JP2009105960A - Photographic device and program used in the same, as well as image storage method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To store a photographed image in a storage medium after performing a compression at a compression rate corresponding to the photographed image. <P>SOLUTION: The photographed image is JPEG-compressed at a compression rate ρ that is a default value (S110) and degree of block noise in the JPEG-compressed image is determined (S120). A block noise evaluation value B calculated as the degree of block noise is compared with a set value Bset (S130). If the block noise evaluation value B is greater than the set value Bset, the JPEG-compression is performed until the block noise evaluation value B becomes not greater than the set value Bset while changing the compression rate ρ to lower rate (S140). When the block noise evaluation value B becomes not greater than the set value Bset, an ID of the order of photography is added to the compressed image data and the data is stored in a storage medium (S150). Consequently, the photographed image is compressed at the compression rate corresponding to the photographed image and the image can be stored in the storage medium. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a photographing apparatus, a program used therefor, and an image storage method.

  Conventionally, as this type of photographing apparatus, an apparatus that displays a photographed image on a liquid crystal monitor has been proposed (for example, see Patent Document 1). In this apparatus, the photographed image is displayed on the liquid crystal monitor on the spot, and the photographer confirms the photographed content (image) and stores it in a removable storage medium.

JP 2000-209467 A

  However, in the above-described photographing apparatus, although the photographed image can be visually confirmed on the spot, it is accompanied by compression that can occur in the image stored in the storage medium by performing JPEG (Joint Photographic Experts Group) compression or the like thereafter. Noise cannot be confirmed.

  Noise due to image compression is likely to be affected even by a relatively low compression ratio for images that change color tone and brightness smoothly for visual observation, and relatively for images that change greatly in color tone and brightness. Even at a high compression rate, there is little effect. That is, the noise accompanying image compression differs depending on the image. For this reason, it may be possible to reduce the compression rate uniformly in order to reduce the influence of noise associated with image compression. However, if the compression rate is reduced, the number of compressed images that can be stored in the storage medium decreases. .

  An object of the imaging apparatus of the present invention is to compress and store in a storage medium at a compression rate corresponding to a captured image. Another object of the photographing apparatus of the present invention is to confirm the influence of noise that may occur when an image is compressed. Furthermore, an object of the imaging apparatus of the present invention is to more appropriately determine the influence of noise that may occur when an image is compressed.

  One object of the program for the photographing apparatus of the present invention is to cause the photographing apparatus to function so as to be compressed and stored in a storage medium at a compression rate corresponding to the photographed image. Another object of the program for the photographing apparatus of the present invention is to more appropriately determine the influence of noise that may occur when an image is compressed.

  An object of the image storage method of the present invention is to compress a captured image using a more appropriate compression ratio and store the compressed image in a storage medium. Another object of the image storage method of the present invention is to more appropriately determine the influence of noise that may occur when compressing an image and to compress the image and store it in a storage medium.

  The photographing apparatus of the present invention, the program used therefor, and the image storage method employ the following means in order to achieve at least a part of the above object.

The photographing apparatus of the present invention
An imaging device for taking an image,
A compressed image generating means for generating a compressed image obtained by dividing a photographed image into blocks each having a predetermined number of pixels in length and width;
Storage means capable of storing the compressed image;
Block noise determination means for determining the degree of block noise that may occur at a block boundary accompanying compression with respect to the compressed image;
When the determined block noise level is equal to or higher than a predetermined block noise level, the image compression unit is controlled so that a compressed image with a reduced compression rate of the captured image is generated, and the determined block noise level is determined. Image compression storage control means for controlling the compressed image to be stored in the storage means when the degree is equal to or less than the predetermined block noise;
It is a summary to provide.

  In the photographing apparatus of the present invention, a compressed image is generated by dividing a photographed image into blocks each having a predetermined number of pixels in the vertical and horizontal directions, and block noise that may occur at the block boundary due to compression of the compressed image is generated. The degree of block noise is determined, and when the determined block noise level is equal to or higher than a predetermined block noise level, a compressed image with a reduced compression rate of the captured image is created. The degree of block noise is determined again for the compressed image thus created. When the determined block noise level is less than or equal to the predetermined block noise level, the compressed image is stored in the storage means. Therefore, the photographed image can be stored as a compressed image having a predetermined block noise level or less. In other words, it can be compressed and stored in the storage means at a compression rate corresponding to the photographed image.

  In such a photographing apparatus of the present invention, the block noise determination means calculates a luminance intensity difference between the pixels based on a luminance component with respect to a pixel adjacent in a predetermined direction with respect to each pixel in the compressed image. Calculating the smoothness of the luminance change in each pixel on the basis of the difference in luminance intensity between before and after in the predetermined direction, and the block with respect to the average of the smoothness of the luminance change in pixels not located at the block boundary A block noise evaluation index is calculated based on an average ratio of smoothness of changes in luminance at pixels located at the boundary of the block, and the degree of block noise is determined based on the calculated block noise evaluation index You can also By so doing, the degree of block noise is determined based on the smoothness of the luminance change between the pixel located at the boundary of the block and the adjacent pixel, and therefore the degree of block noise can be determined more appropriately. Moreover, since the calculation is performed only in accordance with the standard, the degree of block noise can be determined more quickly.

