JP2000059653A - Electronic still camera, and method for correcting luminance of photographed image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct uneven illuminance in the case of photographing an object lighted by an artificial light by storing dispersion in luminous quantity of a light emitted onto the object as correction data and using the correction data so as to correct a photographed image thereby utilizing an image processing function of the electronic still camera. SOLUTION: Dispersion in luminous quantity of a light emitted onto the object is stored as correction data and a photographed image is corrected by using the correction data. In the case of using the electronic still camera 10, first a preliminary photographing mode is selected and setting such as fine adjustment of a position of a camera is made and a shutter key 14 is depressed. Then a test plate is removed and an object of a close-up object is placed instead, the electronic still camera 10 is selected in the main photographing mode and the shutter key 14 is depressed. That is, the electronic still camera 10 conducts preliminary photographing by using the test plate and then the main photographing is conducted after that. In the case of conducting the photographing above, the electronic still camera 10 executes a prescribed program.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic still camera and a method for correcting the brightness of a photographed image, and more particularly, to photographing a subject illuminated by an artificial light source (hereinafter, referred to as "artificial light") such as a strobe or incandescent lamp. The present invention relates to an electronic still camera and a method of correcting the brightness of a captured image, which makes it possible to correct “illuminance unevenness” when performing the processing.

[0002]

2. Description of the Related Art In daytime outdoor photography, sufficient brightness can be obtained by sunlight. Since the position of the light source is very far from the earth, this sunlight can be regarded as almost parallel rays, and the illuminance (per unit area of a certain surface) (The amount of light received by the light source) is uniform. Therefore, by setting the exposure and the shutter speed in accordance with the brightness of an arbitrary part of the subject, a good photograph can be taken regardless of the type of camera (electronic still camera or film camera).

[0003]

On the other hand, when an image is taken using a light source other than the sun, that is, an artificial light such as a strobe light or an incandescent lamp, the position of the light source is much closer to the sun, so From the light source, and a difference occurs in the distance between each part of the subject and the light source. Therefore, due to the nature of light that the illuminance at a certain point is inversely proportional to the square of the distance between the point and the light source, "irregularity" occurs in the illuminance at each part of the subject. Setting the exposure and shutter speed,
There is a disadvantage that the set value is not always appropriate in other parts. This will be described with an actual example. FIG. 13 shows a printed matter or an arbitrary object (hereinafter, referred to as “subject”).
FIG. 1 is a view showing an instrument (hereinafter referred to as a “stand” for convenience) for taking a close-up photograph neatly. A stand 100 has an arm 103 attached to a tip of a pole 102 erected on a stage 101. The incandescent lamps 104 and 105 are attached to both ends of the arm 103. The procedure of the close-up photography performed using the stand 100 is as follows. The camera 106 is set on the pole 102 and the position of the camera 106 is finely adjusted while illuminating the subject placed on the stage 102 with the incandescent lamps 104 and 105. Then, the exposure and the shutter speed are determined and the shutter key of the camera 106 is pressed.

FIG. 14 shows the close-up photography.
FIG. 5 is a conceptual diagram of an illuminance distribution₀Is a light source (for convenience
The incandescent lamp 104) on the left side of FIG.₁~ P_ThreeIs the stay
Some lighting points on the di 100. Where the light source
P₀And each lighting point P₁~ P_ThreeThe distance to₁, R_Two, R_ThreeTo be
And the light source P₀Lighting point P close to₁Distance r₁Is the shortest,
Light source P₀Lighting point P far from_ThreeDistance r_ThreeIs the longest, medium
Lighting point P between_TwoDistance r 2 is the length in between, so each
Illumination point P₁~ P_ThreeThe illuminance of P₁→ L₁, P_Two→ L_Two, P_Three→ L_Three
The light properties (the illuminance at a point is
Is inversely proportional to the square of the distance between₁> L_Two>
L_ThreeIrradiance at each part of the subject
"Mura" (for example, L₁And L_TwoDifference, L_TwoAnd L_ThreeDifference)
Will happen.

Accordingly, an object of the present invention is to provide a new technique for correcting uneven illuminance when an object illuminated by artificial light is photographed by using an image processing function of an electronic still camera.

[0006]

According to a first aspect of the present invention, there is provided an electronic still camera wherein a variation in the amount of light hitting a subject is stored as correction data, and a captured image is corrected using the correction data. It is characterized by. An electronic still camera according to a second aspect of the present invention is an electronic still camera that converts an image of a subject captured through a photographic lens into a two-dimensional image signal and records the image signal, and the overall luminance of the image signal Value, and a deviation amount between the overall luminance value and the luminance value of each pixel constituting the image signal or a value correlated with the deviation amount is stored as correction data of each pixel, and an arbitrary subject is stored. When taking an image, after converting the image of the arbitrary subject captured through the photographic lens into a two-dimensional image signal, the luminance value of each pixel constituting the image signal is corrected with the correction data. I do. An electronic still camera according to a third aspect of the present invention is the electronic still camera according to the second aspect, wherein the image signal for obtaining the overall luminance value is a test plate having a uniform light reflectance or color temperature. It is characterized by having been done. An electronic still camera according to a fourth aspect of the present invention is the electronic still camera according to the first or second aspect, wherein the light that strikes the subject is light of a strobe built in a camera body. The electronic still camera according to the invention described in claim 5 is:
In the invention according to claim 2, the light hitting the subject is light of a strobe built in a camera body, and the image signal for obtaining the overall luminance value is a light reflectance or a color temperature. It is characterized in that the object is a uniform test plate. An electronic still camera according to a sixth aspect of the present invention is a digital still camera, comprising: a mode switching unit that switches between a pre-photographing mode and a main photographing mode; and a photographed image that is photographed while being switched to the pre-photography mode by the mode switching unit. Calculating means for calculating a brightness correction value of each pixel based on the correction value for correcting the brightness value of each pixel of a captured image taken in a state where the mode is switched to the main shooting mode by the mode switching means; Means. In the electronic still camera according to the seventh aspect of the present invention, a mode switching unit that switches between a pre-photographing mode and a main photographing mode, and a shutter key is pressed while the mode is switched to the pre-photographing mode by the mode switching unit. Computing means for photographing a test plate having a uniform light reflectance and computing a luminance correction value for each pixel based on a luminance value of the entire screen of the photographed image or a value correlated with the luminance value; When the shutter key is pressed while the mode is switched to the main shooting mode by the switching unit, a correction unit that corrects the brightness value of each pixel of the captured image at that time with the brightness correction value, and a reflectance of the test plate. Setting means for setting an exposure for photographing in the pre-photographing mode and the main photographing mode based on the photographing mode. The brightness correction method for a captured image according to the invention according to claim 8, wherein in the method for correcting the brightness of a captured image, the captured image is corrected by using correction data indicating a variation in the amount of light of a subject image included in the captured image. Is corrected.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. An electronic still camera converts an image of a subject through a photographic lens into a video signal using a two-dimensional image sensor (generally a CCD: charge coupled device), displays the video signal on a liquid crystal display, and uses a nonvolatile semiconductor memory. Or to memorize it. This camera has many features not found in conventional film cameras, such as the ability to play images on the spot and transfer images to remote locations, and is widely used in various fields, both public and private. In recent years, with the advent of inexpensive CCDs with more than 1 million pixels, many devices capable of recording extremely high-definition images have been circulating, and have reached a level comparable to the image quality of conventional cameras. .

