JPH06130908A - Picture quality correcting method - Google Patents

Abstract

PURPOSE:To display a picture of high picture quality by repeatedly, minutely changing the display position of the display picture to smooth oblique lines. CONSTITUTION:This method smooths oblique lines by repeated minute movement of the display position of the display picture to correct the picture quality. Since the display time (frequency in display) is proportional to the density, (display time) (density) is true. That is, when the density of a picture element displayed at all of eight display times is defined as '8', the density of a picture element displayed at one of eight display times is '1' and is relatively 1/8 of the former picture element. The density of a picture element displayed at two of eight display times is '2' and is relatively 2/8. That is, since the density of the center part is made higher but that of the peripheral part is made lower (gray) by increasing the frequency in display of an original picture O, a conventional staircase shape is inconspicuous. Consequently, oblique lines are smoothed to display natural graphics of high picture quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting the image quality of a display image in an image processing device using an LCD display and various other electronic devices, and more particularly, in a LCD display, a staircase-shaped display portion caused by a shaded portion is displayed. The present invention relates to an image quality correction method capable of displaying a natural and smooth diagonal line portion by smoothing and enabling high-quality image display.

[0002]

LCD displays, or LCDs
In an electronic device such as an electronic file with a type of bitmap display, the pixels displayed on the screen of the LCD display are square or rectangular.

Therefore, compared with a CRT display,
The expression of diagonal lines is inferior. Here, as an example thereof, a case where a graphic in which rectangles are arranged in an oblique direction is displayed on an LCD display will be described.

FIG. 12 is a diagram showing an example of an image in which rectangles are arranged diagonally. FIG. 13 is a diagram showing a display example in which the image of FIG. 12 is binarized.

As shown in FIG. 12, when a rectangular image having diagonal sides is displayed on the LCD display, it is displayed on the screen as a step-like line as shown in FIG. In this way, when the diagonal lines are displayed in the digital image, the lines are not the smooth lines of the original image but the staircase lines.

Such a phenomenon occurs not only in the LCD display but also in the CRT display. That is, the diagonal lines are not displayed smoothly, and are displayed as stair-like unnatural lines.
This phenomenon is an essential problem common to both LCD and CRT displays.

However, in the case of LCD displays, in particular, the pixels are square or rectangular and the edges of the pixels are well defined. Therefore, the step portion of the diagonal lines is more conspicuous as compared with the CRT display in which the pixel shape is close to a circle and the edge is relatively ambiguous, and as a result, the image quality is inferior to that of the CRT display. .

However, in the conventional LCD display, no method has been proposed for correcting the deterioration of image quality caused by such a shaded area.

[0009]

According to the present invention, such inconveniences that occur in the conventional LCD display,
That is, since the pixel is a square or a rectangle and the edge of the pixel is clear, the problem that the step shape of the shaded portion is more conspicuous and the image quality is inferior to that of the CRT display is solved, and the display image is displayed. An object of the present invention is to provide an image quality correction method in which a line in an oblique direction is smoothed by repeatedly changing the position to a small size so that high quality display can be performed.

[0010]

According to the present invention, firstly,
This is an image quality correction method for smoothing diagonal lines by repeatedly changing the display position of a display image in an electronic device using an LCD as a display unit.

Secondly, in the first image quality correction method, the change in the display position is an image quality correction method in which one dot is moved in the vertical and horizontal directions.

Thirdly, in the second image quality correction method, the display position is changed only in the sub-scanning direction.

Fourth, in the second image quality correction method, the display position is changed only in the main scanning direction.

Fifth, in the fourth image quality correction method, there is provided means for calculating a logical sum of the image whose display position has been moved and the original image, and the logic of the image whose display position has been moved and the original image. This is an image quality correction method that performs sum processing.

[0015]

According to the present invention, in an electronic device equipped with an LCD type bitmap display, the pixels are square or rectangular, and the edges of the pixels are clear. Although it decreases, if the density of this part is made thin, the overall figure is clear and the step of the shaded part is not so noticeable, and by repeatedly moving the display position of the display image small, The diagonal line is smoothed. Specifically, when the display position of the original image is temporally changed and, for example, one dot is moved vertically and horizontally, the "original image" is displayed.
→ "Move up" → "Original image" → "Move right" → "Original image" → "Move down" → "Original image" → "Move left" The density of the central part of the image that is always displayed (8 times) and
Peripheral density displayed only once (1 /
8)), the density is changed stepwise, and the density of the peripheral part where the step is particularly noticeable is displayed relatively thin so that a diagonal line with a natural appearance and high quality can be obtained. (The inventions of claims 1 and 2).