  In the photographing apparatus according to the aspect of the invention in which the degree of block noise is determined based on the smoothness of the luminance change between the pixel located at the boundary of the block and the adjacent pixel, the predetermined directions are the vertical direction and the horizontal direction. Or two directions. In this case, the block noise determination means may be means for calculating a block noise evaluation index based on an average of the ratio in the vertical direction and the ratio in the horizontal direction.

  In the photographing apparatus of the present invention in which the degree of block noise is determined based on the smoothness of the luminance change between the pixel located at the block boundary and the adjacent pixel, the predetermined direction is the vertical direction or the horizontal direction. It can also be one of the directions. In this way, the degree of block noise can be determined more quickly.

  Furthermore, in the photographing apparatus according to the aspect of the present invention in which the degree of block noise is determined based on the smoothness of the luminance change between the pixel located at the block boundary and the adjacent pixel, the block noise determination unit includes: On the other hand, it may be a means for calculating a difference in luminance components with respect to pixels adjacent in a predetermined direction as a luminance intensity difference between the pixels. Further, the block noise determination means is a means for calculating the sum of absolute values of differences in luminance intensity between the pixels in the predetermined direction as the smoothness of the luminance change in the pixels. You can also. Alternatively, the block noise determination means may be means for calculating a block noise evaluation index so that the block noise evaluation index becomes a larger value as the degree of block noise increases.

  In the photographing apparatus of the present invention, the compressed image creating means may be a means for creating a compressed image of the photographed image using a predetermined compression rate as a default value. In this way, first, a compressed image can be created using the default compression rate. The default compression ratio can be a relatively large compression ratio that is less susceptible to noise associated with compression in a normal image taken as a snapshot. In this way, a large number of captured images can be stored in the storage means as compressed images with a relatively large compression rate.

  In the photographing apparatus of the present invention, the image compression / storage control means sequentially selects a predetermined compression rate to be reduced in steps when the determined block noise level is equal to or higher than a predetermined block noise level. The image compression means may be a means for controlling the image compression means so that a compressed image of the photographed image is created. In this way, it is not necessary to set the compression rate, and it is possible to efficiently create a compressed image of an image taken by changing the compression rate.

  The imaging apparatus of the present invention includes display means capable of displaying display information such as images and characters, and block noise display control means for displaying the determined degree of block noise on the display means. You can also. By doing so, it is possible to make the operator confirm the degree of noise that may occur when compressing the image.

  In the photographing apparatus of the present invention in which the degree of block noise is displayed on the display means, the block noise display control means is means for displaying the determined degree of block noise on the display means with a numerical value and / or a graph. It can also be assumed. In this way, the degree of block noise can be displayed more accurately.

  Further, in the photographing apparatus of the present invention in which the degree of block noise is displayed on the display means, the image compression storage control means is instructed by an operator to create a compressed image with a reduced compression rate of the photographed image. It is also possible to control the image compression means so that a compressed image with a reduced compression rate of the photographed image is sometimes created. In this way, the compressed image can be stored in the storage means as the degree of block noise desired by the operator.

The program for the photographing apparatus of the present invention is
A program for a photographing apparatus having a storage means capable of storing a photographed image,
(A) a module that generates a compressed image obtained by dividing a captured image into blocks each having a predetermined number of pixels in the vertical and horizontal directions;
(B) a module that determines the degree of block noise that may occur at a block boundary accompanying compression with respect to the compressed image;
(C) When the determined block noise level is equal to or higher than a predetermined block noise level, the image compression unit is controlled to create a compressed image with a reduced compression rate of the captured image, and the determined A module for controlling the compressed image to be stored in the storage means when the level of block noise is less than or equal to the predetermined level of block noise;
It is a summary to provide.

In the program for the photographing apparatus of the present invention, when the photographing apparatus is installed and activated, the photographing apparatus generates a compressed image in which the photographed image is compressed by dividing the photographed image into blocks each having a predetermined number of pixels. A compressed image in which the degree of block noise that can occur at the block boundary in connection with compression is determined for this compressed image, and when the determined block noise level is greater than or equal to a predetermined level of block noise, the compression rate of the captured image is reduced Can be made to function as an apparatus that stores the compressed image in the storage means when the determined block noise level is less than or equal to the predetermined block noise level. Therefore, the photographed image can be stored as a compressed image having a predetermined block noise level or less.

