JP2014056144A - Image display device provided with suppression function of screen capture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image display device provided with a suppression function of a screen capture capable of preventing content from being duplicated in a normal state even when screen capture processing is performed without preventing the screen capture processing itself.SOLUTION: After generating an initial bit map image from read character string data (a), a color of a character is set to a color different from a color of the other characters every fourth character, a character set to the color different from the color of the other characters is shifted by one character at a time to generate four kinds of bit map images (b) to (e), and the four kinds of bit map images are sequentially transferred to a memory for display in a predetermined time interval (f). When screen capture is performed, only the bit map images recorded in the memory for display are recorded (h).

Description

  The present invention relates to an image display device that displays an image by raster conversion in a character code format such as a book, or an image display device that displays an image in a bitmap format such as a comic, a picture book, a photo book, and the like. The present invention relates to an image display apparatus that prevents duplication of a captured image.

  In recent years, electronic books that display and browse electronic book contents on a screen have become widespread. Since the electronic book content that is digital data is illegally copied as it is, various measures to prevent duplication are taken. As a main anti-copying measure, DRM (Digital Rights Management) technology is adopted for electronic book content. By adopting this DRM (Digital Rights Management) technology, even if an electronic book content is copied, it cannot normally be reproduced on another PC.

  However, if screen capture is executed in a state where each page of the electronic book content is normally displayed on a PC that is permitted to be browsed, the screen data displayed on the screen is acquired. If this screen data is converted into a PDF document or the like, illegally duplicated content that can be played back on various PCs or tablet terminals can be created. In recent years, a program that controls mouse operations and can perform page turning operations and screen capture operations fully automatically (not shown for violations of public order and morals) has been developed, making it possible to create illegally duplicated content without taking time and effort. ing.

  As a technique for restraining screen capture, there has been proposed a technique (see Patent Document 1) in which the keyboard assignment is temporarily changed so that the “PrtSC” key for starting screen capture cannot be used. Also, the activation of the screen capture API is monitored, and at the same time as the activation, the video memory is exclusively locked to temporarily prevent the screen capture from being executed, while the contents of the video memory are rewritten while the screen capture is executed. A technique for copying a rewritten check message (refer to Patent Document 2, Cipher Tech CypherGuard, etc. as a specific product) has also been proposed. In addition, two types of brightness modified images are obtained by dividing and dividing the still image to be protected at a predetermined interval, and increasing the brightness value in one image and decreasing the brightness value in the other image in each partition. By creating and displaying these two types of images while alternately switching at a high speed, the image is displayed on the screen without much difference from the original image, but even if screen capture is executed, either of the two types of brightness modified images is displayed. Has been proposed in which only a distorted image that is significantly different from the original image is obtained (see Patent Document 3).

Japanese Patent No. 3953690 Japanese Patent No. 4299249 Japanese Patent Laying-Open No. 2005-167683

  However, although the technique described in Patent Document 1 is effective for manual illegal copying, the screen capture API is automatically activated by software control as in the case of copying using the illegal copying support tool described above. It is powerless for the case. In the technique described in Patent Document 2, if the process for monitoring the activation of the screen capture API is forcibly terminated or the process for executing the exclusive lock to the video memory is prevented, the screen capture is performed as usual. There is a problem of end. (In actuality, there is an example in which means for preventing the activation of the Cypher Tech CypherGuard SDK and allowing the screen capture to be executed is provided.) In the technique described in Patent Document 3, the increase / decrease width of the luminance is large. When the flicker occurs on the display screen and the increase / decrease width of the luminance is reduced in order to suppress the flicker, there is a problem that the distortion of the luminance modified image is weakened and the check effect is also weakened.

  Therefore, the present invention is a screen capture suppression function that can prevent duplication of contents in a normal display state even when the screen capture process is performed without blocking the screen capture process itself. It is an object of the present invention to provide an image display device including the above.

  In order to solve the above problems, in the first aspect of the present invention, a character string extracted from a given document file is converted into a bitmap image with a predetermined typeface, point, character spacing, and line spacing, and an image by screen capture is obtained. A character string reading means for reading character string data from a given document file, a font, and an image display device for displaying a bitmap image recorded in the display memory to be acquired Refer to the data, convert the read character string data into a bitmap format, set the color of the character for each N (integer of N> 2) to a color different from the other characters, and A bitmap image generation means for generating a bitmap image of M (M is an integer of 2 <M ≦ N) by shifting characters to be set in different colors one by one; A bitmap image transfer means for sequentially transferring M kinds of bitmap images to the display memory at predetermined time intervals; and a bitmap image display means for displaying the bitmap images recorded in the display memory. An image display device having a screen capture suppression function is provided.

  According to the first aspect of the present invention, by setting the predetermined time interval to be transferred sufficiently short, the viewer recognizes as a normal screen in which all the characters have a uniform color. Only a bitmap image with poor legibility that is partially changed in color can be acquired, and duplication of a normal bitmap image in which all characters have a uniform color can be prevented.

