JP2015046701A - Image compression method and image compression device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image compression method and an image compression device which allows for reduction in the amount of data while maintaining the image quality.SOLUTION: In an image compression method for storing image data, composed of pixel data including a color channel for specifying the color information by a gradation value of a predetermined bit length, in a memory, generating a data stream by sequentially reading the gradation value of each color channel from the memory, detecting a plurality of partial data streams matching each other from the data stream thus generated, and then encoding the data stream based on the partial data streams thus detected, the least significant bit of each gradation value composing the data stream is rewritten to a common value of 0 or 1.

Description

  The present invention relates to an image compression method and an image compression apparatus that can reduce the amount of data while suppressing deterioration in image quality.

  In recent years, stores providing games such as game centers have installed many photo sticker creation apparatuses that take pictures and output sticker prints. Such a photo sticker creating apparatus generally captures a user, who is a subject, with a camera attached to the apparatus, displays the obtained photographed image on a tablet display or the like, and inputs characters or figures with an attached touch pen. Those with editing functions called graffiti and drawing are becoming common. Then, the edited and edited image is combined with the captured image, and the combined image is printed by a printer and provided to the user.

  In addition, the photo sticker creating apparatus includes a communication unit, and the photographed image or the composite image created by the photo sticker creating apparatus can be transmitted to an external server device via a network, stored, and distributed to a user's mobile phone or the like. An image distribution system like this has appeared.

  With regard to a technique for distributing such an image to a mobile phone, for example, Patent Document 1 discloses a terminal such as an arbitrary mobile phone, PHS, PDA, etc. via a communication line. A technique for transmitting data to and displaying it is disclosed.

JP 2001-245290 A

  In the above-described photo sticker creating apparatus, a photographed image or a composite image edited by the user is printed on a sticker sheet and provided to the user, so a relatively high-definition image is often used for printing. That is, an image having a large number of pixels is prepared by the camera attached to the photo sticker creating apparatus, and an edit input for the image is received and printed on the sticker paper. The amount of data is often large compared to an image for screen display.

  In addition, some photo sticker creation apparatuses have an additional function such as a shooting function called bonus shooting, an image creation function called bonus graffiti, or the like that generates an image for use in a user's weblog or SNS. There is a tendency that the number of images distributed to the user's mobile phone via the network increases as compared with the conventional case.

  For this reason, when the photographed image or composite image created by the photo sticker creating device is uploaded to the server device without being compressed, it takes a very long time. In particular, in amusement facilities such as a game center where a photo sticker creation apparatus is installed, the radio wave condition of the wireless communication environment is unstable, and it is difficult to transmit data with a large amount of data.

  It is possible to reduce the amount of data by compressing a photographed image or composite image created by the photo sticker creating apparatus at a high compression rate. However, when the image is compressed at a high compression rate in order to reduce the data amount, there is an aspect that the image quality is likely to be deteriorated. In recent mobile phones such as smartphones, the resolution of displays has been increasing, so images provided to users are required to have high resolution, and images with degraded image quality due to compression at a high compression rate are required. Has a problem that it is not suitable as a browsing image provided to the user.

  There has been a demand for the development of an image compression method capable of reducing the amount of data without degrading the image quality in various apparatuses that process and record image data, not limited to the above-described photo sticker creating apparatus.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an image compression method and an image compression apparatus that can reduce the amount of data while suppressing deterioration in image quality.

  The image compression method according to the present invention stores, in a memory, image data composed of pixel data including a color channel that specifies color information with a gradation value having a predetermined bit length, and each pixel data from the memory is stored in each memory. The color channel gradation values are sequentially read out to generate a data string, a plurality of partial data strings that match each other are detected from the generated data string, and the data string is encoded based on the detected partial data string In the image compression method for compressing image data, the least significant bit of each gradation value constituting the data string is rewritten to a common value of 0 or 1.

  The image compression method according to the present invention is characterized in that each pixel data further includes an alpha channel for designating transparency with the gradation value of the bit length.

  The image compression method according to the present invention counts the appearance frequency of each gradation value for each color channel, and based on the counted appearance frequency of each gradation value, rewrites the least significant bit. A channel is determined, and rewriting of the least significant bit in the gradation value of the determined color channel is prohibited.

  In the image compression method according to the present invention, the appearance frequency of each gradation value is counted for each color channel, and the higher-order bit from the least significant bit is set to 0 based on the appearance frequency of each gradation value for each color channel. Alternatively, a color channel to be rewritten to a common value of 1 is determined, and a bit higher than the least significant bit in the gradation value of the determined color channel is rewritten to a common value of 0 or 1.

  The image compression method according to the present invention determines, for each pixel data, whether or not the transparency specified by the alpha channel is greater than or equal to a threshold, and for the pixel data for which the transparency is determined to be greater than or equal to the threshold, A bit higher than the least significant bit in the key value is rewritten to a common value of 0 or 1.

  An image compression apparatus according to the present invention stores image data composed of pixel data including color channels that specify color information with gradation values of a predetermined bit length in a memory, and each pixel data from the memory is stored in each memory. The color channel gradation values are sequentially read out to generate a data string, a plurality of partial data strings that match each other are detected from the generated data string, and the data string is encoded based on the detected partial data string An image compression apparatus for compressing image data includes means for rewriting the least significant bit of each gradation value constituting the data string to a common value of 0 or 1.

  The image compression apparatus according to the present invention is characterized in that each pixel data further includes an alpha channel for designating transparency with the bit length gradation value.

  The image compression apparatus according to the present invention prohibits rewriting of the least significant bit based on the means for counting the appearance frequency of the gradation value for each color channel and the appearance frequency of the gradation value for each color channel. The method further comprises means for determining a color channel to be changed and means for prohibiting rewriting of the least significant bit in the gradation value of the determined color channel.

  The image compression apparatus according to the present invention includes means for counting the appearance frequency of the gradation value for each color channel, and a higher-order bit than the least significant bit based on the counted appearance frequency of the gradation value for each color channel. Means for determining a color channel that rewrites a common value of 0 or 1 and means for rewriting a bit higher than the least significant bit in the gradation value of the determined color channel to a common value of 0 or 1 It is characterized by providing.

  The image compression apparatus according to the present invention is configured to determine, for each pixel data, whether or not the transparency specified by the alpha channel is greater than or equal to a threshold value, and for the pixel data for which the transparency is determined to be greater than or equal to the threshold value, And means for rewriting the higher-order bits than the least significant bit in the grayscale value to a common value of 0 or 1.

  One feature of the present application is that the least significant bit of each gradation value is rewritten to a common value of 0 or 1 before the encoding process of the data string is executed. Since the gradation value to be converted in the bit conversion process is only 1, it is almost impossible to recognize this difference as a color difference by human eyes. On the other hand, by rewriting the least significant bit in the gradation value and alpha value of each color to a common value of 0 or 1, the number of values that appear in the data string to be encoded is 256 (each gradation value is 8 bits). In the subsequent encoding process, it is possible to detect more partial data strings that match each other, and to detect partial data strings that match with a longer match length. As a result, the compression rate can be increased.

