JP5526195B2 - Image display apparatus and gradation conversion method - Google Patents

Description

  The present invention relates to an image display apparatus and a gradation conversion method that make watermark display in an electronic document, an image, etc. inconspicuous.

  Image display devices (monitors) are not only used in offices and homes, but are also used in various specialized fields such as graphic design and medical treatment. The image display device is mainly used by being connected to a personal computer (PC), and displays various electronic data such as an electronic document and an image.

  Various electronic data such as electronic documents and images (hereinafter referred to as electronic documents) are available in word format (Word is a Microsoft product name), PDF format (Portable Document Format developed and proposed by Adobe Systems), TIFF format (Microsoft and It is created in various data file formats such as Tagged Image File Format) developed and proposed by Adobe Systems.

  These electronic documents are given stamp notations such as “CONFIDENTIAL”, “confidential”, “confidential”, “copy prohibited”, “sample”, etc., depending on the nature of the document such as confidentiality. Such electronic documents are usually protected for security reasons so that the documents are not tampered with. FIG. 7 exemplifies an electronic document 201 with a watermark display. A “sample” character is overlaid on a character in the document to form a watermark display 301. Depending on the application software, this watermark display may be referred to as a stamp display. In this specification, a display overlaid on characters in a document is generally referred to as a watermark display. When the electronic document 201 is printed, the watermark display 301 is usually lifted, emphasized, and displayed darkly. On the other hand, when an electronic document or the like is displayed as an image on a known image display device, it often happens that it is difficult to read the character 401 where the watermark display 301 overlaps.

  As a countermeasure against the above phenomenon, for example, if the background color of the background 501 of the electronic document 201 is white (255 gradation) and the character color of the character 401 of the electronic document 201 is black (0 gradation), The color of the character 401 and the color of the watermark display 301 are made different so that the character color of the watermark display 301 is red. However, it is not so much improved that the character 401 is difficult to read. Further, when an electronic document 201 with a watermark display as shown in FIG. 7 is displayed on a known image display device (monitor), if the image quality adjustment for changing the display gradation is performed on the monitor side, the watermark display is performed. The gradation difference between the gradation of 301 and the gradation of the character 401 becomes small, and conversely to the intention (intention to make the character easy to see), a situation may occur where the character 401 becomes extremely unclear.

  As a measure for making the characters easy to see, it is not impossible to process the watermark display 301 itself by using image processing software dedicated to image processing. Since 201 will be falsified, it is not realistic.

  As an image processing apparatus for processing a document image, for example, Patent Documents 1-3 are publicly known.

Patent Document 1 relates to a color copying machine, in order to improve the reproducibility of the background color of the original image (white of the original paper), prescan the color original to be read, input R, G, B signals, and count the histogram. The circuit counts the appearance frequency of the input R, G, B signals, extracts a combination of RGB values having the maximum appearance frequency from the histogram, and based on the extracted R, G, B values, R, G of the color document , B signal is described as non-linear transformation.
Patent Document 2 relates to a color copying machine, and in order to improve the reproducibility of the background color of the original image (white of the original paper) when the characters are thinned to reduce the show-through of the original, the color image that is input The document describes that the density distribution of the document is calculated based on the data, the background density level of the document is calculated based on the data, the density conversion table is created, and the image density of the input color image data is converted. .
Patent Document 3 relates to a color copying machine, in order to reduce the show-through of an original, obtains a gradation range of an unnecessary image portion for each color component from gradation data of all pixels of an input image, and based on this gradation range. The removal gradation condition for each color component is set, and for each pixel of the input image, a pixel satisfying this removal gradation condition for all color components is determined as the removal pixel, and the gradation of the removal pixel is zero (original paper In white).

  That is, in Patent Documents 1-3, the gradation of unnecessary portions such as show-through is set to zero (white of the original paper) in order to make the original easy to see and copy.