FIG. 1 is an external view of an electronic still camera. Although not particularly limited, the illustrated electronic still camera 10 is divided into a main body portion 11 and a camera portion 12 rotatably attached to the main body portion 11, and is provided on the front surface (the back surface side in the drawing) of the camera portion 12. Denotes a photographic lens not shown. A CCD, also not shown, is attached to the back of the photographic lens, and converts a subject image taken from the photographic lens into a video signal in a recording mode (pre-photographing mode and main photographing mode) described later. By converting, a high-resolution frame image can be generated. On the other hand, a flat panel display device, for example, a liquid crystal display 13 for confirming an image (through image for composition adjustment or recorded captured image) is attached to the main body 11, and a shutter key 14 Are provided at appropriate positions. The types and names of the operation keys vary depending on the manufacturer and model, and cannot be uniquely specified.
5, minus key 16, menu key 17, power switch 18, display key 19, recording mode key 20,
Self-timer key 21, strobe mode key 22, R
The EC / PLAY key 23 and the like (the functions (roles) of these keys) are as follows.

(1) Shutter key 14: In the recording mode, as the name implies, it functions as a "shutter key" (fixing exposure and focus by half-pressing and capturing an image by full-pressing). When the menu key 17 is pressed in a playback mode (a mode in which a captured image is played back or output to another device), a YES key for confirming various selection items displayed on the liquid crystal display 13 is pressed. It is a multi-function key that also works. (2) Plus key 15: a key used to select a reproduced image and various system settings. “Plus” means the selection direction, which is the direction of the latest image in the case of image selection, and the scanning direction of the liquid crystal display 13 in the case of system setting selection. (3) Minus key 16: Same function as the plus key except that the direction is reversed.

(4) Menu key 17: A key for performing various system settings. For example, in the recording mode, various items (definition of the recorded image, auto focus on / off, etc.) necessary for recording the image are displayed on the liquid crystal display 13, and in the reproduction mode, the delete mode (image erasing mode) is displayed. The first various items are displayed on the liquid crystal display 13. (5) Power switch 18: A switch for turning on and off the power of the camera. (6) Display key 19: A key for overlappingly displaying various information on the image displayed on the liquid crystal display 13. For example, in the recording mode, the remaining number of recordable images and the form of photographing (normal photographing, panoramic photographing, Information such as macro shooting is displayed in an overlapped manner, and in the playback mode, attribute information (page number, definition, etc.) of the playback image is overlapped and displayed.

(7) Recording mode key 20 (mode switching means): This key can be used only in the recording mode. In addition to selecting normal shooting, panoramic shooting, etc., the details will be described later, but in the present embodiment, it is particularly used for selecting a “pre-shooting mode” and a “main shooting mode”. (8) Self-timer key 21: A key for turning on / off the self-timer function. (9) Strobe mode key 22: This key is used for various settings related to the strobe, for example, for forcibly emitting light, prohibiting light emission, and preventing red-eye. (10) REC / PLAY key 23 This is a key for switching between a recording mode and a reproduction mode. In this example, the switch is a slide switch. When the switch is slid up, the recording mode is set, and when the switch is slid down, the playback mode is set.

FIG. 2 is a block diagram of the electronic still camera according to the present embodiment. The electronic still camera according to the present embodiment has an automatic exposure function, an automatic focus function, and a strobe function, and includes elements specific to these functions (for example, a light amount measurement sensor, a distance measurement sensor, and an auto focus drive mechanism). , A strobe lamp (generally a xenon tube) and a control mechanism thereof), but are not shown in the block diagram for simplification of the drawing. 2, reference numeral 30 denotes a photographic lens, 31 denotes a CCD (image sensor), 32 denotes a horizontal / vertical driver, 33 denotes a timing generator (TG: Timing Generator), 34 denotes a sample and hold circuit, 35 denotes an analog / digital converter, 36 Is a color process circuit, 37 is a DMA controller, 38 is a DRAM interface, 39 is a DRAM, 40 is a flash memory, 41 is a CPU, 42 is a JPEG circuit,
43 is a VRAM, 44 is a VRAM controller, 45 is a digital video encoder, 46 is a key input unit, 47
Is a bus.

The functions of these units are generally as follows. (A) Photo lens 30: This is for forming an image of a subject on the light receiving surface of the CCD 31, and has a focusing mechanism for an automatic focusing function. Note that a zoom function may be provided, or a retractable type may be provided. (B) CCD 31: a solid-state imaging device that transfers electric charges in an array. Also called a charge-coupled device. Although some are used for analog delay lines and the like, this specification particularly refers to a so-called solid image sensor that converts two-dimensional optical information into a time-series (serial string) electric signal.

In general, a CCD has a photoelectric conversion section in which a large number of photoelectric conversion elements are arranged in an array, a charge storage section for storing output charges of the photoelectric conversion elements, and a charge readout for reading out charges in the charge storage section in a predetermined manner. And each of the photoelectric conversion elements becomes a pixel. For example, in a CCD having one million effective pixels, at least one million cells in the array are arranged. Hereinafter, for convenience of explanation, the number of effective pixels of the illustrated CCD 31 is 1280 × 96.
Set to 0. That is, 1280 in the row direction (lateral direction),
12 pixels composed of 960 pixels in the column direction (vertical direction)
Assume that it has an array structure of 80 columns × 960 rows. Note that the CCD 31 of the present embodiment is a color CCD.
Generally, since the pixel information of the CCD itself does not have color information, a color filter (a primary color filter using three primary colors of light or a complementary color filter using three primary colors) is mounted on the front surface of a color CCD. In addition, CCDs can be divided into two types according to a charge reading method. The first type is a "jump-out readout method" (also referred to as an interlaced CCD) in which pixels are skipped one by one when reading out a signal. Say) type. Although the second type is frequently used in electronic still cameras, the first type may be used in recent megapixel-class electronic still cameras exceeding one million pixels. Hereinafter, for convenience of explanation, the CCD 31 of the present embodiment is of a second type (full-surface reading method).

(C) Horizontal / vertical driver 32 and timing generator 33: This is a part for generating a drive signal necessary for reading the CCD 31, and the CCD 31 of this embodiment is
Since it is assumed that the entire surface is read out, a drive signal capable of transferring (reading out) pixel information in units of rows while designating each column of the CCD 31 one after another, in other words, 12
It generates horizontal and vertical drive signals for serially reading out pixel information in the direction from the upper left to the lower right of the array structure of 80 columns × 960 rows (this direction is similar to the television scanning direction). . (D) Sampling and holding circuit 34 for sampling a time-series signal (an analog signal at this stage) read from the CCD 31 at a frequency suitable for the resolution of the CCD 31 (for example, correlated double sampling). . Note that automatic gain adjustment (AGC) may be performed after sampling. (E) Analog-to-digital converter 35: Converts a sampled signal into a digital signal.

(F) Color process circuit 36: a part for generating a luminance / color difference multiplex signal (hereinafter, referred to as a YUV signal) from the output of the analog-to-digital converter 35. The reason for generating the YUV signal is as follows. The output of the analog-to-digital converter 35 substantially corresponds to the output of the CCD 31 on a one-to-one basis except for the difference between analog and digital and errors in sampling and digital conversion, and is the light primary color data (RGB data) itself. However, this data is large in size, causing disadvantages in terms of limited memory resource utilization and processing time. Therefore,
It is necessary to reduce the amount of data to some extent by some method. In general, each component data (R data, G data, and B data) of RGB data can be represented by three color difference signals GY, RY, and BY with respect to the luminance signal Y. If the redundancy of these three color difference signals is removed, GY need not be transferred, and GY = α (R−
Y) -β (BY), which is a kind of data amount reduction signal based on the principle that the signal can be reproduced. here,
α and β are synthesis coefficients.

The YUV signal is converted to a YCbCr signal (Cb
And Cr may be referred to as BY and RY, respectively, but in this specification, they are unified to YUV signals. The signal format of the YUV signal is composed of three fixed-length blocks called "components" each independently including a luminance signal and two color difference signals, and has a length (number of bits) of each component. The ratio is called the component ratio. Although the component ratio of the YUV signal immediately after the conversion is 1: 1: 1, the two components of the color difference signal are shortened, that is, 1: x: x (where x
<1) can also reduce the data amount. This utilizes the fact that human visual characteristics are less sensitive to color difference signals than luminance signals.

(G) DMA controller 37: Data transfer between the color process circuit 36 and the DRAM 39 (more precisely, the DRAM interface 38) is performed without the intervention of the CPU 41, so-called direct memory transfer (DMA). memory access). It may be abbreviated as DMAC. Generally, DMAC
In small computer systems, CPUs and I / Os
It controls data transfer between memory and memory or between memory and I / O instead of the O processor. It generates a source address and a destination address necessary for data transfer, and reads a source read cycle and a destination. The CPU or the I / O processor sets the initial address, cycle type, transfer size, and the like to the DMAC, and then transfers control to the DMAC. Data transfer is
It starts after receiving a DMA transfer request signal from an I / O device or an I / O processor. (H) DRAM interface 38: a signal interface between the DRAM 39 and the DMA controller 37;
And a signal interface between the DRAM 39 and the bus 47.

(I) DRAM 39: A kind of rewritable semiconductor memory. Generally, a DRAM is a static RAM (SRA) in that data is dynamically rewritten (refreshed) in order to retain stored contents.
Although different from M), although the writing and reading speeds are inferior to those of the SRAM, it is particularly suitable for an electronic still camera because the unit price per bit is low and a large-capacity temporary storage can be configured at low cost. However, the present invention is not limited to a DRAM. Any rewritable semiconductor memory may be used.

(J) Flash memory 40: rewritable read-only memory (PROM: programmable area)
d only memory) that can be electrically rewritten by erasing the contents of all bits (or blocks). Flash EEPROM (flash electrically era
sablePROM). The flash memory 40 in the present embodiment may be a fixed type that cannot be removed from the camera body, or may be a removable type such as a card type or a package type. The flash memory 40, whether built-in or removable, must be initialized (formatted) in a predetermined format. In the initialized flash memory 40, the number of images corresponding to the storage capacity can be recorded.

(K) CPU 41 (calculation means, correction means,
Setting means): centrally controls the operation of the camera by executing a predetermined program. The program is, for example, C
The program for the mode is written in the instruction ROM inside the PU 41 in the recording mode, and the program for the mode is read from the instruction ROM in the recording mode.
Loaded into AM and executed. (L) JPEG circuit 42: A part that performs JPEG compression and decompression. JPEG compression parameters are provided from the CPU 41 each time compression processing is performed. The JPEG circuit 4
2 should be dedicated hardware in terms of processing speed, but it can also be performed by the CPU 41 in software.

