JP6874562B2 - Electromagnetic information leakage prevention methods, devices, and programs - Google Patents

Description

The present invention relates to an electromagnetic information leakage prevention method, an apparatus, and a program for applying to an electronic device such as a computer and preventing information leakage due to leakage electromagnetic waves from the electronic device.

In general, weak unnecessary electromagnetic waves (leakage electromagnetic waves) are usually emitted from information terminals such as computers and communication devices (sometimes collectively referred to as electronic devices). Such leaked electromagnetic waves are often radiated from signal processing circuits in electronic devices, internal signal interfaces, and the like. Leaked electromagnetic waves include various types of information handled in electronic devices, such as image signals for configuring the display screen of a display, input signals of a keyboard and mouse, and signals communicating via an external interface. There may be.

The information contained in the leaked electromagnetic waves from the electronic device can be reproduced by receiving the leaked electromagnetic waves by the receiving device and performing appropriate demodulation processing if the interface and signal method are known. Is. In particular, the image signal corresponding to the screen information has a frequency of leaked electromagnetic waves of about several hundred MHz, which is in a frequency band where it is easy to leak from electronic devices and it is easy to receive electromagnetic waves. Furthermore, it is known that the strength of leaked electromagnetic waves is relatively strong, the interface is often not encrypted, screen information can be easily reproduced from leaked electromagnetic waves, and the risk of information leakage is high. There is. For example, for the conventionally used analog R, G, and B interfaces such as VGA, XGA, and SVGA, the signal that receives the leaked electromagnetic wave and is demodulated by AM, and the horizontally-synchronized signal and vertically-synchronized signal generated externally are used for monitoring. It is known that the original image can be restored by adding it to the display (see Non-Patent Document 1).

In order to prevent such leakage of image information, for example, by inserting an appropriate filter circuit into the image signal interface in the electronic device, it is possible to suppress the radiation of the leaked electromagnetic wave. However, although this method is effective when the interface is the main source of leaked electromagnetic waves, it is not effective against leaked electromagnetic waves radiated from a circuit board such as an image signal interface circuit or a graphic card. It has been confirmed that. In addition, in the case of an electronic device such as a laptop computer in which an image signal interface is built in the main body of the device, it is necessary to have a built-in filter circuit at the time of manufacture, and there is a problem that retrofit measures cannot be taken. was there.

There is also a method of attenuating leaked electromagnetic waves by applying an electromagnetic shield to the main body of the electronic device or the display. However, this method requires that the electromagnetic shield be completely covered with the electronic device body and the display, including the interface cable and its connector, so it can be very costly to take complete measures. It was a problem.

Further, in order to interfere with electromagnetic eavesdropping, a jamming means has been proposed in which a false interfering signal is generated to make it difficult for the leaked electromagnetic wave to be eavesdropped (see Non-Patent Document 2). This method can take measures against existing electronic devices, and the cost of measures can be relatively suppressed. However, for small mobile terminals such as mobile terminals, smartphones, and tablet terminals, there has been a problem that the size and weight of the terminal are increased by attaching such an additional device, and the usability is impaired.

On the other hand, a method has been proposed in which signal processing is applied to the image signal of the original image to make it difficult to reproduce the original image even when the image signal is radiated and stolen. Specifically, when the image signal interface is an analog R, G, B interface, when the contrast changes suddenly on the screen such as the boundary between a white background and black characters, the leaked electromagnetic wave is emitted at that timing. It has been confirmed that it is strongly radiated. Therefore, a method has been proposed in which the steep edge is smoothed and electromagnetic radiation is suppressed by applying an appropriate low-pass filter to the image signal of the original image (see Non-Patent Document 3). In this method, although the amount of electromagnetic radiation is reduced, the radiation is not completely eliminated, so that a sufficient anti-sniffing effect may not be obtained. Further, since the boundary of the original image is blurred, the image quality and visibility may be deteriorated depending on the image.

Also, when the image signal interface is a digital interface such as DVI, HDMI (registered trademark), Displayport, etc., the timing at which the sign of the digital image signal changes, for example, the rise of 0 → 1 (L → H) or 1 → 0 It has been confirmed that strong electromagnetic waves are generated at the falling timing of (H → L). In this case, since the intensity of the electromagnetic wave changes depending on the code indicating the brightness of each pixel, the electromagnetic screen eavesdropping of the screen information can be performed by using the reception and demodulation method equivalent to the analog image signal. In the case of such a digital image signal, as a measure to prevent eavesdropping, a means for randomizing the lower bits of the image signal of the original image has been proposed. When this method is used, the radiant intensity of the entire screen becomes uniform, so that it becomes difficult to reproduce the eavesdropping image (see Non-Patent Document 3). However, even in this method, since the radiation intensity of each pixel fluctuates according to the frequency of the sign change of the high-order bits that are not randomized, a sufficient anti-sniffing effect may not be obtained. Further, the image quality of the original image depends on how finely the gradation of brightness can be set, but this is determined by the number of high-order bits that are not randomized. Therefore, when randomizing is performed, the image quality of the original image deteriorates as the number of high-order bits decreases. In particular, in order to improve the eavesdropping prevention effect, it is necessary to increase the number of bits to be randomized, but in that case, the number of high-order bits that affect the gradation of brightness decreases, so that the image quality of the original image is further deteriorated. There was a trade-off of doing it.

U.S. Pat. No. 4,486,739

Wim van Eck: Electromagnetic Radiation from Video Display Units: An Eavesdropping Risk Computers & Security, Vol. 4, pp.269-286, 1985. Y. Suzuki and Y. Akiyama; Jamming Technique to Prevent Information Leakage Caused by Unintentional Emissions of PC Video Signals, Proc. IEEE EMC 2010, pp.132-137, July 2010. Markus G. Kuhn: Compromising emanations: eavesdropping risks of computer displays, University of Cambridge (Computer Laboratory) Technical Report Number 577, UCAM CL TR 577, ISSN 1476-2986, 2003. URL: http://www.cl.cam. ac.uk/techreports/UCAM CL TR 577.html Digital Visual Interface DVI revision 1.0, Digital Display Working Group, 02 April 1999. IEEE 802.3-2015, "IEEE Standard for Information technology Telecommunications and information exchange between systems Local and metropolitan area networks Specific requirements Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA / CD) Access Method and Physical Layer Specifications". Meryem Primmer: “An Introduction to Fiber Channel,” Hewlett Packard Journal, Article 11, October 1996.

Although it is effective to take measures by software that use a method of preventing information leakage due to electromagnetic screen voyeurism (electromagnetic screen voyeurism), that is, reproduction of the voyeur image by signal processing for the image signal of the original image. The countermeasure effect is not sufficient, and it is difficult to completely prevent information leakage due to reproduction of voyeur images. Further, there is a problem that the image quality of the original image is deteriorated when trying to enhance the countermeasure effect.

Therefore, an object of the present invention is to minimize the deterioration of the image quality of the original image and effectively prevent the leakage of electromagnetic information that receives the leaked electromagnetic wave and reproduces the original image.

The electromagnetic information leakage prevention method of the present invention extracts an image signal contained in a leaked electromagnetic wave radiated from an electronic device and reproduces a display screen. In order to prevent electromagnetic screen eavesdropping, the original image is displayed in the electronic device. This is a method of effectively preventing the reproduction of screen information from leaked electromagnetic waves by adding signal processing to the image signal of.