  In the second aspect of the present invention, in the image display device having the screen capture suppression function of the first aspect of the present invention, a check character string is prepared separately from the character string in the document file, The bitmap image generation means overwrites the character extracted from the check character string on a character set in a color different from the other characters when generating the M bitmap images. A feature is that a bitmap image is generated.

  According to the second aspect of the present invention, the bitmap image obtained by screen capture becomes more difficult to read as a sentence, and it is possible to prevent duplication of a normal bitmap image in which all characters have a uniform color. it can.

  According to the third aspect of the present invention, in the image display device having the screen capture suppression function according to the first or second aspect of the present invention, the value of each pixel of the bitmap image is R, G, B. Each bit is set at a predetermined gradation (for example, 256 levels from 0 to 255), and the bitmap image generating means sets the background color of the character to the vicinity of the maximum value (for example, R: R, G, B). 255, G: 255, B: 255), the R or B component of the character color set for each of the N characters is set near the maximum value (for example, 255), and the color of the other characters Is set in the vicinity of the minimum value for all of R, G, and B (for example, R: 0, G: 0, B: 0). Note that R, G, and B correspond to the three primary colors of light, red (R), green (G), and blue (B), respectively. The color of can be expressed.

  According to the third aspect of the present invention, since the G component of all characters having the highest wavelength sensitivity characteristic of the human visual system is set to be uniform 0, some characters are predetermined in the image display device. Since only the instant of the time interval changes from black to red or blue, the color change is difficult to perceive and the occurrence of flicker can be suppressed. On the other hand, a bitmap image obtained by screen capture is observed in a stationary state in which the character color changes to red or blue for every N characters, so that it is difficult to read as a sentence, and the color of all characters is uniform. It is possible to prevent copying of a normal bitmap image.

  According to the fourth aspect of the present invention, in the image display device having the screen capture suppression function according to the second aspect of the present invention, each pixel value of the bitmap image has predetermined values R, G, and B. The color of the character to be overwritten is such that the R and G components are set near the maximum value (for example, 255), the B component is set near the maximum value, and the R and G components are set in gradation. Is set to a value smaller than the component (for example, 200), or the G and B components are set near the maximum value (for example, 255), and the R component is near the maximum value and smaller than the G and B components. A value (for example, 200) is set.

  According to the fourth aspect of the present invention, in the image display device, the character to be overwritten is displayed in a color close to white from the background color only at a predetermined time interval, so that the color change is difficult to perceive. Can be suppressed. On the other hand, the bitmap image obtained by screen capture is a normal bit map in which the characters to be overwritten are observed in a static state with a color close to white, so it is difficult to read as text, and the color of all characters is uniform. Duplication of images can be prevented. Further, since it is difficult to remove characters to be overwritten using image processing, the effect of preventing duplication can be further enhanced.

  In the fifth aspect of the present invention, the given image data is converted into a bitmap image, written in a display memory that is an acquisition target of an image by screen capture, and the bitmap image recorded in the display memory is displayed. An image display device that reads image data and divides the read image data into sections of X columns × Y rows, and N (N> 2 is an integer) for each row or each column. For each section, set the color of the pixels in the section to a color different from the other sections, and shift the section to be set to a color different from the other sections by one section, and M (M is an integer of 2 <M ≦ N) Bitmap image generating means for generating street bitmap images, bitmap image transfer means for sequentially transferring the M bitmap images to the display memory at predetermined time intervals, and the table An image display device including a bitmap image display means for displaying the bitmap image recorded in use the memory, the function of suppressing screen capture, characterized in that it comprises a.

  According to the fifth aspect of the present invention, when the predetermined time interval to be transferred is made sufficiently short, the viewer recognizes as a normal screen in which the colors of all sections are uniform, but when screen capture is performed Only the bitmap image with poor legibility in which the colors of some sections are changed can be acquired, and it is possible to prevent the reproduction of a normal screen in which the colors of all sections are uniform.

  According to a sixth aspect of the present invention, in the image display device having a screen capture suppression function according to the fifth aspect of the present invention, a check pixel array having the same size as the section is prepared in advance, and the bitmap image is prepared. When generating the M number of bitmap images, the generation unit overwrites the pixels in the check pixel array on the pixels of the section set to a color different from the other sections, and generates the M number of bitmap images. It is characterized by generating.

  According to the sixth aspect of the present invention, the bitmap image acquired by screen capture becomes more difficult to see as an image, and it is possible to prevent duplication of a normal bitmap image in which the colors of all sections are uniform. .

  In the seventh aspect of the present invention, in the image display device having the screen capture suppression function according to the fifth or sixth aspect of the present invention, the values of each pixel of the bitmap image are R, G, and B. Each bit is set at a predetermined gradation (for example, 256 stages of 0 to 255), and the bitmap image generation means sets the R or B component as a color different from the other sections near the maximum value ( For example, it is set to 255), and the R, G, and B components are set to a gray scale having the same value as the color of the other section.

