used for creating an image having a low contrast, and the table having the gradation conversion characteristic indicated by the image is a high-contrast image. Is a gradation conversion table used to create the image. Then, the gradation conversion process is performed by automatically selecting which gradation conversion table to use according to the luminance of the scene.

Next, a method of selecting a gradation conversion table will be described. The digitized CCD image pickup signal output from the A / D conversion circuit 4 is a digital value before gradation conversion of the gradation conversion table, and this value is subjected to gradation conversion processing in correspondence with the gradation conversion table. However, when actual imaging is performed with an electronic camera, it is necessary to perform exposure control (AE) before performing actual imaging. In this exposure control, the brightness (luminance) of a scene is measured. I do. There are various methods for measuring the brightness of the scene. In this embodiment, for example, the brightness of the scene is measured from the output of the image sensor 2, and based on the measured brightness of the scene, FIG. The shutter speed and the aperture value are set along the solid line of the program diagram as shown.

When the shutter speed and the aperture value are determined, it is possible to determine the brightness of the scene. In the example shown in FIG. 3, the luminance range of the scene is divided into three regions.
That is, a dark scene in which the shutter speed in the lower left area of the graph is slow and the exposure value is smaller and the aperture value is larger is taken as the area of the luminance range 1, and the exposure amount in the upper right area where the shutter speed is faster and the aperture value is larger is reduced. A bright scene has a luminance range of 3 and an intermediate area has a luminance range of 2.
, The brightness range is divided into three regions, and which of the gradation conversion tables is automatically selected and set depending on which brightness range contains the scene. For example, the simplest selection setting method is to use a gradation conversion table in the case of the luminance range 2 in the standard state and to use a gradation conversion table for lowering the gradation (contrast) in the dark part of the luminance range 1. A tone conversion table is used, and in the case of the luminance range 3, a tone conversion table is used. Such a selection setting method is the simplest method.

As a method of selecting and setting a gradation conversion table, there is the following setting method other than the above method. Determines not only the contrast of the actually captured image itself, that is, the brightness of the scene, but also the contrast of the captured image data, that is, the aspect of how bright and dark parts are included in the image. Therefore, it is not a preferable direction to further increase an image having an originally high contrast, so that such gradation conversion processing is not performed, and it is not possible to further reduce an image having an originally low contrast. Since it deviates from the preferred direction, a setting method that does not perform such gradation conversion processing can also be used.

Here, a method of determining the image contrast used in the above setting method will be described with reference to the relationship diagram between the histogram and the contrast in FIG.
In this histogram, the horizontal axis represents the digital value (0
255255), and the vertical axis indicates the frequency of appearance of pixels having the digital value. In FIG. 4, Min-10% is a digital value (pixel value) in which the area ratio of the left skirt portion is 10% with respect to the entire area of the histogram (the total number of pixels), and Max-10% is a right value with respect to the entire area. It shows the digital value where the area ratio of the skirt becomes 10%, and the difference [Max-10% -Min-10%]
Is defined as the contrast of the image. The method of this definition is a method for avoiding the influence of noise, and according to the above definition, the contrast corresponds to the width of the peak of the histogram obtained by cutting both sides of the histogram, and the width of the peak is narrow. If it is distributed in a part, it is regarded as an image with low contrast (such as a morning misty scene), and if it is distributed with a wide mountain range, an image with high contrast (shadow on a clear day Scenes).

After the contrast of the image is obtained in this way, the gradation conversion process is performed by associating the gradation conversion table with the luminance range as follows. That is, scene brightness (brightness ranges 1, 2, 3) and contrast (0 to 255)
) And the gradation conversion table, FIG.
As shown in FIG. 7, the luminance ranges 1, 2, 3 do not correspond directly to the gradation conversion tables. It is not preferable to apply such a method, because the contrast of the scene is originally high and the contrast is further increased. This is not a preferable direction. Or applying a low-contrast image such as a gradation conversion table to an image in a luminance range 1 region where the luminance of the scene is very low, because the contrast is originally low, Since the contrast is lowered, which is not a preferable direction, such a gradation conversion process is not performed, and a standard gradation conversion table is used. To.

That is, in a simple method, originally,
The gradation conversion table may correspond to any contrast image for the region in the uppermost luminance range 3 in FIG. 5. Only the standard gradation conversion table is used for the case. In addition, a standard gradation conversion table is used for an image having a low contrast even for an image in the lowest luminance range 1 region.

As described above, the gradation conversion process is performed by changing the gradation conversion table in the standard state because the gradation conversion table is used for a scene having a high luminance and a standard or low contrast. Conversion processing is performed, or only when gradation conversion processing is performed on a dark or low-scene scene with a standard or high contrast using a gradation conversion table. By performing the gradation conversion processing in such a relationship, a gradation conversion image having extremely preferable image quality can be obtained.

Note that at the time of photographing with flash emission, the flash is originally illuminated when the scene is dark, and the image contrast is controlled so as to improve the image contrast to some extent when the flash is emitted. When the gradation conversion processing is added, the image quality may be rather deteriorated. Therefore, the setting is made such that the gradation conversion process is performed as standard when the strobe light is emitted.