  In such a program for the photographing apparatus of the present invention, the module (b) calculates a luminance intensity difference between the pixels based on a luminance component with respect to a pixel adjacent in a predetermined direction to each pixel in the compressed image. Calculating the smoothness of the luminance change in each pixel based on the difference between the luminance intensity differences between the pixels in the predetermined direction, and averaging the smoothness of the luminance change in the pixels not located at the block boundary A block noise evaluation index based on a ratio of average smoothness of luminance change in pixels located at the block boundary with respect to the block, and a module for determining the level of block noise based on the calculated block noise evaluation index It can also be. By so doing, the degree of block noise is determined based on the smoothness of the luminance change between the pixel located at the boundary of the block and the adjacent pixel, and therefore the degree of block noise can be determined more appropriately.

The image storage method of the present invention includes:
An image storage method for storing an image,
(A) generating a compressed image obtained by dividing the image into blocks each having a predetermined number of pixels in length and width, and compressing the image;
(B) Determining the degree of block noise that can occur at the block boundary along with compression of the compressed image;
(C) When the determined block noise level is equal to or higher than the predetermined block noise level, a compressed image with a reduced compression rate of the image is created, and the determined block noise level is equal to the predetermined block noise level. When the degree is below, the compressed image is stored,
This is the gist.

  In this image storage method of the present invention, a compressed image is generated by dividing an image into blocks each having a predetermined number of pixels in the vertical and horizontal directions, and the degree of block noise that may occur at the block boundary along with the compression of the compressed image When the determined block noise level is equal to or higher than the predetermined block noise level, a compressed image with a reduced image compression rate is created. The compressed image created in this way determines the degree of block noise again. When the determined block noise level is less than or equal to the predetermined block noise level, the compressed image is stored in the storage means. Therefore, the image can be stored as a compressed image having a predetermined block noise level or less.

  In such an image storage method of the present invention, the step (b) calculates a luminance intensity difference between each pixel based on a luminance component for a pixel adjacent in a predetermined direction with respect to each pixel in the compressed image, The smoothness of the luminance change in each pixel is calculated based on the difference between the luminance intensity differences between the pixels in the predetermined direction, and the average of the smoothness of the luminance change in the pixels not located on the block boundary is calculated. A step of calculating a block noise evaluation index based on an average ratio of smoothness of luminance change in pixels located at a block boundary, and determining a degree of block noise based on the calculated block noise evaluation index It can also be. By so doing, the degree of block noise is determined based on the smoothness of the luminance change between the pixel located at the boundary of the block and the adjacent pixel, and therefore the degree of block noise can be determined more appropriately.

1 is a perspective view illustrating the appearance of a digital camera 20 according to a first embodiment. FIG. 3 is a rear view illustrating the rear surface of the digital camera 20 according to the first embodiment. 1 is a block diagram illustrating functional blocks of a digital camera 20 according to a first embodiment. 6 is a flowchart illustrating an example of image storage processing. The flowchart which shows an example of the determination process of block noise. 12 is a flowchart illustrating an example of image storage processing according to the second embodiment. Explanatory drawing which shows the back surface 30 at the time of displaying the operation screen.

  Next, the best mode for carrying out the present invention will be described using examples.

  FIG. 1 is a perspective view illustrating the external appearance of a digital camera 20 that is a photographing apparatus as an embodiment of the present invention, FIG. 2 is a rear view illustrating the back surface of the digital camera 20 of the embodiment, and FIG. It is a block diagram which illustrates the functional block of the digital camera 20 of an Example.

  As shown in FIG. 1, the digital camera 20 according to the embodiment has a zoom mechanism lens 21 that can perform optical 3x zoom on the front, and a self-timer lighting that indicates that the self-timer is operating by blinking. A mode dial 23 for selecting a mode, a power button 22 disposed at the center of the mode dial 23, and a shutter button 24. In addition, as shown in FIG. 2, the digital camera 20 includes a liquid crystal display 31 disposed on the left side of the center, a four-way button 32 disposed on the right side thereof and operable in the vertical and horizontal directions, as shown in FIG. The print button 33 arranged at the upper left of the back 30, the W button 34 a and the T button 34 b for operating the zoom function, the menu button 35 arranged at the upper left of the four-direction button 32, and the left and right below the liquid crystal display 31. There are provided an A button 36 and a B button 37 arranged, a display button 38 arranged on the lower left of the four-direction button 32 for switching the display on the liquid crystal display 31, and a review button 39 arranged on the right side thereof.

