JP4921759B2 - Image processing apparatus and image processing method - Google Patents

Description

  The present invention relates to an image processing apparatus and an image processing method for executing interpolation processing.

  Generally, in a computer, scaling processing for enlarging or reducing an image is performed. The image enlargement is used, for example, when a certain original image is displayed on a full screen on a computer display monitor. The process for enlarging the image is executed using interpolation.

  As an interpolation method, an interpolation method using a piecewise polynomial approximating a sin (x) / x function is known. In this interpolation method, a weighted average value of, for example, 4 × 4 original pixels surrounding the interpolation target pixel is calculated as the pixel value of the interpolation target pixel. A 4 × 4 weighting coefficient is used to calculate the weighted average value of the 4 × 4 original pixels.

Bicubic interpolation is widely known as one of the interpolation methods described above. Patent Document 1 discloses an apparatus that generates a display image by bicubic interpolation.
Japanese Patent Laid-Open No. 11-203467

  By the way, generally, when an original image is enlarged by interpolation processing, the enlarged image tends to be a blurred image without a stereoscopic effect.

  In the interpolation method using a piecewise polynomial that approximates the sin (x) / x function, the effect of the image generated by the interpolation process can be achieved by manipulating the values of the weighting coefficient group. However, if the values of the weighting factor group are simply manipulated, overcorrection will occur depending on the content of the original image, and this may lead to problems such as generating unnatural images or generating unnatural singularities. Become.

  The present invention has been made in consideration of the above-described circumstances, and provides an image processing apparatus and an image processing method capable of generating a magnified image with a three-dimensional effect without causing problems due to overcorrection. Objective.

In order to solve the above-described problem, the present invention provides a pixel value of an interpolation target pixel by using an interpolation process using a piecewise polynomial approximating a sin (x) / x function. An image processing apparatus that calculates a plurality of types of operation coefficients each including a plurality of weighting coefficients corresponding to each of the plurality of original pixels; and An original pixel on an extension line of a straight line connecting the nearest neighbor original pixel of the interpolation target pixel and the interpolation target pixel, and among the pixels other than the nearest neighbor pixel, the nearest neighbor element Detecting means for detecting an absolute value of a difference in pixel value between two predetermined original pixels located on both sides of the pixel; and one of the plurality of types of calculation coefficients according to the absolute value of the detected difference. Selecting means for selecting and calculating a pixel value of the interpolation target pixel; For this purpose, the image processing apparatus includes a calculation unit that calculates a weighted average of the plurality of original pixels using the calculation coefficient selected by the selection unit.

  According to the present invention, it is possible to generate a magnified image having a stereoscopic effect without causing a problem due to overcorrection.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, with reference to FIG. 1 and FIG. 2, the configuration of an information processing apparatus equipped with an image processing apparatus according to an embodiment of the present invention will be described. This information processing apparatus is realized as, for example, a notebook portable personal computer 10.

  FIG. 1 is a perspective view of the personal computer 10 with the display unit opened. The computer 10 includes a computer main body 11 and a display unit 12. The display unit 12 incorporates a display device composed of a TFT-LCD (Thin Film Transistor Liquid Crystal Display) 17, and the display screen of the LCD 17 is positioned substantially at the center of the display unit 12. The LCD 17 has a display screen size (resolution) corresponding to, for example, an HD (High Definition) standard.

  The display unit 12 is attached to the computer main body 11 so as to be rotatable between an open position and a closed position. The computer main body 11 has a thin box-shaped casing, and a keyboard 13, a power button 14 for turning on / off the computer 1, an input operation panel 15, and a touch pad 16 are arranged on the upper surface. Has been.

  The input operation panel 15 is an input device that inputs an event corresponding to a pressed button, and includes a plurality of buttons for starting a plurality of functions. These button groups also include a TV start button 15A and a DVD / CD start button 15B. The TV activation button 15A is a button for activating a TV function for reproducing, viewing, and recording TV broadcast program data. When the TV activation button 15A is pressed by the user, a TV application program for executing the TV function is automatically activated.

  The DVD / CD start button 15B is a button for playing back video content recorded on a DVD or CD. When the DVD / CD activation button 15B is pressed by the user, a reproduction application program for reproducing video content is automatically activated.

  Next, the system configuration of the computer 10 will be described with reference to FIG.

