JP2007208833A - Digital camera and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital camera in which a high-contrast image easy to watch can be displayed with a simple configuration, and an image processing method used therefor. <P>SOLUTION: An AE detection part 58 calculates an AE integration value integrating luminance signals of image data which are imaged by a CCD 46 and subjected to various kinds of image processes, and a gradation conversion part 60 calculates an average luminance value per pixel of the image data and selects a gamma curve having gradation characteristics in which the inclination of a predetermined range including the average luminance value is greater than the inclination outside that predetermined range. The gradation conversion part 60 generates image data for display thereafter by applying gradation conversion to the image data on the basis of the gamma curve. A system controller 40 displays the gradation converted display image data on an LCD 16. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital camera that converts gradation of image data obtained by imaging with a solid-state imaging device into display image data having the number of gradations that can be displayed and displays it on a display unit, and an image processing method thereof.

  In recent years, digital cameras that store image data obtained by imaging with a solid-state imaging device such as a CCD image sensor in a storage unit have become widespread, and an LCD or the like is used for displaying a through image or reproducing and displaying a captured image. Display means.

  Such digital cameras have improved solid-state imaging devices and image processing techniques, have improved ISO sensitivity, and can shoot in dark places. However, even if the ISO sensitivity is improved, an image having no contrast is displayed in the case of a display means having a small number of gradations, that is, a narrow dynamic range. For this reason, there was a problem that the photographer decided to abandon the shooting because the photographer judged that he could not take a picture by looking at the black through image displayed on the display means even though the shooting was actually possible. .

As described above, in order to solve the problem that an image without contrast is displayed on a display means having a narrow dynamic range (small number of gradations), an input video signal converted into a digital signal is converted into a predetermined number of gradations. A distribution state detection unit is provided for detecting the distribution state (number of distributions) of the input video signal by dividing the region into regions and determining whether or not the number of distributions of each gradation region exceeds a predetermined reference value. Video that, when it is below the reference value, removes the signal corresponding to the gradation area of this distribution number from the input video signal, and converts this removed input video signal to the number of bits necessary for the number of gradations of the display means A signal processing apparatus is known (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 06-332398

  However, when the video signal processing apparatus described in Patent Document 1 is applied to a digital camera, it is necessary to newly provide a distribution state detection unit, which increases the manufacturing cost of the digital camera, and distribution state detection processing. Therefore, there is a problem that the image display processing takes time.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a digital camera capable of displaying a high-contrast, easy-to-view image with a simple configuration, and an image processing method used therefor. To do.

  In order to solve the above problems, the digital camera of the present invention performs predetermined signal processing on image data captured and digitally converted by a solid-state imaging device, and then performs gradation conversion on the image data. A digital camera that performs processing to generate display image data having the number of gradations that can be displayed on the display means, and displays a through image on the display means based on the display image data, based on the image data A photometric means for calculating an integrated luminance value of the subject image, and an average luminance value per pixel of the image data based on the integrated value, and a predetermined range including the average luminance value A gradation conversion unit that converts the image data into the display image data based on a gradation conversion characteristic that is greater than a gradient outside the predetermined range; Based on the converted the display image data, is characterized in that it comprises a control means for displaying the through image by controlling the display means.

  Further, the photometric means divides the image data into a plurality of areas, calculates the integrated value for each of these areas, the gradation conversion means calculates the average luminance value for each of the areas, The image data may be converted into the display image data for each area based on the gradation conversion characteristic in which the inclination of the predetermined range including the average luminance value is larger than the inclination outside the predetermined range. .

  Further, it comprises a counting means for counting a vertical synchronizing signal inputted to the display means, and when displaying a through image on the display means, when the count number of the counting means reaches a preset set number, It is preferable that a gradation conversion unit changes the gradation conversion characteristic based on the integrated value. Further, it is preferable to display the character image using a flat gradation portion of the display image data.