  As functionally illustrated in FIG. 3, the digital camera 20 of the embodiment has a CPU 40a as a central processing unit, a ROM 40b for storing processing programs, a work memory 40c for temporarily storing data, and set data. The flash memory 40d and the like for storing the information in a nonvolatile manner are mainly used. The digital camera 20 stores, as a photographing system, an optical system 42 configured by a lens, a diaphragm, and the like, and electric charges obtained by photoelectrically converting an optical image formed by the optical system 42 for each light receiving cell for a certain period of time. From the image sensor 43 that outputs an electrical signal corresponding to the amount of light received for each light receiving cell, a sensor controller 44 as a drive circuit that outputs to the image sensor 43 a drive pulse required to drive the image sensor 43, and the image sensor 43 An analog front end (AFE) unit 45 that quantizes an electrical signal to be output and converts it into a digital signal, image formation processing, white balance correction, γ correction, and color space conversion for the digital signal output from the AFE unit 45 Are used to represent the R, G, and B tone values and the Y, Cb, and Cr tone values for each pixel. Digital image processing unit 46 that outputs an image, digital image sequence conversion (discrete cosine transform, wavelet transform, etc.) and entropy encoding (run length encoding, Huffman encoding, etc.) A compression / decompression unit 47 that decompresses the digital image by performing inverse transformation is provided. The digital camera 20 according to the embodiment includes a frame buffer for storing data for one screen of the liquid crystal display 31 and a display circuit for driving the liquid crystal display 31 based on a digital image stored in the frame buffer. An input / output interface 52 for controlling the input of the display controller 50, the mode dial 23, the four-direction button 32, the various buttons 24, 33 to 39, and the input / output to the storage medium 53 such as a removable flash memory, USB (Universal Serial Bus) A USB host controller 54 and a USB device controller 56 that manage communication exchanges with devices (computers and printers) connected to the connection terminal 55 are also provided. In the embodiment, the compression / decompression unit 47 designates the compression rate and compresses the image data by JPEG (Joint Photographic Experts Group) compression that compresses each block of 8 pixels in length and width. The compressed image data is returned to normal image data by JPEG expansion. The image data image-processed by the digital image processing unit 46 and the image data JPEG-compressed or JPEG-developed (compressed / expanded) by the compression / decompression unit 47 are temporarily written in the work memory 40c and adapted by block noise determination processing described later. The image data is then given a file name as an ID in the order of shooting, and is written as an image file in the storage medium 53 via the input / output interface 52.

Next, the operation of the digital camera 20 of the embodiment configured as described above, particularly the operation when storing captured image data in the storage medium 53 will be described. FIG. 4 is a flowchart illustrating an example of an image storage process executed by the CPU 40 a when storing captured image data in the storage medium 53. When the image storage process is executed, the CPU 40a first sets the default value to the compression rate ρ (step S100), and performs JPEG compression on the captured image data at the compression rate ρ (step S110). Here, the default value of the compression rate ρ is largely influenced by noise (hereinafter referred to as block noise) that may occur at the block boundary associated with image compression when an image whose color tone or brightness changes greatly is subjected to JPEG compression. It is set as no degree. The JPEG compression with the compression ratio ρ is executed by the compression / decompression unit 47 on the image data that has been subjected to image processing by the digital image processing unit 46 and stored in the work memory 40c. As described above, the compressed image data compressed by JPEG is written in the work memory 40c.

  Next, the degree of block noise of the compressed image compressed with JPEG is determined (step S120). The determination of the degree of block noise is executed by a block noise determination processing routine illustrated in FIG. The description of the image storage process is interrupted, and the block noise determination process will be described.

  To determine block noise, first, an image (RGB image) expressed in the color system of red (R), green (G), and blue (B) to be JPEG-developed is expressed by the following equation (1). Conversion into a YIQ color space consisting of three elements (luminance), I (orange-cyan), and Q (green-magenta) (step S200).

続いて、ＹＩＱ色空間に変換した画像のＹチャンネルを用いて水平方向と垂直方向における各画素間の輝度強度差を計算する（ステップＳ２１０）。実施例では、輝度強度差は、水平方向の輝度強度差をｄｘ（ｘ，ｙ）とし、垂直方向の輝度強度差をｄｙ（ｘ，ｙ）とし、各画素の輝度をＹ（ｘ，ｙ）とすると、次式（２）および式（３）により計算される。この輝度強度差は、式（２）および式（３）から解るように、隣接する画素間の輝度の偏差を表わす。

Subsequently, the luminance intensity difference between the pixels in the horizontal direction and the vertical direction is calculated using the Y channel of the image converted into the YIQ color space (step S210). In the embodiment, the luminance intensity difference is dx (x, y) in the horizontal direction, dy (x, y) in the vertical direction, and Y (x, y) in each pixel. Then, it is calculated by the following equations (2) and (3). This luminance intensity difference represents a luminance deviation between adjacent pixels, as can be seen from the equations (2) and (3).

dx (x, y) = Y (x + 1, y) -Y (x, y) (2)
dy (x, y) = Y (x, y + 1) -Y (x, y) (3)
Next, the smoothness of the luminance change in each pixel in the horizontal direction and the vertical direction is calculated from the calculated luminance intensity difference (step S220). In the embodiment, the smoothness of the luminance change in each pixel is sx (x, y), and the smoothness of the luminance change in the vertical pixel is sy (x , Y), it is calculated by the following equations (4) and (5). The smoothness of the luminance change in this pixel represents the sum of the absolute values of the luminance deviations between adjacent pixels, as can be seen from the equations (4) and (5).