  As shown in FIG. 2, the computer 10 includes a CPU 111, a north bridge 112, a main memory 113, a graphics controller 114, a south bridge 119, a BIOS-ROM 120, a hard disk drive (HDD) 121, and an optical disk drive (ODD) 122. A TV tuner 123, an embedded controller / keyboard controller IC (EC / KBC) 124, a network controller 125, and the like.

  The CPU 111 is a processor provided to control the operation of the computer 10 and executes an operating system and various application programs loaded from the hard disk drive (HDD) 121 to the main memory 113. In this embodiment, a video application program such as a TV application program and a playback application program is executed.

  The video application program is used for original images such as image data (moving image data) included in TV broadcast program data received by the TV tuner 123 and image data (moving image data) read from the optical disc drive (ODD) 122. Various image processing. As shown in FIG. 3, the video application program 201 includes a noise reduction module 210, an IP (Interlace / Progressive) conversion module 211, a black extension module 212, a white extension module 213, a sharpness module 214, and an interpolation process as shown in FIG. A module (scaler) 215 is provided.

  For example, the noise reduction module 210 executes a process for removing noise from image data included in broadcast program data received by the TV tuner 123. The IP conversion module 211 performs a progressive conversion process for converting original image data from an interlaced video to a progressive video having twice the data amount. The black extension module 212 and the white extension module 213 execute processing for extending and correcting the black and white gradations, respectively. The sharpness module 214 executes sharpness processing for contour enhancement and the like. The interpolation processing module (scaler) 215 executes interpolation processing for enlarging the resolution (image size) of the original image to the resolution of the LCD 17. By this interpolation processing, for example, an original image having an image size (resolution) corresponding to the SD (Standard Definition) standard is enlarged to an image size (resolution) corresponding to the HD (High Definition) standard.

  The image data enlarged by the interpolation processing is written into the video memory 114A of the graphics controller 114 via the display driver 202. The display driver 202 is software for controlling the graphics controller 114.

  The interpolation process can also be executed by hardware. In this case, an interpolation processing unit (scaler) 301 provided in the graphics controller 114 executes the above-described interpolation processing.

  The CPU 111 also executes a system BIOS (Basic Input Output System) stored in the BIOS-ROM 120. The system BIOS is a program for hardware control.

  The north bridge 112 is a bridge device that connects the local bus of the CPU 111 and the south bridge 119. The north bridge 112 also includes a memory controller that controls access to the main memory 113. The north bridge 112 also has a function of executing communication with the graphics controller 114 via an AGP (Accelerated Graphics Port) bus or the like.

  The graphics controller 114 is a display controller that controls the LCD 17 used as a display monitor of the computer 10. The graphics controller 114 displays the image data written in the video memory (VRAM) 114A on the LCD 17.

  The south bridge 119 controls each device on an LPC (Low Pin Count) bus and each device on a PCI (Peripheral Component Interconnect) bus. The south bridge 119 incorporates an IDE (Integrated Drive Electronics) controller for controlling the HDD 121 and the ODD 122. Further, the south bridge 119 has a function for controlling access to the BIOS-ROM 120.

  The HDD 121 is a storage device that stores various software and data. An optical disk drive (ODD) 123 is a drive unit for driving a storage medium such as a DVD or a CD in which video content is stored. The TV tuner 123 is a receiving device for receiving broadcast program data such as a TV broadcast program.

  The embedded controller / keyboard controller IC (EC / KBC) 124 is a one-chip microcomputer in which an embedded controller for power management and a keyboard controller for controlling the keyboard (KB) 13 and the touch pad 16 are integrated. . The embedded controller / keyboard controller IC (EC / KBC) 124 has a function of powering on / off the computer 10 in accordance with the operation of the power button 14 by the user. The operation power supplied to each component of the computer 10 is generated from a battery 126 built in the computer 10 or an external power supply supplied from the outside via the AC adapter 127.

  The network controller 125 is a communication device that executes communication with an external network such as the Internet.

  Next, the interpolation processing of this embodiment will be described.

  FIG. 4 shows a pixel position relationship between the original image data and the output image data generated by the interpolation process.

  In FIG. 4, in order to simplify the description of the interpolation processing, it is assumed that the original image data is composed of 25 pixels from P1 to P25.