When the display position is changed by moving the original image by 1 dot each, if the horizontal direction is the main scanning direction, the original image may be moved by 1 dot only in the sub-scanning direction, that is, only in the vertical direction. (Invention of item 3) On the contrary, by moving one dot only in the main scanning direction, that is, only in the horizontal direction (invention of claim 4), the moving process of the original image is simplified. Furthermore, when moving one dot only in the main scanning direction, that is, only in the left-right direction, if the shaded portion constitutes a part of the line, the density may decrease, so only 1 in the left-right direction. By performing a logical sum operation of the dot-moved image and the original image and displaying the logical sum image and the original image, the line portion (black dot) is prevented from disappearing, and the image quality is corrected. Invention of 5).

[0017]

First Embodiment As described above, the image quality correction method of the present invention smoothes diagonal lines by repeatedly moving the display position of a display image small in an electronic device equipped with an LCD type bitmap display. This is a method of correcting the image quality. This embodiment corresponds to the inventions of claims 1 and 2, but is also related to the inventions of claims 3 to 5. First, the principle of image quality correction will be described.

FIG. 1 is a diagram for explaining the principle of the image quality correction method of the present invention. In the center (O), a display example of the original image is shown, and in the upper part (U), the original image (O) is directed upward 1. Display example when the dots are moved, (D) below that is an example of display when the original image (O) is moved downward by one dot, and (L) on the left is the same original image (O) to the left. A display example when one dot is moved, and (R) on the right side thereof shows a display example when the original image (O) is also moved one dot to the right.

For example, for the original image (O) in FIG. 1, it is assumed that the display order is determined as follows, and one cycle of display is performed by moving vertically, horizontally and eight times. "Original image" (O) →
"Move Up" (U) → "Original Image" (O) → "Move Down" (D) → "Original Image" (O) → "Move Right"
(R) → “original image” (O) → “move left” (L),
When displayed in this order, an image having a gradation density as shown in FIG. 2 is displayed on the display screen.

FIG. 2 shows an example of display when the original image is moved four times and the image is moved vertically and horizontally at the same time intervals with respect to the diagonal rectangle shown in FIG. FIG. The numbers in the figure indicate the number of times of display.

In FIG. 2, of the eight times of display, the pixel at the central position shown by "8" is displayed at all times of eight times, but "7", "6", and The pixel of "5" is
The display time becomes shorter, such as 7 times, 6 times, and 5 times out of 8 times. Then, the pixels of "1" located in the periphery are displayed only once, and the pixels of "2" are displayed only twice.

Since the display time (display count) is proportional to the density, it corresponds to (display time) .apprxeq. (Density) in FIG. Although not particularly shown, the outside of the rectangle is white (dots of “0”). That is, if the density of the pixel displayed for all eight times is “8”, the density of the pixel whose display time is “1” is “1”, so that the relative density is 1
/ 8.

Similarly, the density of the pixel whose display time is "2" is "2", which is 2/8 of the relative density. As described above, when the number of times of displaying the “original image” (O) in FIG. 1 is increased, the density of the central portion becomes darker, and the density of the peripheral portion becomes relatively lighter than the central portion (gray). ), So that the staircase like in the past becomes inconspicuous.

Therefore, as compared with FIG. 13 showing the conventional example, the diagonal line is smoothed and a natural and high quality graphic is displayed (the invention of claim 2). However, it is not always necessary to display one cycle by moving up, down, left, and right eight times, and for example, one cycle can be displayed by moving six times up, down, left, and right in FIG.

In this case, the original image (O) is displayed twice,
The original image is displayed once for each image that has been moved vertically and horizontally.
(O) → "Move up" (U) → "Move left"
(L) → "Original image" (O) → "Move down" (D) →
When the images are displayed in the order of "move to the right" (R), an image having a gradation density as shown in FIG. 3 is displayed on the display screen.

FIG. 3 shows an example of display when the original image is moved twice and the image moved vertically and horizontally is changed at equal time intervals for the diagonal rectangle shown in FIG. FIG. The numbers in the figure indicate the number of times of display.