  According to the present invention, the amount of image data can be reduced while maintaining the image quality, so that the communication cost can be suppressed, the time for uploading image data to an external server device, and the user from the external server Time for downloading image data to the terminal can be shortened.

It is a perspective view which shows the external appearance of the photograph sticker production apparatus which concerns on this Embodiment. It is a perspective view which shows the external appearance of the photograph sticker production apparatus which concerns on this Embodiment. It is a block diagram which shows typically the structure of the photograph sticker production apparatus which concerns on this Embodiment. It is a block diagram which shows typically the structure of the photograph sticker production apparatus which concerns on this Embodiment. It is a block diagram which shows an example of a functional structure of an image process part. It is explanatory drawing explaining the bit conversion process which concerns on this Embodiment. It is a flowchart which shows the procedure of the process which the photograph sticker production apparatus which concerns on this Embodiment performs. It is a flowchart which shows the production | generation procedure of the image data for transmission. 10 is a flowchart showing a procedure for generating transmission image data according to the second embodiment. 10 is a flowchart showing a procedure for generating transmission image data according to the third embodiment. 14 is a flowchart showing a procedure for generating transmission image data according to the fourth embodiment.

Hereinafter, as one application example of the present invention, an embodiment in which the image compression method of the present application is applied to a photographic sticker creating apparatus will be specifically described with reference to the drawings.
Embodiment 1 FIG.
1 and 2 are perspective views showing the external appearance of the photographic sticker creating apparatus according to the present embodiment. The photo sticker creating apparatus is a box-shaped apparatus having a substantially rectangular parallelepiped shape as a whole, and a partition is provided so as to divide it substantially in the vertical direction. The photo sticker creating apparatus is divided into a photographing space R1 and an editing space R2 by this partition. FIG. 1 is an external perspective view mainly viewed from the photographing space R1 side of the photo sticker creating apparatus, and FIG. 2 is an external perspective view of the photo sticker creating apparatus viewed mainly from the editing space R2 side.

  As shown in the perspective view of FIG. 1, the imaging space R1 is a space surrounded by a frame that forms a substantially rectangular parallelepiped. The shooting space R1 is a space for accepting the input of a fee from the user and for taking a picture of the user. The photographing space R1 is provided with a receiving unit 1 that accepts a predetermined fee on the outside, and devices such as a camera 21 and a display 22 for photographing a user on an inner wall surface corresponding to a partition with the editing space R2. An imaging unit 2 including is provided.

  The reception unit 1 includes a coin insertion slot 10 that accepts coin insertion, a coin selector 11 that determines the authenticity of coins inserted from the coin insertion slot 10, and various types of information such as the total amount of coins inserted or the amount remaining. And a display panel 12 for displaying. The coin selector 11 determines the authenticity of the coin inserted from the coin insertion slot 10 and sends a determination signal. The coin selector 11 discharges a coin to a coin return port (not shown) when the coin is determined to be false or while it is set not to accept a coin. The display panel 12 is composed of a liquid crystal panel, a segment LED, etc., and receives a control signal to prompt the insertion of coins, a charge to be inserted, the total amount to be inserted, the remaining amount, or another user is shooting and accepts the insertion of a coin A message indicating that it has not been displayed.

  The display panel 12 and the coin selector 11 included in the receiving unit 1 are connected to a control mechanism housed in a first housing described later, and a determination signal, a control signal, and the like are transmitted to the control mechanism. Send and receive.

  The user can receive a service from the photo sticker creating apparatus by inserting coins corresponding to a predetermined fee from the coin insertion slot 10 of the reception unit 1.

  In the imaging space R1, that is, inside the imaging booth, each device constituting the imaging unit 2 is installed. A first housing 20 containing a control mechanism for controlling each device is installed at the lower part of the wall surface that partitions the space with the editing space R2 inside the photographing booth. A camera 21 is installed above the first housing 20 and at a height that is approximately the height of the standing user. A touch panel display 22 that displays a preview screen based on a video signal output from the camera 21 and accepts a user operation is set below the camera 21. Further, a strobe lamp 23 for irradiating the subject with light is provided so as to surround the camera 21 and the display 22. Speakers 24 and 24 for outputting music and guidance voice are installed on the upper portion of the first housing 20.

  The camera 21, the display 22, the strobe lamp 23, and the speakers 24 and 24 constituting the photographing unit 2 are respectively connected to a control mechanism installed in the first housing 20.

  The camera 21 is a digital camera that includes an imaging element such as a lens group, a diaphragm, a shutter, and a CCD (Charge Coupled Device) in order to photograph a user as a subject. The camera 21 takes a picture by acquiring and storing a still image from the imaging device by operating a shutter by a timer function. While the camera 21 is activated, the camera 21 outputs a digitized video signal output from the image sensor to the control mechanism. The control mechanism outputs a captured image for displaying a preview screen based on the video signal.

  The display 22 has a liquid crystal panel for displaying an operation screen for guiding operations during shooting and a preview screen, and accepts an image output from the control mechanism based on a video signal output from the camera 21 in real time. To display. Further, the display 22 is a touch panel type, and a signal including information on a position on the screen at a location touched by the user is output to the control mechanism.

  The strobe lamp 23 is a lighting device in the photographing booth and functions as a flash when taking a picture. In the present embodiment, the strobe lamp 23 is divided into seven as shown in the figure, and the timing of each light emission is taken by the camera 21 via the control base included in the control mechanism (the operation of the shutter). ) Is controlled in synchronization with

  The outer periphery of the photography booth is covered with a light-shielding sheet material (not shown). This sheet material blocks external light, prevents peeping from the outside, and realizes a private space where the user can freely pose in the shooting booth.

  In addition, the sheet material viewed from the inside of the photographing booth has uniform color tone and brightness. When viewed from the camera 21, the rear side of the user has the same color tone and lightness of the sheet material, so that the chroma key process for making the area other than the area in which the user is visible transparent becomes possible, as will be described later.

  The user enters the shooting booth, operates the operation screen according to the guidance displayed on the display 22 and the guidance voice output from the speakers 24, 24, determines the pose by receiving illumination from the strobe lamp 23, and uses the camera 21. A photo shoot can be performed. First, the user can select a foreground image and / or a background image that decorates a photograph taken by the user from an operation screen displayed on the touch panel display 22. When the user selects the foreground image and / or the background image, the display 22 displays an image output in real time from the camera 21 via the control mechanism, that is, a captured image output from the camera 21, and the selected foreground. A print result preview screen based on the image and / or the background image is displayed. The user can determine a pose while confirming the preview screen, and execute a photo shoot.

  When a photograph is taken, the control mechanism acquires a still image stored by the camera 21 and copies it as an image for later accepting an editing operation by the user and an image for later printing out.