A feature of the present invention is a process of acquiring image coding information corresponding to all pixels constituting the original image of the display screen in an electromagnetic information leakage prevention method applied to an electronic device that processes an image signal, and the image code. as the frequency of sign changes of each bit of reduction information is constant, and outputs the process for performing code conversion of the original image for each pixel, the image coding information more obtained process for performing the transcoding In the process of executing the process and the process of executing the code conversion, the total value of the number of bit transitions is calculated for each pixel in the image coding information represented by a plurality of bits for each pixel constituting the original image. The configuration includes the process of inverting or maintaining the lower bits of the image coding information so that the calculated total value is leveled to a predetermined value.
A feature of the present invention is a process of acquiring image coding information corresponding to all pixels constituting the original image of a display screen in an electromagnetic information leakage prevention method applied to an electronic device that processes an image signal, and the image code. A process of executing the code conversion of the original image for each pixel and a process of outputting the image coded information obtained by the process of executing the code conversion so that the frequency of the code change of each bit of the conversion information is constant. And, in the process of executing the code conversion, each of the plurality of pixels constituting the original image has the number of bits (3n) of each n (n is an integer of 2 or more) bits of R, G, and B. In the image coding information consisting of, the process of calculating the total value of the number of bit transitions for each pixel and the leveling of the total value to the minimum integer value N exceeding 3n / 2 of each of the n bits. The configuration includes a process of inverting or maintaining a lower bit.
A feature of the present invention is a process of acquiring image coding information corresponding to all pixels constituting the original image of the display screen in an electromagnetic information leakage prevention method applied to an electronic device that processes an image signal, and the image code. A process of executing the code conversion of the original image for each pixel and a process of outputting the image coded information obtained by the process of executing the code conversion so that the frequency of the code change of each bit of the conversion information is constant. And, the image coding information in which each of the plurality of pixels constituting the original image is composed of the number of bits (3n) of each n (n is an integer of 2 or more) bits of R, G, and B is subjected to a predetermined code conversion rule. The n / m conversion process of converting each pixel into image coding information consisting of the number of bits (3 m) of m bits based on the above is executed, and the process of executing the code conversion is the n / m conversion process. The process of calculating the number of bit transitions for the m-bit image coding information converted by the above, the process of calculating the most frequent value among the calculated number of bit transitions, and the number of calculated bit transitions. Is a configuration including a process of changing the image coding information of the m-bit so as to be uniform to the most frequent value.
A feature of the present invention is a process of acquiring image coding information corresponding to all pixels constituting the original image of the display screen in an electromagnetic information leakage prevention method applied to an electronic device that processes an image signal, and the image code. A process of executing the code conversion of the original image for each pixel and a process of outputting the image coded information obtained by the process of executing the code conversion so that the frequency of the code change of each bit of the conversion information is constant. And the image coding information in which each of the plurality of pixels constituting the original image is composed of the number of bits (3n) of each n (n is an integer of 2 or more) bits of R, G, and B, according to a predetermined code conversion rule. The n / m conversion process of converting each pixel into image coding information consisting of the number of bits (3 m) of m bits based on the above is executed, and the process of executing the code conversion is the image code of each pixel. Regarding the conversion information, the process of calculating the number of bit transitions (BT) for the m-bit image coding information converted by the n / m conversion process and the number of bit transitions (BT) calculated are the highest. In the process of calculating the number of frequency bit transitions (BTo) and the converted m-bit image coding information, the calculated number of bit transitions (BT) is the number of most frequent bit transitions (BTo). ) Is maintained, and if it is different, the image that matches the number of bit transitions (BTo) and has the closest numerical value of n-bit image coding information before code conversion. The configuration includes a process of searching for coding information and replacing the numerical value of the code with the numerical value of the searched m-bit image coding information.

It is possible to obtain the effect of minimizing the deterioration of the image quality of the original image and effectively preventing the leakage of electromagnetic information that receives the leaked electromagnetic wave and reproduces the original image.

The block diagram which shows the structural example of the electronic device which concerns on 1st Embodiment of this invention. The figure for demonstrating the mechanism of image information leakage which concerns on 1st Embodiment. The figure for demonstrating an example of the image conversion process which concerns on 1st Embodiment. The figure for demonstrating an example of the image conversion process which concerns on 1st Embodiment. The figure for demonstrating an example of the image conversion process which concerns on 1st Embodiment. The flowchart for demonstrating an example of the procedure of image conversion processing which concerns on 1st Embodiment. The flowchart for demonstrating an example of the procedure of image conversion processing which concerns on 1st Embodiment. The figure for demonstrating the effect of 1st Embodiment. The block diagram which shows the structural example of the electronic device which concerns on 2nd Embodiment of this invention. The block diagram which shows the structural example of the image transmission interface which applied the 8b / 10b code conversion method which concerns on 2nd Embodiment. The block diagram which shows the structural example of the image transmission interface which applied the 8b / 10b code conversion method which concerns on 2nd Embodiment. It is a figure which shows an example of the 8b / 10b code conversion table which concerns on 2nd Embodiment. The figure for demonstrating the 8b / 10b code conversion process which applied the TMDS method which concerns on 2nd Embodiment. It is a figure which shows an example of the 8b / 10b code conversion table which concerns on 2nd Embodiment. The figure for demonstrating 8b / 10b code conversion processing which applied the IBM method which concerns on 2nd Embodiment. The flowchart for demonstrating an example of the procedure of 8b / 10b code conversion processing which concerns on 2nd Embodiment.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a block diagram showing a configuration of an electronic device 10 according to the first embodiment. The electronic device 10 is an information terminal or a communication device, for example, a personal computer (PC) or a smartphone. As shown in FIG. 1, the electronic device 10 has a processor (CPU) 11 as a main part, and a storage device 15 and a display 16 as peripheral parts.

The CPU 11 realizes the functions of the image acquisition unit 12 and the image conversion unit 13 by executing the software stored in the storage device 15. That is, the image acquisition unit 12 and the image conversion unit 13 are implemented as software inside the electronic device 10, and effectively perform screen reproduction due to electromagnetic leakage of the present embodiment, that is, electromagnetic screen voyeurism (voyeur). Generate a preventable image (image coding information).

The image acquisition unit 12 acquires an image signal (original image) of the display screen generated by the processing of the CPU 11. As will be described later, the image conversion unit 13 executes a code conversion process for converting the original image (hereinafter, referred to as the original image) acquired by the image acquisition unit 12 into image coding information. As a code conversion process, the image conversion unit 13 of the present embodiment converts electromagnetic screen voyeurism (voyeurism) into image coding information that can be effectively prevented, as will be described later.

The image display unit 14 includes an image controller, and executes display control for displaying an image based on the image coding information from the image conversion unit 13 on the screen of the display 16.
[Action and effect of the first embodiment]
Hereinafter, with reference to FIG. 2, the mechanism of electromagnetic information leakage due to the leakage electromagnetic wave of the image signal according to the present embodiment will be described. Here, FIG. 2 (A) shows the original image, and FIG. 2 (B) shows the eavesdropping reproduction image. Further, FIG. 2C shows time-series data of the leaked electromagnetic wave. FIG. 2D shows the timing and radiation intensity of the bit transition described later.

In the electronic device 10, a digital image signal (hereinafter, simply an image signal) of a display screen is radiated to the outside of the electronic device 10 as leaked electromagnetic waves from an image interface or the like included in the electronic device 10. Here, the image signal is one in which the brightness of each of red (R), green (G), and blue (B) is arranged in chronological order as digital data (luminance data) for one pixel. FIG. 2A shows a raster scan method in which pixels are sequentially drawn for each horizontal scanning line on the display screen and the original image is displayed.