  According to the seventh aspect of the present invention, by setting the G component of all the sections having the highest wavelength sensitivity characteristics of the human visual system to around a uniform minimum value (for example, 0), a part of the image display device Since the section of the color is only changed from grayscale to red or blue only at the moment of a predetermined time interval, the color change is hardly perceived and the occurrence of flicker can be suppressed. On the other hand, since the bitmap image obtained by screen capture is observed in a stationary state in which the color of the pixels in the section changes to red or blue every N sections, it becomes difficult to see as an image, and the colors of all sections It is possible to prevent duplication of a uniform normal bitmap image.

  According to the eighth aspect of the present invention, in the image display device having the screen capture suppression function according to the sixth aspect of the present invention, R, G, and B each have a predetermined value for each pixel of the bitmap image. The color of the pixel to be overwritten is set to a value close to the maximum value (for example, 255) or the color of the pixel to be overwritten is set to G (for example, 256 levels of 0 to 255), or G And B components are set near the maximum value (for example, 255).

  According to the eighth aspect of the present invention, in the image display device, since the section to be overwritten is displayed in a color in which the two components are maximized only at a predetermined time interval, the color change is difficult to perceive. Can be suppressed. On the other hand, a bitmap image acquired by screen capture is observed in a stationary state with a pixel in which two components are maximized in a color where the two components are maximized, so that it is difficult to see as an image, and the colors of all sections are uniform. Duplication of the bitmap image can be prevented. In addition, since it is difficult to remove pixels to be overwritten using image processing, the effect of preventing duplication can be further enhanced.

  According to a ninth aspect of the present invention, in the image display device having a screen capture suppression function according to any one of the first to eighth aspects of the present invention, the bitmap image transfer means includes the M bitmaps. Images are sequentially transferred to the display memory at time intervals of 1/30 seconds or less.

  According to the ninth aspect of the present invention, the M bitmap images are sequentially transferred to the display memory at a time interval of 1/30 second or less, which is the minimum time that is maintained as an afterimage in human vision, Since the displayed bitmap image is switched at high speed, the color change is not perceived, and flicker can be reduced.

  According to the present invention, it is possible to prevent duplication of contents in a normal state even when the screen capture process is performed without blocking the screen capture process itself.

It is a figure which shows the basic concept of the 1st Embodiment of this invention. It is a hardware block diagram of the image display apparatus provided with the suppression function of the screen capture which concerns on 1st, 2nd embodiment of this invention. It is a functional block diagram which shows the structure of the image display apparatus provided with the suppression function of the screen capture which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the processing operation of the image display apparatus provided with the suppression function of the screen capture which concerns on the 1st Embodiment of this invention. It is a figure which shows the outline | summary of the application example of the 1st Embodiment of this invention. It is a figure which shows the basic concept of the 2nd Embodiment of this invention. It is a functional block diagram which shows the structure of the image display apparatus provided with the suppression function of the screen capture which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the processing operation of the image display apparatus provided with the suppression function of the screen capture which concerns on the 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<1. First Embodiment>
First, a first embodiment of the present invention will be described.
<1.1. Basic Concept of First Embodiment>
First, the basic concept of the first embodiment of the present invention will be described. FIG. 1 is a diagram showing the basic concept of the first embodiment of the present invention. In the present invention, N (N is an integer of N> 2) is obtained from an initial bitmap image (a character code included in a document file is converted into a bitmap format and arranged) as shown in FIG. In the example of FIG. 1, N = 4) A bitmap image in which the color is changed for each character is created. For example, the color-changed bitmap image F1 shown in FIG. 1B has the characters “A”, “E”, “I”, “M”, “Q”, “U”, and “Y” on the bitmap image, The color is changed every four characters. In FIG. 1, the character whose color has been changed is indicated by shading for convenience of expression.

  The color-changed bitmap images are generated in M (M is an integer of 2 <M ≦ N). In the example of FIG. 1, four bitmap images F1 to F4 shown in FIGS. 1B to 1E are generated. As shown in FIGS. 1B to 1E, the four bitmap images F1 to F4 are color-changed for characters that are shifted by one character. All four generated bitmap images are written in the off-screen memory. The off-screen memory is an area excluding a part normally reserved in the video memory and used as a display memory in the video memory. Then, the four bitmap images written in the off-screen memory are sequentially written in the display memory while switching one by one. The image written in the display memory is set to be displayed on the display device as it is. In the example of FIG. 1F, a state where the bitmap image F1 is written in the display memory is shown.

  When switching at high speed (for example, 1/30 seconds or less) and repeatedly writing four types of bitmap images to the memory for display, the display device switches the four types of bitmap images at short time intervals. Is displayed. However, due to the afterimage effect, the viewer who sees the screen displayed on the display device appears to display an image whose color has not been changed, as shown in FIG. This is because each character is changed in color only once every four times, and the remaining three times are the same as the original image.

  Usually, a personal computer or a tablet terminal is equipped with a screen capture function, and when screen capture is executed, data written in the display memory can be recorded. Therefore, when screen capture is executed, only the bitmap image written in the display memory at that time is recorded. Therefore, when screen capture is executed in the state shown in FIG. 1 (f), the bitmap image F1 is recorded as a screen capture image in the storage device as shown in FIG. 1 (h). That is, when viewing the screen of the display device, as shown in FIG. 1 (g), it looks like a normal image that has not been color-changed. However, when copying by screen capture is attempted, the color is changed. Only acquired images can be acquired.