Note that JPEG is a joint photographic.
An abbreviation of experts group, an international coding standard for color still images (full-color or grayscale still images that do not include binary or moving images). In JPEG, lossless encoding that can completely restore compressed data,
Two methods of irreversible coding that cannot be undone are defined, but in most cases, the latter irreversible coding with a high compression ratio is used. The ease of use of JPEG lies in the fact that the degree of image quality degradation accompanying encoding can be freely changed by adjusting parameters used for compression (compression parameters). That is, on the encoding side, an appropriate compression parameter can be selected from the trade-off between image quality and file size, or on the decoding side, the decoding speed is increased at the expense of some quality, or it takes time. Is easy to use because you can choose to play it at the highest quality. The practical compression ratio of JPEG is about 10: 1 to 50: 1 for lossy codes. Generally, if the ratio is from 10: 1 to 20: 1, visual deterioration does not occur, but if some deterioration is allowed, even from 30: 1 to 50: 1 can be used sufficiently. Incidentally, the compression ratio of another encoding system is, for example, GIF (graphics interchange format).
In the case of (1), since the ratio is only about 5: 1, the superiority of JPEG is apparent.

(M) VRAM 43: so-called video RA
M, and when a through image or a reproduced image is written in the VRAM 43, the image is sent to the liquid crystal display 13 via the digital video encoder 45 and displayed. Some video RAMs have two ports for writing and reading, and can write and read an image simultaneously and in parallel. The VRAM 43 of the present embodiment also has this type of port. Video RA
M may be used. (N) VRAM controller 44: A part for controlling data transfer between the VRAM 43 and the bus 47 and between the VRAM 43 and the digital video encoder 45. In short, writing of an image for display to the VRAM 43 and reading of the same image from the VRAM 43 Is the part that controls If a dual port type video RAM is used,
The VRAM controller 44 may be unnecessary or simplified.

(O) Digital video encoder 45:
The digital value display image read from the VRAM 43 is converted into an analog voltage and is sequentially output at a timing according to the scanning method of the liquid crystal display 13. (P) Key input unit 46: A unit for generating operation signals for various key switches provided on the camera body. (Q) Bus 47: A data (and address) transfer path shared among the above-described units. Although not shown in the figure, necessary control lines (control lines) are also provided between the units.

Here, the storage capacity of the DRAM 39 must satisfy the following conditions. The first condition is that the capacity is such that a temporary storage space for a captured image can be secured. This storage space stores at least information (1280 × 9) of a high-definition image generated by the color process circuit 36.
It must be large enough to store 60 pixel image information and a YUV signal having a 1: 1: 1 component ratio. The second condition is that the capacity is such that a sufficient work space required for the CPU 41 can be secured. The size of the work space depends on the architecture of the CPU 41, the OS (Operating System) and its OS.
Since it is determined by various application programs executed under the management of S, it is sufficient to consider these specifications and make the size appropriate without excess or deficiency. It must have sufficient capacity to secure a "two-dimensional array" according to the pixel array of the captured image. FIG. 3 is a conceptual diagram of a two-dimensional array, and represents, for example, an array declared as name (n, m) in the BASIC language. Here, name is the name of the array, n is the maximum row of the array, and m is the maximum column of the array. If name (1,1) = a, the value a is put in (1,1) of the array coordinates, and if name (n, m) = b, the value b is in (n, m) of the array coordinates. enter.

Next, the operation will be described. First, an outline of recording and reproduction of an image will be described. <Recording mode> CC arranged behind the photographic lens 30
D31 is driven by a signal from the horizontal / vertical driver 32, and the video collected by the photographic lens 30 is photoelectrically converted at regular intervals to output a video signal for one screen. Then, the video signal is sampled by a sampling and holding circuit 34 and converted into a digital signal by an analog-to-digital converter 35, and then a YUV signal is generated by a color process circuit 36. This YUV signal is transferred to the DRAM 39 via the DMA controller 37 and the DRAM interface 38, read out by the CPU 41 after the transfer to the DRAM 39 is completed, and sent to the liquid crystal display 13 via the VRAM controller 44 and the digital video encoder 45. Is displayed.

When the direction of the camera is changed in this state, the composition of the image displayed on the liquid crystal display 13 changes, and the shutter key 14 is "half-pressed" at an appropriate time (when a desired composition is obtained). After the exposure and focus are set and “full press”, the YUV signal stored in the DRAM 39 is fixed at the current YUV signal,
Further, the image displayed on the liquid crystal display 46 is also fixed to the image at the same point. And at that time, DRAM3
9 is sent to the JPEG circuit 42 via the DRAM interface 38, and the Y, C
Each of the components b and Cr is JPEG-encoded in a unit called a basic block of 8 × 8 pixels, written into the flash memory 40, and recorded as a captured image for one screen.

<Reproduction Mode> From CCD 31 to DRAM 3
9 is stopped, and the latest captured image is read from the flash memory 40 and sent to the liquid crystal display 13 for display. The desired image is displayed by pressing the plus key 15 or the minus key 16. .

<Flow of Close-up Shooting> Close-up shooting (also called macro shooting) in the present embodiment
In the same manner as in the related art at the beginning, a camera 106 (the electronic still camera 10 in FIG. 1 in the present embodiment) is set on the pole 102 in FIG. 13 and the subject placed on the stage 102 is incandescent lamps 104 and 105. It is performed while illuminating, but differs in that it is performed in two stages, “pre-photographing” and “main photographing”.