The luminance data of each pixel is represented by, for example, a bit string having an 8-bit length for each of R, G, and B. That is, when R, G, and B each have an 8-bit length, 24-bit information is included in the entire pixel, which corresponds to 16,777,216 kinds of color tones. Specifically, when the brightness of each of R, G, and B is 256, for example, when the brightness of (R, G, B) is (0, 0, 0), white, ( The color tone and brightness are determined by mixing three colors, such as black for 255, 255, 255), red for (255, 0, 0), and yellow for (255, 255, 0). .. Since the brightness of these 256 gradations corresponds to 8 bits as a digital signal, the total of 3 colors is a 24-bit (about 16 million colors) image signal.

These image signals are transferred as digital pulses on the image interface as shown in FIG. 2 (D). In this case, at the momentary rise and fall, which is the timing of the bit transition, the electromagnetic wave is efficiently radiated because the instantaneous frequency component is high. FIG. 2D shows that short pulsed electromagnetic radiation is generated at the timing. As shown in FIG. 2D, when the 8-bit code differs depending on the pixel, the frequency of bit transitions also differs, so that an electromagnetic pulse is emitted at a density (radiant intensity) corresponding to the frequency.

When the leaked electromagnetic wave shown in FIG. 2C is received and demodulated, the image can be reproduced from the leaked electromagnetic wave by drawing the average electromagnetic field strength 22 that changes for each pixel as a screen (FIG. 2 (C)). B)). That is, an intensity change 20 corresponding to the radiation intensity in each pixel of the original image shown in FIG. 2 (A) occurs, and as shown in FIG. 2 (B), the screen reproduction 21 is performed with reference to the period T of the scanning lines. It will be possible.

Next, with reference to FIGS. 3 to 7, an image conversion process by the image conversion unit 13 of the present embodiment will be described in order to prevent screen reproduction from the above-mentioned leaked electromagnetic wave. The image conversion process of the present embodiment is generally to perform code conversion of the original image so that the intensity of electromagnetic radiation is constant in all the pixels of the original image. In other words, the code conversion of the original image is performed so that the frequency of the code change (bit transition) of each bit is constant in all the pixels.

3 to 5 are diagrams for explaining the contents of the code conversion process performed on the image signal (original image data) of the original image in the image conversion process. FIG. 3 is a diagram for explaining the leveling process of the image code and the number of bit transitions in the case of parallel transmission in which the luminance data of each pixel of the original image is a bit string having an 8-bit length for each of R, G, and B. is there. FIG. 4 is a diagram for explaining the leveling process of the image code and the number of bit transitions in the case of serial transmission. FIG. 5 is a diagram for explaining a specific example of the leveling process in the case of serial transmission.

As shown in FIG. 3, the image conversion process of the present embodiment generates the image data 34 of the code string obtained by code-converting the code string of the image data 30 for one pixel of the original image. As shown in FIG. 3A, the image data 30 of the original image is composed of code strings 31, 32, and 33 indicating R, G, and B, each of which is an 8-bit bit string. Here, the code strings 31, 32, and 33 represent 149, 58, and 103 in decimal numbers, respectively. Further, as shown in FIG. 3B, the code-converted image data 34 includes code sequences 35, 36, and 37 indicating R, G, and B. Here, for convenience, it is assumed that the code strings of the same signal are continuously transmitted for all of R, G, and B. Even in an actual image signal, it often occurs when pixels having the same color tone and gradation are continuous, such as when a wide screen area has the same color.

In the image conversion process of the present embodiment, the number of bit transitions during the period for transmitting the image data for one pixel, here, the code changes from 0 to 1 or 1 to 0 during the transmission of 8-bit data. The code conversion process is such that the number of cases is a fixed number in the image data after the code conversion. Bit transitions in 8-bit data occur at least 0 times to at most 8 times depending on the code, considering the transitions between adjacent pixels. In this case, the least significant or most significant bit of the 8-bit determines whether or not there is a bit transition with the bit string of the adjacent pixel. At this time, it may be decided that the number of bit transitions is counted between the bit and the bit before it, or between the bit and the subsequent bits, and whichever is adopted. The count number is the same.

In the case shown in FIG. 3, it is an example of counting the bit transitions between the bit and the bit before it. On the other hand, in 4-bit data, the number of bit transitions is from 0 at least to 4 at maximum. Therefore, for 8-bit data, as shown in FIG. 3B, the number of bit transitions for 8 bits after code conversion is performed by leaving the upper 4 bits as they are and performing code conversion only for the lower 4 bits. Can always be 4 times. In general, the number of bit transitions of N (bit) data is code-converted only for the lower N / 2 (bit) (rounded up to the nearest whole number when N is odd), and the number of bit transitions after conversion is performed. Can always be N / 2 times (rounded down when N is odd).

In the image conversion process of the present embodiment as described above, the number of bit transitions in each pixel is set to a constant value (12 times in this case) by inverting the minimum number of bits from the lower bits of each color of RGB. Perform code conversion. Therefore, it is possible to prevent electromagnetic screen voyeurism (voyeurism) that reproduces the original image by receiving and reproducing the change in the intensity of electromagnetic radiation for each pixel. Here, in the code conversion of the present embodiment, since the upper 4 bits that greatly affect the color tone and the gradation are the same as the original image data, for example, the gradation by converting the code of the upper 5th bit among the 8 bits. The change of is suppressed to 4% or less (1/2 ^{5) of all gradations.} Further, by performing the code conversion from the lower bits, it is possible to minimize changes in the color tone and gradation of the image data after the code conversion, and to minimize the deterioration of image quality and visibility.

In the example shown in FIG. 3, since the image data of R, G, and B are transmitted in parallel, the 8-bit image data indicating the pixels of each color is transmitted at the same timing. In this case, the number of bit transitions is the sum of the number of bit transitions of each of R, G, and B. As shown in FIG. 3, when 8-bit image data is transmitted in parallel in 3 lanes, the total number of bit transitions is from 0 at least to 24 at maximum, but the code conversion that aligns this total value to 12 times. It is possible to perform operations on arbitrary image data.

Here, regarding the code string of the original image data 30, the number of bit transitions is 6 times for the R data, 4 times for the G data, and 4 times for the B data. On the other hand, in the image data 34 after the code conversion, the total number of bit transitions is increased to 12 by converting the code of the second bit from the lower part of the code string of the R image data from "0" to "1". I'm changing. For a code string having a total number of bit transitions greater than or less than 12 as described above, code conversion is sequentially performed from the lower bits until the number of bit transitions matches 12 times. The number of bit transitions including the preceding and following pixels is always an even number, and the unit of increase / decrease in the number of bit transitions when 1-bit code conversion is performed is always a multiple of 2 (2 increases, 2 decreases, Or no increase or decrease).

Next, the image conversion process (code conversion process) of the present embodiment will be described with reference to FIG. 4 in the case of serial transmission in which image data is serially transmitted in the order of R, G, and B.