As shown in FIG. 3, the original image (O) is set to 2
When the image is displayed twice, the number of times the pixel of the original image is displayed is reduced by two times as compared with the case of FIG. 2 described above, the maximum density becomes “6”, and “7” changes to “5”. However, in the peripheral portion, since the stepwise density becomes low, a high-quality rectangle is displayed as in the case of FIG.

As described above, according to the image quality correction method of the present invention, the diagonal line located in the peripheral portion is smoothed by repeatedly changing the display position of the display image to a small size. Invention). If the change in the display position is movement of one dot in the vertical and horizontal directions, a high quality image as shown in FIGS. 2 and 3 can be obtained (the invention of claim 2).

The number of times the “original image” (O) is displayed in FIG. 1 and the order of moving each dot is not limited to the case described in the embodiment. In short, if the images as shown in FIG. 1 are combined and displayed in an appropriate order, the diagonal edges that have become stepwise in FIG.
Smoothed out in gray to give a natural quality display image.

FIG. 4 is a functional block diagram showing an example of the essential structure of an electronic apparatus for carrying out the image quality correction method of the present invention. In the figure, 1 is a CPU, 2 is a GD
C, 3 VRAM, 4 data shifter, 5 LCD, 6
Is an HDD, 7 is an HDC, 8 is a first RAM, and 9 is a second RAM.

The electronic device shown in FIG. 4 is basically the same as the conventional electronic device except that the LCD 5 is provided as a display unit and the data shifter 4 is provided. The function of each unit common to the conventional electronic device is roughly as follows. The CPU 1 has a function of controlling the entire system.

GDC (graphic controller) 2
Is the HDD 6 or the first RAM under the control of the CPU 1.
8. The image data stored in the second RAM 9 is developed into an image such as a figure and is output to the VRAM 3 and the LCD 5. The HDD 6 is controlled by the HDC 7.

The newly added data shifter 4 has a function of moving in the main scanning direction. Next, the data shifter 4 will be described in detail.

FIG. 5 is a diagram showing an embodiment of a detailed circuit of the data shifter used in the image quality correction method of the present invention when the data bus width of the LCD / VRAM is 4 bits. In the figure, 41 to 45 are first to fifth flip-flop circuits, 46 to 49 are first to fourth selectors, V0 to V3 are output signals of VRAM3, and L0 to L3.
Indicates an input signal of the LCD display, and S0 and S1 indicate select signals.

In FIG. 5, "0" indicates the leading bit. The output signals V0 to V3 of the VRAM 3 are delayed by one dot by the flip-flop circuits 41 to 45 and input to the selectors 46 to 49, respectively.

When the A input is selected, the selectors 46 to 49 operate so that the image moved by one dot in the scanning direction is displayed. When the B input is selected, the image is output at the original position (the position corresponding to the input), and when the C input is selected, the image moved by one dot in the direction opposite to the scanning direction is displayed.

Regarding this selector, claim 3
Since it is also related to the invention of claim 4, detailed description will be given later. The movement in the sub-scanning direction can be easily realized by changing the display address to the GDC 2 or by shifting the timing of the scanning start signal for the LCD display by one line.

[0038]

Second Embodiment A second embodiment of the image quality correction method of the present invention will be described. This embodiment corresponds to the invention of claim 3. In the first embodiment described above, the case of moving the original image in the four directions of up, down, left and right has been described, but the second embodiment is characterized in that it is moved only in the sub-scanning direction. have.

Assuming that the left and right directions are the main scans in FIG. 1, the display position changes only in the up and down directions in the second embodiment. For example, the original image (O) is displayed twice, and the images moved up and down are displayed once each, and "original image" (O) → "move upward" (U) → "original image"
When the images are displayed in the order of (O) → “move downward” (D), an image having a gradation density as shown in FIG. 6 is displayed on the display screen.

FIG. 6 shows an example of display when the original image is moved twice and the image vertically moved is changed at equal time intervals for the diagonal rectangle shown in FIG. It is a figure. The numbers in the figure indicate the number of times of display.