JP 05-063968 A Japanese Patent Laid-Open No. 11-187266 JP 2001-094804 A

  However, as described above, the image display apparatus (monitor) performs image quality adjustment such as gamma correction (γ correction), and the gradation 255 of the original image may be smaller than 255 in the display image. For this reason, in the case of a copying machine, “show-through” can be removed by setting the gradation to zero, but it cannot be sufficiently removed by a monitor in a state where image quality adjustment such as γ correction is performed.

  In addition, the monitor is used in connection with a PC, and various electronic data such as electronic documents and images may be displayed in a so-called multi-window, and if a predetermined gradation or less is uniformly converted as in the prior art. This may affect electronic documents and images of windows that are not originally related, and may cause a bad effect of deteriorating appearance. The watermark display usually has a color such as red, and the image quality is different from the show-through of the document.

  Accordingly, an object of the present invention is to reduce the watermark display without falsifying the electronic document or the like when displaying the electronic document or image or the like with a watermark display on the image display device. A display device and a gradation conversion method are provided.

An image display apparatus according to the present invention includes a tone conversion unit capable of converting an input tone of an image input signal into an output tone value different for each input tone value, and an output tone value in the tone conversion unit. A control circuit for rewriting is provided, and among the gradation values set in the control circuit, among the gradation values obtained by removing the values at both ends, the input gradation is equal to the gradation value indicating the background of the document image. get the correspondence was output tone values, the acquisition of all the gradation values equal to the input floor output grayscale value associated with the tone of a predetermined width including a gradation value that indicates the watermark display of the document image a gradation value close to the output tone values associated with the gray-scale value equal to the input gradation that indicates the base of the same gradation value or the acquired output tone value the document image than the output tone value replacement, characterized in that it is configured to reduce the watermark display.

  According to the present invention, it is possible to perform gradation conversion limited to the gradation to be removed.

  In the present invention, for example, the image is a document image, the one set gradation value is a gradation for displaying a background of the document image, and the other set gradation value is a floor for displaying the background of the document image. The gradation value is within the range of the gradation and the gradation for displaying the character. According to the present invention, it is possible to suppress the influence on other regions and windows as much as possible while reducing unnecessary display without falsifying an electronic document or the like.

  In the present invention, for example, the image is a document image including a watermark image, the one set gradation value is a gradation for displaying a background of the document image, and the other set gradation value is a watermark image. The gradation value is within the range of the gradation to be displayed. According to the present invention, it is possible to suppress the influence on other regions and windows as much as possible while reducing watermark display without falsifying an electronic document or the like.

  The gradation converting means is a mechanism capable of converting the input gradation of the image input signal into an output gradation value that differs for each input gradation value, and more specifically, uses a lookup table (LUT). LUT is an abbreviation for Look Up Table, and is an output gradation allocation table for input gradations. For example, the LUT has 256 data storage numbers for 256 gradations. In this LUT, an output gradation for each input gradation is created in advance, and gradation conversion is performed by referring to the LUT. For example, data that can be calculated in advance is calculated in advance, and the value is stored in the LUT.

  Here, the fact that the output gradation value associated with the watermark gradation value of the gradation converting means is the same as or close to the background output gradation value is the background of the electronic document or the like. Points to the correct value. For example, if the background of the electronic document or the like is white, if the gradation value is 255, the background output gradation value is the same value. For example, if the gradation value is set to a value within the range of 200 to 254, the value is close to the background output gradation value.

  The background gradation value as the background of the electronic document or the like uses a fixed value set in advance, or is calculated by a processing circuit or a processing program in the image display device, or the user visually recognizes the display screen. Then, it is determined by operating an operation menu on the display screen or an operation button of the image display device. Similarly, for the watermark gradation value to be displayed as a watermark, a preset fixed value is used, or it is calculated by a processing circuit or a processing program in the image display device, or the user visually recognizes the display screen. Then, it is determined by operating an operation menu on the display screen or an operation button of the image display device.

  The background gradation value is set within a predetermined range. Examples of the pinpoint value include a gradation value that can be easily used as a watermark display. For example, an output gradation value associated with the watermark gradation value can be set as a fixed value. Examples of the fixed value include 205, 210, 215, 220, 225, 230, and the like.

In the present invention, when the watermark gradation value, the background gradation value, and the output gradation value associated with the watermark gradation value are input to the control circuit, the control circuit It is preferable to replace the output tone value associated with the value with the background output tone value.
According to the present invention, a watermark gradation value that is a watermark display of the electronic document or the like is automatically acquired without bothering the user, which is easy to use. In order to cope with the multi-window, a window area for displaying the electronic document or the like is designated, and the gradation conversion of the present invention is performed only in that area.

The gradation conversion method of the present invention includes a gradation conversion unit capable of converting an input gradation of an image input signal into an output gradation value different for each input gradation value, and an output gradation value in the gradation conversion unit. In the image display device having the control circuit for rewriting the tone value, the tone value indicating the background of the document image among the tone values obtained by removing the values at both ends from those values in the plurality of tone values set in the control circuit If equal acquires the output grayscale value associated with the input tone, the document image output tone associated with the gray scale value equal to the input grayscale of a predetermined width including a gradation value that indicates the watermark display all the acquired output gradation value equal gradation value or the acquired than the output gradation value indicating the background of the document image gradation value equal to the input gradation in correspondence was output tone value of the value It is characterized in that the watermark display is reduced by replacing with a gradation value close to.

  According to the present invention, gradation conversion can be performed only for gradations to be removed by using a computer connected to an existing image display device or using a built-in computer.

  A watermark display reduction program to which the gradation conversion method of the present invention is applied is installed in a control circuit having a computer function in the image display device or a peripheral mechanical unit having a computer function, or the image display device. It is installed on a computer connected to and used. The display reduction program is installed via a medium such as a USB memory or a CD-ROM, or is downloaded and installed using a network line such as the Internet or an intranet. Here, the program indicates a programmed command and includes software and firmware.

  The image display apparatus to which the present invention is applied only needs to have an image display panel or an image display unit such as a cathode ray tube or a CRT. Examples of the image display panel include a liquid crystal display panel, an organic electroluminescence display panel, and a plasma display panel.

  The gradation converting means is provided before the image quality adjustment circuit that adjusts the image quality such as contrast, brightness, brightness, and gamma correction, or is provided after the image quality adjustment circuit.

An image display apparatus according to the present invention includes an image quality adjustment circuit that adjusts image quality such as contrast, brightness, brightness, and gamma correction, and the gradation conversion unit is provided in a stage preceding the image quality adjustment circuit. .
The gradation conversion method of the present invention is characterized in that the watermark display is reduced before the image quality such as contrast, brightness, brightness, and gamma correction is adjusted.

  According to the present invention, since the watermark display of the electronic document or the like is image-processed without being influenced by the image quality adjustment circuit, there is no possibility that the gradation difference between the watermark display and the character in the electronic document or the like is eliminated. And there is no worry of affecting the electronic document, image, etc. of the window which is not related originally.

  The output gradation value associated with the watermark gradation value is set as a pinpoint or within a predetermined range. Examples of the pinpoint value include a gradation value that can be easily used as a watermark display, and an output gradation value associated with the watermark gradation value can be set as a fixed value in advance. Examples of the fixed value include 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 254, and 255.

  For example, in an electronic document that is stamped on paper paper as “confidential” with vermilion, and then scanned and converted with a scanner or the like, vermilion shades, blurring, and uneven color occur, resulting in multiple gradations in the watermark display. Will be included. Further, depending on the scanning conditions when creating the electronic document, the watermark display may include a plurality of gradations.

  The image display device of the present invention assumes that the watermark gradation value is a gradation value having a predetermined width, and the output gradation value associated with the watermark gradation value is the same as or close to the background output gradation value. It is good also as a structure replaced with a value. According to this configuration, even when the watermark display includes a plurality of gradations, or even if there is a reading error in the output gradation value associated with the watermark gradation value, the watermark display is It will reduce more reliably.

  The gradation value of the predetermined width is an output gradation value associated with the watermark gradation value, and uses a preset fixed value, or by a processing circuit or a processing program in the image display device. It is calculated or determined by the user viewing the display screen and operating an operation menu on the display screen or an operation button of the image display device. For example, a user may operate a slider or a knob on the display screen while visually recognizing the display screen, or the user may specify an area using a mouse.

  As the gradation value of the predetermined width, a value in a predetermined range including a gradation value that is easily used as a watermark display can be adopted, and a predetermined width can be set. Examples of the fixed width value include 200 to 210, 205 to 225, 210 to 230, 220 to 240, 225 to 250, 225 to 254, 225 to 255, and the like.

  In the image display device of the present invention, for example, the output gradation value associated with the watermark gradation value is set to 1 or more and 254 or less. According to this configuration, the output gradation value associated with the watermark gradation value is set to 1 or more and 254 or less so that it does not overlap with the black of the zero gradation and the white of 255 gradations. Therefore, it is difficult to cause a sense of incongruity so that the watermark display of the electronic document can be completely seen through.

  In the present invention, a histogram of an input image is calculated from the electronic document as an output gradation value associated with the watermark gradation value, and a gradation value estimated based on the calculated histogram is used. it can. In other words, the present invention can calculate a histogram of an input image from the electronic document or the like, and estimate an output gradation value associated with the watermark gradation value based on the calculated histogram. According to the present invention, for example, a window region for displaying the electronic document or the like is designated, and it is easy to deal with multi-windows such as performing gradation conversion of the present invention only in that region.

  According to the present invention, the output tone value associated with the watermark tone value among the output tone values of the tone converting means is replaced with a value that is the same as or close to the background output tone value, and the signal output Since it is displayed on the screen, gradation conversion can be performed only for the gradation to be removed. Therefore, it is possible to suppress the influence on other regions and windows as much as possible while reducing the watermark display without falsifying the electronic document or the like. According to the present invention, the watermark gradation value that is the watermark display of the electronic document or the like is automatically acquired without bothering the user, which is easy to use. In order to deal with multi-windows, a window area for displaying the electronic document or the like may be designated, and gradation conversion of the present invention may be performed only within that area. In addition, since the watermark display of the electronic document or the like is image-processed without being affected by the image quality adjustment circuit, there is no possibility that the gradation difference between the watermark display and the character in the electronic document or the like is eliminated.

  According to the present invention, there is no fear of affecting an electronic document, an image, or the like of a window that is not originally related. And even if a plurality of gradations are included in the watermark display, the watermark display is more reliably reduced. By setting the output gradation value associated with the watermark gradation value to 1 or more and 254 or less, it does not overlap with the black of the zero gradation on the screen and overlaps with the white of the 255 gradation. Therefore, it is difficult to cause an uncomfortable feeling that the watermark display of the electronic document is completely transparent on the screen and the background can be seen. Further, since the electronic document or the like has not been altered, the watermark is displayed on the printed paper.

  According to the present invention, gradation conversion can be performed only for gradations to be removed by using a computer connected to an existing image display device or using a built-in computer.

It is a block block diagram which illustrates the image display apparatus with a watermark display reduction function of embodiment of this invention. It is a block block diagram which illustrates the image display apparatus using the watermark display reduction program of embodiment of this invention. It is a graph which illustrates the relationship between the conventional input gradation and output gradation. It is a graph which illustrates the relationship between the input gradation and output gradation when performing the gradation conversion of this invention. It is a graph which illustrates the relationship between the input gradation and output gradation when performing the gradation conversion of this invention. It is a figure which illustrates the electronic document when performing the gradation conversion of this invention. It is a figure which illustrates the conventional electronic document.

  Hereinafter, specific embodiments for carrying out the present invention will be described with reference to the drawings.

(Image display device of the present invention)
FIG. 1 is a block diagram illustrating an image display device with a watermark display reduction function according to an embodiment to which the present invention is applied. The image display apparatus 1 according to the present embodiment includes a gradation conversion unit 2 that can convert an input gradation of an image input signal into an output gradation value that differs for each input gradation value, and a control circuit 7 that controls various signals. The image is output from the gradation converting means 2, and the image quality adjustment circuit 51 adjusts the image quality such as contrast, brightness, brightness, and gamma correction, and the image is displayed on the image display panel 52. In the configuration shown in FIG. 1, the gradation converting means 2 is provided in the preceding stage of an image quality adjustment circuit 51 for adjusting image quality such as contrast, brightness, brightness, and gamma correction.

  Examples of the image display panel 52 include a liquid crystal display panel, an organic electroluminescence display panel, and a plasma display panel.

  FIG. 7 exemplifies an electronic document 201 with a watermark display. A “sample” character is overlaid on a character 401 in the document to form a watermark display 301.

  FIG. 3 is a graph illustrating the relationship between the input gradation and output gradation of each of R, G, and B in the conventional image processing apparatus. The horizontal axis of the graph is the input gray scale, and the vertical axis is the output gray scale, which is 0 to 255 gradations, respectively. The character 401 in the document in the electronic document 201 is generally black or a color scheme close to black. If the character 401 is black, the gradation is 0. If the character 401 has a color scheme close to black, the gradation is close to 0. The background 501 in the electronic document 201 is generally white or a color scheme close to white. If the background 501 is white, there are 255 gradations. If the background 501 has a color scheme close to white, the gradation is close to 255. The watermark display (“sample” character) 301 in the electronic document 201 has a gradation represented by the symbol C2. The color scheme of the gradation value C2 is often a light color scheme such as gray or red, and the gradation value C2 that can be easily used as the watermark display 301 is, for example, 205, 210, 215, 220, 225, 230. Etc.

  Conventionally, image display devices (monitors) have been subjected to image quality adjustment such as gamma correction (γ correction), and there are cases where a gradation that is smaller in a display image than in an original image occurs (see FIG. 3). That is, the 255 gradation of the background 501 and the gradation value C2 of the watermark display 301 may be smaller than the 255 gradation or the gradation value C2 in the output gradation.

  The gradation converting means 2 is a mechanism capable of converting the input gradation of the image input signal into different output gradation values for each input gradation value, and more specifically uses a look-up table (LUT). (FIG. 1). An output gradation for each input gradation is created in advance in the LUT, and gradation conversion is performed by referring to the LUT.

  In FIG. 1, the background gradation value (input gradation Z) is input to the control circuit 7 by the background gradation value setting means 3, and the watermark gradation value (input gradation C) is input by the watermark gradation value setting means 4. Is input to the control circuit 7. At the same time, an output gradation value (output gradation value Z) previously associated with the watermark gradation value is input to the control circuit 7 by the output gradation acquisition means 5. Thereafter, the control circuit 7 obtains an output gradation value (output gradation C) previously associated with the set watermark gradation value (input gradation C) to the output gradation changing means 6. Further, replacement with the output gradation value Z is executed. The output signal from the gradation converting means 2 is input to an image quality adjustment circuit 51 that adjusts image quality such as contrast, brightness, brightness, and gamma correction, and an image is displayed on the image display panel 52 by the output signal from the image quality adjustment circuit 51. Is displayed. According to this embodiment, the watermark gradation value corresponding to the watermark display 301 of the electronic document 201 is automatically acquired without bothering the user, which is convenient.

  FIG. 4 is an example of a graph illustrating the relationship between the input gradation and the output gradation when the gradation conversion of the present invention is performed. The watermark display (“sample” character) 301 in the electronic document 201 has a gradation represented by the symbol C2. In the example shown in FIG. 4, the watermark gradation value C2 is pinpointed and replaced with a value that is the same as or close to the background output gradation value. Examples of the pinpoint value include 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 254, and 255. According to the present embodiment, since the watermark gradation value C2 is set as the background gradation value at a pinpoint, the influence on the characters 401 other than the watermark display 301 in the electronic document 201 can be suppressed as much as possible.

  FIG. 5 is another example of a graph illustrating the relationship between the input gradation and the output gradation when the gradation conversion of the present invention is performed. The watermark display (“CONFIDENTIAL” character) 301 in the electronic document 201 has a gradation represented by reference numeral C2, but the watermark display may include a plurality of gradations due to the color scheme. In the example shown in FIG. 5, the output gradation values associated with the watermark gradation values C1 to C3 are assumed to be gradation values having a predetermined width from the gradation values C1 to C3 across the watermark gradation value C2. Is replaced with a value that is the same as or close to the background output gradation value. Examples of the gradation value having the predetermined width include 200 to 210, 205 to 225, 210 to 230, 220 to 240, 225 to 250, 225 to 254, 225 to 255, and the like. According to the present embodiment, even if the watermark display 301 includes a plurality of gradations, the watermark display 301 is more reliably reduced.

  FIG. 6 is a diagram illustrating an electronic document when the gradation conversion of the present invention is performed. The watermark display (“sample” character) 302 in the electronic document 202 after gradation conversion is replaced with a value that is the same as or close to the background output gradation value of the background 501. For example, when the background 501 is white, the watermark display 302 is replaced with the same white color, cream color or light yellow color. Therefore, the watermark display 302 is in a state close to the background 501, and the characters 401 in the area where the watermark display 302 overlaps are easy to read. According to the present embodiment, it is possible to suppress the influence on other regions and windows as much as possible while reducing the watermark display without falsifying an electronic document or an image. In order to cope with the multi-window, for example, a window area for displaying the electronic document or the like is specified, and the gradation conversion of the present invention is performed only in that area. Since the electronic document, the image, etc. are not altered at all, the watermark 301 is displayed on the printed paper.

(Watermark display reduction program of the present invention)
FIG. 2 is a block diagram illustrating an image display apparatus using a watermark display reduction program according to an embodiment to which the present invention is applied. Here, the same reference numerals indicate the same functions, and description thereof will be omitted as appropriate. The watermark display reduction program according to the present embodiment is represented by reference numeral 18 in FIG. The watermark display reduction program 18 is used in the image display apparatus 101 provided with the gradation conversion means 2 capable of converting the input gradation of the image input signal into different output gradation values for each input gradation value. This is used when displaying an image with reduced watermark display. In the configuration shown in FIG. 2, the gradation converting means 2 is provided in the preceding stage of an image quality adjustment circuit 51 that adjusts image quality such as contrast, brightness, brightness, and gamma correction.

  In this embodiment, an image input signal is input to the image display apparatus 101 from a computer 17 connected to the existing image display apparatus 101. In the present embodiment, when the watermark display reduction program 18 is started on the computer 17, the output gradation value associated with the watermark gradation value among the output gradation values of the gradation converting means 2 is output to the background. Replace with a value that is the same as or close to the gradation value.

  In FIG. 2, a background gradation value (input gradation Z) is set by the background gradation value setting step 3 and inputted to the computer 17, and a watermark gradation value (input gradation) is set by the watermark gradation value setting step 4. C) is set and input to the computer 17. At the same time, an output tone value (output tone value Z) previously associated with the watermark tone value is obtained from the tone converting means 2 in the output tone obtaining step 5 and input to the computer 17. Thereafter, in response to a command from the computer 17, an output gradation value (output) associated with the watermark gradation value (input gradation C) in advance is output to the gradation converting means 2 in the output gradation changing step 6. The gradation C) is replaced with the acquired output gradation value Z. The output signal from the gradation converting means 2 is input to an image quality adjustment circuit 51 that adjusts image quality such as contrast, brightness, brightness, and gamma correction, and an image is displayed on the image display panel 52 by the output signal from the image quality adjustment circuit 51. Is displayed. According to the present embodiment, the electronic document 201 can be stored in the computer 17 that is connected to or built in the existing image display apparatus 101 by simply installing the watermark display reduction program 18 without bothering the user 50. Since the watermark display 301 can be reduced, it is easy to use.

  When the watermark display 301 includes a plurality of gradations, for example, the user 50 visually recognizes the display screen 52 and operates an operation menu on the display screen or an operation button of the image display device 101. Alternatively, the user 50 may designate the area using the mouse.

  In the present embodiment, the output gradation value associated with the watermark gradation value does not necessarily need to be replaced with the output gradation value associated with the background gradation value in advance, but corresponds to the watermark gradation value in advance. It may be executed so as to set a gradation value larger than the attached output gradation value.

  In the present embodiment, a histogram of an input image can be calculated from the electronic document 201 as the background gradation value and the watermark gradation value, and the gradation value estimated based on the calculated histogram can be used. This eliminates the troublesome work of setting both gradation values by the user. According to the present embodiment, for example, a window area for displaying an electronic document, an image, or the like is designated, and multi-window handling such as performing gradation conversion of the present invention only in the area is facilitated. The area may be designated by the user using a mouse or the like, or the window area may be estimated from an edge detected from the input image.

  As described above, the present invention is not limited to the embodiment described above. For example, the background gradation value as the background of the electronic document or the like uses a fixed value set in advance, or is calculated by a processing circuit or a processing program in the image display device, or the user can display the display screen. Is determined by operating the operation menu on the display screen or the operation button of the image display device. Similarly, for the watermark gradation value to be displayed as a watermark, a preset fixed value is used, or it is calculated by a processing circuit or a processing program in the image display device, or the user visually recognizes the display screen. Then, it is determined by operating an operation menu on the display screen or an operation button of the image display device.

  In the above description, the gradation converting means has been described as being provided in the preceding stage of an image quality adjustment circuit that adjusts image quality such as contrast, brightness, brightness, and gamma correction, but in conjunction with contrast adjustment and γ value, If the gradation value and the gradation width can be readjusted, it is possible to provide the gradation conversion section after the image quality adjustment circuit. The image quality adjustment circuit may be realized by hardware or may be realized by software. The present invention can be applied to various image display devices such as liquid crystal, organic EL, and plasma. Thus, it goes without saying that the present invention can be modified as appropriate without departing from the spirit of the present invention.

1 image display device of the present invention,
2 gradation conversion means,
3 background gradation value acquisition means (background gradation value acquisition step),
4 watermark gradation value acquisition means (watermark gradation value acquisition step),
5 output gradation acquisition means (output gradation acquisition step),
6 Output gradation changing means (output gradation changing step),
7 Control circuit,
17 computer,
18. A watermark display reduction program of the present invention,
51 Image quality adjustment circuit,
52 Image display panel,
101 Existing image display device

Claims (4)

A gradation conversion unit capable of converting an input gradation of an image input signal into an output gradation value different for each input gradation value; and a control circuit for rewriting the output gradation value in the gradation conversion unit, Output tone value corresponding to the input tone value that is the same as the tone value indicating the background of the document image among the tone values obtained by excluding the values at both ends from the tone values set in the circuit All of the output gradation values associated with the input gradation equal to the gradation value of the predetermined width including the gradation value indicating the watermark display of the document image are the same as the acquired output gradation value The watermark display is reduced by replacing the gradation value with a gradation value closer to the output gradation value associated with the input gradation that is equal to the gradation value indicating the background of the document image than the acquired output gradation value. image display device characterized in that it is configured. Contrast, brightness, lightness, includes an image quality adjustment circuit for adjusting the image quality such as a gamma correction, an image display apparatus according to claim 1, wherein said gradation conversion means in front of the image quality adjustment circuit is provided . Image display comprising gradation conversion means capable of converting input gradation of an image input signal into different output gradation values for each input gradation value, and a control circuit for rewriting the output gradation value in the gradation conversion means In the apparatus, among the plurality of gradation values set in the control circuit, the gradation values obtained by removing the values at both ends from the values are associated with the input gradation equal to the gradation value indicating the background of the document image. and it obtains the output tone value, the document image output floor all output tone values associated with the same input gradation and the gradation value of a predetermined width and the acquired including gradation value indicating the watermark display watermark by replacing the gradation value close to the output tone values associated with the gray-scale value equal to the input gradation that indicates the base of the document image than the same gradation value or the acquired output tone value and tone value A gradation conversion method characterized by reducing display. 4. The gradation conversion method according to claim 3 , wherein the watermark display is reduced at a stage before adjusting image quality such as contrast, brightness, brightness, and gamma correction.

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