  In the image processing method of the present invention, after predetermined signal processing is performed on image data captured and digitally converted by a solid-state imaging device, gradation conversion processing is performed on the image data to display means. An image processing method for generating display image data having the number of gradations that can be displayed on the image, and calculating an integrated value of luminance of a subject image based on the image data, and based on the integrated value, An average luminance value per pixel is calculated, and the image data is converted into the display image data based on a gradation conversion characteristic in which the inclination of the predetermined range including the average luminance value is larger than the inclination outside the predetermined range. It is characterized by gradation conversion.

  According to the present invention, even when the number of gradations that can be displayed by the display unit is smaller than the number of gradations of the image data obtained by imaging with the solid-state imaging device, the image is displayed on the display unit in an easy-to-read manner can do. For this reason, it is possible to prevent the photographer from giving up shooting while seeing a dark through image, although the actual shooting is possible.

  Further, when the vertical synchronization signal is counted and the count reaches the set value, the gradation conversion means changes the gradation conversion characteristic based on the integrated value, so that flickering of the image can be prevented. . Further, when the character image is displayed on the display image, the character image is displayed using the flat portion of the gradation characteristics of the display image data, so that the character image can be displayed in an easy-to-see manner.

  A digital camera 10 shown in FIG. 1 includes a lens barrier 12 that can be slid on the front surface of a camera body 11. By sliding the lens barrier 12 to the open position (position shown in FIG. 1), the photographing lens 13 and the strobe light emitting unit 14 are exposed on the front surface. Further, a finder objective window 15 constituting an optical finder is provided on the front surface of the camera body 11.

  The above-described lens barrier 12 also serves as a power operation member, and when the slide operation is performed to the above-described open position, the power source of the camera body 11 is turned on and the photographing lens 13 and the strobe light emitting unit 14 are shielded. When the camera is slid, the camera body 11 is turned off.

  Further, as shown in FIG. 2, on the back surface of the camera body 11, an LCD 16 serving as a display means for displaying an image, a finder eyepiece window 17 constituting an optical finder, and an operation unit 18 constituted by a plurality of operation members are provided. It has been. The LCD 16 displays a through image, a reproduced image, various setting screens, and the like.

  The operation unit 18 includes a changeover switch 21, a return button 22, a feed button 23, a zoom button 24, a menu button 25, a cancel button 26, and a display button 27.

  The changeover switch 21 is slid when the mode is switched between the shooting mode and the reproduction mode. The feed button 23 and the return button 22 are pressed when the playback image is forwardly and backwardly fed in the playback mode. The zoom button 24 is pressed in the vertical direction when changing the optical photographing magnification.

  The menu button 25 is pressed when a menu screen is displayed on the LCD 16. The cancel button 26 is pressed to stop various setting operations on the menu screen or return to the previous screen. The display button 27 is pressed when the LCD 16 is switched on and off.

  A shutter button 28 is provided on the upper surface of the camera body 11. The shutter button 28 is a two-stage push button. When the shutter button 28 is half-pressed, various shooting preparation processes are executed. When the shutter button 28 is further pressed halfway down and fully pressed, the shooting process is executed. Is done.

  A memory card slot 30 is provided on the side surface of the camera body 11. The memory card slot 30 is detachably loaded with a memory card 31 which is a storage means for storing image data.

  Next, the electrical configuration of the digital camera 10 will be described. As shown in FIG. 3, the digital camera 10 includes a system controller 40 that is a control unit that controls the entire camera. The system controller 40 includes a ROM 41, a RAM 42, a timing generator (hereinafter referred to as TG) 43, and a VSYNC counter 44 which is a counting means.

  The ROM 41 stores a control program for controlling each unit in the camera body 11, various control data, and the like, and the RAM 42 temporarily stores work data. The system controller 40 controls each unit based on these programs and various control data.

  The operation unit 18 and the shutter button 28 described above are connected to the system controller 40. The system controller 40 acquires operation signals from the operation buttons 21 to 28 when the operation buttons 21 to 27 constituting the operation unit 18 and the shutter button 28 are operated, and executes processing corresponding to the operation signals. To do.