<1.2. Device configuration>
FIG. 2 is a hardware configuration diagram of an image display apparatus having a screen capture suppression function according to the first embodiment of the present invention. An image display device having a function of suppressing screen capture can be realized by a general-purpose computer. As shown in FIG. 2, a CPU (Central Processing Unit) 1 and a RAM (Random Access Memory) which is a main memory of the computer. ) 2, a large-capacity storage device (for example, a hard disk, a flash memory, etc.) 3 for storing programs and data executed by the CPU 1, a key input I / F (interface) 4 such as a keyboard and a mouse, and a bit Video memory (also called a frame memory or graphics memory) 5 that is a volatile memory for storing map images, a display unit 6 that is a display device such as a liquid crystal display, an external device (such as a data storage medium), and data A data input / output I / F (interface) 7 for communication, It is connected through the scan.

  FIG. 3 is a functional block diagram showing a configuration of an image display device having a screen capture suppression function according to the first embodiment of the present invention for electronic book content based on character codes. In FIG. 3, 10 is a character string reading means, 20 is a bitmap image generation means, 30 is a bitmap image transfer means, 40 is a display memory, 50 is a bitmap image display means, and 60 is a document file storage means.

  The character string reading unit 10 reads a character string from the document file stored in the document file storage unit 60. The bitmap image generation means 20 converts the character string read by the character string reading means 10 into a bitmap image. The bitmap image transfer unit 30 transfers the bitmap image generated by the bitmap image generation unit 20 to the display memory 40. The display memory 40 is a non-volatile memory that temporarily stores a bitmap image for display on the bitmap image display means 50, and is secured in a predetermined area in the video memory 5. The bitmap image display means 50 is means for displaying a bitmap image stored in the display memory 40 and is realized by the display unit 6. The document file storage unit 60 is a storage unit that stores a document file, and is realized by the storage device 3. The character string reading unit 10, the bitmap image generation unit 20, and the bitmap image transfer unit 30 are realized by the CPU 1 executing a program stored in the storage device 3.

  Each component shown in FIG. 3 is actually realized by mounting a dedicated program on hardware such as a computer and its peripheral devices as shown in FIG. That is, the computer executes the contents of each means according to a dedicated program. Note that in this specification, a computer means a device having an arithmetic processing unit such as a CPU and capable of data processing, and is a multifunctional mobile phone such as a smartphone or a tablet that is a tablet portable PC. It is a concept that includes a terminal.

  In the storage device 3 of FIG. 2, a dedicated program for operating the CPU 1 and causing the computer to function as an image display device having a function of suppressing screen capture is installed. By executing this dedicated program, the CPU 1 realizes functions as the character string reading means 10, the bitmap image generation means 20, and the bitmap image transfer means 30. The storage device 3 not only functions as the document file storage unit 60 but also stores various data necessary for processing.

<1.3. Processing action>
Next, the processing operation of the image display apparatus having the screen capture suppression function shown in FIGS. 2 and 3 will be described with reference to the flowchart of FIG. When the user designates a document file to be displayed via the key input I / F 4, the character string reading unit 10 acquires the designated document file from the document file storage unit 60, and the character string in the document file is acquired. Is read (step S1). Specifically, a character code string recorded in a document file is read.

  Next, the bitmap image generation means 20 converts each character code into a bitmap format arranged in a set format, and generates a bitmap image representing a character string as an initial bitmap image (step S2).

  Specifically, each character code is converted into a bitmap format of set points by a known character font raster conversion function, arranged at the set character spacing and line spacing, and the color set for each pixel To generate an initial bitmap image.

  Subsequently, the bitmap image generation means 20 changes the color of the initial bitmap image generated in step S2 (step S3). Specifically, the color-changed bitmap image is generated by changing the pixel color in units corresponding to the original character for every N characters.

  In this embodiment, a process of changing the color every four characters is performed. Specifically, for the initial bitmap image generated in step S2, the first character, the second character, the third character, and the fourth character are used as the first changed characters, and thereafter the color is changed every four characters. As a result, four types of bitmap images are generated. For example, four types of bitmap images as shown in FIGS. 1B to 1E are generated.

  The color to be changed can be set as appropriate, but in this embodiment, the background color of the character is R: 255, G: 255, B: When 255 is set to white (white display) and the initial setting value of the character color is set to R: 0, G: 0, B: 0 (black display) in each of 256 steps of R, G, B, the color to be changed is R Alternatively, the value of either B is set to 255, and the values of the other two components are set to 0. That is, the color to be changed is set to R: 255, G: 0, B: 0, R: 0, G: 0, B: 255. For the color to be changed, it is not always necessary to set the value of either R or B to the maximum value of 255, as long as it is a value near the maximum value. For example, it may be a value close to the maximum value of 255, such as 200 or more. (Practically, if set to 255, flicker may occur depending on the terminal, so it is often set to 200.) Also, the other two components of the color to be changed need not necessarily be set to 0. For example, it may be a value close to 0 of the minimum value such as 15 or less. That is, the set values of R, G, and B only need to be able to recognize the color difference by the human eye, and therefore do not need to be the maximum value (255) and the minimum value (0), and are each near the maximum value (200 or more). It may be in the vicinity of the minimum value (15 or less). In the case of realizing gradations other than 256 levels, values near the maximum value and the minimum value may be set according to the gradation.