  Next, each component installed in the editing space R2 shown in the perspective view of FIG. 2 will be described. The editing space R2 is a space behind the wall where the camera 21, display 22, strobe / lamp 23, speakers 24 and 24, and the first housing 20 are installed, and the user can take photographs. This is a space where an image can be edited after shooting. The editing space R2 shown in FIG. 2 is partitioned from other spaces by a curtain-like sheet material (not shown) attached to a bar extending from the upper surface of the photographing space R1. The editing space R <b> 2 is provided with a substantially rectangular parallelepiped second housing 30 having the following components inside and outside.

  One side surface of the second housing 30 is in contact with a wall surface that is a partition with the imaging space R1, and a photographed image and other images are edited on the opposing surfaces of the other three side surfaces, respectively. A first editing unit 4a and a second editing unit 4b having an interface for the above are provided. On the other side, a printing unit 5 is provided for printing out the edited image on a predetermined photo sticker sheet. In addition, a control mechanism that controls each component of the first editing unit 4 a, the second editing unit 4 b, and the printing unit 5 is installed in the second housing 30.

  Note that the surfaces of the first casing 20 and the second casing 30 that are in contact with each other communicate with each other through an opening (not shown) of each, and are installed inside the first casing 20. The control mechanism of the photographing unit 2 and the control mechanism of the first editing unit 4a, the second editing unit 4b, and the printing unit 5 installed in the second housing 30 are connected by a plurality of cables. Has been.

  The first editing unit 4a includes a tablet display 40a that displays an operation screen for editing a photographed image and other images, two touch pens 41a and 42a, and a speaker 43a. Note that the second editing unit 4b described later also includes a tablet display 40b, two touch pens 41b and 42b, and a speaker 43b. The tablet displays 40a and 40b, the touch pens 41a, 42a, 41b, and 42b, and the speakers 43a and 43b of the first editing unit 4a and the second editing unit 4b are installed so as to face the opposing surfaces of the second housing 30, respectively. Has been. The tablet displays 40 a and 40 b, the touch pens 41 a, 42 a, 41 b and 42 b and the speakers 43 a and 43 b are connected to a control mechanism inside the second housing 30.

  The printing unit 5 displays a printer 50 that is installed inside the second housing 30 and prints an image on a predetermined sheet, a seal discharge port 51 through which the printed sheet is discharged from the printer, and various types of information. Display panel 52. The display panel 52 is connected to a control mechanism installed inside the second housing 30, and the printer 50 is also connected to the control mechanism inside the second housing 30.

  The user can perform operations such as selecting an image to be printed by the first editing unit 4a or the second editing unit 4b and graffiti on the selected image after completing the shooting by the shooting unit 2 in the shooting booth. On the tablet displays 40a and 40b of the first editing unit 4a and the second editing unit 4b, both the image acquired by executing the photography and the selected foreground image and / or background image are displayed. The The tablet displays 40a and 40b are configured to accept operations by the touch pens 41a, 42a, 41b, and 42b installed together, and the user selects an image to be printed by the touch pens 41a, 42a, 41b, and 42b, and selects the selected image. Operations such as insertion of characters and stamp-like patterns.

  The control mechanism performs a correction process on the photographed image by an image processing unit 7 (see FIG. 3) described later. When the editing by the user is completed, the selected foreground image and / or background image, and characters, designs, and the like based on the editing result are combined with the print output image after the correction process. The combined image is printed on a predetermined sticker sheet by a printer 50 installed in the second housing 30 and discharged to the sticker discharge port 51 as a photographic sticker. The user can obtain the completed photo sticker from the sticker discharge port 51, thereby realizing a photo sticker photographing providing service.

  3 and 4 are block diagrams schematically showing the configuration of the photo sticker creating apparatus according to the present embodiment. 3 mainly shows configurations of the control unit 6, the image processing unit 7, the power supply unit 8, the communication unit 9, and the receiving unit 1 described below. FIG. 4 shows the photographing unit 2, the first editing unit 4a, and the first unit. 2 shows the configuration of the editing unit 4b and the printing unit 5. As shown in FIGS. 3 and 4, the photo sticker creating apparatus includes a control unit 6 that controls each component, an image processing unit 7 that corrects a captured image, and a power supply unit 8 that supplies power from an AC power source. A communication unit 9 capable of communicating with an external network N such as the Internet, a reception unit 1 including the above-described coin insertion slot 10, coin selector 11 and display panel 12, a camera 21, a display 22, a strobe lamp 23 and a speaker. The first editing unit 4a including the photographing unit 2 including 24 and 24, the tablet display 40a, the two touch pens 41a and 42a, and the speaker 43a, and the second editing including the tablet display 40b, the two touch pens 41b and 42b, and the speaker 43b. Each unit is connected to the printing unit 5 including the unit 4b, the printer 50, the seal discharge port 51, and the display panel 52. Constituted by a bus 100. The control unit 6, the image processing unit 7, the power supply unit 8, the communication unit 9, and the bus 100 correspond to control mechanisms installed inside the first casing 20 and the second casing 30.

  As described above, the hardware configuring the reception unit 1, the photographing unit 2, the first editing unit 4a, the second editing unit 4b, and the printing unit 5 can be operated by the user of the photo sticker creating apparatus. It is installed in the imaging space R1 and the editing space R2, and is connected to the bus 100 in the control mechanism installed in the first housing 20 and the second housing 30. On the other hand, the control unit 6, the image processing unit 7, the power supply unit 8, and the communication unit 9 are included in a control mechanism installed inside the first casing 20 and the second casing 30. Are connected to the bus 100.

  The control mechanism includes a plurality of personal computers (hereinafter referred to as PC: Personal Computer) installed in the first housing 20 and the second housing 30, the above-described reception unit 1, imaging unit 2, and first editing. And a control base for controlling each hardware constituting the unit 4a, the second editing unit 4b, and the printing unit 5 from a PC. Note that the functions of each of the plurality of PCs are divided depending on the control target. For example, the PC that controls the reception unit 1 of the imaging space R1, the PC that controls the imaging unit 2, the PC that controls the first editing unit 4a and the second editing unit 4b, and the captured image are subjected to image processing. The PC that is output by the printing unit 5 is configured so that the functions are divided and operated. In the present embodiment, in order to mainly describe image processing, a first PC that virtually controls the receiving unit 1, the photographing unit 2, the first editing unit 4a, and the second editing unit 4b, and a printing unit that performs image processing. It will be described below that each component is controlled by the operation with the second PC that outputs at 5.

  The control unit 6 includes a CPU 60 provided in the first PC that controls hardware of each component, a memory 61 such as a DRAM (Dynamic Random Access Memory) that temporarily stores information generated by the operation of the CPU 60, An HDD (Hard Disk Drive) 62 for storing various data and a capture / chroma keyboard 63 for capturing a still image as a photographed image from a video signal output from the camera 21 of the photographing unit 2 and executing chroma key processing. included.