sx (x, y) = | dx (x-1, y) -dx (x, y) | + | dx (x, y) -dx (x + 1, y) | (4)
sy (x, y) = | dy (x, y-1) -dy (x, y) | + | dy (x, y) -dy (x, y + 1) | (5)
When the smoothness of the luminance change of each pixel is calculated in this way, the average ave of the smoothness of the luminance change in the horizontal direction and the vertical direction in the pixel (hereinafter referred to as the boundary pixel) located at the boundary of the block used for JPEG compression. (Psx) and ave (psy) are calculated (step S230), and the average smoothness ave (nsx) of the luminance change in the horizontal direction and the vertical direction in pixels other than the boundary pixels (hereinafter referred to as internal pixels), ave (nsy) is calculated (step S240). Specifically, the average ave (psx) of the smoothness of the luminance change at the boundary pixels in the horizontal direction is calculated by dividing the sum of sx (x, y) where x is a multiple of 8 by the number, and the vertical direction The average ave (psi) of the smoothness of the luminance change at the boundary pixels of the pixel is calculated by dividing the sum of sx (x, y), where y is a multiple of 8, by the number, and the luminance change at the horizontal internal pixel Is calculated by dividing the sum of sx (x, y) where x is not a multiple of 8 by the number of average ave (nsx) of the smoothness of the pixel, and the average ave of the smoothness change of the luminance in the vertical internal pixels (Nsy) is calculated by dividing the sum of sx (x, y) where y is not a multiple of 8 by the number.

  The ratio of the average smoothness ave (psx) of the luminance change in the horizontal boundary pixel to the average smoothness ave (nsx) of the luminance change in the horizontal inner pixel {ave (psx) / ave (nsx )} Is calculated as a block noise evaluation value Bh in the horizontal direction (step S250), and the luminance change smoothness in the vertical boundary pixels with respect to the average ave (nsy) of the luminance change smoothness in the inner pixels in the vertical direction is smoothed. The block noise evaluation value Bv in the vertical direction is calculated as a ratio of average ave (psy) {ave (psy) / ave (nsy)} (step S260), and the block noise evaluation value Bh in the horizontal direction and the block in the vertical direction are calculated. The average of the noise evaluation value Bv is calculated as the block noise evaluation value B in the image. (Step S270). Since the block noise evaluation value Bh in the horizontal direction and the block noise evaluation value Bv in the vertical direction are ratios of the smoothness of the luminance change in the boundary pixels to the average smoothness of the luminance change in the internal pixels, the degree of block noise When the value is small, the value is close to value 1, and when the degree of block noise is large, the value is larger than value 1. In addition, when the average smoothness of the luminance change in the internal pixels is small, for example, in an image where the color tone or brightness changes smoothly, the average smoothness of the luminance change in the boundary pixels is prominent. When the average of the smoothness of the luminance change in the internal pixel is large, for example, in the image in which the color tone or the brightness changes greatly, the average smoothness of the luminance change in the boundary pixel is buried. The block noise evaluation value is small. Therefore, the degree of block noise can be expressed more appropriately. Then, the degree of block noise is determined based on the block noise evaluation value B (step S280). In the embodiment, the block noise evaluation value B is 1 when there is no block noise, and close to 10 when the block noise is severe. Therefore, the degree of block noise can be determined within the range of the value 1 to 10. it can.

  When the degree of block noise is determined in this way, the calculated block noise evaluation value B is compared with the set value Bset in the image storage process of FIG. 4 (step S130). Here, the set value Bset is set as an evaluation value of the block noise to the extent that the block noise cannot be discerned by visual observation. For example, a value 1.5, a value 2, a value 2.5, etc. Can be determined. When the calculated block noise evaluation value B is greater than the set value Bset, it is determined that the degree of block noise in the compressed image is large, and the compression rate ρ is multiplied by a reduction factor k that is greater than the value 0 and smaller than the value 1. Decrease (step S140), return to step S110, execute JPEG compression with the reduced compression rate ρ on the image data written in the work memory 40c, and the block noise evaluation value B is set to the set value by the processing of step S130. The process of calculating the block noise evaluation value B, that is, the processes of steps S110 to S140, is repeated until the compression rate ρ is reduced and the JPEG compression is performed until Bset becomes equal to or lower than Bset.

  When the block noise evaluation value B is equal to or less than the set value Bset, the compressed image data is assigned a shooting order ID and JPEG saved in the storage medium 53 via the input / output interface 52 (step S150), and image storage processing is performed. finish.

According to the digital camera 20 of the above-described embodiment, the compression rate at which the block noise evaluation value B is equal to or less than the set value Bset set as the block noise evaluation value at which the block noise cannot be visually determined. Since the compressed image data compressed by JPEG by ρ is stored in the storage medium 53, the captured image can be compressed using a more appropriate compression ratio and stored in the storage medium 53.