  The bitmap image generation means 20 holds the four generated bitmap images. Actually, it is held by writing to a predetermined area in the video memory 5. When the four bitmap images are generated, the bitmap image transfer means 30 performs a process of determining whether or not a predetermined time has elapsed (step S4). In this embodiment, 1/30 second is set as the predetermined time. If the predetermined time has elapsed, the bitmap image transfer means 30 transfers one of the four bitmap images to the display memory 40 (step S5). In the display memory 40, the transferred bitmap image is overwritten on the already written content. Subsequently, the bitmap image display means 50 performs a process of displaying the bitmap image written in the display memory 40. The bitmap image transfer means 30 transfers the next bitmap image to the display memory 40 when a predetermined time has passed again after the transfer. By repeatedly executing the processing of steps S4 to S6, four types of bitmap images are sequentially switched and displayed on the bitmap image display means 50. The processing of steps S4 to S6 is repeated endlessly by independent thread processing on the software as an infinite loop unless there is an end instruction. The predetermined time is preferably set to 1/30 seconds or less. By setting the predetermined time to 1/30 seconds or less, bitmap images are switched and displayed at intervals of 1/30 seconds or less, and the occurrence of flicker can be reduced.

  When screen capture is executed in this state, the bitmap image written in the display memory 40 is captured and recorded. Therefore, the initial bitmap image that has not been color-changed cannot be duplicated.

<1.4. Application example>
An application example of the first embodiment will be described. In the application example, check character string data is prepared, and when four types of bitmap images are generated, the check character string data is converted into a bitmap format and superimposed on the color-changed character. FIG. 5 is a diagram illustrating an outline of an application example of the first embodiment. Since the character string recorded in the document file is the same as that in the first embodiment, FIGS. 5A and 5G are the same as FIGS. 1A and 1G. In the case of the application example, since the check characters are overlapped, as shown in FIGS. 5B to 5E, the check characters are overlaid on the characters that are shifted by one character. All the bitmap images on which the check characters are superimposed are written in the off-screen memory and sequentially written in the display memory while switching one by one. In the example of FIG. 5F, a state where the bitmap image F11 is written in the display memory is shown.

  The color of the check character can be changed as appropriate, but in this embodiment, the R and G components are set near the maximum value (value close to 255 or 255). The B component is set to a value that is greater than or equal to a predetermined value (eg, 200) and smaller than the R and G components, or the G and B components are set near the maximum value, and the R component is set to G and B. Set to a value smaller than the component of. In the case of 256 gradations from 0 to 255, a value near the maximum value is assumed to be 200 or more.

  Also in this case, as described above, when switching is performed at high speed (for example, 1/30 seconds or less) and four bitmap images are sequentially written in the display memory, the display device has a short time interval. The four bitmap images F11 to F14 are switched and displayed. However, due to the afterimage effect, the viewer who has viewed the screen displayed on the display device appears to display the initial bitmap image whose color has not been changed, as shown in FIG.

  When screen capture is executed in the state of the display memory shown in FIG. 5F, the bitmap image F11 on which the check characters are superimposed is stored in the storage device as shown in FIG. 5H. Is recorded. In other words, when viewing the screen of the display device, a normal bitmap image that has not been color-changed is displayed, but if duplication is attempted illegally, only the bitmap image that has been color-changed is acquired. Can not do it. In this case, not only the color change but also the check characters different from those in the original document file are displayed in an overlapping manner, so even if you look at the duplicated bitmap image, the document contents are more difficult to understand. It becomes. Further, it is possible to reproduce the initial bitmap image as shown in FIG. 1A by making full use of the image processing for the color-changed bitmap image as shown in FIG. However, it is extremely difficult to reproduce the initial bitmap image as shown in FIG. 5A by using image processing for the bitmap image in which the check characters as shown in FIG. Have difficulty. For this reason, a higher copy suppression effect can be obtained.

  In the first embodiment, use of an electronic book is assumed. By using the book data of the electronic book as the document file and performing the display process, as shown in FIGS. 1 (g) and 5 (g), the user can browse the electronic book normally. . However, even if screen capture is executed to copy, it is not possible to copy in a normal state as shown in FIGS. 1 (h) and 5 (h).

<2. Second Embodiment>
A second embodiment of the present invention will be described.
<2.1. Basic Concept of Second Embodiment>
The basic concept of the second embodiment of the present invention will be described. FIG. 6 is a diagram showing a basic concept of the second embodiment of the present invention for electronic comics / contents based on bitmap images. In the present invention, an initial bitmap image as shown in FIG. 6A (if the read image data is other than the bitmap format, converted to the bitmap format) is X columns × Y rows (FIG. 6). In the example of FIG. 6, the section is divided into X = 6 and Y = 4), and for each row, the color is changed for each of the N sections (N is an integer of N> 2 and N = 4 in the example of FIG. 6) and further adjacent For the row, a bitmap image in which the color of the section shifted by one column is changed is created.