As shown in FIG. 6, the original image (O) is set to 2
When the image is displayed once and the image moved in the vertical direction is displayed once, the number of times of display of the pixel in the central portion is four, and the number of times of display of the pixel adjacent thereto is three. Further, since the movement is only in the vertical direction, the number of times of displaying the pixel is one in the peripheral portion in the vertical direction, and the pixels are displayed twice in the horizontal direction.

In the case of FIG. 6 as well, since the staircase-like density becomes thin in the peripheral portion, a high-quality rectangle is displayed as in the case of FIG. Here, the selector used when moving in the sub-scanning direction will be described.

FIG. 7 is a diagram showing an example of the circuit configuration of the selector used in the second embodiment of the present invention. In the figure, AND1 to AND3 indicate AND gate circuits, OR indicates an OR gate circuit, A to C indicate input signals, D indicates output signals, and S0 and S1 indicate gate control signals.

The circuit shown in FIG. 7 is similar to a normal selector. In the selector of FIG. 7, when only the input signal B is selected, the gate control signals S0 and S1 are both given as "0".

In this case, the AND gate circuit AND2
Gates of the AND gates are opened, but AND gate circuits AND1 and A
In ND3, the AND condition is not satisfied, so the gate remains closed. Therefore, only the input signal B is input to the OR gate circuit OR, and the output signal D is generated.

When only the input signal A is selected, one gate control signal S0 is given as "1" and the other S1 is given as "0". In this case, the gate of the AND gate circuit AND1 is opened, but in the AND gate circuit AND2, the gate control signal S0 is "1" (the inverting input becomes "0"), and in the AND gate circuit AND3. Since the AND condition is not satisfied, the gate remains closed.

Therefore, only the input signal A is input to the OR gate circuit OR, and the output signal D is generated. Further, when only the input signal C is selected, the gate control signal S0
Are both given as "1".

In this case, the AND gate circuit AND3
The gate is opened, but in the AND gate circuit AND1, the gate control signal S1 is "1" (the inverting input is "0"), the AND condition is not satisfied, and in the AND gate circuit AND2, the gate is Control signal S0 is "1"
(The inverting input becomes “0”), and the gate remains closed in both cases. Therefore, only the input signal C is
The output signal D is generated by being input to the OR gate circuit OR.

In the second embodiment, the display position changes only in the sub-scanning direction, and the movement in the sub-scanning direction can be realized without changing the hardware. Therefore, it can be most easily implemented.

[0050]

Third Embodiment A third embodiment of the image quality correcting method of the present invention will be described. This embodiment corresponds to the invention of claim 4. In the second embodiment, the case where the original image is moved only in the sub-scanning direction has been described. However, the third embodiment is characterized in that it is moved only in the main scanning direction. is doing.

In FIG. 1, if the left and right direction is the main scanning, the change of the display position is only in the left and right direction in the third embodiment. For example, the original image (O) is displayed twice, and the images that have been moved to the left and right are displayed once, and the “original image” is displayed.
(O) → “Move left” (L) → “Original image” (O) →
When the images are displayed in the order of "move to the right" (R), an image having the gradation density as shown in the next FIG. 8 is displayed on the display screen.

FIG. 8 shows a display example when the original image is moved twice and the image moved once in the left-right direction is changed at equal time intervals for the diagonal rectangle shown in FIG. It is a figure. The numbers in the figure indicate the number of times of display.

As shown in FIG. 8, the original image (O) is set to 2
When the image is displayed once and the image moved in the left-right direction is displayed once, the number of times of display of the pixel in the central portion is four, and the number of times of display of pixels adjacent thereto is three. Further, since the movement is only in the left-right direction, the number of times the pixel is displayed is one in the peripheral portion in the left-right direction, and the pixels are displayed twice in the vertical direction.

As shown in FIG. 8, the original image (O) is set to 2
When the image is displayed twice, the number of times the pixel of the original image is displayed is reduced by 2 times as compared with the case of FIG. 2 above, the maximum density becomes “6”, and “7” changes to “5”. However, in the peripheral portion, since the stepwise density becomes low, a high-quality rectangle is displayed as in the case of FIG.

In the third embodiment described above, the display position changes only in the main scanning direction, and the movement in the sub scanning direction is not used. Therefore, the present invention can be sufficiently applied to an LCD display of a split screen simultaneous display system which is generally adopted for a large LCD display.