As shown in FIG. 4, the image conversion process of the present embodiment generates the image data 44 of the code string obtained by code-converting the code string of the image data 40 for one pixel of the original image. The image data 40 of the original image is composed of code strings 41, 42, and 43 indicating R, G, and B, each of which is an 8-bit bit string. The image data 44 after the code conversion is composed of code strings 45, 46, 47 indicating R, G, and B. Also in this example, for convenience, it is assumed that the code strings of the same signals are continuously transmitted for all of R, G, and B, and after the transmission of B is completed, the transmission is started again in order from R. Therefore, parallel transmission shown in FIG. 3 shows that R, G, and B are adjacent to each other, and the most significant bit and the least significant bit of each color are the least significant bit and the most significant bit of different colors, respectively. It is different from the case of. Further, the transmission period for one pixel is three times as long as that in the case of parallel transmission shown in FIG.

In the case of serial transmission as in the case of parallel transmission, in the image conversion process of the present embodiment, the number of bit transitions during the period of transmitting the image data 40 for one pixel is a fixed number in the image data 44 after the code conversion. The code conversion is performed so as to be. Even in this case, for 8-bit data, the upper 4 bits are left as they are, and the code conversion is performed only for the lower 4 bits, so that the total number of bit transitions of R, G, and B after the code conversion is always 12 times. It is possible.

Here, regarding the code string of the original image data 40, the number of bit transitions is 7 times for the R data, 5 times for the G data, and 4 times for the B data, for a total of 16 times. On the other hand, in the image data 44 after the code conversion, the sign of the lowest bit of the code string of the R image data is converted from "1" to "0", and the sign of the lowest bit of the code string of G is changed. By converting from "0" to "1", the total number of bit transitions is changed to 12 times. As in the case of parallel transmission shown in FIG. 3, for a code string in which the total number of bit transitions is more than or less than 12 times, the codes are sequentially coded from the lower bits until the number of bit transitions matches 12 times. Perform the conversion.

In the image conversion process (code conversion process) of the present embodiment described with reference to FIGS. 3 and 4 as described above, FIG. 5 shows specific examples of code conversion procedures and conversion rules for the original image data. It is a figure for demonstrating. Although FIG. 5 is a diagram assuming the case of parallel transmission, it can be similarly applied to the case of serial transmission.

First, the case where the number of bit transitions increases or decreases will be described. The number of bit transitions is assumed to be 3 bits including the two bits before and after the bit adjacent to the bit. As a pattern in which the number of bit transitions increases by converting the sign of the central bit in these 3 bits,
(a) When three consecutive "000" with "0" sign are converted to "010"
(b) Only two cases when three consecutive "111" of "1" sign are converted to "101" correspond. On the contrary, as a pattern in which the number of bit transitions decreases,
(c) When the sign "010" is converted to three consecutive "000" with the sign "0"
(d) Only two cases are applicable when the code "101" is converted into three consecutive "111" codes of "1".

Based on such conversion rules (a) to (d), the code conversion of the present embodiment is performed in the following procedures (1) to (4). The following procedure shows a procedure for performing code conversion on a pixel-by-pixel basis, and the procedure is actually performed sequentially for each pixel. In addition, the cases in parentheses in steps (1) to (4) indicate the reverse case.

Step (1) calculates the number of bit transitions for the entire pixel. As shown in FIG. 5, bit transitions occur 7 times for the image data 51 of R, 5 times for the image data 52 of G, and 4 times for the image data 53 of B, and 16 times for the entire pixel. It becomes.

In step (2), when the number of bit transitions in the entire pixel calculated in step (1) is more (less) than 12 times, the code processing for reducing (increasing) the number of bit transitions is performed in order from the lower bits. In the case of FIG. 5, since the number of bit transitions is 16, the conversion process for reducing this by 4 times is performed.

In step (3), the conversion rule (c) or conversion rule (d) (conversion rule (a) or conversion rule (b) is described for the least significant bit and the bits before and after each of R, G, and B. ))), That is, whether or not there is a code "010" or a code "101" (a code "000" or a code "111") is confirmed. If there is this pattern, the sign conversion of the sequential conversion rule (c) or conversion rule (d) (conversion rule (a) or conversion rule (b)) is performed. Since the number of bit transitions decreases (increases) by 2 times for each code conversion, this code conversion process is performed until the number of bit transitions reaches 12.

Here, the order of the code conversion process is arbitrary, but for example, the code conversion process is performed in the order of R → G → B, and the code conversion process is stopped when the number of bit transitions reaches 12. As shown in FIG. 5, the R image data 51 is subjected to code conversion of the pattern according to the conversion rule (c) to be converted to the code 54 of “000”. The image data 52 of G is subjected to the code conversion of the pattern of the conversion rule (d) to be converted to the code 55 of “111”. At the time of performing such code conversion, the number of bit transitions is 12, so the processing is stopped.

In step (4), in the coding processing of the least significant bit of step (3), the bit transition is reduced (increased). The above-mentioned conversion rule (c) or conversion rule (d) (conversion rule (a) or conversion rule (b)). ), Or if the number of bit transitions does not reach 12 even after code conversion of the least significant bit, the second bit from the bottom is targeted and the third bit from the least significant bit is targeted. For the 3 bits up to, the same code conversion process as in step (3) is performed. If the number of bit transitions does not reach 12 even in this process, the same code conversion process is performed sequentially from the lower bits, but the number of bit transitions is always reduced (increased) to 12 by performing the process up to the lower 4 bits. )be able to.

Here, the bit transition in the digital code of 24 bits per pixel includes a minimum of 0 times (for example, when all 24 bits are 0) to a maximum of 24 times (when 0,1 is repeated; a transition between adjacent pixels is included. ) Will occur. In order to make the number of bit transitions constant for each pixel, for example, the upper 4 bits of the 8-bit codes of each of the R, G, and B colors are left as they are, and the lower 4 bits are appropriately changed. It is possible to fix the number of bit transitions of all pixels to 12 times. At this time, the code of the lower 4 bits is an arbitrary bit array such that the number of bit transitions of the lower 4 bits is (4-N) times if the number of bit transitions of the code of the upper 4 bits is N times. As a result, the number of bit transitions for each of the R, G, and B colors can be set to 4 times, and the number of bit transitions for all 24 bits can be fixed to 12 times. Depending on the code of the original image, the number of bit transitions can be leveled by leaving more high-order bits and changing only the low-order 3 bits or low-order 2 bits.

6 and 7 are flowcharts showing the procedure of the code conversion process for the original image data (image signal for one pixel) described above in the image conversion process executed by the image conversion unit 13.

The image conversion unit 13 acquires image data (3N = 24 bits) for one pixel of each N bit (for example, N = 8) of R, G, and B (step S1). Next, as the procedure (1), the number of bit transitions in the entire pixel is calculated, and it is determined whether or not the number of bit transitions is "3N / 2 times, here 12 times" (step S2). Here, when the number of bit transitions is 12, the code conversion process is stopped (Yes in step S2).

In the present embodiment, as shown in FIG. 5, since the number of bit transitions is 16, the process shifts to the process of increasing or decreasing the number of bit transitions as the procedure (2) (No in step S2). Here, in order to perform the process of increasing / decreasing the number of bit transitions in order from the lower bits, the initial value (M = 1) of the lower bits M is set (step S3). If the number of bit transitions is less than 12, the process proceeds to the process of increasing the number of bit transitions (Yes in step S4, which will be described later with reference to FIG. 7).