  P1 to P5 are pixels located at equal intervals in the horizontal direction, and P6 to P10 exist at positions spaced apart at the same intervals as the pixel intervals in the horizontal direction in the vertical direction with respect to P1 to P5. P11 to P15 exist at positions that are the same as the pixel interval in the horizontal direction in the vertical direction with respect to P10, and are also located at the same distance as the pixel interval in the horizontal direction in the vertical direction with respect to P11 to P15. P16 to P20 exist, and P21 to P25 exist at positions that are spaced apart from P16 to P20 in the vertical direction at the same interval as the horizontal pixel interval. Thus, P1 to P25 have a 5 × 5 square lattice positional relationship.

  Q13a is located at a distance of 1/4 in the horizontal direction from P13 to P14 and 1/4 distance in the vertical direction from P13 to P18, and Q13a is rotated 90 degrees counterclockwise about P13. Q13b is located at a position obtained by rotating Q13b 90 degrees counterclockwise about P13, and Q13d is located at a position obtained by rotating Q13c 90 degrees counterclockwise about P13.

  Now, when focusing on P13, what is indicated by Q13a, Q13b, Q13c, and Q13d shows the positions of the four pixels that are created around P13, and from the pixels of P13 and the surrounding pixel group by interpolation processing , Q13a to Q13d pixels are created. M1 to m25 are pixel values of the pixels P1 to P25, and m13a to m13d are pixel values of Q13a to Q13d.

  When the original image is magnified 4 times (when the pixel density is quadrupled), each of the pixels P1 to P25 is replaced with the surrounding 4 pixels.

  In general, as a method of performing pixel interpolation, a method of performing interpolation using pixel values of a plurality of original pixels surrounding an interpolation target pixel is known.

  In this case, if a function having sin (x) / x characteristics as shown in FIG. 5 is used as an interpolation function, and a product obtained by multiplying this function and the pixel values of surrounding pixels is convolved, accurate interpolation is performed. It is known that can be performed.

  However, it is not realistic to design an interpolation filter having the characteristics as shown in FIG. 5, and functions having characteristics approximating the waveform characteristics shown in FIG. 5 have been used.

  As a function approximating sin (x) / x shown in FIG. 5, an interpolation method using a bicubic function is generally known. A function approximating sin (x) / x can be defined by the following piecewise polynomial.

Piecewise polynomial interval
(X ³ + 5X ² + 8X + 4) / 2 -2 <= X <-1 --- a
(-3X ³ -5X ² +2) / 2 -1 <= X <0 --- b
(3X ³ -5X ² +2) / 2 0 <= X <1 --- c
(-X ³ + 5X ² -8X + 4) / 2 1 <= X <2 --- d
Here, the value of X represents the inter-pixel distance, and the inter-pixel distance in the horizontal or vertical direction of the original image in FIG. The characteristics of the bicubic function are shown in FIG.

  Hereinafter, an example in which four pixels Q13a, Q13b, Q13c, and Q13d are created around Q13 in FIG. 4 will be described.

  When creating the interpolation target pixel Q13a, the 16 original pixels P7, P8, P9, P10, P12, P13, P14, P15, P17, P18, P19, P20, P22, P23, P24 surrounding the interpolation target pixel Q13a , P25 pixel values are used.

  When creating Q13b, Q13c, and Q13d, the peripheral pixels to be used are pixel groups that are rotated 90 degrees in order counterclockwise around P13. That is, when creating the interpolation target pixel Q13b, the pixel values of P17, P12, P7, P2, P18, P13, P8, P3, P19, P14, P9, P4, P20, P15, P10, P5 are used. The When creating the interpolation target pixel Q13c, the pixel values of P19, P18, P17, P16, P14, P13, P12, P11, P9, P8, P7, P6, P4, P3, P2, and P1 are used. When creating the interpolation target pixel Q13d, the pixel values of P9, P14, P19, P24, P8, P13, P18, P23, P7, P12, P17, P22, P6, P11, P16, and P21 are used.

  Here, the calculation process when creating Q13a will be described.

  Pixel values of P7, P8, P9, P10, P12, P13, P14, P15, P17, P18, P19, P20, P22, P23, P24, P25 are m7, m8, m9, m10, m12, m13, m14, Since m15, m17, m18, m19, m20, m22, m23, m24, and m25, the relationship between these pixel values and the weighting coefficient for each of these pixel values is as follows.