  The CPU 60 reads and executes a later-described control program 6P stored in the HDD 62, thereby accepting a judgment signal from the coin selector 11 of the accepting unit 1, and sending a control signal to the display panel 12 in accordance with the accepted judgment signal. Send out and realize acceptance of a predetermined charge. Further, the CPU 60 reads out and executes the control program 6P, thereby performing control to synchronize the photographing with the camera 21 of the photographing unit 2 and the operation with the strobe lamp 23, and the print photographed by the camera 21 and stored. A process of acquiring an image for output; a process of acquiring a video signal output from the camera 21 as a captured image for a preview screen and an editing screen via the capture / chroma keyboard 63; a process of displaying on the display 22; Various processes such as a process of accepting editing by the first editing unit 4a and the second editing unit 4b are executed.

  The HDD 62 stores a control program 6P for the CPU 60 to control the hardware of each component. When the CPU 60 reads the control program 6P from the HDD 62 to the memory 61 and executes it, control of each hardware and various software functions are realized.

  In addition to the control program 6P, the HDD 62 includes a foreground / background image to be combined with a photographed printout image, and a foreground / background image to be displayed on the display 22 of the photographing unit 2 together with the photographed image. Is remembered. The HDD 62 further includes images used for operation screens displayed on the display 22 of the photographing unit 2, images used for editing screens displayed on the tablet displays 40a and 40b of the first and second editing units 4a and 4b, Data such as a text file and voice data such as guidance voices output to the speakers 24, 24, 43a, and 43b are stored. The HDD 62 also includes a composite image obtained by executing a composite process with a print output image, foreground image, and / or background image acquired from the camera 21 by the CPU 60 when the user has taken a picture. An edited image obtained by the editing process is stored.

  The capture / chroma keyboard 63 acquires, for example, 30 still images per second from the received video signal and outputs them, and recognizes pixels of a predetermined color tone and brightness from each captured still image, and has a certain range. Hardware having a chroma key function for transparentizing and outputting an alpha value (transparency) for pixels having the same color and lightness. The capture / chroma keyboard 63 is connected to receive a video signal output from the camera 21. The still image after the capture and chroma key processing is written in a memory (not shown) built in the capture / chroma keyboard 63. The CPU 60 reads a still image from the memory as a photographed image for preview, performs a chroma key process, and executes a process for displaying on the preview screen of the display 22.

  In addition, the capture / chroma keyboard 63 can set the number of still images acquired every second by the driver software, and a predetermined color tone and lightness to be made transparent, for example, RGB values. The CPU 60 instructs to make the color tone and lightness of the area in which the sheet material located behind the user in the image photographed by the camera 21 is shown transparent. As a result, the CPU 60 can obtain a person image of only the person who has been subjected to the chroma key processing with the capture / chroma keyboard 63, and can display a preview screen superimposed on the foreground image and / or the background image.

  The image processing unit 7 stores a CPU 70 provided in the second PC for controlling the hardware of each component, a memory 71 such as a DRAM for temporarily storing information generated by the operation of the CPU 70, and various data. An HDD 72 and a graphic board 73 that receives an image and a drawing command and performs a drawing process are included.

  The CPU 70 reads out and executes an image processing program 7P, which will be described later, stored in the HDD 72, thereby realizing image processing for processing an image photographed by the camera 21 by photographing based on the control of the control unit 6. Specifically, under the control of the control unit 6, an image taken by the user and photographed by the camera 21 is delivered to the image processing unit 7. The CPU 70 obtains a photographed image from the control unit 6, writes it in the memory 71, and executes image processing so as to improve the appearance such as making the user's face in the image a small face. .

  The HDD 72 stores an image processing program 7P for the CPU 70 to perform image processing such as processing on the acquired image. The image processing program 7P may be a copy of the image processing program recorded on a recording medium such as a CD-ROM or DVD (not shown) in the HDD 72, or may be acquired via the communication unit 9.

  The graphic board 73 is hardware for drawing an image in a built-in memory (not shown) based on the received image and drawing command. The CPU 70 uses the graphic board 73 to perform image processing on the image acquired from the control unit 6 and temporarily stored in the memory 71. Specifically, the CPU 70 gives an image and a drawing command accompanying the image processing to the graphic board 73 to perform the drawing processing, and acquires the image obtained by the drawing processing in the memory 71.

  The power supply unit 8 realizes power supply from the AC power supply to each component as well as the first PC and the second PC. The photo sticker creating apparatus is provided with a power switch (not shown) for turning on the power, and is connected to the power supply unit 8. The power supply unit 8 detects the on / off of the power switch, and switches the operation / operation of the photo sticker creating apparatus. The power supply unit 8 includes a UPS (Uninterruptible Power Supply) unit 80. Even when the power from the AC power supply is suddenly cut off by the UPS unit 80, damage to each component can be reduced. When the power switch is switched off, the UPS unit 80 outputs a power failure signal to the CPU 60, and the CPU 60 performs predetermined termination processing when the power failure signal is detected, and turns off the power of the entire photo sticker creating apparatus.

  The communication unit 9 includes a PHS unit 90 and is connected to the control unit 6 (CPU 60) via the internal bus 100. The PHS unit 90 is connected to an external network N such as the Internet to realize data transmission / reception. The CPU 60 can transmit and receive data by communicating with other devices on the external network N via the PHS unit 90 of the communication unit 9. In the photo sticker creating apparatus according to the present embodiment, the CPU 60 connects image data after being shot and edited to an external network N together with identification information such as a user name, mail address, or a URL of a transmission destination (not shown). It has the function to transmit (upload) to the server device. With this function, the user's own image stored in the server device can be viewed from the mobile phone or home PC, and the user's own image data stored in the server device can be downloaded to the mobile phone or PC. Realize a service that can.

  In this embodiment, after the user edits the image taken by the photo sticker creation device, the photo sticker is created by printing on the sticker paper, and the image data edited by the user is encoded. Is compressed and then uploaded to the server device.

  Hereinafter, the image data compression processing executed by the photo sticker creating apparatus will be described. FIG. 5 is a block diagram illustrating an example of a functional configuration of the image processing unit 7. In the example shown in FIG. 5, only the functional configuration related to the compression processing of the image data is shown, and the configuration of other functions provided in the image processing unit 7 is not shown. The image processing unit 7 is configured to function as the image compression apparatus of the present application by the CPU 70 reading and executing the image processing program 7P stored in the HDD 72.

  The image processing unit 7 includes a data input unit 701, an input buffer 702, a bit conversion processing unit 703, an encoding processing unit 704, and a data output unit 705 as functional configurations.

  The image data to be compressed is image data related to a photographed image taken by the camera 21 or image data related to a composite image edited by the user, and is stored in the HDD 62 under the control of the control unit 6. This image data is composed of a plurality of pixel data, and each pixel data is represented by a plurality of color channels (for example, 8-bit gradation values) that specify color information with gradation values having a predetermined bit length. RGB color channels). Each pixel data may include not only a color channel but also an alpha channel that specifies transparency (alpha value) in each pixel.

  The data input unit 701 acquires image data to be compressed from the HDD 62. The input buffer 702 is a storage unit that temporarily stores data having an appropriate size. From the image data acquired by the data input unit 701, the gradation value (RGB value and alpha value) of each pixel by the buffer size. Are sequentially read and stored. For example, when the input buffer 702 has a buffer size of 512 bytes, and each RGB color and alpha value in the image data to be compressed has 8-bit gradation values, the RGB value and alpha value for 128 pixels are to be compressed. Can be read from the image data and stored in the input buffer 702.