  Behind the photographic lens 13 is provided a CCD image sensor (hereinafter simply referred to as a CCD) 45 that is a solid-state imaging device, and subject light that has passed through the photographic lens 13 enters the light receiving surface of the CCD 45. The CCD 45 is connected to the system controller 40 via a CCD driver 46.

  The CCD driver 46 receives the vertical synchronization signal VI and the horizontal synchronization signal HI generated by the TG 43 described above, generates a vertical transfer signal and a horizontal transfer signal based on these signals, and outputs them to the CCD 45. Based on the vertical transfer signal and horizontal transfer signal, the CCD 45 captures a subject image and outputs an analog image signal.

  A correlated double sampling circuit (CDS) 47 is connected to the CCD 45, and an analog imaging signal is input. The CDS 47 removes noise from the image signal and then outputs the image signal to the AMP 48. The AMP 48 amplifies the imaging signal with a gain corresponding to the imaging sensitivity set by the system controller 40, and then outputs the imaging signal to the A / D converter 49.

  The A / D converter 49 converts the imaging signal from an analog signal to a digital signal and outputs it as image data. An image input controller 50 is connected to the A / D converter 49, and image data is output to the image input controller 50.

  The image input controller 50 controls input of image data to the data data bus 51. In addition to the system controller 40 and the image input controller 50, an SDRAM 52, a VRAM 53, an image processor 54, a compression / decompression processor 55, a media controller 56, a video encoder 57, and an AE detector 58 are connected to the data bus 51. Yes. The system controller 40 controls these via the data bus 51 and can exchange data with each other.

  The image input controller 50 stores the image data acquired from the A / D converter 49 in the SDRAM 52 or the VRAM 53. The image signal processing unit 54 performs various types of image processing such as white balance correction, YC conversion processing, and gradation conversion processing on the image data while the image data is temporarily stored in the SDRAM 52.

  The compression / decompression processing unit 55 performs compression processing on the image data on which image processing has been performed using a compression format such as the JPEG method. Thereafter, the system controller 40 controls the media controller 56 to store the compressed image data in the memory card 31. The compression / decompression processing unit 55 performs decompression processing on the compressed image data when reproducing the image data stored in the memory card 31.

  The VRAM 53 temporarily stores image data when an image is displayed on the LCD 16, and the above-described various image processing is performed by the image processing unit 54. The image processing unit 54 is provided with a gradation conversion unit 60. As will be described later, the gradation conversion unit 60 performs gradation conversion processing on the image data temporarily stored in the VRAM 53 to generate display image data.

  An LCD driver 61 is connected to the video encoder 57, and the display image data stored in the VRAM 53 is displayed on the LCD 16 by controlling the LCD driver 61. The video encoder 57 controls the LCD driver 61 based on the vertical synchronization signal VD and the horizontal synchronization signal HD input from the TG 43 to control the display on the LCD 16.

  The AE detector 58 is a photometric unit that performs photometry by integrating the luminance signal Y of the image data subjected to the YC conversion process. That is, the AE detection unit 58 calculates the AE integrated value of each area by dividing the image data into 16 areas and integrating the luminance signal Y of each area, for example. Thereafter, in the case of the center-weighted photometry method, the photometric value is calculated by multiplying each AE integrated value by a coefficient so that the weight of the central portion is increased, and this photometric value is output to the system controller 40. .

  When the shutter button 28 is half-pressed, the system controller 40 changes the electronic shutter speed of the CCD 45 or the aperture value of an aperture device (not shown) based on the photometric value acquired from the AE detection unit 58. Control to perform shooting preparation processing.

  Next, the gradation conversion unit 60 will be described. The gradation conversion unit 60 includes a ROM 60a in which tables corresponding to a plurality of gamma curves having different gradation conversion characteristics are stored. The gradation conversion unit 60 acquires the AE integrated value from the AE detection unit 58 and calculates the average luminance value per pixel of the image data. After that, the gradation converting unit 60 has a floor in which the slope of a predetermined range including the average brightness value (for example, a range of about ± 50 average brightness values) is larger than the slope outside the predetermined range (for example, 10 times or more). A table corresponding to the gamma curve of the tone conversion characteristic is selected, and based on this table, the image data stored in the VRAM 53 is gradation-converted to generate display image data. However, the predetermined range is not limited to the range of the average luminance value ± 30, and can be changed as appropriate, and the inclination within the predetermined range and outside the predetermined range can also be changed as appropriate. Further, the inclination outside the predetermined range may be “0”.

  In the above-described gradation conversion process, the gradation conversion unit 60 calculates the average luminance value for each area based on the AE integrated value of each area, and then calculates the average luminance value of the image data that is the average of these areas. The gradation conversion processing is performed based on the calculated average luminance value. Further, when calculating the average luminance value of the image data, the AE integrated value of each region may be summed to calculate the average luminance value per pixel of the image data.

  Further, in the above-described gradation conversion process, the average luminance value of each area is calculated, and the gradation conversion process is performed for each area of the image data on each area based on each average luminance value to display the area. Image data may be generated.

  For example, as shown in FIG. 4, a case where the AE detection unit 58 calculates the AE integrated value by dividing the image data into 16 regions will be described. First, a case will be described in which tone conversion is performed by calculating an average luminance value of image data using an average luminance value for each region. The gradation conversion unit 60 calculates the average luminance value of the image data = (3 + 3 + 7 + 7 + 10 + 10 + 10 + 10 + 30 + 30 + 20 + 20 + 20 + 30 + 30 + 40) /16=17.5 when the average luminance value of each region is the value shown in FIG.

  Thereafter, the gradation converting unit 60 selects a gamma corresponding to the average luminance value (= 17.5) from the table stored in the RAM 60a described above, and uses this gamma curve. Then, gradation conversion processing is performed on the image data to generate display image data.

  Next, a case where gradation conversion processing is performed for each region will be described. In this case, the gradation conversion unit 60 selects a gamma curve for each of the average luminance values in each region. For example, when the average luminance value of each region is 50, the gamma curve shown in FIG. 6A is selected. When the average luminance value of each region is 150, the gamma curve shown in FIG. 6B is selected. When the average luminance value of each region is 240, the gamma curve shown in FIG. 6C is selected.

  Thereafter, the gradation conversion unit 60 performs gradation conversion processing on the image data corresponding to each region based on the gamma curve. That is, an optimal gamma curve is selected for each region, and gradation conversion processing is performed for each region to generate display image data.

  In the digital camera 10 of the present embodiment, a method of generating image data for display by converting the gradation of image data with one gamma curve, and a display of the image data after converting the gradation with a gamma curve selected for each region. A method for generating image data for use is selectable by the operation unit 18.

  Next, the VSYNC counter 44 will be described. The VSYNC counter 44 is a counting unit that counts the vertical synchronization signal VD generated by the TG 43. When the count value of the VSYNC counter 44 reaches the set value, the system controller 40 controls the gradation conversion unit 60 to change the gamma curve based on the AE integrated value, thereby adjusting the gradation characteristics of the image data. Change. At this time, the system controller 40 resets the VSYNC counter 44.

  The video encoder 57 described above has a function of monitoring the gradation characteristics of the through image, and sequentially detects a flat region of the gradation characteristics of the display image data during the display of the through image. When the video encoder 57 obtains a command to display a character image from the system controller 40, the video encoder 57 displays the character image using a flat region of the gradation characteristics of the display image data.

  Next, through image display processing of the digital camera 10 having the above-described configuration will be described with reference to the flowchart of FIG. When the power of the digital camera 10 is turned on and the photographing mode is set, the system controller 40 determines whether or not to display a through image. This determination is made based on whether or not the power of the LCD 16 is turned on by the display button 27.

  When it is determined that the through image is not displayed, that is, it is determined that the power of the LCD 16 is turned off, the through image display process is terminated. When it is determined that the through image is displayed, that is, it is determined that the power of the LCD 16 is turned on, the system controller 40 determines whether to set the gradation characteristics for each region.

  When it is determined that the gradation characteristic is set for each region, the gradation conversion unit 60 calculates an average luminance value of each region and selects a gamma curve from the ROM 60a for each region based on the average luminance value. . After that, the gradation conversion unit 60 performs gradation conversion processing for each area of the image data based on each gamma curve to generate display image data. Thereafter, the process proceeds to a process of displaying a through image.

  When it is determined that the gradation characteristics are not set for each region, that is, when it is determined that the gradation conversion is performed on the image data with one gamma curve, the gradation conversion unit 60 performs the conversion of each region. Based on the average luminance value, an average luminance value of the image data arithmetic unit is calculated.

  Thereafter, the gradation conversion unit 60 selects a gamma curve corresponding to the average luminance value from the ROM 60a, and performs gradation conversion processing on the image data using the gamma curve to generate display image data. . Thereafter, the system controller 40 displays a through image on the LCD 16 based on the display image data on which the gradation conversion process has been performed.

  The VSYNC counter 44 detects and counts the vertical synchronization signal VD. The system controller 40 determines whether this count value has reached the set value. When it is determined that the count value has not reached the set number, the process returns to the process of displaying a through image, and the image data subjected to gradation conversion using the same gamma curve is displayed on the LCD 16.

  When it is determined that the count value has reached the set number, the system controller 40 determines whether or not to end the display of the through image. This determination process is performed by determining whether the power of the LCD 16 is turned off or whether the mode is changed to a mode other than the shooting mode.

  If it is determined not to end the display of the through image, the process returns to the process of determining whether to set the gradation characteristics for each region. If it is determined that the display of the through image is to be ended, the display process of the through image is ended.

  Next, display processing of a character image on a through image will be described with reference to the flowchart of FIG. When the power of the digital camera 10 is turned on and the photographing mode is set, the system controller 40 determines whether or not to display a through image. This determination is made based on whether or not the power of the LCD 16 is turned on by the display button 27.

  When it is determined that the through image is not displayed, that is, it is determined that the power of the LCD 16 is turned off, the through image display process is terminated. If it is determined that a through image is to be displayed, the system controller 40 changes the gamma curve based on the average luminance value, and displays the through image on the LCD 16 while changing the gradation characteristics.

  At this time, the video encoder 57 monitors the state of the gradation characteristic of the live view image, and uses this flat area where the live view gradation characteristic is flat (an area where the inclination outside the predetermined range is substantially 0). A character image is displayed at a position corresponding to a region. For example, when gradation conversion is performed on image data using the gamma curve shown in FIG. 9A, the input luminance values 63 to 255 have flat gradation characteristics. As shown in FIG. 9B, gradation conversion processing is performed on the character image using the flat gradation portion.

  When the image data is subjected to gradation conversion using the gamma curve shown in FIG. 10A, the input luminance values 0 to 90 have flat gradation characteristics. In this case, FIG. As shown in B), gradation conversion processing is performed on the character image using the flat gradation portion. Furthermore, when the image data is subjected to gradation conversion using the gamma curve shown in FIG. 11A, the input luminance values 0 to 210 have flat gradation characteristics. In this case, FIG. As shown in B), gradation conversion processing is performed on the character image using the flat gradation portion. 9 to 11 indicate the gradation characteristics before gradation conversion.

  Thereafter, the system controller 40 displays a character image 81 at a position corresponding to a flat gradation portion in the through image displayed on the LCD 80 as shown in FIG. At this time, the VSYNC counter 44 detects the vertical synchronization signal VD and counts this number in the same manner as in the case of the through image display process described above. The system controller 40 determines whether or not the count number has reached a set value.

  When it is determined that the count number has not reached the set value, the process returns to the process of detecting the vertical synchronization signal VD. When it is determined that the count number has reached the set value, the system controller 40 determines whether or not to end the display of the character image.

  If it is determined not to end the display of the character image, the process returns to the process of monitoring the gradation characteristics of the through image. If it is determined that the character image display is to be terminated, the character image display process is terminated.