Pixel position
m7 m8 m9 m10
m12 m13 m14 m15
m17 m18 m19 m20
m22 m23 m24 m25
Weighting factor corresponding to each pixel position
w7 w8 w9 w10
w12 w13 w14 w15
w17 w18 w19 w20
w22 w23 w24 w25
The weighting coefficient at each pixel position is actually obtained from a piecewise polynomial according to the positional relationship between the interpolation target pixel and each original pixel. The pixel value m13a of the interpolation target pixel Q13a is obtained by the sum of the multiplication of the pixel values of the plurality of original pixels and the corresponding weighting factors. That is, the pixel value m13a of Q13a is
m13a = m7 × w7 + m8 × w8 + m9 × w9 + m10 × w10 + m12 × w12 + m13 × w13 + m14 × w14 + m15 × w15 + m17 × w17 + m18 × w18 + m19 × w19 + m20 × w20 + m22 × w22 + m23 × w23 + m24 × w24 + m25 × w25
It becomes.

  An example of a specific 4 × 4 weighting coefficient obtained using a piecewise polynomial is shown below as the first calculation coefficient. The first calculation coefficient includes 16 weight coefficients corresponding to the 16 original pixels used for the interpolation process. The first calculation coefficient is expressed with 16-bit accuracy. The pixel value of the interpolation target image is obtained by calculating the sum of the multiplication of the pixel value of each of the plurality of original pixels and the corresponding weight coefficient, and then dividing the sum by 65536 (16 bits). That is, the pixel value m13a of Q13a is generated by calculating a weighted average of 16 original pixels using a 4 × 4 weighting coefficient.

First calculation coefficient
324 -3996 -1044 108
-3996 49284 12876 -1332
-1044 12876 3364 -348
108 -1332 -348 36
In the interpolation method using a normal bicubic function, the pixel value of the interpolation target pixel is obtained by the above method.

  However, with such a pixel interpolation method, the generated image becomes a blurred image. In addition, if the weighting factor is easily manipulated, overcorrection may occur depending on the content of the original image, resulting in an unnatural image or an unnatural singularity.

  In view of such a phenomenon, in the interpolation processing according to the present embodiment, a plurality of types prepared in advance according to the difference value of pixel values between two or more predetermined original pixels located in the vicinity of the interpolation target pixel. One of the calculation coefficients is selected. Then, a weighted average of a plurality of original pixels surrounding the interpolation target pixel is calculated using the selected calculation coefficient. As a result, it is possible to effectively emphasize the minute signal component while suppressing overcorrection of a large signal change portion and occurrence of an unnatural singularity, and to produce a stereoscopic effect of the generated image. It becomes possible.

  FIG. 7 shows a specific configuration example of the interpolation processing unit 301.

  The interpolation processing unit 301 obtains the pixel value of the interpolation target pixel based on the pixel values of the plurality of original pixels surrounding the interpolation target pixel by interpolation using a piecewise polynomial approximating the sin (x) / x function. This is a calculation device, and includes a pixel replacement circuit 200 and a pixel value difference detection circuit 300.

  The pixel replacement circuit 200 is for generating an output image signal from an input image signal, and includes an arithmetic circuit 210, an arithmetic coefficient storage unit 220, and a coefficient selector switch 230. The calculation coefficient storage unit 220 stores a plurality of types of calculation coefficients k1 to kn. Each of the operation coefficients k1 to kn is composed of 16 weight coefficients corresponding to 16 pixels.

  The input image signal is supplied to the pixel replacement circuit 200 and the pixel value difference detection circuit 300. The pixel value difference detection circuit 300 detects a difference value of pixel values between two or more predetermined original pixels located in the vicinity of the interpolation target pixel, and uses the detected difference value as a coefficient switching signal to the coefficient switching switch 230. Supply.

  The coefficient changeover switch 230 selects one of a plurality of types of calculation coefficients k1 to kn according to the coefficient changeover signal. The arithmetic circuit 210 calculates a weighted average of the 16 original pixels surrounding the interpolation target pixel using the selected calculation coefficient (16 weighting coefficients), and uses the calculated weighted average value as the pixel value of the interpolation target pixel. Output as.

  Here, each calculation coefficient stored in the calculation coefficient storage unit 220 will be described.

  The first calculation coefficient k1 is composed of 16 weight values each obtained from a piecewise polynomial. In the second calculation coefficient k2 and the third calculation coefficient k3, the value of each weighting coefficient is different from that of the first calculation coefficient k1. Numerical examples of the second calculation coefficient k2 and the third calculation coefficient k3 are shown below.