  The bit conversion processing unit 703 performs processing for rewriting the least significant bit of each gradation value stored in the input buffer 702 to a common value of 0 or 1. The bit conversion processing unit 703 writes the value 0 or 1 to the least significant bit of each gradation value stored in the input buffer 702, thereby setting all the least significant bits of each gradation value stored in the input buffer 702 to 0 (or all 1), and by rewriting the least significant bit of each gradation value stored in the input buffer 702 to 0 (or 1 to which the least significant bit of each gradation value is not 0), The least significant bits of each gradation value stored in the input buffer 702 may be all 0 (or all 1).

  FIG. 6 is an explanatory diagram for explaining the bit conversion processing according to the present embodiment. FIG. 6A shows a data string before the bit conversion process, and FIG. 6B shows a data string after the bit conversion process. It is assumed that each RGB color of the image data to be compressed has an 8-bit gradation value, and an 8-bit alpha value is set for each pixel. When the RGB value and the alpha value in each pixel are sequentially read out from the image data to be compressed to generate a gradation value data string, for example, as shown in FIG. 6A, “148, 126, 92, 0”. , 148, 126, 100, 0, ... "is generated.

  In this embodiment, since the bit conversion process for rewriting the least significant bit in each gradation value to a common value of 0 or 1 is executed, for example, when the bit conversion process for rewriting the least significant bit to 1 is executed, FIG. As shown in (b), a data string “149, 127, 93, 1, 149, 127, 101, 1,...” Is generated.

  The encoding processing unit 704 performs an encoding process on the data string after the bit conversion processing unit 703 rewrites the least significant bit of each gradation value to a common value of 0 or 1. In the present embodiment, a data string is encoded using a compression algorithm employed in PNG (Portable Network Graphics). In the PNG compression algorithm, a data string is encoded by deflate compression combining LZSS, which is an improved algorithm of LZ77, and Huffman encoding.

In LZSS, a plurality of partial data strings that match each other are detected from the data string to be encoded, and the data string to be encoded is encoded based on the matching length and the matching position. Huffman coding separates a character string at every fixed bit, statistically processes the separated character string, and encodes the data string by giving a short code to the character string with the highest number of occurrences. To do.
In the PNG compression algorithm, the data including the partial data string and the matching length are combined and encoded with one Huffman code, and the matching position is encoded with another Huffman code.

  The encoding processing unit 704 causes the data output unit 705 to generate compressed image data by sequentially writing the encoded data sequence to the data output unit 705.

Hereinafter, processing executed by the photo sticker creating apparatus will be described.
FIG. 7 is a flowchart showing a procedure of processing executed by the photo sticker creating apparatus according to the present embodiment. The CPU 60 provided in the control unit 6 of the photo sticker creating apparatus determines whether or not a coin satisfying a predetermined fee is inserted from the coin insertion slot 10 (step S1). If it is determined that no coin satisfying the predetermined fee has been inserted (S1: NO), the CPU 60 returns to step S1 and waits until it is determined that a coin satisfying the predetermined fee has been inserted. During this time, the CPU 60 outputs a control signal to the display panel 12 so as to display the total amount of coins already inserted on the display panel 12.

  When the CPU 60 determines in step S1 that coins satisfying a predetermined fee have been inserted (S1: YES), the CPU 60 displays a guidance information screen on the display panel 12, and further displays an operation screen on the display 22 of the photographing unit 2, Further, a guidance voice is output from the speaker (step S2), and the user is prompted to enter the shooting booth and execute shooting. Thereby, the provision of the photo print service is started.

  The CPU 60 determines whether the foreground image and / or the background image to be combined is selected by operating the operation screen on the display 22 and the photographing is executed and completed (step S3). Specifically, when a foreground image and / or a background image is selected, counting for operating the shutter is started, and a preview screen is displayed on the display 22. Then, the CPU 60 determines that the count has been incremented, operates the shutter, and executes photography. The shooting is completed depending on whether the user operates a button or the like indicating that the image is determined by looking at the preview screen, or whether a predetermined number of times of shooting such as six times is completed. If the CPU 60 determines that shooting has not been completed (S3: NO), it returns the process to step S3 and waits until shooting is completed.

  If the CPU 60 determines that shooting has been completed (S3: YES), the CPU 60 acquires a photographed image from the camera 21 by operating the shutter, and associates it with the selected foreground image and / or background image in the memory 61. Save (step S4). The CPU 60 displays the guidance information screen on the display 22, displays the operation screen on the tablet displays 40a and 40b of the first editing unit 4a or the second editing unit 4b, and outputs guidance voices through the speakers 24 and 24 ( Step S5), prompting the user to move to the editing space R2 and perform an editing operation.

  Next, the CPU 60 transfers the photographed image stored in the memory 61 to the image processing unit 7 to execute image processing (step S6). The CPU 60 accepts editing on the operation screen of the tablet displays 40a and 40b (step S7). At this time, the image of the user displayed on the operation screen may be an image after image processing. In this case, the CPU 60 performs chroma key processing on the captured image that has been processed to make a small face after image processing, creates an image of only the person, and displays the image on the operation screen so as to overlap the foreground image and / or the background image.

  The CPU 60 determines whether the editing is completed due to the operation for instructing the completion of editing and whether the image processing by the image processing unit 7 is completed (step S8). If the CPU 60 determines that either editing or image processing by the image processing unit 7 has not been completed (S8: NO), the process returns to step S8 and waits until both are completed.

  When the CPU 60 determines that both editing and image processing have been completed (S8: YES), the processed image that has been processed by the image processing by the image processing unit 7, information such as characters or images of the editing result, A synthesis process is performed on the background image and / or the foreground image selected and associated and stored in the memory 61 to generate a synthesized image (step S9).

  Next, the CPU 60 generates image data for transmission to the external server device based on the generated composite image (step S10). At this time, the CPU 60 gives an instruction to the image processing unit 7 to perform a smoothing process on the composite image, and further performs an encoding process to generate image data for transmission.

  The image processing unit 7 sends the image data for transmission subjected to the smoothing process and the encoding process in step S <b> 10 to the control unit 6. The control unit 6 stores the image data acquired from the image processing unit 7 in the HDD 62. Then, under the control of the control unit 6, the encoded image data stored in the HDD 62 is transmitted to an external server device via the communication unit 9.

  In addition, the CPU 60 displays the composite image generated in step S9 on the operation screen and outputs it to the printer 50 of the printing unit 5 to instruct printing output (step S11). At this time, the CPU 60 may accept a print layout selection and a print instruction on the operation screen.