[0056]

Fourth Embodiment A fourth embodiment of the image quality correction method of the present invention will be described. This embodiment corresponds to the invention of claim 5. The fourth embodiment is characterized in that, in the third embodiment (the invention of claim 4), the logical sum processing of the image whose display position is moved and the original image is performed.

In the image quality correction methods described in the first to third embodiments, in the case of an image such as the rectangle shown in FIG. 13, since the stairs in the peripheral portion are not conspicuous, a high quality image display is possible. You can do it. However, in the case of a figure composed of thin lines, if the processing is performed as in the above embodiment, the lines may become thin and may not be visible.

If it is attempted to increase the number of times the original image (O) shown in FIG. 1 is displayed in order to avoid such an inconvenience, the time (display number) of each display state is unevenly assigned. , Control becomes complicated. In addition, LC with fast reaction
In the case of D, the image of a light portion may have flickering, and the image quality deteriorates.

In the fourth embodiment, the logical sum processing is performed on the original image (O) shown in FIG. 1 and (L) and (R) obtained by moving the original image (O) by one dot in the horizontal direction. (OR processing) to create logical sum images (LO) and (RO).
Here, an example of the logical sum images (LO) and (RO) will be described.

FIG. 9 shows an example of an image obtained by logically ORing the original image (O) of FIG. 1 and the images (L) and (R) obtained by moving the original image (O) one dot to the left or to the right. It is a figure which shows the example of a display. The numbers in the figure indicate the number of times of display.

FIG. 9 shows an image obtained by logically ORing an original image and an image obtained by moving the original image one dot to the left or to the right with respect to the diagonal rectangle shown in FIG. As is apparent from FIG. 9, the image obtained by the logical sum processing has "1" in the peripheral portion and "2" in the central portion.

That is, the difference in density between the central portion and the peripheral portion is small, and particularly when the peripheral portion is a fine line, the preservability of the fine line is high as is often used in ordinary image processing. Therefore, as shown in FIG. 9, if an OR image of an original image and an image obtained by moving the original image by one dot in the left-right direction is used, an image with a small change in the display position (the number of states) can be displayed in the thin line portion. Can be clearly displayed.

FIG. 10 is a view showing a display example used in the fourth embodiment of the image quality correction method of the present invention. The left (LO) is the original image (O) shown in FIG. 1 and the left direction. The display image in the case where the (L) moved by 1 dot to the right is ORed, and the right (RO) is the same as the display image in the case where the original image (O) and the (R) moved to the right by 1R are ORed. The display image is shown.

As already mentioned many times, the reason why such logical sum processing is performed is that the thin part is thin in the original image, especially when the peripheral part includes the thin line. , Because it may appear to disappear.
In the fourth embodiment, the original image (O) shown in FIG.
Then, as shown in FIG. 10, the logical sum images (LO) and (RO) of the original image (O) and the images (L) and (R) obtained by moving the original image (O) by one dot in the horizontal direction are created.

Then, (LO) and (R
O) and the original image (O) in FIG. 1 are, for example, (O) →
Changes are made at equal time intervals in the order of (LO) → (O) → (RO). In this way, if the original image (O) and the images (L) and (R) obtained by moving the original image (O) by one dot in the left and right direction are used, the original image is obtained. The part that was black in the section is always black, so it is excellent in terms of preserving fine lines.

Moreover, since the number of states in which the number of times each image is displayed becomes a problem can be reduced, the possibility of flickering is reduced in an LCD display having a fast reaction. next,
The selector used in the fourth embodiment will be described.

FIG. 11 is a diagram showing an example of the circuit configuration of the selector used in the fourth embodiment of the present invention. Reference numerals in the figure are the same as those in FIG.

The selector shown in FIG. 11 has an input signal B
In this case, the gate control signals S0 and S1 are both given as "0". When the input signal A or B is selected (OR output), the gate control signal S0 is "1",
S1 is given as "0".

Further, when the input signal B or C is selected (OR output), the gate control signals S0 and S1 are both given as "1". In the circuit of FIG. 11, the input signal B
1 is given as input data, and as the input signal A, for example, (L) of FIG. 1, that is, data of an image obtained by moving the original image (O) leftward by one dot is input. As the signal B, (R) in FIG. 1, that is, the original image (O)
The data of the image obtained by shifting 1 dot to the right may be given respectively.