  The color-changed bitmap images are generated in M (M is an integer of 2 <M ≦ N). In the example of FIG. 6, the four patterns shown in FIGS. 6B to 6E are generated. As shown in FIGS. 6B to 6E, the four bitmap images F21 to F24 are color-changed at the sections shifted by one section. All four generated bitmap images are written in the off-screen memory. Then, the four bitmap images written in the off-screen memory are sequentially written in the display memory while switching one by one. The image written in the display memory is set to be displayed on the display device as it is. In the example of FIG. 6F, a state in which the bitmap image F21 is written in the display memory is shown.

  When switching at high speed (for example, 1/30 seconds or less) and repeatedly writing four types of bitmap images to the memory for display, the display device switches the four types of bitmap images at short time intervals. Is displayed. However, due to the afterimage effect, a viewer who has viewed the screen displayed on the display device appears to display an image whose color has not been changed, as shown in FIG. This is because the color of each section is changed only once every four times, and the remaining three times are the same as the original image.

  Usually, a personal computer or a tablet terminal is equipped with a screen capture function, and when screen capture is executed, data written in the display memory can be recorded. Therefore, when screen capture is executed, only the bitmap image written in the display memory at that time is recorded. Therefore, when screen capture is executed in the state shown in FIG. 6F, the bitmap image F21 is recorded as a screen capture image in the storage device as shown in FIG. 6H. That is, when looking at the screen of the display device, it looks like a normal image that has not been color-changed. However, if an attempt is made to duplicate illegally, only the color-changed image can be acquired.

<2.2. Device configuration>
Similar to the first embodiment, the hardware configuration of an image display device having a screen capture suppression function according to the second embodiment is as shown in FIG. 2, and is a general-purpose computer, a multi-function mobile phone (smart phone) ), And can be realized with a tablet device.

  FIG. 7 is a functional block diagram illustrating a configuration of an image display apparatus having a screen capture suppression function according to the second embodiment. In FIG. 7, components having the same functions as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. In FIG. 7, 11 is an image data reading means, 21 is a bitmap image generating means, and 61 is an image data storage means.

  The image data reading unit 11 reads the image data stored in the image data storage unit 61. The bitmap image generation means 21 converts the image data read by the image data reading means 11 into a bitmap image. The image data storage unit 61 is a storage unit that stores image data, and is realized by the storage device 3. The image data reading unit 11, the bitmap image generation unit 21, and the bitmap image transfer unit 30 are realized by the CPU 1 executing a program stored in the storage device 3.

  As in the first embodiment, each component shown in FIG. 7 is realized by mounting a dedicated program on hardware such as a computer and its peripheral devices as shown in FIG. That is, the computer executes the contents of each means according to a dedicated program.

  In the storage device 3 of FIG. 2, a dedicated program for operating the CPU 1 and causing the computer to function as an image display device having a function of suppressing screen capture is installed. By executing this dedicated program, the CPU 1 realizes functions as the image data reading unit 11, the bitmap image generation unit 21, and the bitmap image transfer unit 30. The storage device 3 not only functions as the image data storage unit 61 but also stores various data necessary for processing.

<2.3. Processing action>
Next, the processing operation of the image display device having the screen capture suppression function according to the second embodiment will be described with reference to the flowchart of FIG. When the user designates image data to be displayed via the key input I / F 4, the image data reading means 11 reads the designated image data from the image data storage means 61 (step S11).

  Next, the bitmap image generation means 21 sets image data in a predetermined format as an initial bitmap image (step S12).

  Subsequently, the bitmap image generation means 21 changes the color of the obtained initial bitmap image (step S13). Specifically, the bitmap image with the color changed is generated by dividing the initial bitmap image into a plurality of sections and changing the color of the pixels included in the predetermined section.

  Since the image data has pixels arranged in a two-dimensional plane, in this embodiment, when the xy plane is defined, the x direction (lateral direction in FIG. 6) is the X section, and the y direction (vertical direction in FIG. 6). (Direction) is divided into Y sections. Therefore, the image data is divided into X × Y sections. Then, the sections to be subjected to color change (hereinafter referred to as “color change target sections”) are N (N> 2) integers for each row. For example, in FIG. 6, assuming that the upper left corner of the image is the starting point (x, y) = (1, 1) and N = 4, in the first row (y = 1), the section (1, 1) is subject to color change. In the case of the section, the section (5, 1) moved four sections from the section (1, 1) becomes the color change target section. Further, in the second row (y = 2), when the section (2, 2) is the color change target section, the section (6, 2) moved by four sections from the section (2, 2) is the color change target section. It becomes.

  In addition, for the adjacent row sections, whether or not the same column section as the color change target section of the adjacent row is set as the color change target section can be appropriately set. In the example of FIG. The color change target section is set in the direction shifted by one column from the color change target section. Accordingly, in the second row (y = 2), the color change target section (1, 1) in the first row (y = 1) and the section (2, 2) shifted by one column are set as the color change target section. The It is possible to appropriately set how many columns the color change target sections of adjacent rows are shifted.

  In the present embodiment, the color change target section is further moved by one section, two sections, and three sections in the x direction from the color change target section of the bitmap image that has been color-changed first. , M (M is an integer satisfying 2 <M ≦ N). For example, four types of bitmap images F21 to F24 as shown in FIGS. 6B to 6E are generated.

  The color change target section can be set as appropriate, but in the present embodiment, the color of the original image is set in 256 steps for each of R, G, and B. When the R, G, and B components are grayscale images having the same value, the R or B component of the color change target section is set to 255. The R or B component need not necessarily be the maximum value of 255, but may be in the vicinity of the maximum value (specifically, 200 or more and 255 or less). Since the R or B component is set near the maximum value as the color of the color change target section, the color change target section only changes from grayscale to red or blue at the moment of a predetermined time interval. It is difficult to perceive the color change and the occurrence of flicker can be suppressed. On the other hand, since the bitmap image obtained by screen capture is observed in a stationary state in which the color of the pixels in the section changes to red or blue every N sections, it becomes difficult to see as an image, and the colors of all sections It is possible to prevent duplication of a uniform normal bitmap image. In the case of realizing gradations other than 256 levels, a value near the maximum value may be set according to the gradation.

  The bitmap image generation means 21 holds the four generated bitmap images. Actually, it is held by writing to a predetermined area in the video memory 5. When four types of bitmap images are generated, the bitmap image transfer means 30 performs a process of determining whether or not a predetermined time has elapsed (step S14). In this embodiment, 1/30 second is set as the predetermined time, as in the first embodiment. When the predetermined time has elapsed, the bitmap image transfer means 30 transfers one of the four bitmap images to the display memory 40 (step S15). In the display memory 40, the transferred bitmap image is overwritten on the already written content. Subsequently, the bitmap image display means 50 performs a process of displaying the bitmap image written in the display memory 40. The bitmap image transfer means 30 transfers the next bitmap image to the display memory 40 when a predetermined time has passed again after the transfer. By repeatedly executing the processing of steps S14 to S16, four types of bitmap images are sequentially switched and displayed on the bitmap image display means 50. The predetermined time is preferably set to 1/30 seconds or less. By setting the predetermined time to 1/30 seconds or less, bitmap images are switched and displayed at intervals of 1/30 seconds or less, and the occurrence of flicker can be reduced.

  When screen capture is executed in this state, the bitmap image written in the display memory 40 is captured and recorded. Therefore, as in the first embodiment, an initial bitmap image that has not been color-changed cannot be copied.

<2.4. Application example>
An application example of the second embodiment will be described. In the application example, when generating M color-changed bitmap images, another fixed pixel pattern having the same partition size is superimposed on the color-changed partition. Specifically, a hatching pattern having the same pixel size as each section is prepared, and the color of the pixel in the image area is set to R: 255, G: 255, B: 0, or R: 0, G: 255, B: set to 255 and overwritten (pixels in the background portion of the hatching pattern are treated as transparent without being drawn). Here, instead of the maximum value of 255, a value close to 255 (for example, 200 or more) may be used, or instead of the minimum value of 0, a value close to 0 (for example, 15 or less) may be used. That is, the set values of R, G, and B need only be able to recognize the color difference by the human eye, and therefore need not be the maximum value (255) and the minimum value (0), but near the maximum value (200 or more), It may be near the minimum value (15 or less).

  Also in this case, as described above, when switching is performed at high speed (for example, 1/30 seconds or less) and four bitmap images are sequentially written in the display memory, the display device has a short time interval. The four bitmap images are switched and displayed. However, due to the afterimage effect, a viewer who looks at the screen displayed on the display device appears to display a bitmap image that has not been color-changed. In this case, since not only the color change but another pattern is displayed in an overlapping manner, even if the copied image is viewed, the content of the image becomes more difficult to understand. Further, it is possible to reproduce the initial bitmap image as shown in FIG. 6A by making full use of image processing for the color-changed bitmap image as shown in FIG. However, it is extremely difficult to reproduce an initial bitmap image as shown in FIG. 6A by making full use of image processing on a bitmap image displayed with another pattern superimposed thereon. For this reason, a higher copy suppression effect can be obtained.

<3. Modifications common to all embodiments>
As mentioned above, although it limited about the suitable embodiment of the present invention, the present invention is not limited to the above-mentioned embodiment, and various modifications are possible. For example, in the above embodiment, the display memory 40 in which the bitmap image to be displayed on the bitmap image display means 50 is recorded is secured in the video memory 5, and a plurality of color-changed bitmap images are also stored in the video memory 5. Although writing is performed in the off-screen memory, only the display memory 40 may be secured in the video memory 5 and the off-screen memory may be secured in the RAM 2. Further, the display memory 40 may be secured in the RAM 2 and the off-screen memory may be written in the RAM 2. The storage areas of the RAM 2 and the video memory 5 that are volatile memories can be flexibly used according to the design.