That is, as shown in FIG.
In the present embodiment, the electronic still camera 10 is mounted on the stage 102 (S1), a predetermined test plate (described later) is placed on the stage 102 (S2), and the illumination (the incandescent lamps 104 and 105 in FIG. 13) is turned on. While (S
3) First, the electronic still camera 10 is switched to the "pre-shooting mode", and fine adjustment of the camera position, setting of exposure and shutter speed are performed in this state, and then the shutter key 14 is pressed (S4). Then, the test plate is removed, a subject to be close-up is placed instead (S5), the electronic still camera 10 is switched to the "real shooting mode", and the shutter key 14 is pressed in that state (S6). Performing “pre-shooting” using a test plate and “main shooting” after the pre-shooting
Is different from the prior art in that the electronic still camera 10 executes a program described below when performing these two shootings.

<Program for Pre-Shooting> FIGS. 5 and 6
5 is a flowchart of a program (hereinafter, referred to as a “pre-shooting program”) executed by the electronic still camera 10 during the pre-shooting. In this flowchart, i
And j are counter variables for repetition processing, and ΣY is a variable for accumulating and storing luminance values for each pixel of a captured image.

The pre-shooting program corresponds to step S in FIG.
4, that is, pressing the shutter key 14 of the electronic still camera 10 set in the pre-shooting mode to
This is executed immediately after photographing the test plate on 2.
When the program is started, first, initial values (“1”) are set to variables i and j (S10), and then the luminance value of the (i, j) pixel of the captured image is stored in a variable ΣY (S11).
However, at this stage, since i = j = 1, ΔY is (1,
1) The pixel luminance value [Y (1, 1)] is stored, and this operation is repeated until i = n (n is the maximum row of the array) (S12, S
13) Repeat. By this repetition operation, the value of ΣY becomes ΣY = Y (1,1) ΣY = Y (1,1) + Y (2,1) ΣY = Y (1,1) + Y (2,1) + Y (3,1) 1) and when i = n, the value of ΣY is: ΣY = Y (1,1) + Y (2,1) + Y (3,1) +.
.. + Y (n, 1), which is a value obtained by integrating the luminance values of n pixels in the first column (j = 1) of the array (n pixels in the first vertical column at the left end in FIG. 3). i = n
Then, the variable j is incremented by one (S14, S
15, S16), the above operation is repeated, and when i = n again, the value of ΣY becomes: ΣY = Y (1,1) + Y (2,1) + Y (3,1) +.
.. + Y (n, 1) + Y (1, 2) + Y (2, 2) + Y
(3,2) +... + Y (n, 2), and the first column (j = 1) and the second column (j = 2) of the array
2 × n pixels.

Then, when J = m, the value of ΣY is given by ΣY = Y (1,1) + Y (2,1) + Y (3,1) +... + Y (n, 1) + Y (1,2) + Y (2,2) + Y (3,2) +... + Y (n, 2) + Y (1,3) + Y (2,3) + Y (3,3) +. .. + Y (n, 3) [omitted during this time] + Y (1, m) + Y (2, m) + Y (3, m) +... + Y (n, m) Since the luminance value of n × m pixels from the eye (j = 1) to the m-th column (j = m) is integrated, this ΣY is divided by the number of pixels (n × m), and the result is The variable AVE is stored as the average luminance value of the captured image (S17).

Next, after initial values ("1") are set to variables i and j (S18), AVE is divided by Y (i, j) and the result is stored in variable Δ (i, j). (S19)
At this stage, since i = j = 1, Δ (1,1)
AVE / Y (1, 1) is stored, and this operation is repeated until i = n (S20, S21). By this repetitive operation, the value of Δ (i, j) becomes Δ (1,1) = AVE / Y (1,1) Δ (2,1) = AVE / Y (2,1) Δ (3,1 ) = AVE / Y (3,1) [omitted during this period] Δ (n, 1) = AVE / Y (n, 1) and the operation is repeated until j = m (S2
2 to S24) By repeating, AVE / Y (1, 1) to AVE / Y are added to all the arrays of Δ (i, j).
(N, m) will be stored. As described above, the programs in FIGS. 5 and 6 basically sum the luminance values of all the pixels of the image (the image of the test plate) captured in the pre-photographing mode and store the averaged value in the variable AVE. Further, a luminance correction value [AVE / Y (i, j)] for each pixel is calculated using the average value (AVE).

FIG. 7 is a diagram schematically showing luminance values of all pixels of an image (image of a test plate) photographed in the pre-photographing mode. However, n = 7 and m = 10. The numerical values (100, 90,..., 60) in the cells are brightness values for convenience, and the larger the numerical value, the higher the illuminance. Therefore, FIG. 7 shows a state in which the illumination is applied from the left. In FIG. 7, a boundary line between pixels having different luminance values is indicated by a bold line, but undesired uneven illuminance occurs near the boundary line. On the other hand, FIG. 8 is a diagram schematically showing a two-dimensional array in which luminance correction values are stored, and an appropriate luminance correction value is stored in an array corresponding to each pixel in FIG. For example, a correction value of “0.85” is stored in the array of coordinates (1, 1), and a correction value of “0.94” is stored in the array of coordinates (1, 3). A correction value of “1.06” is stored in the array of coordinates (1, 5), and a correction value of “1.21” is stored in the array of coordinates (1, 7). In the array of (1, 9) and coordinates (n, m), a correction value of “1.42” is stored.

These correction values are based on the luminance value of each pixel shown in FIG. 7, and the integrated value of the luminance values ΣYΣY = 100 × 22 pixels + 90 × 14 pixels + 80 × 14
Pixel + 70 × 14 pixels + 60 × 6 pixels = 5920 is obtained, and this ΔY is divided by the number of pixels (nm = 70) to obtain an average value AVE AVE = 5920/70 ≒ 85. It is divided by the luminance value of the pixel. That is, 85/100 = 0.85 85/90 ≒ 0.95 85/80 ≒ 1.06 85/70 ≒ 1.21 85/60 ≒ 1.42.

<Program for Main Shooting> FIG. 9 is a flowchart of a program (hereinafter referred to as “main shooting program”) executed by the electronic still camera 10 during the main shooting. In this flowchart, i and j are counter variables for the repetition processing. The main photographing program is executed in step S6 of FIG. 4, that is, immediately after the shutter key 14 of the electronic still camera 10 set to the main photographing mode is pressed and the object on the stage 102 is photographed. Here, the subject is a printed matter or an arbitrary object to be subjected to close-up photographing, and in actual photographing, is other than a “test plate” used in pre-photographing. For the purpose of explaining "illuminance unevenness", the test plate will be treated as a subject.