  Further, according to the digital camera 20 of the embodiment, since the degree of block noise is determined based on the smoothness of the luminance change at the boundary pixel, the degree of block noise can be more appropriately determined. In addition, since the block noise evaluation value B is calculated as the ratio of the smoothness of the luminance change in the boundary pixel to the average smoothness of the luminance change in the internal pixel, the boundary is not used in an image in which the color tone or brightness changes smoothly. The block noise evaluation value B is calculated as a large value that emphasizes the average smoothness of the luminance change in the pixels, and the average smoothness of the luminance change in the boundary pixels is buried in the image in which the color tone and the brightness change greatly. Since the block noise evaluation value B is calculated as a small value, the evaluation based on the block noise evaluation value B can correspond to the visual evaluation. As a result, the degree of block noise can be determined more appropriately. Further, since the block noise evaluation value B in the range of the value 1 to the value 10 is used, the block noise can be determined by a numerical value. As a result of properly determining such block noise, it is possible to more appropriately determine the influence of noise that may occur when compressing an image, compress the image, and store the image in a storage medium.

  In the digital camera 20 of the embodiment, the compression / decompression unit 47 corresponds to the compressed image generation unit, the storage medium 53 corresponds to the storage unit, and the CPU 40a that executes the block noise determination process of FIG. 5 corresponds to the block noise determination unit. The CPU 40a that executes the image storage process of FIG. 4 corresponds to the image compression / storage control means.

  Next, a digital camera 20B as a second embodiment of the present invention will be described. The digital camera 20B of the second embodiment has the same hardware configuration as the digital camera 20 of the first embodiment. For this reason, the hardware configuration of the digital camera 20B of the second embodiment is denoted by the same reference numeral as the hardware configuration of the digital camera 20 of the first embodiment, and detailed description thereof is omitted. In the digital camera 20B of the second embodiment, when an image is taken, the image storage process of FIG. 6 is executed instead of the image storage process of FIG.

  When the image storage process of FIG. 6 is executed, the CPU 40a sets the default value to the compression ratio ρ (step S300) and compresses the captured image data, similarly to steps S100 to S120 of the image storage process of FIG. JPEG compression is performed at the rate ρ (step S310), and the degree of block noise of the compressed image compressed with JPEG is determined using the block noise determination method illustrated in FIG. 5 (step S320). Then, an operation screen including the block noise evaluation value B is displayed on the liquid crystal display 31 (step S330). FIG. 7 shows the back surface 30 in a state where an example of the operation screen is displayed on the liquid crystal display 31. In the example of FIG. 7, the captured image is displayed on the liquid crystal display 31 and the block noise evaluation value B is displayed as a bar graph at the bottom of the screen together with the numerical value. Further, “change compression ratio” and “save” are displayed on the left and right sides of the operation screen so as to correspond to the A button 36 and the B button 37. The operator can change the compression rate ρ in JPEG compression by operating the A button 36 in the state of this operation screen. Further, the operator can store the compressed image data compressed with JPEG in the storage medium 53 by operating the B button 37 in the state of the operation screen.

When the operator operates the A button 36 or the B button 37 on the operation screen, the operation button operation is determined (step S340). When the A button 36 is operated and the change of the compression rate is selected, The compression rate ρ is reduced by multiplying the compression rate ρ by the reduction factor k (step S
350), returning to step S310, JPEG compression is performed on the image data written in the work memory 40c with the reduced compression rate ρ, the degree of block noise is determined again (step S320), and the block noise evaluation value is determined. The operation screen including B is displayed again on the liquid crystal display 31 (step S330). As described above, when the A button 36 is operated while the operation screen is displayed, the process of determining the degree of block noise by reducing the compression rate ρ in JPEG compression and performing JPEG compression is repeated.

  On the other hand, when the operator operates the B button 37 on the operation screen, a shooting order ID is assigned to JPEG-compressed compressed image data, and JPEG is saved in the storage medium 53 via the input / output interface 52 (step S360). Then, the image storage process ends.

  According to the digital camera 20B of the second embodiment described above, the block noise evaluation value B of a compressed image obtained by JPEG compression of a captured image can be confirmed and stored. Moreover, since the compressed image obtained by JPEG compression by changing the compression rate ρ can be stored, the captured image can be stored by JPEG compression at an appropriate compression rate ρ. Of course, since the block noise level is determined by the block noise determination method illustrated in FIG. 5, the block noise level can be determined more appropriately.

  In the digital camera 20B of the second embodiment, the compression / decompression unit 47 corresponds to the compressed image generation unit, the storage medium 53 corresponds to the storage unit, and the CPU 40a that executes the block noise determination process of FIG. The liquid crystal display 31 corresponds to the display means, the CPU 40a that executes the process of step S330 in the image storage process of FIG. 6 corresponds to the block noise display control means, and the CPU 40a that executes the image storage process of FIG. This corresponds to image compression storage control means.

  In the digital camera 20B of the second embodiment, every time the block noise evaluation value B is calculated, the operation screen is displayed on the liquid crystal display 31. However, only when the block noise evaluation value B is a predetermined value or less, the block noise is displayed. When the evaluation value B is displayed on the liquid crystal display 31 and the block noise evaluation value B is larger than a predetermined value, the compression rate ρ may be reduced and the JPEG compression may be performed again without checking with the operator.

  In the digital camera 20B of the second embodiment, the block noise evaluation value B is displayed on the liquid crystal display 31 by a bar graph and a numerical value. However, only the block noise evaluation value B in a graph such as a bar graph is displayed on the liquid crystal display 31. The block noise evaluation value B may be displayed as a numerical value on the liquid crystal display 31 and may not be displayed as a bar graph.

  In the digital cameras 20 and 20B of the first and second embodiments, as a block noise determination method, the block noise evaluation value B is calculated as an average of the block noise evaluation value Bh in the horizontal direction and the block noise evaluation value Bv in the vertical direction. Although only the block noise evaluation value Bh in the horizontal direction is calculated, the calculated block noise evaluation value Bh may be handled as the block noise evaluation value B of the image, or the block noise evaluation in the vertical direction may be calculated. Only the value Bv may be calculated, and the calculated block noise evaluation value Bv may be handled as the block noise evaluation value B of the image. In this way, the amount of calculation for calculating the block noise evaluation value B can be reduced.

  In the digital cameras 20 and 20B of the first embodiment and the second embodiment, the block noise evaluation value B in the range of value 1 to value 10 is used as the block noise determination method, but the block noise evaluation value B is value 1. It is good also as what adjusts to become what ranges, such as the range of -value 100.

  In the digital cameras 20 and 20B of the first and second embodiments, the smoothness of the luminance change in the pixels is calculated for all the pixels (pixels) as the block noise determination method. The smoothness of the luminance change in the pixels is calculated for all pixels, but some of the internal pixels, for example, pixels that produce a remainder of 1, 4 or 2, 6 when x or y is divided by 8 The smoothness of the luminance change in the pixel may be calculated only for the pixel that occurs.

  In the first and second embodiments, JPEG compression is performed to compress a captured image as a block of 8 pixels in length and width, and the degree of block noise that may occur at the block boundary due to compression of the compressed image is determined, and a predetermined degree Although the compressed image is described as being stored in the storage medium 53 in the following manner, the compressed image is not limited to JPEG compression as long as it is compressed as a block of a predetermined size in the vertical and horizontal directions. It can also be applied to.

  In the embodiment, the digital camera 20 has been described as a digital camera 20 that shoots and JPEG-compresses multiple images, determines the degree of block noise that may occur at the block boundary along with the compression, and saves the compressed image as a predetermined level or less in the storage medium 53. However, it may be in the form of a program or an image storage method used for such a digital camera 20. In the case of a program, the image storage process illustrated in FIGS. 4 and 6 and the block noise determination process illustrated in FIG. 5 may be programmed in an appropriate programming language as each procedure.

  The best mode for carrying out the present invention has been described with reference to the embodiments. However, the present invention is not limited to these embodiments, and various modifications can be made without departing from the gist of the present invention. Of course, it can be implemented in the form.

  The present invention can be used in the imaging device manufacturing industry.

20, 20B digital camera, 21 lens with zoom mechanism, 22 power button, 23 mode dial, 24 shutter button, 25 self-timer lighting part, 30 back, 31 liquid crystal display, 324 4-way button, 33 print button, 34a W button, 34b T button, 35 menu button, 36 A button, 37 B button, 38
Display button, 39 Review button, 40a CPU, 40b ROM, 40c Work memory, 40d Flash memory, 42 Optical system, 43 Image sensor, 44 Sensor controller, 45 Analog front end (AFE) section, 46 Digital image processing section, 47 Compression Expansion unit, 50 display controller, 52 input / output interface, 53 storage medium, 54 USB host controller, 55 USB connection terminal, 56 USB device controller.

Claims (17)