When the gate control signals S0 and S1 are switched at regular time intervals, the output signal D is (O) .fwdarw. (LO) .fwdarw. (O) .fwdarw. (RO), as described above.
The image data is obtained in the order of. It should be noted that in any of the embodiments, optimization can be performed by adjusting the use order, time ratio, etc. of each state according to the properties of the LCD display used and the original. For example, in the case of a rectangular figure as shown in FIG. 13, the first to third examples are suitable, and when the figure composed of thin lines is included, the fourth example is the best. is there.

[0071]

According to the image quality correction method of the first aspect, the slanting line is smoothed by repeatedly changing the display position of the display image to a small size. Therefore, the slanted edges that have become stepwise are smoothed in gray, and a display image of natural and smooth quality can be obtained.

In the image quality correction method of the second aspect, the change in the display position is the movement of one dot in the vertical and horizontal directions. Therefore, the smoothing effect is maximized.

In the image quality correction method of the third aspect, the change of the display position is only in the sub-scanning direction, and the movement in the sub-scanning direction can be realized without changing the hardware. Therefore, it can be most easily implemented.

In the image quality correction method according to the fourth aspect, the display position changes only in the main scanning direction, and the movement in the sub scanning direction is not used. Therefore, the present invention can be sufficiently applied to an LCD display of a split screen simultaneous display system, which is generally used for a large LCD display.

According to the image quality correction method of the fifth aspect, in the image quality correction method of the fourth aspect, the logical sum processing of the image whose display position is moved and the original image is performed. Therefore, FIG.
Since the black portion is always black, the thin line is excellent in storability, and there is little possibility of flickering even in an LCD display with a small number of states and a fast reaction.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of an image quality correction method of the present invention.

FIG. 2 is a diagram showing a display example when the original image is moved four times and the image is vertically and horizontally moved once in the diagonal rectangle shown in FIG. 13 at equal time intervals. is there.

FIG. 3 is a diagram showing a display example when the original image is moved twice and the image moved once in the vertical and horizontal directions is changed at equal time intervals in the diagonal rectangle shown in FIG. is there.

FIG. 4 is a functional block diagram showing an example of a main part configuration of an electronic device that implements the image quality correction method of the present invention.

FIG. 5 is a diagram showing an embodiment of a detailed circuit of the data shifter used in the image quality correction method of the present invention when the data bus width of the LCD / VRAM is 4 bits.

6 is a diagram showing a display example when the original image is moved twice and the image vertically moved is changed at equal time intervals with respect to the diagonal rectangle shown in FIG. .

FIG. 7 is a diagram showing an example of a circuit configuration of a selector used in the second embodiment of the present invention.

8 is a diagram showing a display example when the original image is moved twice and the image moved once in the left-right direction is changed at equal time intervals in the diagonal rectangle shown in FIG. .

9 is a display example of an image obtained by performing a logical sum processing of the original image (O) in FIG. 1 and the images (L) and (R) obtained by moving the original image (O) leftward or rightward by one dot. FIG.

FIG. 10 is a fourth view of the image quality correction method of the present invention.
FIG. 7 is a diagram showing a display example used in the embodiment of FIG.

FIG. 11 is a diagram showing an example of a circuit configuration of a selector used in a fourth embodiment of the present invention.

FIG. 12 is a diagram showing an example of an image in which rectangles are arranged in an oblique direction.

FIG. 13 is a diagram showing a display example in which the image of FIG. 12 is binarized.

[Explanation of symbols]

 1 CPU 2 GDC 3 VRAM 4 Data shifter 5 LCD 6 HDD 7 HDC 8 First RAM 9 Second RAM

Claims (5)

[Claims] 1. An image quality correction method for an electronic device using an LCD as a display unit, wherein an oblique line is smoothed by repeatedly changing a display position of a display image to be small. 2. The image quality correction method according to claim 1, wherein the change of the display position is a movement of one dot in the vertical and horizontal directions. 3. The image quality correction method according to claim 2, wherein the display position is changed only in the sub-scanning direction. 4. The image quality correction method according to claim 2, wherein the display position is changed only in the main scanning direction. 5. The image quality correction method according to claim 4, further comprising means for calculating a logical sum of an image whose display position has been moved and an original image, and a logical sum processing of the image whose display position has been moved and the original image. An image quality correction method characterized by: