JP2004252009A - Display control method, display control device and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display control method capable of realizing a high quality image after enlargement/reduction processing and reducing the data transfer quantity related to frame memory capacity and frame memory when a plurality of images are multiply displayed. <P>SOLUTION: The display control method comprises a process S23 of writing a plurality of image signals into the frame memory, a process S25 of reading the written image signals and a process S31 of compositing the read image signals according to the preset conditions and displaying the composited image signals on the display screen. Therein, prior to the process S23 of writing a plurality of image signals into the frame memory, the position on the display screen of a part of the image signal which becomes undisplayed due to the composition is calculated based on the set conditions (S22), the image signals besides the part corresponding to the calculated position are written into the frame memory (S23) and the written image signals are read (S25) and are cmposited (S31). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a display control method, a display control device, and a display control method for writing a plurality of image signals input from a computer or the like into a frame memory, respectively reading and combining the written image signals, and displaying the combined image signals. The present invention relates to a display device provided with a control device.
[0002]
[Prior art]
When a plurality of images input from a computer or the like are displayed in a multiplexed manner (Picture-In-Picture), the resolution is different for each image and the pixel transfer speed is often different. Therefore, these image signals are temporarily written to a frame memory. After that, it is necessary to read, combine and display. In addition, since a flat panel display such as a liquid crystal display device has a fixed driving frequency, it is necessary to perform a so-called frame rate conversion in which writing is performed in a frame memory at a frequency of an input image and reading is performed at a driving frequency of the display device.
[0003]
In the conventional display control method, for example, as shown in FIG. 7, two input images A and B are written into the frame memory 5 at respective input frequencies, read at the drive frequency of the display device, and read in the composite image. In accordance with the size of each image, each image is enlarged / reduced and then combined and displayed.
In this case, the image to be reduced in the composite image is reduced before writing to the frame memory 5 so that the data transfer amount and the data amount to be written to the frame memory are reduced.
[0004]
[Patent Document 1]
JP-A-08-9343
[Patent Document 2]
Japanese Patent No. 2970592
[Patent Document 3]
JP-A-10-177374
[Patent Document 4]
JP 2001-75552 A
[0005]
[Problems to be solved by the invention]
In the display control method for handling a high-resolution screen as described above, an SDRAM (Synchronous DRAM) is used as a frame memory because the amount of data to be stored is large and the cost is low. In the SDRAM, since the write port and the read port are shared, when a plurality of images are multiplexed and displayed, the data transfer capability becomes a problem.
[0006]
For example, with respect to the transfer capability of a frame memory (about 7000 Mbit / s), in the case of a resolution (1024 × 768 pixels) of a so-called XGA (extended graphics array; a name of a general resolution), writing and reading are performed per screen. Therefore, a transfer capability of 3120 Mbit / s is required, and a transfer capability of 6240 Mbit / s is required for a two-screen display. Further, at the resolution of SXGA (1280 × 1024 pixels), a transfer capability of 5232 Mbit / s is required for writing and reading per screen, and a transfer capability of 10644 Mbit / s is required for two-screen display. There is a problem that the transfer capacity of the data is exceeded.
Regarding the data transfer capability, increasing the data bus width (the number of data terminals) is disadvantageous in terms of cost. On the other hand, to increase the data transfer capability per data terminal, it is necessary to increase the operating frequency. There is a problem that it is technically difficult.
[0007]
As a technique related to the technique described above, Patent Document 1 discloses a video signal conversion device that converts video signals having different specifications into video signals having desired specifications. Patent Literature 2 discloses a video processing method that performs picture-in-picture processing simultaneously with scan conversion. Patent Document 3 discloses an on-screen display system capable of simultaneously displaying a plurality of different images (for example, a bit map, a graphic, a still video image, a still image, a moving image, and a background color image). Have been. Patent Literature 4 discloses an image processing device that performs enlargement / reduction processing of a display image by digital signal processing.
[0008]
The present invention has been made in view of the above-described circumstances, and in the first and second inventions, when multiple images are multiplexed and displayed, a high-quality enlarged / reduced image can be realized. It is an object of the present invention to provide a display control method capable of reducing a data transfer amount related to a capacity and a frame memory.
It is an object of the third and fourth inventions to provide a display control device capable of reducing a frame memory capacity and a data transfer amount related to a frame memory when a plurality of images are multiplexed and displayed.
[0009]
According to the fifth and sixth aspects of the present invention, there is provided a display control device capable of realizing a high-quality enlarged / reduced image when multiple images are multiplexed and displaying, and reducing a frame memory capacity and a data transfer amount related to the frame memory. The purpose is to do.
A seventh object of the present invention is to provide a display control device capable of displaying the boundaries of a plurality of images in a multi-format manner.
In an eighth aspect, an object is to provide a display device including any of the display control devices according to the third to seventh aspects.
[0010]
[Means for Solving the Problems]
A display control method according to a first aspect of the present invention is a display control method for writing a plurality of image signals to a frame memory, reading the written image signals, synthesizing them according to preset conditions, and displaying the synthesized image signals on a display screen. In the method, prior to writing the plurality of image signals into a frame memory, a position on the display screen of a portion of the image signal which is not displayed by being synthesized is calculated based on the condition, and a portion corresponding to the calculated position is calculated. Is written to the frame memory, read out, and synthesized.
[0011]
In this display control method, a plurality of image signals are written in a frame memory, the written image signals are read out, synthesized according to preset conditions, and the synthesized image signals are displayed on a display screen. Prior to writing a plurality of image signals to the frame memory, a position on the display screen of a portion of the image signal which is not displayed due to the combination is calculated based on the set conditions, and a portion corresponding to the calculated position is excluded. The read image signal is written to a frame memory, read, and synthesized.
This makes it possible to realize a display control method that can reduce the frame memory capacity and the data transfer amount related to the frame memory when multiple images are multiplexed and displayed.
[0012]
A display control method according to a second invention is a display control method for writing a plurality of image signals to a frame memory, reading the written image signals, synthesizing them according to preset conditions, and displaying the synthesized image signals on a display screen. In the method, prior to reading out the written image signal from the frame memory, a position on the display screen of a portion of the image signal which is not displayed by the combining is calculated based on the condition, and a portion corresponding to the calculated position is calculated. Is read out from the frame memory and synthesized.
[0013]
In this display control method, a plurality of image signals are written in a frame memory, the written image signals are read out, synthesized according to preset conditions, and the synthesized image signals are displayed on a display screen. Prior to reading out the written image signal from the frame memory, the position on the display screen of the portion of the image signal which is no longer displayed due to the combination is calculated based on the set conditions, and the portion corresponding to the calculated position is excluded. The read image signal is read from the frame memory and synthesized.
[0014]
This makes it possible to realize a display control method that can reduce the amount of data transfer related to the frame memory when multiple images are multiplexed and displayed.
Compared to the first invention, in the second invention, since the data is written in the frame memory without removing the portion that is no longer displayed from the input image, a reduction in the frame memory capacity cannot be expected. However, if the frequencies of a plurality of input images to be combined are different, the scanning position of each image is not synchronized. Therefore, even if the image area to be excluded when writing to the frame memory as in the first invention is set, the effective peak A reduction in the amount of data transfer at the time cannot be expected. In order to solve such a problem, the second invention realizes an effective reduction of the amount of data transfer except for an image area which is not displayed from a plurality of synchronized input images after the frame rate conversion.
[0015]
A display control device according to a third aspect of the present invention writes a plurality of input image signals into a frame memory, reads out the written image signals, combines them according to preset conditions, and displays the combined image signals on a display screen. In a display control device that outputs the plurality of image signals to a frame memory, means for calculating, based on the condition, a position on the display screen of a portion of the image signal that is not displayed by being synthesized, before the plurality of image signals are written into a frame memory; Means for writing an image signal excluding a portion corresponding to the position calculated by the means into the frame memory, wherein the image signal written by the means is read and synthesized.
[0016]
In this display control device, a plurality of input image signals are written in a frame memory, the written image signals are read out, synthesized according to preset conditions, and the synthesized image signals are output to be displayed on a display screen. Prior to writing the plurality of image signals into the frame memory, the calculating unit calculates the position on the display screen of the portion of the image signal that is not displayed due to the combination, based on the set conditions. The writing means writes the image signal excluding the portion corresponding to the position calculated by the calculating means to the frame memory, and reads and synthesizes the image signal written by the writing means.
As a result, it is possible to realize a display control device capable of reducing the frame memory capacity and the data transfer amount related to the frame memory when multiple images are multiplexed and displayed.
[0017]
A display control device according to a fourth aspect writes a plurality of input image signals into a frame memory, reads out the written image signals, combines them according to preset conditions, and displays the combined image signals on a display screen. A display control device for outputting the written image signal from the frame memory, calculating a position on the display screen of a portion of the image signal that is not displayed by combining the image signal based on the condition, Means for reading, from the frame memory, an image signal excluding a portion corresponding to the position calculated by the means, wherein the image signal read by the means is combined.
[0018]
In this display control device, a plurality of input image signals are written in a frame memory, the written image signals are read out, synthesized according to preset conditions, and the synthesized image signals are output to be displayed on a display screen. Prior to reading out the written image signal from the frame memory, the calculating means calculates the position on the display screen of the portion of the image signal that is no longer displayed due to the combination, based on the set conditions. The reading means reads out the image signal excluding the portion corresponding to the position calculated by the calculating means from the frame memory, and combines the read out image signals.
[0019]
This makes it possible to realize a display control device that can reduce the amount of data transfer related to the frame memory when multiple images are multiplexed and displayed.
Compared with the third invention, in the fourth invention, since the data is written in the frame memory without removing the portion that is no longer displayed from the input image, a reduction in the frame memory capacity cannot be expected. However, if the frequencies of a plurality of input images to be combined are different, the scanning position of each image is not synchronized. Therefore, even if an image area to be excluded when writing to the frame memory is set as in the third invention, an effective peak A reduction in the amount of data transfer at the time cannot be expected. In order to solve such a problem, the fourth aspect of the present invention realizes an effective reduction in the amount of data transfer except for an image area which is not displayed from a plurality of synchronized input images after the frame rate conversion.
[0020]
The display control device according to a fifth aspect of the present invention further includes a unit that processes the image signal so as to reduce the image when the image of the input image signal is to be reduced and displayed, the unit performs the processing. An image signal is written in the frame memory.
[0021]
In this display control device, when the image of the input image signal is to be displayed in a reduced size, the processing means processes the image signal to reduce the image, and stores the processed image signal in the frame memory. Write.
As a result, when multiple images are multiplexed and displayed, a high-quality reduced image can be realized, and a display control device that can reduce the frame memory capacity and the data transfer amount related to the frame memory can be realized.
[0022]
The display control device according to a sixth aspect of the present invention further comprises means for processing the image signal to enlarge the image when the image of the image signal read from the frame memory is to be enlarged and displayed, Is characterized in that it is intended to combine the processed image signals.
[0023]
In this display control device, when the image of the image signal read from the frame memory is to be displayed enlarged, the processing means processes the image signal so as to enlarge the image, and synthesizes the image signal with the processed image signal. I do.
As a result, when multiple images are multiplexed and displayed, a high-quality enlarged processed image can be realized, and a display control device capable of reducing the frame memory capacity and the data transfer amount related to the frame memory can be realized.
[0024]
A display control device according to a seventh aspect of the present invention includes a means for calculating a position on the display screen of a boundary portion where the plurality of image signals are synthesized and overlapped, and outputs a predetermined image signal corresponding to the position calculated by the means. Means for displaying a predetermined image signal output by the means at the position.
[0025]
In this display control device, the calculating means calculates a position on the display screen of a boundary portion where a plurality of image signals are synthesized and overlapped, and the outputting means outputs a predetermined image signal corresponding to the calculated position. Then, the output predetermined image signal is displayed at the calculated position.
When any one of the two image signals is enlarged and synthesized, as shown in FIG. 8, new pixels c0 to c2 are created and inserted by interpolation based on the original pixels a0 to a2 and b0 to b2. In the vicinity of the boundary, the pixels a3 to a5 to be used for interpolation are removed as the pixels in the pixel extraction region V, so that new pixels c3 to c5 cannot be created, and the pixels near the boundary are not displayed. There is a problem.
However, according to the seventh aspect of the invention, it is possible to realize a display control device capable of displaying the boundaries of the plurality of images in multiple appearances.
[0026]
A display device according to an eighth aspect of the present invention includes the display control device according to any one of claims 3 to 7, and a display unit that displays an image signal output by the display control device.
[0027]
In this display device, the display means displays the image signal output by the display control device according to any one of claims 3 to 7, so that when a plurality of images are multiplexed and displayed, the frame memory capacity and the frame memory are limited. A display device capable of reducing the amount of related data transfer can be realized.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings showing the embodiments.
Embodiment 1 FIG.
FIG. 1 is a block diagram illustrating a main configuration of a display control method, a display control device, and a display device according to a first embodiment of the present invention. In this display device, a plurality of (here, two) input image signals A and B are given to the reduction filter 3, and the reduction filter 3 outputs the image signals A and B in accordance with an instruction from the control unit 7. The image signals A and B are processed so that the image is reduced. The image signals A and B for which there is no instruction for reduction are passed without processing.
[0029]
The input image signals A and B are also provided to the input image state detection unit 4, and the input image state detection unit 4 detects the states of the image signals A and B, and notifies the control unit 7 of the result. .
The image signals A and B output from the reduction filter 3 are supplied to a frame memory control unit 6, which processes the image signals A and B according to an instruction from the control unit 7, and Write to each. The frame memory control unit 6 reads out the written image signals A and B from the frame memory 5 according to an instruction from the control unit 7 and supplies the read image signals A and B to the enlargement filter 8.
The enlargement filter 8 processes the image signals A and B according to an instruction from the control unit 7 so that the images of the image signals A and B are enlarged. The image signals A and B for which there is no instruction for enlargement are passed without processing.
[0030]
The image signals A and B output from the enlargement filter 8 are provided to a synthesis processing unit 9.
The frame image creation unit 10 creates a frame image signal that indicates the boundary between the image signals A and B when the image signals A and B are combined according to an instruction from the control unit 7, and supplies the frame image signal to the combination processing unit 9.
The synthesizing unit 9 synthesizes the supplied image signals A and B and the frame image signal in accordance with an instruction from the control unit 7 and supplies the synthesized image signal to the display unit 2. The display unit 2 has a display screen, and displays a given image signal on the display screen.
The control unit 7 provides an instruction signal to each unit described above according to the conditions set by the operation unit 11.
Of the above-described units, each unit except the display unit 2 constitutes the display control device 1.
[0031]
Hereinafter, the operation of the display device having such a configuration will be described with reference to the flowchart of FIG. 2 showing the operation.
The control unit 7 first sets the display order (front or background) of the input image signals A and B on the display screen of the display unit 2 as shown in FIG. (S20). Next, it is determined whether or not the image of the image signals A and B should be reduced (S21). If the image is set to be reduced by the operation unit 11 and there is an image signal to be reduced, Then, as shown in FIG. 3B, the reduction filter 3 is caused to perform a reduction process according to the set ratio (S22).
[0032]
Next, the control unit 7 sets the position on the display screen of the display unit 2 of the pixel-excluded region that is not displayed when the image signals A and B are combined and displayed in a superimposed manner, by using the condition (image (Including reduction / enlargement) (S23). The operation unit 11 can be realized not only in the form of operation buttons provided on the display control device 1 but also in the form of an external control device such as a computer provided outside the display control device 1. is there.
[0033]
If the image of the image signals A and B should not be reduced (S21), the control unit 7 calculates the position of the pixel-free area on the display screen of the display unit 2 without performing the reduction processing (S22). (S23).
Next, the control unit 7 causes the frame memory control unit 6 to write the image signals A and B into the frame memory 5, excluding the calculated pixel-excluding area, as shown in FIG. (S24), the image signals A and B are stored in the frame memory 5 (S25).
[0034]
Next, the control unit 7 causes the frame memory control unit 6 to read out the image signals A and B stored in the frame memory 5 (S26), and then reads out the read out image signal as shown in FIG. It is determined whether or not the signals A and B should be enlarged (S27). If the image is set to be enlarged by the operation unit 11 and there is an image signal to be enlarged, the enlargement filter 8 is caused to enlarge the image by the set magnification as shown in FIG. 3D (S28). ).
[0035]
Next, when the image signals A and B are combined and superimposed and displayed, the control unit 7 determines the position of the boundary portion on the display screen of the display unit 2 based on the condition set by the operation unit 11. Then, the image signal F of the “screen frame” corresponding to the calculated position is generated by the frame image generating unit 10 (S29).
At that time, as shown in FIG. 4, the frame image creation unit 10 is determined in advance corresponding to the boundary portion regardless of the original pixels b0 to b5 and the pixels a3 to a5 of the pixel extraction region V. The image signal F of the “screen frame” of the mode is created.
If the image signals A and B should not be enlarged (S27), the controller 7 creates the image signal F of the "screen frame" without performing the enlargement processing (S28) (S29).
[0036]
Next, the control unit 7 determines the display position of the image signal (S20) determined on the front (child) screen based on the condition set by the operation unit 11 (S30).
Next, based on the determined display order and display position, the control unit 7 determines the image signals A and B determined for the front (child) screen and the background (parent) screen, respectively, and “ The image signal F of the "screen frame" is subjected to the composition processing by the composition processing unit 9, and is displayed on the display screen of the display unit 2 as shown in FIG. 3E (S31), and the process returns.
[0037]
Embodiment 2 FIG.
FIG. 5 is a flowchart illustrating the operation of the display control method, the display control device, and the display device according to the second embodiment of the present invention. Note that the configuration of the main part of the second embodiment is the same as the main part of the display device described in the first embodiment, and a description thereof will be omitted.
Hereinafter, the operation of the display device according to the second embodiment will be described with reference to the flowchart in FIG.
The control unit 7 first sets the display order (front or background) of the input image signals A and B on the display screen of the display unit 2 using the operation unit 11 as shown in FIG. It is determined based on the set conditions (S1). Next, it is determined whether or not the image of the input image signals A and B should be reduced (S2), and the operation unit 11 is set to reduce the image, and there is an image signal to be reduced. Then, as shown in FIG. 6B, the reduction filter 3 is caused to perform a reduction process according to the set ratio (S3).
[0038]
Next, the controller 7 causes the frame memory controller 6 to write the image signals A and B into the frame memory 5 (S4), and stores the image signals A and B in the frame memory 5 (S5).
If the image of the image signals A and B is not to be reduced (S2), the control unit 7 sends the image signal A and B to the frame memory 5 without performing the reduction process (S3). (S4).
Next, the control unit 7 sets the position on the display screen of the display unit 2 of the pixel-excluded region that is not displayed when the image signals A and B are combined and displayed in a superimposed manner, by using the condition (image (Including reduction / enlargement of the image) (S6).
[0039]
Next, the control unit 7 causes the frame memory control unit 6 to read out the image signals A and B from the frame memory 5 excluding the image signal corresponding to the calculated position (S6) of the pixel extraction area (S7). Then, it is determined whether or not the image signals A and B read as shown in FIG. 6C should be enlarged (S8). The image is set to be enlarged by the operation unit, and if there is an image signal to be enlarged, the enlargement filter 8 is caused to enlarge the image by the set magnification as shown in FIG. 6D (S9). .
[0040]
Next, when the image signals A and B are combined and displayed in a superimposed manner, the control unit 7 calculates the position of the boundary portion on the display screen of the display unit 2 based on the condition set by the operation unit. Then, the frame image creation unit 10 creates the image signal F of the “screen frame” corresponding to the calculated position (S10).
At that time, as shown in FIG. 4, the frame image creation unit 10 is determined in advance corresponding to the boundary portion regardless of the original pixels b0 to b5 and the pixels a3 to a5 of the pixel extraction region V. The image signal F of the “screen frame” of the mode is created.
If the image signals A and B should not be enlarged (S8), the control unit 7 creates the image signal F of the "screen frame" without performing the enlargement processing (S9) (S10).
[0041]
Next, the control unit 7 determines the display position of the image signal (S1) determined on the front (child) screen based on the condition set by the operation unit 11 (S11).
Next, based on the determined display order and display position, the control unit 7 determines the image signals A and B determined for the front (child) screen and the background (parent) screen, respectively, and “ The image signal of the "screen frame" is subjected to the combining processing by the combining processing unit 9 to be displayed on the display screen of the display unit 2 as shown in FIG. 6E (S12), and the process returns.
[0042]
【The invention's effect】
According to the display control method according to the first aspect of the invention, it is possible to realize a display control method capable of reducing a frame memory capacity and a data transfer amount related to the frame memory when a plurality of images are multiplexed and displayed.
[0043]
According to the display control method according to the second aspect of the invention, it is possible to realize a display control method capable of reducing a data transfer amount related to a frame memory when multiple images are multiplexed and displayed. Further, even when the synchronization frequencies of a plurality of images are different, a reduction in the data transfer amount can be expected.
[0044]
According to the display control device according to the third aspect of the invention, it is possible to realize a display control device capable of reducing a frame memory capacity and a data transfer amount related to the frame memory when multiple images are multiplexed and displayed.
[0045]
According to the display control device according to the fourth aspect of the invention, it is possible to realize a display control device capable of reducing the amount of data transfer related to a frame memory when multiple images are multiplexed and displayed. Further, even when the synchronization frequencies of a plurality of images are different, a reduction in the data transfer amount can be expected.
[0046]
According to the display control device according to the fifth aspect of the present invention, when multiple images are multiplexed and displayed, a high-quality reduced image can be realized, and the frame memory capacity and the data transfer amount related to the frame memory can be reduced. The device can be realized.
[0047]
According to the display control device of the sixth aspect, when multiple images are multiplexed and displayed, high-quality enlarged processed images can be realized, and the frame memory capacity and the data transfer amount related to the frame memories can be reduced. The device can be realized.
[0048]
According to the display control device according to the seventh aspect of the invention, it is possible to realize a display control device capable of displaying the boundaries of the plurality of images in multiple appearance when displaying multiple images.
[0049]
According to the display device of the eighth aspect, it is possible to realize a display device capable of reducing a frame memory capacity and a data transfer amount related to the frame memory when multiple images are multiplexed and displayed.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a main configuration of an embodiment of a display control method, a display control device, and a display device according to the present invention.
FIG. 2 is a flowchart illustrating an example of an operation of the display control device and the display device according to the present invention.
FIG. 3 is an explanatory diagram showing operations of a display control device and a display device according to the present invention.
FIG. 4 is an explanatory diagram showing operations of the display control device and the display device according to the present invention.
FIG. 5 is a flowchart illustrating an example of an operation of the display control device and the display device according to the present invention.
FIG. 6 is an explanatory diagram showing operations of the display control device and the display device according to the present invention.
FIG. 7 is an explanatory diagram showing the operation of a conventional display control device and display device.
FIG. 8 is an explanatory diagram showing the operation of a conventional display control device and display device.
[Explanation of symbols]
1 Display control device
2 Display
3 Reduction filter
4 Input image state detector
5 frame memory
6 Frame memory controller
7 control section
8 Enlargement filter
9 Composition processing section
10 Frame image creation unit
11 Operation unit

Claims (8)

In a display control method of writing a plurality of image signals to a frame memory, reading the written image signals, synthesizing them according to preset conditions, and displaying the synthesized image signals on a display screen,
Prior to writing the plurality of image signals into the frame memory, a position on the display screen of a portion of the image signal which is no longer displayed due to the combination is calculated based on the condition, and a portion corresponding to the calculated position is excluded. And writing the read image signal to the frame memory, reading the image signal, and synthesizing the read image signal. In a display control method of writing a plurality of image signals to a frame memory, reading the written image signals, synthesizing them according to preset conditions, and displaying the synthesized image signals on a display screen,
Prior to reading out the written image signal from the frame memory, a position on the display screen of a portion of the image signal which is not displayed due to the combination is calculated based on the condition, and a portion corresponding to the calculated position is excluded. Displaying the read image signal from the frame memory and synthesizing the read image signal. A display control device that writes a plurality of input image signals to a frame memory, reads out the written image signals, combines them according to preset conditions, and outputs the combined image signals to be displayed on a display screen.
Means for calculating, based on the condition, a position on the display screen of a portion of the image signal which is no longer displayed by combining before the plurality of image signals are written to the frame memory, corresponding to the position calculated by the means. Means for writing an image signal excluding a portion to be written into the frame memory, wherein the image signal written by the means is read out and synthesized. A display control device that writes a plurality of input image signals to a frame memory, reads out the written image signals, combines them according to preset conditions, and outputs the combined image signals to be displayed on a display screen.
Prior to reading out the written image signal from the frame memory, means for calculating, based on the condition, a position on the display screen of a portion of the image signal which is no longer displayed by synthesis, and corresponding to the position calculated by the means. Means for reading out an image signal excluding a portion to be read from the frame memory, wherein the means for synthesizing the image signal read out by the means is provided. When an image of the input image signal is to be displayed in a reduced size, the image signal processing device further comprises means for processing the image signal so as to reduce the image, and writing the image signal processed by the means to the frame memory. The display control device according to claim 3, wherein When the image of the image signal read from the frame memory is to be displayed in an enlarged manner, the image processing apparatus further comprises a unit for processing the image signal so as to enlarge the image. The display control device according to claim 3, wherein: Means for calculating a position on the display screen of a boundary portion where the plurality of image signals are synthesized and overlapped, and means for outputting a predetermined image signal corresponding to the position calculated by the means, further comprising: 7. The display control device according to claim 3, wherein the output predetermined image signal is displayed at the position. A display device, comprising: the display control device according to claim 3; and display means for displaying an image signal output by the display control device.

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