  The CPU 60 determines whether or not printing has been completed (step S12). If it is determined that printing has not been completed (S12: NO), the process returns to step S12 and waits until it is determined that printing has been completed. To do. When the CPU 60 determines that the printing in the printer 50 is completed (S12: YES), the CPU 60 displays a guidance display indicating that the printing is completed on the display panel 52, the first editing unit 4a, or the second editing unit 4b of the printing unit 5. The information is displayed on the tablet displays 40a and 40b, guidance voices are output from the speakers 43a and 43b (step S13), and the process is terminated.

  At this time, since the printed photo sticker is discharged to the sticker discharge port 51, the user can obtain the photo sticker in which the user is photographed. Thus, the provision of a photo print service is realized.

  Next, details of step S10 of the flowchart shown in FIG. 7 will be described. FIG. 8 is a flowchart showing a procedure for generating image data for transmission. The image processing unit 7 acquires the image data to be compressed from the HDD 62 in the control unit 6 (step S101). The acquired image data is stored in the data input unit 701 in the image processing unit 7.

  The image processing unit 7 sequentially reads the gradation value (RGB value and farfa value) of each pixel from the acquired image data by the buffer size of the input buffer 702 and stores it in the input buffer 702 (step S102).

The bit conversion processing unit 703 performs processing to rewrite the least significant bit of each gradation value stored in the input buffer 702 to a common value of 0 or 1 (step S103).
Next, the image processing unit 7 determines whether or not the bit conversion processing for all the pixels stored in the input buffer 702 is completed (step S104), and the bit conversion processing is completed for all the pixels in the input buffer 702. If not (S104: NO), the process returns to step S103.

  When it is determined that the bit conversion processing for all the pixels stored in the input buffer 702 has been completed (S104: YES), the input buffer 702 outputs the data string after the bit conversion processing to the encoding processing unit 704.

  Next, the image processing unit 7 determines whether or not the bit conversion processing has been completed for all the pixels constituting the image data acquired in step S101 (step S105). If the bit conversion process has not been completed for all the pixels constituting the image data (S105: NO), the image processing unit 7 returns the process to step S102, and continues the processes after S102.

  When it is determined that the bit conversion processing has been completed for all the pixels constituting the image data acquired in step S101 (S105: YES), the encoding processing unit 704 sets the least significant bit of each gradation value to 0 or 1 in common. Encoding processing is performed on the data string for all the pixels rewritten to values (step S106). The encoding processing unit 704 can encode the data string using, for example, a compression algorithm adopted by PNG. The encoding processing unit 704 outputs the encoded data string to the data output unit 705.

The image processing unit 7 determines whether or not the encoding process for all the image data has been completed (step S107). If unprocessed image data exists (S107: NO), the image processing unit 7 returns the process to step S101, and continues the processes after step S101.
When the encoding process for all the image data is completed (S107: YES), the image processing unit 7 ends the process according to this flowchart, and the compressed image data generated in the data output unit 705 is transmitted as the transmission image data. Output as.

   The first embodiment is characterized in that the least significant bit of each gradation value is rewritten to a common value of 0 or 1 before executing the data string encoding process. Since the gradation value to be converted in the bit conversion process is only 1, it is almost impossible to recognize this difference as a color difference by human eyes. On the other hand, by rewriting the least significant bit of each RGB color and alpha value to a common value of 0 or 1, the number of gradations appearing in the data sequence to be encoded is 256 (when each gradation value is 8 bits). Since it can be reduced to 128, in the subsequent encoding process, when detecting partial data strings that match each other, the possibility that more partial data strings can be detected increases, and a part that matches with a longer match length The possibility that the data string can be detected increases. As a result, the compression rate can be increased as compared with the compression algorithm used in the conventional PNG format.

  For example, a bitmap image of 640 pixels × 767 pixels in which the image data before compression has a data size of 1.9 MB and each pixel is composed of three color channels of RGB and one alpha channel is converted into a conventional PNG format. When compression was performed using a compression algorithm (the highest level 9 compression was selected), the size of the compressed image data was 884 KB. On the other hand, when the image compression method of the present invention is applied, the size of the compressed image data is 720 KB, which is about 120% higher compression than the highest compression PNG format of level 9. Became possible.

  As described above, in the present embodiment, the amount of image data can be reduced while maintaining the image quality required by the photo sticker creation device, so image data can be transferred from the photo sticker creation device to an external server device. The upload time and the time for downloading the image data from the external server device to the user terminal can be shortened, and the communication cost can be suppressed.

Embodiment 2. FIG.
In the first embodiment, the least significant bit is rewritten to a common value of 0 or 1 for each of the three RGB color channels and one alpha channel, but based on the appearance frequency of each gradation value for each color channel. Thus, a configuration may be adopted in which a color channel that should prohibit rewriting of the least significant bit is determined.
In the second embodiment, a color channel that should prohibit rewriting of the least significant bit is determined based on the appearance frequency of each gradation value for each color channel, and rewriting of the least significant bit is prohibited for the determined color channel Will be described. Note that the configuration of the photo sticker creating apparatus according to the second embodiment is exactly the same as that of the first embodiment, and thus the description thereof is omitted.

  FIG. 9 is a flowchart showing a procedure for generating image data for transmission according to the second embodiment. The image processing unit 7 acquires the image data to be compressed from the HDD 62 in the control unit 6 (step S121). The acquired image data is stored in the data input unit 701 in the image processing unit 7.

  The image processing unit 7 counts the appearance frequency of each gradation value for each color channel in the image data stored in the data input unit 701 (step S122), and holds the count result in the memory 71.

  Next, the image processing unit 7 determines a color channel for which bit conversion processing is prohibited based on the appearance frequency of each gradation value for each counted color channel (step S123). At this time, the image processing unit 7 generates a histogram for the appearance frequency of each gradation value for each color channel. Then, for example, the image processing unit 7 obtains the median value of the histogram for each color channel, and determines that the bit conversion processing for the color channel having the largest obtained median value should be prohibited.

  In this embodiment, the color channel for which bit conversion processing should be prohibited is determined based on the median value of the histogram. However, the image quality may be affected based on the appearance frequency of each gradation value for each color channel. The color channel having a high value may be determined as a color channel to be prohibited, and may be determined using not only the median value of the histogram but also an average value, a gradation value that gives the peak maximum value of the histogram, and the like.

  Next, the image processing unit 7 sequentially reads the gradation value (RGB value and alpha value) of each pixel from the image data stored in the data input unit 701 by the buffer size of the input buffer 702 and stores it in the input buffer 702. (Step S124).

The bit conversion processing unit 703 sets the least significant bit to 0 for the color channel and the alpha channel other than the color channel for which the bit conversion processing is prohibited among the least significant bits of each gradation value in the data string generated in the input buffer 702. Alternatively, a bit conversion process for rewriting to a common value of 1 is performed (step S125).
Next, the image processing unit 7 determines whether or not the bit conversion processing for all the pixels stored in the input buffer 702 has been completed (step S126), and the bit conversion processing has been completed for all the pixels in the input buffer 702. If not (S126: NO), the process returns to step S125.

  When it is determined that the bit conversion processing has been completed for all the pixels stored in the input buffer 702 (S126: YES), the input buffer 702 outputs the data string after the bit conversion processing to the encoding processing unit 704.