An imaging device for taking an image,
A compressed image generating means for generating a compressed image obtained by dividing a photographed image into blocks each having a predetermined number of pixels in length and width;
Storage means capable of storing the compressed image;
Block noise determination means for determining the degree of block noise that may occur at a block boundary accompanying compression with respect to the compressed image;
When the determined block noise level is equal to or higher than a predetermined block noise level, the image compression unit is controlled so that a compressed image with a reduced compression rate of the captured image is generated, and the determined block noise level is determined. Image compression storage control means for controlling the compressed image to be stored in the storage means when the degree is equal to or less than the predetermined block noise;
An imaging device comprising:   The block noise determination unit calculates a luminance intensity difference between the pixels based on a luminance component with respect to a pixel adjacent in a predetermined direction with respect to each pixel in the compressed image, and the predetermined luminance intensity difference between the pixels is calculated. The luminance at the pixel located at the boundary of the block is calculated by calculating the smoothness of the luminance change at each pixel based on the difference between before and after in the direction of, and the average of the smoothness of the luminance change at the pixel not located at the block boundary 2. The photographing apparatus according to claim 1, which is a means for calculating a block noise evaluation index based on an average ratio of smoothness of changes and determining a degree of block noise based on the calculated block noise evaluation index.   The photographing apparatus according to claim 2, wherein the predetermined direction is two directions of a vertical direction and a horizontal direction.   The photographing apparatus according to claim 3, wherein the block noise determination unit is a unit that calculates a block noise evaluation index based on an average of the ratio in the vertical direction and the ratio in the horizontal direction.   The photographing apparatus according to claim 2, wherein the predetermined direction is one of a vertical direction and a horizontal direction.   The photographing apparatus according to claim 2, wherein the block noise determination unit is a unit that calculates a difference between luminance components of pixels adjacent to each pixel in a predetermined direction as a luminance intensity difference between the pixels.   7. The block noise determining means is means for calculating a sum of absolute values of differences before and after the luminance intensity difference between pixels in the predetermined direction as smoothness of luminance change in each pixel. Any one of the imaging devices.   The photographing apparatus according to claim 2, wherein the block noise determination unit is a unit that calculates a block noise evaluation index so that the block noise evaluation index becomes larger as the degree of block noise increases.   9. The photographing apparatus according to claim 1, wherein the compressed image creating means is a means for creating a compressed image of the photographed image using a predetermined compression rate as a default value.   The image compression and storage control means sequentially selects a predetermined compression ratio to be reduced in steps when the determined block noise level is equal to or higher than a predetermined block noise level, and the compressed image of the captured image is obtained. 10. The photographing apparatus according to claim 1, wherein the photographing apparatus is a means for controlling the image compression means so as to be created. The imaging device according to any one of claims 1 to 10,
Display means capable of displaying display information such as images and characters;
Block noise display control means for displaying the determined degree of block noise on the display means;
An imaging device comprising:   12. The photographing apparatus according to claim 11, wherein the block noise display control means is means for displaying the degree of the determined block noise on the display means with a numerical value and / or a graph.   The image compression storage control unit is configured to generate a compressed image with a reduced compression rate of the captured image when an operator gives an instruction to create a compressed image with a reduced compression rate of the captured image. The photographing apparatus according to claim 11 or 12, which is means for controlling image compression means. A program for a photographing apparatus having a storage means capable of storing a photographed image,
(A) a module that generates a compressed image obtained by dividing a captured image into blocks each having a predetermined number of pixels in the vertical and horizontal directions;
(B) a module that determines the degree of block noise that may occur at a block boundary accompanying compression with respect to the compressed image;
(C) When the determined block noise level is equal to or higher than a predetermined block noise level, the image compression unit is controlled to create a compressed image with a reduced compression rate of the captured image, and the determined A module for controlling the compressed image to be stored in the storage means when the level of block noise is less than or equal to the predetermined level of block noise;
A program comprising   The module (b) calculates a luminance intensity difference between the pixels based on a luminance component with respect to a pixel adjacent in a predetermined direction with respect to each pixel in the compressed image, and the predetermined luminance intensity difference between the pixels is calculated. The luminance at the pixel located at the boundary of the block is calculated by calculating the smoothness of the luminance change at each pixel based on the difference between before and after in the direction of, and the average of the smoothness of the luminance change at the pixel not located at the boundary of the block The program according to claim 14, which is a module that calculates a block noise evaluation index based on an average ratio of smoothness of changes of the block and determines a degree of block noise based on the calculated block noise evaluation index. An image storage method for storing an image,
(A) generating a compressed image obtained by dividing the image into blocks each having a predetermined number of pixels in length and width, and compressing the image;
(B) Determining the degree of block noise that can occur at the block boundary along with compression of the compressed image;
(C) When the determined block noise level is equal to or higher than the predetermined block noise level, a compressed image with a reduced compression rate of the image is created, and the determined block noise level is equal to the predetermined block noise level. When the degree is below, the compressed image is stored,
Image storage method.   The step (b) calculates a luminance intensity difference between the pixels based on a luminance component with respect to a pixel adjacent in a predetermined direction with respect to each pixel in the compressed image, and the predetermined luminance intensity difference between the pixels is calculated. The luminance at the pixel located at the boundary of the block is calculated by calculating the smoothness of the luminance change at each pixel based on the difference between before and after in the direction of, and the average of the smoothness of the luminance change at the pixel not located at the boundary of the block 17. The image storage method according to claim 16, wherein the block noise evaluation index is calculated based on an average ratio of the smoothness of the change, and the degree of block noise is determined based on the calculated block noise evaluation index.

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