That is, in the following description, the photographed image in the main photographing mode (hereinafter referred to as “main image”) is an image obtained by photographing a test plate in the same manner as in the pre-photographing mode. The image should have the same luminance array as in FIG. 7, and a change in the luminance value near the pixel boundary indicated by the thick line in FIG. 7, that is, undesired illuminance unevenness should have occurred. By executing the photographing program, the luminance value can be made uniform and the illuminance unevenness can be eliminated. When you start the program,
Initial values (“1”) are set to variables i and j (S30),
Next, Y (i, j) is multiplied by Δ (i, j) to obtain Y (i, j).
j), and stores the result in Y (i, j) (S31).
However, since i = j = 1 at this stage, Y (1,1)
(1,1) × Δ (1,1), and this operation is repeated until i = n (S32, S33). By this repetitive operation, the value of Y (i, j) is given by: Y (1,1) = Y (1,1) × Δ (1,1) Y (2,1) = Y (2,1) × Δ (2,1) Y (3,1) = Y (3,1) × Δ (3,1) [Omitted during this period] Y (n, 1) = Y (n, 1) × Δ (n, 1) And this operation is repeated until j = m (S3
4 to S36) By repeating, all of Y (i, j) are updated by multiplying by Δ (i, j).

That is, the pixel having a luminance value of 100 in FIG.
A pixel having 00 × 0.85 = 85 and a luminance value of 90 is 90 × 0.
94 = 84.5, the pixel with the luminance value 80 is 80 × 1.06 =
84.8, a pixel having a luminance value of 70 is 70 × 1.21 = 84.
7, the pixel having a luminance value of 60 is 60 × 1.42 = 85.2, which is eventually corrected so as to converge to the average value (AVE ≒ 85) of the luminance values of all the pixels. It is possible to eliminate or reduce the change in the luminance value near the pixel boundary, and it is possible to perform good image recording while avoiding undesired uneven illuminance.

In the above example, the luminance correction value for each pixel of the main image is calculated based on the average luminance value of all the pixels of the pre-image (the image of the test plate). However, the present invention is not limited to this. . The point is that the luminance correction value for each pixel of the main image may be calculated based on the luminance value of the entire screen of the pre-image or a value correlated with the luminance value. May be calculated based on

<Regarding the Reflectance of the Test Plate> If the reflectance of the test plate used in the pre-photographing mode is known, it can be used as a clue to determine the appropriate exposure of the electronic still camera 10 when performing close-up photography. . That is, assuming now that the reflectance of the test plate is A and the white level of the luminance value in the camera 10 is B, the proper exposure is given by A × B.
If the charge accumulation time of 31 is adjusted to be A × B,
This is preferable because exposure adjustment in close-up photography can be optimized.

<About close-up photography using a strobe> By the way, not only an electronic still camera but also a camera in general is usually equipped with a strobe, and the light of this strobe is an "artificial light". Therefore, the present invention can of course be applied. FIG. 10 is a conceptual diagram of an illuminance distribution when a flat object (for example, printed matter) is photographed in close-up using a strobe, where P ₀ ′ is a light source position of the strobe, and P ₁ ′ to P ₃ ′ are Some lighting points on the subject. Here, assuming that the distance between the light source P ₀ ′ and each of the illumination points P ₁ ′ to P ₃ ′ is r ₁ ′, r ₂ ′, r ₃ ′, the distance r of the illumination point P ₂ ′ close to the light source P ₀ ′ ₂ ′ is the shortest, and the distances r ₁ ′, r ₃ ′ between the illuminating points P ₁ ′, P ₃ ′ far from the light source P ₀ ′ are the longest, so that the respective illuminating points P ₁ ′ to P ₃ ′
Is expressed as P ₁ ′ → L ₁ ′, P ₂ ′ → L ₂ ′, P ₃ ′ → L ₃ ′, the above-mentioned property of light (the illuminance at a certain point is the square of the distance between the point and the light source) L ₁ ′ <
L ₂ ′> L ₃ ′, and as in the case of the incandescent lamp,
Unevenness in the illuminance at each part of the subject (for example,
L ₁ ′ and L ₂ ′, and L ₂ ′ and L ₃ ′).

The difference from the incandescent lamp is only the position of the light source. In general, the strobe is built in near the lens of the camera body (even if it is an external strobe, it is often directly attached to the camera body), and the optical axes of the strobe and the photographic lens are provided on the stand in FIG. This is because the optical axis of the incandescent lamp is not extremely displaced. For this reason, when shooting is performed in the above-described pre-shooting mode using a strobe, the luminance values of all pixels of the shot image (the image of the test plate) are distributed as shown in FIG.

In FIG. 11, numerical values (100,
90... 70) are convenient luminance values, and the larger the numerical value, the higher the illuminance. As described above, since the optical axis of the strobe and the optical axis of the photographic lens are close to each other, if the same optical axis is used for the sake of convenience, the maximum illuminance region (in FIG.
(Range of 0) gathers at the center of the image and has a luminance value distribution in which the illuminance decreases as the distance from the center increases. Therefore, similar to the case of the incandescent lamp, undesired uneven illuminance occurs near the boundary between pixels having different luminance values.

With respect to the image having the luminance value distribution shown in FIG.
When the above-described pre-shooting program (see FIGS. 5 and 6) is applied, the integrated value 輝 度 Y of the luminance value is ΣY = 100 × 12 pixels + 90 × 18 pixels + 80 × 26
Pixel + 70 × 14 pixels = 5880. When ΔY is divided by the number of pixels (nm = 70) to obtain an average value AVE, AVE = 5880/70 = 84, and this AVE (= 84) is shown in FIG. 11 divided by the luminance value of each pixel, the luminance correction value for each pixel, that is, 84/100 = 0.484 85/90 ≒ 0.93 85/80 = 1.05 85/70 = 1. 2 is obtained (see FIG. 12).

Therefore, when the main photographing is performed using the strobe, the above-described main photographing program (see FIG. 9) is executed to correct the luminance value of each pixel of the main image with these luminance correction values. Unwanted illuminance unevenness near the boundary line can be eliminated. That is, assuming that the main image at the time of flash photography is the image of FIG. 11 for convenience, the pixel of the luminance value 100 of FIG. 11 is 100 × 0.84 = 84, and the pixel of the luminance value 90 is 9
0 × 0.93 = 83.7, 80 × 80 pixels
1.05 = 84, 70 × 1.2 = 8 pixels with a luminance value of 70
4 after all, the average value of the luminance values of all the pixels (AVE = 8)
Since the correction is made so as to converge to 4), it is possible to eliminate the change in the brightness value near the pixel boundary indicated by the thick line in FIG.
In other words, it is possible to avoid undesired uneven illuminance and perform good image recording.

When the strobe has a brightness correction value, particularly when the strobe is built in the camera body, the number of times of flash emission is counted, and a correction coefficient corresponding to the number of times is calculated. It is desirable to apply to values. This is because the strobe lamp (generally a xenon tube) has a tendency for the internal gas filling to deteriorate as the number of times of light emission increases and the amount of light tends to decrease. By correcting the brightness correction value in accordance with this decrease, the exposure time and exposure time can be reduced. This is because it is possible to prevent a temporal change in the shutter speed and maintain good photographing performance.

Although it is not limited to the luminance correction value for the strobe, it is preferable from the viewpoint of the correction accuracy to have the luminance correction values for all the pixels uniformly, but it causes a disadvantage that the storage capacity of the ROM is reduced. , From the perspective of data volume reduction,
For example, only the brightness correction values of some pixels in the image are stored, and when performing brightness correction, the brightness correction values of the remaining pixels are interpolated using the stored brightness correction values. You may ask.

Further, the luminance value of the portion where the light from the strobe or the external illumination strikes the strongest is detected using a photo sensor or the like (for example, by a method such as spot photometry), and based on this luminance value, The luminance value of another pixel may be calculated by using the distance from the portion. This utilizes the above-described property of light (inversely proportional to the square of the distance from the light source). For example, considering the case where the luminance at the center of the image is the highest, it is located at the periphery of the image. This is because the luminance of an arbitrary pixel can be obtained by multiplying the distance from the central part to the peripheral part by a predetermined coefficient (an appropriate coefficient in consideration of the above-described properties of light).

It should be noted that the portion where the light from the strobe or the external illumination hits the strongest can be detected by comparing the luminance values of the pixels constituting the image. In this case, a photo sensor or the like is not required. It is preferable because it is possible. In addition, various modifications described below are conceivable. (A) The luminance value of the main image may be corrected by changing the charge accumulation time of each pixel of the CCD based on each luminance correction value. (B) The luminance value of the main image may be corrected by a predetermined key operation, for example, at the time of reproduction, not at the time of shooting. That is, the timing of the luminance correction may be set to an arbitrary “hour”. However, for this purpose, it is needless to say that the main image data and the brightness correction value data must be stored in association with each other. (C) The main image data and the brightness correction value data stored in association with each other at the time of shooting may be imported and stored in an external device such as a personal computer, and the personal computer may correct the luminance value of the main image. (D) Instead of correcting the luminance value of the main image to an average luminance value, the luminance of the main image is corrected so as to have a preset optimal luminance value or a luminance value arbitrarily set by a user or the like. You may make it. In this case, the correction data may be written in advance at the time of shipment or the like.

Since the luminance value is generally recorded in 8 bits, the black level is assigned to 0, the white level is assigned to 255, and the like. In pre-photographing, the reflectance is uniform and the reflectance is known. For example, by using a board of 18%), the charge accumulation time of the CCD is adjusted so that the average of the luminance information obtained at that time becomes the reflectance × 255 (for example, 18% × 255 = 46). , And images can be taken with proper exposure.

[0052]

According to the first aspect of the present invention, the variation in the amount of light hitting the subject is stored as correction data, and the captured image is corrected using the correction data. It is possible to eliminate (or suppress) uneven illuminance of a captured image caused by the variation, and to take a good photograph even under artificial light. According to the second aspect of the present invention, there is provided an electronic still camera that converts an image of a subject captured through a photographic lens into a two-dimensional image signal and records the image signal, and obtains an overall luminance value of the image signal. In the case where the shift amount between the overall brightness value and the brightness value of each pixel constituting the image signal or a value correlated with the shift amount is stored as correction data of each pixel, an arbitrary subject is photographed. Then, after converting the image of the arbitrary object captured through the photographic lens into a two-dimensional image signal, the luminance value of each pixel constituting the image signal is corrected with the correction data. Assuming that the image to be obtained is an image of the entire white level and includes some uneven illuminance, the correction data works in a direction to eliminate (or suppress) the uneven illuminance. Request By applying the correction data to an image captured in the same lighting environment as the image for the image, unevenness in illuminance of the captured image can be eliminated (or suppressed), and a good photograph can be taken even under artificial light. be able to. According to the third aspect of the present invention, in the second aspect of the present invention, the image signal for obtaining the overall luminance value is obtained by using a test plate having a uniform light reflectance or color temperature as a subject. Therefore, the illuminance unevenness of the artificial light can be corrected using a simple plate-shaped member. According to the fourth aspect of the present invention, in the first or second aspect of the present invention, the light that strikes the subject is light of a strobe built in a camera body. Illumination unevenness can be corrected. According to a fifth aspect of the present invention, in the second aspect of the present invention, the light hitting the subject is light of a strobe built in a camera body and an image signal for obtaining the overall luminance value. Is a test plate having a uniform light reflectance or color temperature as a subject, so that it is possible to correct illuminance unevenness during flash photography (particularly macro photography) using a simple plate-shaped member. According to the invention described in claim 6, a mode switching means for switching to one of the pre-shooting mode and the main shooting mode, and each of the images based on a photographed image photographed in a state where the mode is switched to the pre-shooting mode by the mode switching means. Calculating means for calculating the brightness correction value of the pixel; correcting means for correcting the brightness value of each pixel of the captured image shot in a state where the mode is switched to the main shooting mode by the mode switching means with the brightness correction value;
The luminance correction value for each pixel is calculated based on the luminance value of the entire screen of the image (pre-image) photographed in the pre-photographing mode or a value correlated with the luminance value. Can be used to correct the luminance value of each pixel of an image (actual image) photographed in the actual photographing mode. For example, the pre-image is an image of an entire white level, and includes a slight unevenness in illuminance. Since the luminance correction value acts in a direction to eliminate (or suppress) the uneven illuminance, the luminance correction value is applied to the main image photographed in the same illumination environment as the pre-image. In addition, uneven illuminance of the main image can be eliminated (or suppressed), and a good photograph can be taken even under artificial light. According to the seventh aspect of the present invention, the mode switching means for switching to one of the pre-photographing mode and the main photographing mode, and light emitted when the shutter key is pressed in a state where the mode is switched to the pre-photography mode by the mode switching means. A computing means for photographing a test plate having a uniform reflectance and computing a luminance correction value for each pixel based on the luminance value of the entire screen of the photographed image or a value correlated with the luminance value, and the mode switching means When the shutter key is pressed in a state where the mode is switched to the main shooting mode, a correction unit that corrects the brightness value of each pixel of the shot image at that time with the brightness correction value, and the correction unit based on the reflectance of the test plate. Setting means for setting the exposure when shooting in the pre-shooting mode and the main shooting mode. Te can be set exposure when capturing in pre-photographing mode and a main photographing mode, it is possible to allow the setting of exposure suitability based on the actual amount of light from the subject. According to the invention described in claim 8, in the method of correcting the brightness of a captured image, the brightness of the captured image is corrected using correction data indicating a variation in the amount of light of a subject image included in the captured image. For example, the brightness of the photographed image can be corrected using a personal computer or the like.