  Next, the image processing unit 7 determines whether or not the bit conversion processing has been completed for all the pixels constituting the image data acquired in step S121 (step S127). If the bit conversion process has not been completed for all the pixels constituting the image data (S127: NO), the image processing unit 7 returns the process to step S124, and continues the processes after S124.

  When it is determined that the bit conversion processing has been completed for all the pixels constituting the image data acquired in step S121 (S127: YES), the encoding processing unit 704 performs a data sequence for all the pixels after the bit conversion processing is performed. Is subjected to encoding processing (step S128). The encoding processing unit 704 can encode the data string using, for example, a compression algorithm adopted by PNG. The encoding processing unit 704 outputs the encoded data string to the data output unit 705.

The image processing unit 7 determines whether or not the encoding process for all the image data has been completed (step S129). If unprocessed image data exists (S129: NO), the image processing unit 7 returns the process to step S121, and continues the processes after step S121.
When the encoding process for all the image data is completed (S129: YES), the image processing unit 7 ends the process according to this flowchart, and the compressed image data generated in the data output unit 705 is transmitted as the transmission image data. Output as.

  In the second embodiment, since the bit conversion processing is prohibited for the color channel that affects the image quality when the gradation value of the least significant bit is converted to a common value of 0 or 1, the image quality after compression is reduced. Therefore, the improvement of the compression rate can be expected.

Embodiment 3 FIG.
In the first embodiment, the least significant bit is rewritten to a common value of 0 or 1 for each of the three RGB color channels and one alpha channel, but based on the appearance frequency of each gradation value for each color channel. Thus, the color channel for rewriting the higher-order bits than the least significant bit may be determined.
In Embodiment 3, based on the appearance frequency of each gradation value for each color channel, a color channel for rewriting a higher-order bit than the least significant bit is determined, and for the determined color channel, a higher-order bit is set to 0. Or the structure rewritten to the common value of 1 is demonstrated. Note that the configuration of the photo sticker creating apparatus according to the third embodiment is exactly the same as that of the first embodiment, and thus the description thereof is omitted.

  FIG. 10 is a flowchart showing a procedure for generating image data for transmission according to the third embodiment. The image processing unit 7 acquires the image data to be compressed from the HDD 62 in the control unit 6 (step S131). The acquired image data is stored in the data input unit 701 in the image processing unit 7.

  The image processing unit 7 counts the appearance frequency of each gradation value for each color channel in the image data stored in the data input unit 701 (step S132), and holds the count result in the memory 71.

  Next, the image processing unit 7 sets the bits higher than the least significant bit (for example, the second to third bits from the least significant bit) to 0 or 1 based on the appearance frequency of each gradation value for each color channel thus counted. A color channel to be rewritten to a common value is determined (step S133). At this time, the image processing unit 7 generates a histogram for the appearance frequency of each gradation value for each color channel. The image processing unit 7 obtains, for example, a gradation value corresponding to the median value of the histogram for each color channel, the color channel having the smallest obtained gradation value, and a higher-order bit of 0 or 1 in common. The color channel to be rewritten to the value of is determined.

  In this embodiment, the color channel to which the high-order bit is to be converted is determined by the median value of the histogram. However, the high-order bit is converted based on the appearance frequency of each gradation value for each color channel. Even so, it is sufficient to determine a color channel with a low possibility of affecting the image quality, and not only the median value of the histogram but also the average value, the gradation value that gives the peak maximum value of the histogram, etc. May be.

  Next, the image processing unit 7 sequentially reads the gradation value (RGB value and alpha value) of each pixel from the image data stored in the data input unit 701 by the buffer size of the input buffer 702 and stores it in the input buffer 702. (Step S134).

  Next, the bit conversion processing unit 703 rewrites the least significant bit of each gradation value in the data string generated in the input buffer 702 to a common value of 0 or 1, and the least significant side for the color channel determined in step S133. Then, bit conversion processing for rewriting the gradation values of the 2nd to 3rd bits to 0 or 1 common values is performed (step S135).

  Next, the image processing unit 7 determines whether or not the bit conversion processing has been completed for all the pixels stored in the input buffer 702 (step S136), and the bit conversion processing has been completed for all the pixels in the input buffer 702. If not (S136: NO), the process returns to step S135.

  When it is determined that the bit conversion processing has been completed for all the pixels stored in the input buffer 702 (S136: YES), the input buffer 702 outputs the data string after the bit conversion processing to the encoding processing unit 704.

  Next, the image processing unit 7 determines whether or not the bit conversion processing has been completed for all the pixels constituting the image data acquired in step S101 (step S137). If the bit conversion process has not been completed for all the pixels constituting the image data (S137: NO), the image processing unit 7 returns the process to step S134, and continues the processes after S134.

  When it is determined that the bit conversion processing has been completed for all the pixels constituting the image data acquired in step S131 (S137: YES), the encoding processing unit 704 performs a data sequence for all the pixels after the bit conversion processing is performed. Then, the encoding process is performed (step S138). The encoding processing unit 704 can encode the data string using, for example, a compression algorithm adopted by PNG. The encoding processing unit 704 outputs the encoded data string to the data output unit 705.

The image processing unit 7 determines whether or not the encoding process for all the image data has been completed (step S139). If unprocessed image data exists (S139: NO), the image processing unit 7 returns the process to step S131, and continues the processes after step S131.
When the encoding process for all the image data is completed (S139: YES), the image processing unit 7 ends the process according to the flowchart, and the compressed image data generated in the data output unit 705 is transmitted as the transmission image data. Output as.

  In Embodiment 3, not only the least significant bit but also the tone value of the 2nd to 3rd bits is converted to a common value of 0 or 1, a color channel that has little influence on image quality is selected, and the selected color For the channel, the gradation values of the 2nd to 3rd bits as well as the least significant bit are converted to a common value of 0 or 1, so that further improvement of the compression rate can be expected without degrading the image quality Can do.

Embodiment 4 FIG.
In the first embodiment, the least significant bit is rewritten to a common value of 0 or 1 for each of the three color channels of RGB and one alpha channel, but pixels that are set to be substantially transparent by the alpha channel are described. Since the importance as color information specified by the color channel is extremely low, the higher-order bits of such pixels may be rewritten to a common value of 0 or 1.
In the fourth embodiment, it is determined whether or not the transparency of each pixel is equal to or greater than a threshold value. For pixels having a transparency equal to or greater than the threshold value, not only the least significant bit but also the higher-order bit is a common value of 0 or 1. The configuration to be rewritten will be described. In addition, since the structure of the photograph sticker production apparatus which concerns on Embodiment 4 is completely the same as that of Embodiment 1, the description will be omitted.

  FIG. 11 is a flowchart showing a procedure for generating image data for transmission according to the fourth embodiment. The image processing unit 7 acquires the image data to be compressed from the HDD 62 in the control unit 6 (step S141). The acquired image data is stored in the data input unit 701 in the image processing unit 7.