Second calculation coefficient
500 -6000 -2000 200
-6000 52586 14000 -2000
-2000 14000 5000 -500
200 -2000 -500 50
Third calculation coefficient
1000 -10000 -3000 300
-10000 61836 15000 -4000
-3000 15000 8000 -1000
300 -4000 -1000 100
Many numerical examples other than the second and third arithmetic coefficients can be considered, but are omitted here. The sum of 16 weighting factors included in each of the second and third calculation coefficients is the same as the sum of 16 weighting coefficients (= 65536) included in the first calculation coefficient. Further, in each of the second and third calculation coefficients, the absolute value of each weight coefficient is larger than the absolute value of the corresponding weight coefficient included in the first calculation coefficient. In this case, the absolute value of each weight coefficient included in the third calculation coefficient is larger than the absolute value of the corresponding weight coefficient included in the second calculation coefficient.

  Further, in each of the second and third calculation coefficients, the sign of each weighting coefficient is the same as the sign of the corresponding weighting coefficient included in the first calculation coefficient. In each of the second and third calculation coefficients, the magnitude relationship between the weighting coefficients in the first calculation coefficient is maintained as it is. That is, the magnitude relationship between the 16 weighting factors included in each of the second and third calculation coefficients is the same as the magnitude relationship between the 16 weighting factors included in the first calculation coefficient.

  In each of the second and third calculation coefficients, the degree of influence of each peripheral pixel on the interpolation target pixel is greater than that of the first calculation coefficient. Therefore, when pixel interpolation is performed using only the second or third arithmetic coefficient, sharpness can be generated in the entire output image. However, an unnatural output image can be obtained in a place where the change in the pixel value is large. A singular point may occur in the output image. Therefore, in the present embodiment, the calculation coefficient to be used is dynamically switched between a place where the change in pixel value is large and a place where the change is small.

  The pixel value difference detection circuit 300 detects a change in pixel value between peripheral pixels of the interpolation target pixel. A specific example will be described below.

  When the pixel to be interpolated is Q13a in FIG. 4, the pixel value difference detection circuit 300 checks a change in the peripheral pixel value of the nearest neighbor pixel P13 of Q13a. For example, the pixel value difference detection circuit 300 calculates the absolute value of the difference value of the pixel values between the original pixel P7 and the original pixel P19 on the extension line of the straight line connecting P13 and Q13a, that is, | m7−m19 |. . Then, the pixel value difference detection circuit 300 compares the absolute value | m7-m19 | of the pixel difference value with a predetermined threshold value, and determines the magnitude relationship between | m7-m19 | and the threshold value. When the absolute value of the pixel difference value is equal to or greater than the threshold value, the first calculation coefficient is selected by the coefficient changeover switch 230. When the absolute value of the pixel difference value is smaller than the threshold value, the calculation coefficient used is switched in the order of the second calculation coefficient and the third calculation coefficient as the absolute value of the pixel difference value decreases.

  As described above, by appropriately changing the value of the 4 × 4 weighting factor according to the absolute value of the pixel difference value, the image enlarged by the interpolation processing becomes a natural and sharp image.

  Note that the number of original pixels to be compared does not have to be two, and the change in the peripheral pixel values of the interpolation target pixel Q13a may be examined based on the pixel values of a plurality of pixels near the interpolation target pixel Q13a.

  Next, the procedure of the interpolation processing of this embodiment will be described with reference to the flowchart of FIG.

  First, the absolute value of the pixel difference value between two or more pixels in the vicinity of the interpolation target pixel is detected (step S11). Then, one of the first calculation coefficient, the second calculation coefficient, and the third calculation coefficient is selected according to the magnitude of the absolute value of the pixel difference value (steps S12 to S15). Thereafter, an interpolation process is performed in which a weighted average value of 4 × 4 original pixels surrounding the interpolation target pixel is calculated as a pixel value of the interpolation target pixel using a 4 × 4 weighting factor included in the selected calculation coefficient. (Step S16).

  Here, the 4 × 4 weight coefficient value obtained from the piecewise polynomial is used as it is as the first calculation coefficient, but this is not necessarily the case. For example, a part of a 4 × 4 weight coefficient value obtained from a piecewise polynomial may be used as the first calculation coefficient. In this embodiment, the description has been made on the basis of the 4 × 4 16 pixels as the peripheral pixels used when creating the interpolation pixel. However, the pixel need not necessarily be 16 pixels, and the coefficient accuracy is not necessarily 16 bits. There is no need.

  In the above description, it goes without saying that the pixel value may be either a luminance / color difference signal or an RGB signal. It is also possible to perform interpolation processing using only the luminance signal. In addition, similar effects can be obtained by using the configuration described in the present embodiment in other pixel interpolation methods such as bicubic convolution interpolation and fluency theory (Japanese Patent Laid-Open No. 11-353472). Needless to say.

  Further, all of the interpolation processing of this embodiment can be executed by a computer program. Therefore, the same effect as that of the present embodiment can be easily obtained simply by introducing a computer program that causes a computer to execute the interpolation processing procedure to a normal computer through a computer-readable storage medium.

  Further, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine a component suitably in different embodiment.

The perspective view showing the general view of the computer concerning one embodiment of the present invention. The block diagram which shows the system configuration | structure of the computer of FIG. The block diagram which shows the function structure of the video application program used with the computer of FIG. The figure for demonstrating the example of the image data interpolated by the computer of FIG. The figure for demonstrating the function of sin (x) / x. The figure for demonstrating the characteristic of the bicubic function which approximates sin (x) / x. The block diagram which shows the structure of the interpolation process part provided in the computer of FIG. The flowchart explaining the procedure of the interpolation process performed in the computer of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Computer, 111 ... CPU, 114 ... Graphics controller, 201 ... Video application program, 200 ... Pixel replacement circuit, 210 ... Arithmetic circuit, 220 ... Arithmetic coefficient storage unit, 230 ... Coefficient changeover switch, 300 ... Pixel value difference detection circuit .

Claims (12)

An image processing apparatus that calculates a pixel value of an interpolation target pixel based on pixel values of a plurality of original pixels surrounding the interpolation target pixel by an interpolation process using a piecewise polynomial that approximates a sin (x) / x function. There,
Storage means for storing a plurality of types of calculation coefficients each including a plurality of weighting coefficients corresponding to each of the plurality of original pixels;
Among the plurality of original pixels, an original pixel on an extension line of a straight line connecting the nearest original pixel of the interpolation target pixel and the interpolation target pixel, and among the pixels other than the nearest original pixel Detecting means for detecting an absolute value of a difference between pixel values between two predetermined original pixels located on both sides of the nearest original pixel ;
Selection means for selecting one of the plurality of types of calculation coefficients in accordance with an absolute value of the detected difference;
An image processing apparatus comprising: a calculation unit that calculates a weighted average of the plurality of original pixels using the calculation coefficient selected by the selection unit to calculate a pixel value of the interpolation target pixel. .   The image processing apparatus according to claim 1, wherein absolute values of individual weighting coefficients are different between the plurality of types of calculation coefficients. The plurality of types of calculation coefficients include a first calculation coefficient in which a value of each of the plurality of weighting coefficients is calculated according to the piecewise polynomial, and an absolute value of each of the plurality of weighting coefficients is included in the first calculation coefficient. A second arithmetic coefficient larger than the plurality of weighting coefficients,
The selecting means selects the second calculation coefficient when the detected absolute value of the difference is smaller than a predetermined threshold, and when the detected absolute value of the difference is equal to or greater than the threshold, 2. The image processing apparatus according to claim 1, further comprising means for selecting one calculation coefficient. The plurality of types of calculation coefficients include a first calculation coefficient in which a value of each of the plurality of weighting coefficients is calculated according to the piecewise polynomial, and an absolute value of each of the plurality of weighting coefficients is included in the first calculation coefficient. Each of the plurality of weighting factors included in the second calculation coefficient and the magnitude relationship between the weighting factors is the first calculation The sign of each of the plurality of weighting factors included in the coefficient is the same as the sign and the magnitude relationship between the weighting factors,
The selecting means selects the second calculation coefficient when the detected absolute value of the difference is smaller than a predetermined threshold, and when the detected absolute value of the difference is equal to or greater than the threshold, 2. The image processing apparatus according to claim 1, further comprising means for selecting one calculation coefficient. An image processing method for calculating a pixel value of an interpolation target pixel based on pixel values of a plurality of original pixels surrounding the interpolation target pixel by an interpolation process using a piecewise polynomial approximating a sin (x) / x function. There,
Among the plurality of original pixels, an original pixel on an extension line of a straight line connecting the nearest original pixel of the interpolation target pixel and the interpolation target pixel, and among the pixels other than the nearest original pixel Detecting an absolute value of a pixel value difference between two predetermined original pixels located on both sides of the nearest original pixel ;
In accordance with the absolute value of the detected difference, a selection step of selecting one of a plurality of types of calculation coefficients each including a plurality of weighting coefficients corresponding to the plurality of original pixels,
An image processing method comprising: calculating a weighted average of the plurality of original pixels using the selected calculation coefficient in order to calculate a pixel value of the interpolation target pixel.   The image processing method according to claim 5, wherein absolute values of individual weighting coefficients are different between the plurality of types of calculation coefficients. The plurality of types of calculation coefficients include a first calculation coefficient in which a value of each of the plurality of weighting coefficients is calculated according to the piecewise polynomial, and an absolute value of each of the plurality of weighting coefficients is included in the first calculation coefficient. A second arithmetic coefficient larger than the plurality of weighting coefficients,
The selecting step selects the second calculation coefficient when the detected absolute value of the difference is smaller than a predetermined threshold, and when the detected absolute value of the difference is greater than or equal to the threshold, 6. The image processing method according to claim 5, wherein one calculation coefficient is selected. The plurality of types of calculation coefficients include a first calculation coefficient in which a value of each of the plurality of weighting coefficients is calculated according to the piecewise polynomial, and an absolute value of each of the plurality of weighting coefficients is included in the first calculation coefficient. Each of the plurality of weighting factors included in the second calculation coefficient and the magnitude relationship between the weighting factors is the first calculation The sign of each of the plurality of weighting factors included in the coefficient is the same as the sign and the magnitude relationship between the weighting factors,
The selecting step selects the second calculation coefficient when the detected absolute value of the difference is smaller than a predetermined threshold, and when the detected absolute value of the difference is greater than or equal to the threshold, 6. The image processing method according to claim 5, further comprising means for selecting one calculation coefficient. Image processing for calculating a pixel value of an interpolation target pixel based on pixel values of a plurality of original pixels surrounding the interpolation target pixel by interpolation processing using a piecewise polynomial approximating a sin (x) / x function A program for causing a computer to execute
Among the plurality of original pixels, an original pixel on an extension line of a straight line connecting the nearest original pixel of the interpolation target pixel and the interpolation target pixel, and among the pixels other than the nearest original pixel A procedure for causing the computer to execute a process of detecting an absolute value of a difference between pixel values between two predetermined original pixels located on both sides of the nearest original pixel ;
A procedure for causing the computer to perform a selection process for selecting one of a plurality of types of calculation coefficients each including a plurality of weighting coefficients corresponding to the plurality of original pixels according to the detected absolute value of the difference; ,
And a procedure for causing the computer to execute a process of calculating a weighted average of the plurality of original pixels using the selected calculation coefficient in order to calculate a pixel value of the interpolation target pixel. program.   10. The program according to claim 9, wherein absolute values of individual weighting coefficients are different among the plurality of types of calculation coefficients. The plurality of types of calculation coefficients include a first calculation coefficient in which a value of each of the plurality of weighting coefficients is calculated according to the piecewise polynomial, and an absolute value of each of the plurality of weighting coefficients is included in the first calculation coefficient. A second arithmetic coefficient larger than the plurality of weighting coefficients,
The selection process selects the second calculation coefficient when the detected absolute value of the difference is smaller than a predetermined threshold, and when the detected absolute value of the difference is greater than or equal to the threshold, The program according to claim 9, further comprising a process of selecting one arithmetic coefficient. The plurality of types of calculation coefficients include a first calculation coefficient in which a value of each of the plurality of weighting coefficients is calculated according to the piecewise polynomial, and an absolute value of each of the plurality of weighting coefficients is included in the first calculation coefficient. Each of the plurality of weighting factors included in the second calculation coefficient and the magnitude relationship between the weighting factors is the first calculation The sign of each of the plurality of weighting factors included in the coefficient is the same as the sign and the magnitude relationship between the weighting factors,
The selection process selects the second calculation coefficient when the detected absolute value of the difference is smaller than a predetermined threshold, and when the detected absolute value of the difference is greater than or equal to the threshold, The program according to claim 9, further comprising a process of selecting one arithmetic coefficient.

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