  In the above embodiment, a plurality of bitmap images whose colors are changed from the initial bitmap image are generated. However, the bit data whose color is changed from the character data string of the document file or the image data other than the bitmap format is used. When generating a map image, it is also possible to generate a bitmap image whose color has been changed by setting a different color for each N characters or for each N section without generating an initial bitmap image.

1 ... CPU (Central Processing Unit)
2 ... RAM (Random Access Memory)
3 ... Storage device 4 ... Key input I / F
5 ... Video memory 6 ... Display unit 7 ... Data input / output I / F
DESCRIPTION OF SYMBOLS 10 ... Character string reading means 11 ... Image data reading means 20, 21 ... Bitmap image generation means 30 ... Bitmap image transfer means 40 ... Display memory 50 ... Bitmap image Display means 60 ... Document file storage means 61 ... Image data storage means

Claims (10)

A character string extracted from a given document file is converted into a bitmap image with a predetermined typeface, point, character spacing, and line spacing, and written to a display memory, which is a target for acquiring an image by screen capture. An image display device for displaying a bitmap image recorded in
A character string reading means for reading character string data from a given document file;
The font data is referred to, the read character string data is converted into a bitmap format, the character color is set to a color different from other characters for each N (N> 2), and other characters Bitmap image generation means for generating a bitmap image of M (M is an integer of 2 <M ≦ N) by shifting a character set to a color different from the character by one character
Bitmap image transfer means for sequentially transferring the M bit map images to the display memory at predetermined time intervals;
Bitmap image display means for displaying a bitmap image recorded in the display memory;
An image display device having a function of suppressing screen capture. In the image display device having the screen capture suppression function according to claim 1,
Prepare a check character string separately from the character string in the document file,
The bitmap image generation means includes
When generating the M types of bitmap images, the characters extracted from the check character string are overwritten on the characters set in a different color from the other characters to generate M types of bitmap images. An image display apparatus having a screen capture suppression function. In the image display apparatus provided with the screen capture suppressing function according to claim 1 or 2,
The value of each pixel of the bitmap image is such that R, G, B are set at a predetermined gradation,
The bitmap image generating means sets the background color of the character for each of R, G, and B near the maximum value, and sets the R or B component of the character color set for each N character near the maximum value. An image display device having a screen capture suppression function, wherein the colors of the other characters are set to be near the minimum values for all of R, G, and B. In the image display device having the screen capture suppression function according to claim 2,
The value of each pixel of the bitmap image is such that R, G, B are set at a predetermined gradation,
For the color of the character to be overwritten, the R and G components are set near the maximum value, and the B component is set near the maximum value and smaller than the R and G components, or the G and B components Is set in the vicinity of the maximum value, and the R component is set to a value near the maximum value and smaller than the G and B components. An image display device that converts given image data into a bitmap image, writes the image data in a display memory to which an image is acquired by screen capture, and displays the bitmap image recorded in the display memory.
Image data reading means for reading image data;
The read image data is divided into sections of X columns × Y rows, and for each row or column, the color of the pixels in the section is set to a color different from the other sections for each N (N> 2) integer. And a bitmap image generation means for generating a bitmap image of M (M is an integer of 2 <M ≦ N) by shifting a partition to be set to a color different from that of the other partitions one by one;
Bitmap image transfer means for sequentially transferring the M bit map images to the display memory at predetermined time intervals;
Bitmap image display means for displaying a bitmap image recorded in the display memory;
An image display device having a function of suppressing screen capture. In the image display device having the screen capture suppressing function according to claim 5,
Prepare a check pixel array of the same size as the section in advance,
The bitmap image generation means includes
When generating the M kinds of bitmap images, the pixels of the check pixel array are overwritten on the pixels of the sections set to colors different from those of the other sections to generate M kinds of bitmap images. An image display apparatus having a screen capture suppression function. In the image display apparatus provided with the screen capture suppressing function according to claim 5 or 6,
The value of each pixel of the bitmap image is such that R, G, B are set at a predetermined gradation,
The bitmap image generation means sets an R or B component as a color different from the other section near a maximum value, and the R, G, and B components have the same value as the color of the other section. An image display device having a function of suppressing screen capture, which is set to gray scale. The image display device having the screen capture suppression function according to claim 6,
The value of each pixel of the bitmap image is such that R, G, B are set at a predetermined gradation,
The color of the pixel to be overwritten has a screen capture suppression function characterized in that the R and G components are set near the maximum value, or the G and B components are set near the maximum value. An image display device provided. In the image display apparatus provided with the function of suppressing screen capture according to any one of claims 1 to 8,
The bitmap image transfer means includes:
An image display device having a screen capture suppression function, wherein the M bit map images are sequentially transferred to the display memory at a time interval of 1/30 second or less.   The program for functioning a computer as an image display apparatus provided with the screen capture suppression function as described in any one of Claims 1-9.

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