  The image processing unit 7 sequentially reads the gradation value (RGB value and alpha value) of each pixel from the image data stored in the data input unit 701 by the buffer size of the input buffer 702 (step S142), and the input buffer 702. It is determined whether or not the transparency of each of the pixels is greater than or equal to a preset threshold value (step S143). The transparency of each pixel is specified by an alpha value from 0 to 255, for example. When the alpha value is 0, the transparency is transparent, and when it is 255, the alpha value is not more than a predetermined value (for example, 1 or less). In this case, it can be determined that the transparency is equal to or greater than the threshold value.

  When it is determined that the transparency of the specific pixel is equal to or greater than the threshold (S143: YES), the bit conversion processing unit 703 rewrites the least significant bit of the color channel and the alpha channel of the pixel to a common value of 0 or 1. The high-order bits of the color channel are rewritten to a common value of 0 or 1 (step S144). As the high-order bits rewritten by the bit conversion processing unit 703, the second bit may be selected from the least significant side, and the second and third bits may be selected from the least significant side.

  If it is determined that the transparency of a specific pixel is less than the threshold (S143: NO), the bit conversion processing unit 703 sets the least significant bit of the color channel and the alpha channel of the pixel to a common value of 0 or 1. Rewriting is performed (step S145).

  After performing the bit conversion process in step S144 or S145, the image processing unit 7 determines whether or not the bit conversion process for all the pixels stored in the input buffer 702 has been completed (step S146), and the input buffer 702. If bit conversion processing has not been completed for all of the pixels (S146: NO), the processing returns to step S143.

  When it is determined that the bit conversion processing has been completed for all the pixels stored in the input buffer 702 (S146: YES), the input buffer 702 outputs the data string after the bit conversion processing to the encoding processing unit 704.

  Next, the image processing unit 7 determines whether or not the bit conversion processing has been completed for all the pixels constituting the image data acquired in step S141 (step S147). When the bit conversion process has not been completed for all the pixels constituting the image data (S147: NO), the image processing unit 7 returns the process to step S142, and continues the processes after S142.

  When it is determined that the bit conversion processing has been completed for all the pixels constituting the image data acquired in step S141 (S147: YES), the encoding processing unit 704 has a data string for all the pixels after the bit conversion processing is performed. Then, the encoding process is performed (step S148). The encoding processing unit 704 can encode the data string using, for example, a compression algorithm adopted by PNG. The encoding processing unit 704 outputs the encoded data string to the data output unit 705.

The image processing unit 7 determines whether or not the encoding process for all image data has been completed (step S149). If unprocessed image data exists (S149: NO), the image processing unit 7 returns the process to step S141, and continues the processes after step S141.
When the encoding process for all the image data is completed (S149: YES), the image processing unit 7 ends the process according to the flowchart, and the compressed image data generated in the data output unit 705 is transmitted as the transmission image data. Output as.

  In the fourth embodiment, by determining whether or not the transparency of each pixel is equal to or greater than a threshold value, the gradation values of the second to third bits as well as the least significant bit are set to a common value of 0 or 1. Select a pixel that has little effect on image quality even if converted, and for the color channel of the selected pixel, convert not only the least significant bit but also the 2nd to 3rd bit gradation values to a common value of 0 or 1 Therefore, further improvement of the compression rate can be expected without degrading the image quality.

  In the first to fourth embodiments, as an example of application, the form in which the image compression method of the present application is applied to a photo sticker creation apparatus has been described. However, the image compression method of the present application is applied only to a photo sticker creation apparatus. It can be applied to various devices that process and store image data, such as digital cameras, mobile phones such as smartphones, personal computers including slate PCs, portable game machines, and storages that store image data. Of course.

  The embodiment disclosed this time is to be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

2 photographing unit 5 printing unit 6 control unit 7 image processing unit 70 CPU
72 HDD
7P image processing program 701 data input unit 702 input buffer 703 bit conversion processing unit 704 encoding processing unit 705 data output unit

Claims (10)

Image data composed of pixel data including color channels that specify color information with gradation values of a predetermined bit length is stored in a memory, and gradation values of each color channel are sequentially read out from the memory for each pixel data. In the image compression method, a plurality of partial data sequences that match each other are detected from the generated data sequence, and the image data is compressed by encoding the data sequence based on the detected partial data sequence ,
An image compression method, wherein the least significant bit of each gradation value constituting the data string is rewritten to a common value of 0 or 1.   The image compression method according to claim 1, wherein each pixel data further includes an alpha channel for designating transparency with the gradation value of the bit length. Count the appearance frequency of each gradation value for each color channel,
Based on the appearance frequency of each gradation value for each counted color channel, determine a color channel that should be prohibited from rewriting the least significant bit,
The image compression method according to claim 1, wherein rewriting of the least significant bit in the gradation value of the determined color channel is prohibited. Count the appearance frequency of each gradation value for each color channel,
Based on the appearance frequency of each gradation value for each counted color channel, a color channel for rewriting the higher-order bits than the least significant bits to a common value of 0 or 1 is determined,
The image compression method according to claim 1 or 2, wherein a bit higher than the least significant bit in the gradation value of the determined color channel is rewritten to a common value of 0 or 1. It is determined for each pixel data whether or not the transparency specified by the alpha channel is greater than or equal to the threshold,
The pixel data for which the transparency is determined to be greater than or equal to a threshold value, the higher-order bit than the least significant bit in the gradation value of the color channel is rewritten to a common value of 0 or 1. Image compression method. Image data composed of pixel data including color channels that specify color information with gradation values of a predetermined bit length is stored in a memory, and gradation values of each color channel are sequentially read out from the memory for each pixel data. In an image compression apparatus that generates a data sequence, detects a plurality of partial data sequences that match each other from the generated data sequence, and compresses the image data by encoding the data sequence based on the detected partial data sequence ,
An image compression apparatus comprising: means for rewriting the least significant bit of each gradation value constituting the data string to a common value of 0 or 1.   The image compression apparatus according to claim 6, wherein each pixel data further includes an alpha channel that specifies transparency by the gradation value of the bit length. Means for counting the frequency of appearance of gradation values for each color channel;
Means for determining a color channel on which rewriting of the least significant bit should be prohibited, based on the appearance frequency of the gradation value for each counted color channel;
The image compression apparatus according to claim 6, further comprising: means for prohibiting rewriting of the least significant bit in the gradation value of the determined color channel. Means for counting the frequency of appearance of gradation values for each color channel;
Means for determining a color channel for rewriting a bit higher than the least significant bit to a common value of 0 or 1 based on the appearance frequency of the gradation value for each color channel counted;
8. The image compression according to claim 6, further comprising means for rewriting a bit higher than the least significant bit in the gradation value of the determined color channel to a common value of 0 or 1. apparatus. Means for determining for each pixel data whether or not the transparency specified by the alpha channel is greater than or equal to a threshold;
Means for rewriting a bit higher than the least significant bit in the color channel gradation value to a common value of 0 or 1 for the pixel data for which the transparency is determined to be equal to or greater than a threshold value. The image compression apparatus according to claim 7.

Images