Next, an outline of the operation of the entire imaging mode including the above-described gradation conversion processing operation will be described with reference to the flowchart shown in FIG. When the imaging mode is set, it is first determined whether or not the zoom lever is operated (step S1). If the zoom lever is operated, the zoom lens system 1 is set in accordance with the setting of TELE or WIDE. Is driven by the lens driving unit 17 (step S2). If the zoom lever is not operated,
Subsequently, it is determined whether or not the first release pressing operation has been performed (step S3). If the first release pressing operation has been performed, AE, A is determined based on the pre-imaging signal.
The F operation is performed (Step S4). Subsequently, the pressing operation of the second release is determined (step S5).
When the release pressing operation is performed, the main imaging is performed, and the imaging circuit 3 performs the imaging signal processing (Step S).
6) Subsequently, WB (white balance) and color conversion processing are performed (steps S7 and S8).

Next, it is determined whether or not the strobe light has been emitted (step S9). If the strobe light has not been emitted, the luminance range of the scene is determined from the result of the AE (step S10). Is determined from the histogram (step S11), and a gradation conversion table to be used in the gradation conversion processing is selected according to the table shown in FIG. A gradation conversion process is executed (step S13).

The step S for determining the flash emission
In step 9, when strobe light emission is being performed, the standard setting of the gradation conversion table is set for the reason described above (step S14), and gradation conversion processing is performed (step S1).
3). The image data subjected to the gradation conversion processing is then subjected to data compression processing (step S15), and the compressed image data is recorded on the memory card 7 (step S16).

With the above operation, a series of processing in the image pickup mode is completed.
The tone conversion table stored in the M10 is selected according to the scene luminance and the image contrast, and the tone conversion processing using the table is performed by the system controller 21.
The compression processing of the image data subjected to the gradation conversion processing is performed by the image processing unit 8.

In the above description, the photometry for the AE operation is performed based on the pre-imaging signal obtained by the first release pressing operation, but a separate photometry element is provided. The AE operation may be performed using the photometric signal from the photometric element, and the luminance range of the scene may be determined based on the AE operation result. Further, the luminance of the scene may be detected by a separate luminance detecting means without using the AE operation result by photometry.

[0025]

As described above, according to the present invention, according to the present invention, it is possible to change the gradation of an actual photographed image in accordance with the luminance of a scene and obtain an image suitable for human visibility. An electronic camera configured as described above can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an electronic camera according to the present invention.

FIG. 2 is a diagram illustrating a gradation conversion table used in a gradation conversion process.

FIG. 3 is a graph showing a relationship between a program diagram and a luminance range.

FIG. 4 is a diagram showing a relationship between a pixel value histogram and contrast.

FIG. 5 is a graph showing a relationship between a luminance range, a contrast, and a gradation conversion table.

FIG. 6 is a flowchart for explaining an operation in a shooting mode of the embodiment shown in FIG. 1;

FIG. 7 is a diagram showing a relationship between scene brightness and brightness response of a human eye.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Zoom lens system 2 Image sensor 3 Imaging circuit 4 A / D conversion circuit 5 Memory I / F 6 Card slot 7 Memory card 8 Image processor 9 RAM 10 ROM 11 External I / F 12 External I / F terminal 13 Video memory 14 Video Output circuit 15 LCD image display section 16 Video output terminal 17 Lens drive section 18 Lens drive control circuit 19 Strobe light emission section 20 Operation section 21 System controller 22 Power supply section 23 Camera battery 24 External power input terminal

Claims (8)

[Claims] An imaging unit configured to photoelectrically convert the formed subject image to obtain electronic image data; a luminance detection unit configured to detect luminance information of a scene when photographed by the imaging unit; Gradation conversion means for performing gradation conversion processing on the image data obtained by the means, and the gradation conversion means so as to change the gradation conversion characteristics according to the luminance information detected by the luminance detection means. An electronic camera, comprising: control means for controlling the electronic camera. 2. The electronic camera according to claim 1, wherein said luminance detecting means also serves as a photometric means for exposure control. 3. The control means controls the gradation conversion means so as to change a gradation conversion characteristic so as to increase or decrease the contrast in accordance with an increase or a decrease in the value of the luminance information detected by the luminance detection means. 3. The method according to claim 1, wherein
Electronic camera according to the present invention. 4. The control means according to claim 1, wherein when the luminance information detected by said luminance detecting means is higher than a predetermined value, the control means changes the gradation conversion characteristic so that the contrast is higher than a reference gradation conversion characteristic. The electronic camera according to any one of claims 1 to 3, wherein said electronic camera controls said gradation conversion means. 5. When the luminance information detected by the luminance detecting means is higher than a predetermined value and the contrast of the scene is higher than a predetermined value, the control means performs gradation conversion based on a reference gradation conversion characteristic. The gradation conversion means is controlled so as to perform processing.
An electronic camera according to any one of the preceding items 3. 6. The control means for changing a gradation conversion characteristic such that when the luminance information detected by the luminance detection means is lower than a predetermined value, the contrast is lower than a reference gradation conversion characteristic. The electronic camera according to any one of claims 1 to 3, wherein said electronic camera controls said gradation conversion means. 7. When the luminance information detected by the luminance detecting means is lower than a predetermined value and the contrast of the scene is lower than a predetermined value, the control means performs gradation conversion based on a reference gradation conversion characteristic. 4. The method according to claim 1, wherein said tone converting means is controlled so as to perform processing.
An electronic camera according to any one of the preceding claims. 8. A flash unit for emitting light toward a subject, wherein the control unit performs a tone conversion process based on a reference tone conversion characteristic when the flash unit emits light. The electronic camera according to claim 1, wherein the electronic camera controls the gradation conversion unit.