[Brief description of the drawings]

FIG. 1 is an external view of an electronic still camera.

FIG. 2 is a block diagram of an electronic still camera.

FIG. 3 is a conceptual diagram of a two-dimensional array.

FIG. 4 is a flowchart illustrating a procedure of close-up imaging.

FIG. 5 is a flowchart of a pre-photographing program (1/1).
2).

FIG. 6 is a flowchart of a pre-photographing program (2 /
2).

FIG. 7 is a conceptual diagram (using an incandescent lamp) showing a brightness value array of a pre-photographed image.

FIG. 8 is a conceptual diagram (using an incandescent lamp) showing a two-dimensional array of luminance correction values.

FIG. 9 is a flowchart of a main photographing program.

FIG. 10 is an illuminance distribution diagram at the time of close-up shooting using a strobe.

FIG. 11 is a conceptual diagram (using a strobe) showing a brightness value array of a pre-captured image.

FIG. 12 is a conceptual diagram (using a strobe) showing a two-dimensional array of luminance correction values.

FIG. 13 is a configuration diagram of a stand for close-up photography.

FIG. 14 is an illuminance distribution diagram at the time of close-up shooting using an incandescent lamp.

[Explanation of symbols]

 14 Shutter key 20 Recording mode key (mode switching means) 41 CPU (calculation means, correction means, setting means)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H002 AB01 DB21 DB25 EB00 FB21 FB38 GA28 GA35 GA70 HA00 JA07 5C021 PA62 PA66 PA78 XA67 ZA02 5C022 AA13 AB15 AB51

Claims (8)

[Claims] 1. An electronic still camera wherein a variation in the amount of light hitting a subject is stored as correction data, and a captured image is corrected using the correction data. 2. An electronic still camera for converting an image of a subject taken through a photographic lens into a two-dimensional image signal and recording the converted image signal, wherein an overall luminance value of the image signal is obtained. A deviation amount between the luminance value and the luminance value of each pixel constituting the image signal or a value correlated with the deviation amount is stored as correction data of each pixel, and when an arbitrary subject is photographed, it is passed through a photographic lens. An electronic still camera, comprising: converting a captured image of an arbitrary subject into a two-dimensional image signal; and correcting a luminance value of each pixel included in the image signal with the correction data. 3. The electronic still according to claim 2, wherein the image signal for obtaining the overall luminance value is obtained by using a test plate having a uniform light reflectance or color temperature as a subject. camera. 4. The electronic still camera according to claim 1, wherein the light hitting the subject is light of a strobe built in a camera body. 5. The method according to claim 1, wherein the light that strikes the subject is a light of a strobe built in a camera body, and the image signal for obtaining the overall luminance value is a uniform light reflectance or color temperature test. 3. The electronic still camera according to claim 2, wherein the plate is a subject. 6. A mode switching means for switching between a pre-photographing mode and a main photography mode, and a brightness correction value for each pixel based on a photographed image photographed in a state where the mode is switched to the pre-photographing mode by the mode switching means. And a correction unit that corrects the luminance value of each pixel of a captured image captured in a state where the mode is switched to the main capturing mode by the mode switching unit with the luminance correction value. An electronic still camera. 7. A mode switching means for switching to one of a pre-photographing mode and a main photographing mode, and a uniform light reflectance when a shutter key is pressed in a state in which the mode is switched to the pre-photography mode by the mode switching means. A computing means for photographing the test plate and computing a luminance correction value for each pixel based on a luminance value of the entire screen of the photographed image or a value correlated with the luminance value, and switching to the main photographing mode by the mode switching means Correction means for correcting the luminance value of each pixel of the captured image at the time when the shutter key is pressed in the state where the shutter key is pressed with the luminance correction value; and the pre-photographing mode and the main mode based on the reflectance of the test plate. An electronic still camera, comprising: setting means for setting an exposure when shooting in a shooting mode. 8. A method for correcting the brightness of a captured image, wherein the brightness of the captured image is corrected using correction data indicating a variation in the amount of light of a subject image included in the captured image. Image brightness correction method.