On the other hand, as shown in FIG. 5, when the number of bit transitions is 16, a code conversion process for reducing the number of bit transitions by 4 times is executed (No in step S4). Here, as the procedure (3), the code conversion process is executed in the order of R, G, and B, and the code conversion process is stopped when the number of bit transitions reaches 12 (Yes in step S10, Yes in S12, Yes, S12). Yes in S14). Further, as the procedure (3), the above-mentioned conversion rule (c) or conversion rule (d) (conversion rule (a) or conversion rule) is performed for the least significant bit of each of R, G, and B and the three bits before and after the least significant bit. It is confirmed whether or not there is a pattern corresponding to (b)) (steps S5, S6, S7). If there is this pattern (Yes in step S5, Yes in S6, Yes in S7), the code conversion of the sequential conversion rule (c) or conversion rule (d) (conversion rule (a) or conversion rule (b)) is executed. (Steps S9, S11, S13). Since the number of bit transitions decreases by two times for each code conversion, this code conversion process is repeated until the number of bit transitions reaches 12 (No in steps S10, No in S12, No in S14, S8). If there is no pattern, or if the number of bit transitions does not reach 12 even after performing code conversion of the least significant bit, the code conversion process of the above step (4) is performed for the lower 2 bits. I do.

On the other hand, when the number of bit transitions is less than 12 (Yes in step S4), as shown in FIG. 7, code conversion for increasing the number of bit transitions is executed. This code conversion process is the reverse process of the process of reducing the number of bit transitions, and the same procedure (3) and procedure (4) are executed. That is, as the procedure (3), the code conversion process is executed in the order of R, G, and B, and the code conversion process is stopped when the number of bit transitions reaches 12 (Yes in step S24, Yes, S28 in S26). Yes). Further, as the procedure (3), the above-mentioned conversion rule (c) or conversion rule (d) (conversion rule (a) or conversion rule) is performed for the least significant bit of each of R, G, and B and the three bits before and after the least significant bit. It is confirmed whether or not there is a pattern corresponding to (b)) (steps S20, S21, S22). If there is this pattern (Yes in step S20, Yes in S21, Yes in S22), the code conversion of the sequential conversion rule (c) or conversion rule (d) (conversion rule (a) or conversion rule (b)) is executed. (Steps S23, S25, S27). This code conversion process is repeated until the number of bit transitions reaches 12 (No in step S24, No in S26, No in S28, S29). If there is no pattern, or if the number of bit transitions does not reach 12 even after performing code conversion of the least significant bit, the code conversion process of the above step (4) is performed for the lower 2 bits. I do.

8 (A) to 8 (D) are diagrams for explaining the effect of the present embodiment. FIG. 8A shows an example of screen reproduction of the original image, and is a diagram in which an 8-bit 256-gradation gray scale is drawn for each 16 × 16 grid from the upper left to the lower right of the screen. .. Specifically, the upper left square of the screen is (R, G, B) = (255,255,255), and the square to the right of it is (R, G, B) = (254,254). , 254), and so on, the gradation gradually decreases, and in the lower right square, (R, G, B) = (0, 0, 0).

FIG. 8B shows an example in which the screen is reproduced from the leaked electromagnetic waves when the original image is displayed on the display of an actual PC. In this way, the reproduced image has a screen completely different from that of the original image, because the bit transition of the 8-bit digital code of each pixel influences the intensity of electromagnetic radiation of that pixel. Although the order of contrast between the original image and the reproduced image is different, in reality, if black characters are written on a white background and the intensity of electromagnetic radiation between white and black is different, the characters will be reproduced. It can be identified as an image.

FIG. 8C is a reproduced image by simulation in which the number of bit transitions of the 8-bit digital code of each pixel is drawn as it is as shading. The contrast shown in FIG. 8 (B) is almost the same as that in the case of the reproduced image of FIG. 8 (C), and it can be confirmed that the number of bit transitions influences the intensity of electromagnetic radiation of the pixel.

FIG. 8 (D) is a reproduced image obtained by the same simulation as in FIG. 8 (C) when the code conversion processing method of the present embodiment is executed on the original image of FIG. 8 (A). Since the number of bit transitions is the same (12 times) for all pixels, the entire screen has the same gradation (color tone), indicating that electromagnetic screen voyeurism (voyeurism) can be prevented.

In short, according to the present embodiment, the frequency of code change (bit transition) of each bit of the digital code that is the brightness signal of the pixel is constant in all the pixels in the image information included in the leaked electromagnetic wave. , Performs code conversion processing of the original image for each pixel. By such code conversion processing, the radiant intensity of the image signal leaked as an electromagnetic wave is maintained at a constant value without changing with time, so that it is effective to reproduce the image by eavesdropping by a method of detecting the change in radiant intensity. It is possible to prevent it.

Further, the brightness and color tone of each pixel will naturally change due to the code conversion process added to the original image, but it is desirable to minimize the influence on the image quality and visibility of the original image. Therefore, in the present embodiment, the code conversion process is performed on the minimum R, G, and B lower bits required for leveling the number of bit transitions (uniformizing the number of bit transitions of all pixels). Only the minimum required range is changed, and the high-order bits are kept as the code of the original image. Therefore, since the high-order bits that affect the brightness and the color tone can be retained, it is possible to minimize the deterioration of the image quality of the original image.
[Second Embodiment]
FIG. 9 is a block diagram showing a configuration of the electronic device 60 according to the second embodiment. The electronic device 60 is an information terminal or a communication device as in the first embodiment, and is, for example, a personal computer (PC) or a smartphone. As shown in FIG. 9, the electronic device 60 has a processor (CPU) 61 as a main part, and a storage device 67 and a display 66 as peripheral parts.

The CPU 61 realizes the functions of the image acquisition unit 62, the image conversion unit 63, and the 8b / 10b code conversion unit 64 by executing the software stored in the storage device 65. That is, the image acquisition unit 62, the image conversion unit 63, and the 8b / 10b code conversion unit 64 are each implemented as software inside the electronic device 60, and can effectively prevent the electromagnetic screen eavesdropping of the present embodiment. Image is generated.

The image acquisition unit 62 acquires an image signal (original image) of the display screen generated by the processing of the CPU 61. The image conversion unit 63 executes a code conversion process for converting the original image acquired by the image acquisition unit 62 into image coding information. As will be described later, the 8b / 10b code conversion unit 64 converts the image coding information from the image conversion unit 63 into 10 8-bit codes according to a predetermined 8b / 10b code conversion rule applied to the image interface. Performs code conversion to convert to bit code. Further, the image display unit 65 includes an image controller, and executes display control for displaying an image based on the image coding information code-converted by the 8b / 10b code conversion unit 64 on the screen of the display 66.

FIG. 10 is a diagram showing a configuration example of an image transmission interface to which the 8b / 10b code conversion method is applied. As shown in FIG. 10, the source data 70 including the 8-bit image signal and the clock signal CLK for each pixel is transmitted from the transmitting unit 71 to the receiving unit 76, and the original image signal is transmitted on the receiving side. It is restored as and held in the data sink 80.

The transmission unit 71 converts each 8-bit image signal into 10 bits each according to a certain rule by the 8b / 10b encoder (encoding circuit) 72, and transmits the image signal from the gate circuit 74 via the transmission line 75 in parallel. Here, the 8b / 10b encoder 72 is controlled by the PLL 73 operated by the clock signal CLK included in the source data 70. The receiving unit 76 inputs each 10-bit image signal via the gate circuit 77, and converts each 10 bits into the original 8 bits by the 8b / 10b decoder (decoding circuit) 78. The 8b / 10b decoder 78 is controlled by the PLL 79 operated by the clock signal CLK included in the source data 70.

Image interfaces to which such an 8b / 10b code conversion method is applied include DVI (Digital Visual Interface) and HDMI (registered trademark, High-Definition Multimedia Interface), which are defined as TMDS (Transition Minimized Differential Signaling). The 8b / 10b code conversion method described above is used (see, for example, Non-Patent Document 4).

FIG. 11 is a diagram showing another configuration example of the image transmission interface to which the 8b / 10b code conversion method is applied. FIG. 10 is a configuration example in which an image signal of 10 bits each is transmitted in parallel from the transmitting unit 71 to the receiving unit 76. On the other hand, in this configuration example, as shown in FIG. 11, in the transmission unit 91, after each 8-bit image signal is converted into 10 bits by the 8b / 10b encoder 92, a serialization circuit (parallel) is used. It is converted into a serial signal by the serial conversion circuit) 94. The 8b / 10b encoder 92 is controlled by the PLL 93 operated by the clock signal CLK included in the source data 90.

The serial signal is serially transmitted from the transmission unit 91 to the reception unit 97 via the transmission line 96. In the receiving unit 97, the serial signal is input via the gate circuit 98 and then converted into a parallel signal for each of R, G, and B by the parallel circuit (serial-parallel conversion circuit) 99. Further, in the receiving unit 97, each 10 bits is converted into the original 8 bits by the 8b / 10b decoder 100. The 8b / 10b decoder 100 is controlled by the PLL 101 operated by the clock signal CLK included in the source data 70. As a result, the source data 90 including the 8-bit image signal and the clock signal CLK for each pixel is transmitted from the transmitting unit 91 to the receiving unit 97, and is restored as the original image signal on the receiving side. It is held in the data sink 102.

Image interfaces to which such an 8b / 10b code conversion method is applied include Advanced PPmL (Point to Point mini LVDS), V by One HS, and MHL (Mobile High definition Link). In this case, as the 8b / 10b code conversion method, an IBM method (see, for example, Patent Document 1, Non-Patent Documents 5 and 6) is known in addition to the method specified by TMDS described above.

Various methods have been proposed for the 8b / 10b code conversion method, but as described above, the methods usually used in the image interface are roughly classified into the TMDS method and Gigabit Ethernet (registered trademark) and the like. There is an IBM method. The former TMDS method focuses on reducing EMI (Electromagnetic Interference), which is unnecessary electromagnetic radiation, and performs coding that minimizes the number of bit transitions. On the other hand, the latter IBM method is a method that focuses on avoiding the same code continuity as much as possible in order to minimize intersymbol interference and facilitate clock reproduction.

In any of the code conversion methods, in order to enable AC coupling in the receiving circuit via a coupling capacitor, etc., the number of "0" and "1" of the converted code is made equal to DC. Processing to ensure balance is being performed. Therefore, always keep track of the running disparity (RD), which is the integrated value of the parity of the already transmitted codes (the difference between the number of "0" codes and the number of "1" codes), and the RD is plus (+). Occasionally, the parity of the code to be transmitted next is set to minus (-). On the contrary, when the RD is minus (−), the parity of the code to be transmitted next is set to plus (+), so that the RD is always brought close to 0.

In the image interface that performs the 8b / 10b code conversion process in this way, the main electromagnetic leakage occurs on the transmission interface, so it is necessary to take measures against leakage of the converted 10-bit code electromagnetic radiation. .. Since the electromagnetic radiation level at this time depends on the number of bit transitions of the 10-bit code, the number of bit transitions of the 10-bit code is set to a constant value to prevent reproduction due to electromagnetic screen voyeurism (voyeur). Need to keep.
[Action and effect of the second embodiment]
Hereinafter, a method for preventing electromagnetic information leakage by the 8b / 10b code conversion process of the 8b / 10b code conversion unit 64 according to the present embodiment will be described with reference to FIGS. 12 to 16.

FIG. 12 is a diagram showing an example of a code conversion correspondence table applied to the 8b / 10b code conversion process of the present embodiment. Here, FIG. 12A is a diagram showing an example of the 8b / 10b code conversion correspondence table of the TMDS method, and is a conversion for converting an 8-bit code from 128 to 159 in decimal to a 10-bit code. It is a table. FIG. 12B is a diagram showing an example of the 8b / 10b code conversion correspondence table of the present embodiment corresponding to the 8b / 10b code conversion correspondence table of the TMDS method.

In addition, according to the above-mentioned running disparity (RD), the code to be selected when RD is plus (+) is indicated as "RD-" on the table, and the code to be selected when RD is minus (-) is indicated. It is indicated as "RD +" on the table. Furthermore, the number of bit transitions is shown as "BT". In this table, BT is shown when the same code is consecutive before and after the code, but in reality, the value of BT may differ depending on the code before and after.

Generally, when calculating BT of 10-bit code for all codes (0 to 255 in decimal number), BT is from 0 times to 6 times at maximum, but BT appears 4 times most frequently. (See FIG. 12 (A)). Therefore, as shown in FIG. 12B, the 8b / 10b code conversion process to which the TMDS method of the present embodiment is applied is a process of aligning (unifying) the BT of the 10-bit code to the mode of 4 times. Execute.

In the present embodiment, the BTs are set to the mode, but the average value or the median value (MEDIAN) of all BTs may be used. The smaller the BT value to be aligned, the lower the electromagnetic radiation level, and the more effective the screen eavesdropping countermeasure is. On the other hand, when the code conversion process is performed for the purpose of preventing electromagnetic information leakage, the deterioration of the original image increases as the number of codes to be converted increases. Therefore, it is necessary to determine the optimum value for which BT should be adjusted in consideration of these balances.

As shown in FIG. 12 (B), in FIG. 12 (A), the code in which BT is 4 is not subjected to code conversion and is the same code (for example, 131 in decimal). On the other hand, in FIG. 12A, for a code having a BT of 2, 6 or the like (for example, 128-130,132,135,139,141-144,147,149-151,153-158 in decimal), the line closest to this code in the table and By substituting with a code having a BT of 4, the process of adjusting the BT of the code to 4 is performed. By such code conversion, which code corresponds to the original image code is shown in the “decimal” column of FIG. 12 (B).

FIG. 13 is a diagram for explaining the 8b / 10b code conversion process to which the above-mentioned TMDS method is applied, and shows how an example of a code in the table shown in FIG. 12 (A) is replaced with another code. It is shown schematically. As an example, the 10-bit code obtained by converting 147 8-bit codes (10010011) into 8b / 10b in decimal notation is the same code (1110001010) for both RD- and RD +, but its BT is 6 times. Therefore, in the 8b / 10b code conversion process of the present embodiment, the BT of the 10-bit code is replaced with the code of 4 times, which is the mode. In this case, when searching for a code in which BT is 4 times in the line closest to the code, the conversion code of 146 in decimal (0001110011) and the conversion code of decimal 148 (0001110011) are equivalent for RD-. To do. For RD +, 146 conversion codes (1110001110) in decimal and 148 conversion codes (1110011110) in decimal correspond. In this way, when the two codes correspond, either one can be selected, so the rule should be such that one is selected.
In this embodiment, it is always replaced with a code (decimal number smaller code) at the upper part of the table. Therefore, the conversion code of 147 8-bit code (10010011) in decimal notation is replaced with the conversion code of 146 in decimal in the case of RD-, and the conversion code of 146 in decimal in the case of RD +. Replaced with (1110001110) (process 130). In addition, FIG. 13 shows how the code replacement process according to such a rule is applied to other cases as well.

FIG. 14 is a diagram showing an example of a code conversion correspondence table when the above-mentioned IBM method is applied in the 8b / 10b code conversion process of the present embodiment. FIG. 14A shows an example of the 8b / 10b code conversion correspondence table of the IBM method. FIG. 14B is a diagram showing an example of the 8b / 10b code conversion correspondence table of the present embodiment corresponding to the 8b / 10b code conversion correspondence table of the IBM method. Further, FIG. 15 is a diagram for explaining an 8b / 10b code conversion process to which the IBM method is applied.

The procedure and method to which the IBM method of the present embodiment is applied are the same as those to which the TMDS method described with reference to FIGS. 12 and 13 described above is applied. Here, in the IBM method 8b / 10b code conversion, when the BT of the 10-bit code is calculated for all the codes, the BT is from a minimum of 4 times to a maximum of 10 times, but BT appears most frequently. This is the case of 6 times. Therefore, the 8b / 10b code conversion process to which the IBM method of the present embodiment is applied executes a process of aligning (unifying) the BT of the 10-bit code to the mode of 6 times.

In FIG. 14A, the code having a BT of 4, 8 or the like (for example, 130-133,135,137,138,142,145,149,150,154,156,158,159 in decimal) is the code closest to this code in the table and has a BT of 6. Is replaced with the code, so that the BT of the code is adjusted to 6. By such code conversion, which code corresponds to the original image code is shown in the “decimal” column of FIG. 14 (B). Further, as shown in FIG. 15, the conversion code of 149 8-bit codes (10010101) in decimal notation is replaced with the conversion code of 148 in decimal notation (00010110010) in the case of RD-, and in the case of RD +. Replace with 148 conversion codes (0010111101) in decimal (process 150).

FIG. 16 is a flowchart illustrating a procedure for creating a code conversion table and conversion rules in the 8b / 10b code conversion process by the 8b / 10b code conversion unit 64 of the present embodiment.

The 8b / 10b code conversion unit 64 acquires image data for one pixel of each N bit (here, N = 8) of R, G, and B (step S30). Next, an 8b / 10b code conversion table is created for all 8-bit codes based on, for example, the TMDS method 8b / 10b code conversion rule (step S31). As a result, the 8b / 10b code conversion table corresponding to the TMDS method 8b / 10b code conversion correspondence table as shown in FIG. 12 (A) is held (step S33). The 8b / 10b code conversion unit 64 calculates and adds the bit transition number BT of the 10-bit code after the 8b / 10b code conversion to the 8b / 10b code conversion table (step S32).

Next, the 8b / 10b code conversion unit 64 calculates the most frequently appearing bit transition number (BTmax) in the 8b / 10b code conversion table (step S34). Here, for example, the number of most frequent bit transitions is 4 (see FIG. 12A). The 8b / 10b code conversion unit 64 is the most frequent bit transition number (BTmax) from the beginning (M = 1) of the 10-bit code corresponding to the 8-bit code arranged in ascending order in the 8b / 10b code conversion table. Whether or not it is determined (steps S35 and S36). If the determination result is applicable, the determination process for the next (M = M + 1) 10-bit code is performed (Yes, S38 in step S35). This determination process is repeated until the end (M = 257), and the process ends (step S39).

On the other hand, the 8b / 10b code conversion unit 64 searches the 8b / 10b code conversion table for the 10-bit code in which the BT is, for example, 2, 6 or the like, and searches for the M-th closest 10-bit code. The bit code is tentatively set to the M + α th (step S37). Here, if there are two minimum αs of the government, the negative one is selected. Next, the 8b / 10b code conversion unit 64 replaces the M-th 10-bit code with the M + α-th 10-bit code (step S40).

As described above, the 8b / 10b code conversion unit 64 performs the 10-bit code BT at the most frequent value by the processing from steps S35 to S40 based on the 8b / 10b code conversion table held in step S33. For example, a process of aligning (unifying) four times is executed, and an 8b / 10b code conversion table as shown in FIG. 12B, for example, is generated (step S41).

Although the process of creating an 8b / 10b code conversion table to which the TMDS method 8b / 10b code conversion rule is applied has been described with reference to FIG. 16, for example, when the IBM method 8b / 10b code conversion rule is applied. Is the same.

In short, according to the present embodiment, when the 8b / 10b code conversion method is applied, the number of bit transitions is aligned with the number of most frequent bit transitions instead of the 8b / 10b code conversion table based on the existing conversion rules ( The 8b / 10b code conversion process can be executed using the 8b / 10b code conversion table that has been processed (unify) (process to make the number of bit transitions uniform). Therefore, since the number of bit transitions (BT) can be made uniform in the three-color image codes of R, G, and B transmitted serially or in parallel, the electromagnetic radiation level can be made uniform and screen reproduction due to electromagnetic leakage can be prevented. Can be done. That is, it is possible to prevent reproduction by electromagnetic screen voyeurism (voyeurism).

Here, the total value of the total number of bit transitions obtained by combining the codes of all R, G, and B is, for example, 12 (4 × 3) times in the TMDS method 8b / 10b conversion and 18 (6) in the IBM method 8b / 10b conversion. It is also possible to align each pixel at x3) times. In this case, since the number of combinations of R, G, and B increases, the scale of the code conversion table becomes large, but the number of codes to be replaced with another code can be reduced, so that the deterioration of the image quality of the original image is minimized. It can be suppressed.

Depending on the type and method of the image interface, 8b / 10b code conversion may be performed on the original image signal, and the image signal may be transmitted in parallel using multiple transmission lanes, and the frame format at that time also varies. Is. In such a case, for example, when 8b / 10b code conversion is performed, it is necessary to replace the lower bits of the original image signal so that the number of bit transitions of the 10-bit code after the code conversion is kept the same. is there. In code conversion such as 8b / 10b code conversion, the correspondence rule between the code of the original image signal and the code after conversion is determined. Therefore, the conversion rule of the original image signal is based on the code conversion correspondence table. Can be set. If the number of bit transitions after code conversion is kept the same in this way, the radiant intensity of the leaked electromagnetic wave can be increased even when parallel transmission is performed in a plurality of transmission lanes or in any frame format. Since it does not change for each pixel, it is possible to prevent reproduction of the leaked image.

The present invention is not limited to each of the above embodiments as it is, and at the implementation stage, the components can be modified and embodied within a range that does not deviate from the gist thereof. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in each of the above embodiments. For example, some components may be removed from all the components shown in each embodiment. In addition, components from different embodiments may be combined as appropriate.

10,60 ... Electronic equipment, 11,61 ... Processor (CPU),
12, 62 ... Image acquisition unit, 13, 63 ... Image conversion unit, 14 ... Image display unit,
15,67 ... Storage device, 16,66 ... Display,
64 ... 8b / 10b code conversion unit, 65 ... image display unit.

Claims (10)

It is an electromagnetic information leakage prevention method executed by electronic devices that process image signals.
Processing to acquire image coding information corresponding to a plurality of pixels constituting the original image of the display screen, and
A process of executing the code conversion of the original image for each pixel so that the frequency of the code change of each bit of the image coding information is constant.
And outputting the more picture coding information obtained in the process of executing the code conversion,
The execution,
The process of executing the code conversion is
In the image coding information represented by a plurality of bits for each pixel constituting the original image, a process of calculating the total value of the number of bit transitions for each pixel, and
A process of inverting or maintaining the lower bits of the image coding information so that the calculated total value is leveled to a predetermined value.
Electromagnetic information leakage prevention methods including. It is an electromagnetic information leakage prevention method executed by electronic devices that process image signals.
Processing to acquire image coding information corresponding to a plurality of pixels constituting the original image of the display screen, and
A process of executing the code conversion of the original image for each pixel so that the frequency of the code change of each bit of the image coding information is constant.
And outputting the more picture coding information obtained in the process of executing the code conversion,
The execution,
The process of executing the code conversion is
In image coding information in which each of the plurality of pixels constituting the original image consists of the number of bits (3n) of each n (n is an integer of 2 or more) bits of R, G, and B, the number of bit transitions for each pixel. And the process of calculating the total value of
The process of inverting or maintaining the lower bits of each of the n bits so that the total value is leveled to the smallest integer value N exceeding 3n / 2.
Electromagnetic information leakage prevention methods including. It is an electromagnetic information leakage prevention method executed by electronic devices that process image signals.
Processing to acquire image coding information corresponding to a plurality of pixels constituting the original image of the display screen, and
A process of executing the code conversion of the original image for each pixel so that the frequency of the code change of each bit of the image coding information is constant.
And outputting the more picture coding information obtained in the process of executing the code conversion,
Image coding information in which each of the plurality of pixels constituting the original image consists of the number of bits (3n) of each n (n is an integer of 2 or more) bits of R, G, and B is based on a predetermined code conversion rule. The n / m conversion process that converts each pixel into image coding information consisting of the number of bits (3 m) of m bits, and
And
The process of executing the code conversion is
A process of calculating the number of bit transitions for the m-bit image coding information converted by the n / m conversion process, and a process of calculating the number of bit transitions.
The process of calculating the mode among the calculated number of bit transitions and
A process of changing the image coding information of the m bits so that the calculated number of bit transitions becomes uniform to the mode.
Electromagnetic information leakage prevention methods including. It is an electromagnetic information leakage prevention method executed by electronic devices that process image signals.
Processing to acquire image coding information corresponding to a plurality of pixels constituting the original image of the display screen, and
A process of executing the code conversion of the original image for each pixel so that the frequency of the code change of each bit of the image coding information is constant.
And outputting the more picture coding information obtained in the process of executing the code conversion,
Image coding information in which each of the plurality of pixels constituting the original image consists of the number of bits (3n) of each n (n is an integer of 2 or more) bits of R, G, and B is based on a predetermined code conversion rule. The n / m conversion process that converts each pixel into image coding information consisting of the number of bits (3 m) of m bits, and
And
The process of executing the code conversion is
For the image coding information of each pixel, a process of calculating the number of bit transitions (BT) for the m-bit image coding information converted by the n / m conversion process, and a process of calculating the number of bit transitions (BT).
The process of calculating the number of most frequent bit transitions (BTo) among the calculated number of bit transitions (BT), and
In the converted m-bit image coding information, if the calculated number of bit transitions (BT) matches the number of most frequent bit transitions (BTo), the numerical value of the code is maintained and is different. In the case, the image coding information that matches the number of bit transitions (BTo) and has the closest numerical value of the n-bit image coding information before code conversion is searched for, and the searched m-bit image code is searched. The process of replacing the numerical value of the above code with the numerical value of the conversion information,
Electromagnetic information leakage prevention methods including. The process of executing the code conversion is
The replacement process includes a process of creating an n / m conversion table in which the number of bit transitions is made uniform to the number of bit transitions (BTo) of the highest frequency.
Using the n / m conversion table, the n / m conversion process is executed.
The method for preventing electromagnetic information leakage according to claim 4. An electromagnetic information leakage prevention device applied to electronic devices that process image signals.
A means for acquiring image coding information corresponding to a plurality of pixels constituting the original image of the display screen, and
A means for performing code conversion of the original image for each pixel so that the frequency of code change of each bit of the image coding information is constant.
And means for outputting the more picture coding information obtained means for performing the code conversion,
Equipped with
The means for performing the code conversion is
In the image coding information represented by a plurality of bits for each pixel constituting the original image, a means for calculating the total value of the number of bit transitions for each pixel, and
A means for inverting or maintaining the lower bits of the image coding information so that the calculated total value is leveled to a predetermined value.
Electromagnetic information leakage prevention device including. An electromagnetic information leakage prevention device applied to electronic devices that process image signals.
A means for acquiring image coding information corresponding to a plurality of pixels constituting the original image of the display screen, and
A means for performing code conversion of the original image for each pixel so that the frequency of code change of each bit of the image coding information is constant.
And means for outputting the more picture coding information obtained means for performing the code conversion,
Equipped with
The means for performing the code conversion is
In image coding information in which each of the plurality of pixels constituting the original image consists of the number of bits (3n) of each n (n is an integer of 2 or more) bits of R, G, and B, the number of bit transitions for each pixel. Means to calculate the total value of
Means for inverting or maintaining the lower bits of each of the n bits so that the total value is leveled to the smallest integer value N greater than 3n / 2.
Electromagnetic information leakage prevention device including. An electromagnetic information leakage prevention device applied to electronic devices that process image signals.
A means for acquiring image coding information corresponding to a plurality of pixels constituting the original image of the display screen, and
A means for performing code conversion of the original image for each pixel so that the frequency of code change of each bit of the image coding information is constant.
And means for outputting the more picture coding information obtained means for performing the code conversion,
Image coding information in which each of the plurality of pixels constituting the original image consists of the number of bits (3n) of each n (n is an integer of 2 or more) bits of R, G, and B is based on a predetermined code conversion rule. The n / m conversion means for converting each pixel into image coding information consisting of the number of bits (3 m) of m bits, and
Equipped with
The means for performing the code conversion is
A means for calculating the number of bit transitions to the image coding information of m bits converted by the n / m conversion means, and a means for calculating the number of bit transitions.
A means for calculating the mode among the calculated number of bit transitions, and
A means for changing the image coding information of the m-bits so that the calculated number of bit transitions becomes uniform to the mode, and
Electromagnetic information leakage prevention device including. An electromagnetic information leakage prevention device applied to electronic devices that process image signals.
A means for acquiring image coding information corresponding to a plurality of pixels constituting the original image of the display screen, and
A means for performing code conversion of the original image for each pixel so that the frequency of code change of each bit of the image coding information is constant.
And means for outputting the more picture coding information obtained means for performing the code conversion,
Image coding information in which each of the plurality of pixels constituting the original image consists of the number of bits (3n) of each n (n is an integer of 2 or more) bits of R, G, and B is based on a predetermined code conversion rule. The n / m conversion means for converting each pixel into image coding information consisting of the number of bits (3 m) of m bits, and
Equipped with
The means for performing the code conversion is
With respect to the image coding information of each pixel, a means for calculating the number of bit transitions (BT) with respect to the image coding information of m bits converted by the n / m conversion means, and a means for calculating the number of bit transitions (BT).
A means for calculating the frequency of bit transitions (BTo) among the calculated number of bit transitions (BT), and
In the converted m-bit image coding information, if the calculated number of bit transitions (BT) matches the number of most frequent bit transitions (BTo), the numerical value of the code is maintained and is different. In the case, the image coding information that matches the number of bit transitions (BTo) and has the closest numerical value of the n-bit image coding information before code conversion is searched for, and the searched m-bit image code is searched. A means for replacing the numerical value of the above-mentioned code with the numerical value of the conversion information,
Electromagnetic information leakage prevention device including. Electromagnetic information leakage prevention program causing a computer to function as each processing that is executed by electromagnetic information leakage prevention method according to any one of claims 1 to 5.

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