  In the above embodiment, the display processing of the through image and the character image has been described as an example. However, in the case of reproducing the image data stored in the memory card, the gamma curve is selected based on the average luminance value. Then, after the gradation conversion process is performed on the image data, the image is displayed on the LCD 16. In this case, when the image is reproduced, it is possible to prevent the dark reproduced image from being mistakenly erased by being low in contrast even though the image is properly captured. However, when displaying the reproduced image, unlike the case of displaying the through image and the character image, the vertical synchronization signal VD is not detected and counted.

  In the above-described embodiment, the case where the present invention is applied to a digital camera has been described as an example. However, the present invention is not limited to this, and any apparatus capable of reproducing and displaying an image may be used. For example, the present invention may be applied to a digital video camera or a personal computer.

It is a perspective view which shows the structure of the front side of a digital camera. It is a perspective view which shows the structure of the back side of a digital camera. It is a block diagram which shows the electric constitution of a digital camera. It is explanatory drawing which shows the average luminance value for every area | region of image data. It is a graph which shows a gamma curve, and has shown the case where the inclination of the predetermined area | region containing the average luminance value 17.5 is larger than the outside of the area | region. It is a graph which shows a gamma curve, and has shown the case where the inclination of the predetermined area | region containing the average luminance value for every area | region of image data is larger than the outside of the area | region. 14 is a flowchart for explaining through image display processing. It is a flowchart explaining the display process of a character image. It is a graph which shows the gradation characteristic of a through image and a character image, and has shown the case where the gradation characteristic of a through image is flat between the luminance values 63-255. It is a graph which shows the gradation characteristic of a through image and a character image, and has shown the case where the gradation characteristic of a through image is flat between luminance values 0-90. It is a graph which shows the gradation characteristic of a through image and a character image, and has shown the case where the gradation characteristic of a through image is flat between luminance values 0-210. It is explanatory drawing which shows the display of a character image.

Explanation of symbols

10 Digital Camera 11 Camera Body 16 LCD
40 System controller 44 VSYNC counter 45 CCD
54 Image processing unit 58 AE detection unit 60 Gradation conversion unit

Claims (5)

After predetermined signal processing is performed on the image data captured and digitally converted by the solid-state imaging device, the gradation conversion processing is performed on the image data, and the number of gradations that can be displayed on the display unit is determined. In a digital camera that generates display image data and displays a through image on the display unit based on the display image data.
A photometric means for performing photometry by calculating an integrated value of the luminance of the subject image based on the image data;
An average luminance value of the image data is calculated based on the integrated value, and the image data is calculated based on a gradation conversion characteristic in which the inclination of the predetermined range including the average luminance value is larger than the inclination outside the predetermined range. Gradation conversion means for converting the gradation into the display image data;
Control means for controlling the display means to display the through image based on the display image data subjected to gradation conversion by the gradation conversion means;
A digital camera characterized by comprising:   The photometry means divides the image data into a plurality of areas, calculates the integrated value for each of the areas, and the gradation conversion means calculates the average luminance value for each of the areas. The image data is gradation-converted into the display image data for each region based on the gradation conversion characteristic in which the inclination of the predetermined range including the luminance value is larger than the inclination outside the predetermined range. The digital camera according to claim 1.   And a counter for counting a vertical synchronizing signal input to the display, and when the through image is displayed on the display, the gray level is displayed when the count of the counter reaches a preset number. The digital camera according to claim 1, wherein the conversion unit changes the gradation conversion characteristic based on the integrated value.   4. The digital camera according to claim 1, wherein a character image is displayed using a flat gradation portion of the display image data. After predetermined signal processing is performed on the image data captured and digitally converted by the solid-state imaging device, the gradation conversion processing is performed on the image data, and the number of gradations that can be displayed on the display unit is determined. In an image processing method for generating image data for display,
An integrated luminance value of the subject image is calculated based on the image data, an average luminance value of the image data is calculated based on the integrated value, and an inclination of a predetermined range including the average luminance value is the predetermined value. An image processing method comprising: gradation-converting the image data into the display image data based on a gradation conversion characteristic larger than an inclination outside the range.

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