KR20010077514A - Method and Apparatus for Interpolating a Digital Image - Google Patents

Abstract

The present invention relates to a method and apparatus provided for interpolating a digital image according to the required sharpness. An adjustment signal is then generated that represents the required sharpness. Interpolated pixel data is computed based on a quadratic interpolation function for two sampling input pixels using an adjustable weighting factor indicative of the selected sharpness. The apparatus of the present invention mainly includes a control interface, a control unit, a vertical interpolation calculation module, and a horizontal interpolation module. The vertical interpolation calculation module and the horizontal interpolation module are executed according to the interpolation function derived by the present invention. The control unit consists of a lookup table created according to the scaling function of the present invention. The vertical scaling factor and the horizontal scaling factor required for the interpolation function can be obtained by finding the search table according to the adjustment signal and the position of the interpolated pixel. Thus, the present invention can control the sharpness without the need to install an additional sharpness control circuit.

Description

Method and Apparatus for Interpolating Digital Image {Method and Apparatus for Interpolating a Digital Image}

Field of invention

The present invention relates to a method and apparatus for adjusting picture quality of a digital image display screen. More specifically, the present invention relates to a method and apparatus for adjusting the image quality of a liquid crystal display (LCD) according to the required sharpness by providing a second interpolation function.

Background

For digital displays, such as liquid crystal displays (LCDs), digital micro-mirrors (DVDs), and plasma displays, interpolation and frame rates if the resolution or image frame rate is different from the resolution or image frame rate of the source image. You need an image scaler for the transformation. Image up-scaling or image down-scaling refers to a change in image resolution. In order to up-scale the image, the position and gray level of the interpolated pixel must be computed and inserted into a fixed position relative to the interpolated pixel. The newly interpolated pixel is deeply related to its neighboring pixel. The relationship between the interpolated pixel and its neighboring pixels is expressed as the weight of the distance function. Such a relationship is defined as an interpolation function. The newly interpolated pixel may be computed by a convolution operation based on the interpolation function and the sampling input pixel. Moreover, the image quality of the digital image is determined by the interpolation function applied to it.

1 is a schematic diagram showing the structure of a control board of a conventional LCD.

The structure includes an LCD monitor 11, an image scaler 12, and an analog / digital converter 13. The analog-to-digital converter 13 accepts analog input data from a host computer and then converts it to a digital signal. In general, the gray level of a pixel can be represented by 8 bits. Image scaler 12 is responsible for up-scaling or down-scaling of image size, and frame rate conversion. The resulting output of the interpolated image is then shown on the LCD monitor 11.

2 is a schematic diagram showing the resize setting of a digital image.

When the image is scaled up, the input of the image scaler 12 is 8 pixels, while the output of the image scaler 12 is 16 pixels. In this case, the position of the input pixel 21 does not correspond one-to-one with the output pixel 22. As such, to provide smooth continuity on the digital image output, interpolated pixels must be inserted into the source image.

Interpolation techniques determine the image quality of a digital image generated by an image scaler. In theory, the number of sampling input pixels and the order of the interpolation function are proportional to the performance of the calculated result. In practice, however, the most widely used method is to determine interpolated pixel data based on two or three sampling input pixels.

3 is a schematic diagram illustrating an interpolation method based on two sampling input pixels.

The gray level of the interpolated pixel Y (x) may be calculated from A and B, which are sampling input pixels. The gray level of Y (x) can be obtained from the following interpolation function:

About 0≤x <1

Y (x) = (1-S _c (x)) × A + S _c (x) × B; ----------(One)

Where A and B represent the sampling input pixel closest to the interpolated pixel, and x represents the position of the interpolated pixel relative to B. S _c (x) is a scaling function for computing the scaling factor for the interpolation function.

The two most common interpolation methods used in the art are the Linear Interpolation Method and the Near Neighboring Method. The value of the scaling factor according to the near method is shown in FIG. 4. The scaling factor can be obtained by the following formula:

For 0 ≦ x <0.5, S _c (x) = 0;

For 0.5 ≦ x <1, S _c (x) = 1.

The advantage of the near method is that the contrast of the image is satisfactory and the circuit design according to the near method is simple. However, the method has the disadvantage that the interpolated image output cannot be scaled up evenly.

For comparison, the value of the scaling factor S _c (x) according to the linear interpolation method is shown in FIG. 5. The scaling factor S _c (x) can be obtained as follows:

For 0 ≦ x <1, S _c (x) = x.

In general, the image quality generated by the linear interpolation method is superior to the image quality of the near method. The interpolated image output can be scaled up evenly. However, if interpolated according to linear interpolation, the boundary of the image will be blurred in the case of an image having a strong contrast such as text.

As such, the technique of the image scaler as to how to maintain the image quality of the image after resizing and to simplify the circuit design for the interpolation function in hardware / firmware is a significant problem. Moreover, conventional LCD monitors do not provide a function for adjusting the sharpness. It is desirable for the user to provide a function for manually adjusting the sharpness of the source image.

It is an object of the present invention to provide a method and apparatus for adjusting the image quality of a digital image by dynamically adjusting a weighting factor required for the second interpolation function derived by the present invention.

Another object of the present invention is to flexibly adjust the sharpness of an image.

Another object of the present invention is to simplify the circuit design to reduce manufacturing costs.

The above and other objects of the present invention can be achieved by the present invention described below. Hereinafter, the content of the present invention will be described in detail.

1 is a schematic view showing the structure of a conventional LCD control board.

2 is a schematic diagram showing the resize setting of a digital image.

3 is a schematic diagram illustrating an interpolation method based on two sampling input pixels.

4 is a diagram of a scaling factor according to a conventional near neighboring method.

5 is a diagram of a scaling factor according to a conventional linear interpolation method.

6 is a diagram of a scaling factor according to a quadratic interpolation function of a preferred embodiment of the present invention.

7 is an exemplary diagram of a scaling factor according to the quadratic interpolation function of a preferred embodiment of the present invention.

8 is a circuit block diagram showing an interpolation calculation module executed according to a quadratic interpolation function of a preferred embodiment of the present invention.

9 is a circuit block diagram showing an image scaler implemented according to a quadratic interpolation function of a preferred embodiment of the present invention.

10 is a circuit block diagram showing the structure of a control unit of an image scaler according to a preferred embodiment of the present invention.

In one aspect of the invention, the apparatus of the invention mainly comprises a control interface, a control unit, a vertical interpolation calculation module, and a horizontal interpolation module. The control interface generates an adjustment signal in accordance with the required sharpness. The vertical interpolation calculation module and the horizontal interpolation module are executed according to the interpolation function derived by the present invention. The control unit consists of a lookup table created according to the scaling function of the present invention. The lookup table stores the precalculated vertical scaling factor and the horizontal scaling factor of the interpolated function defined as Y (x) = S _c (x) × (BA) + A. The scaling function S _c (x) is defined as follows:

S _c (x) = 2 (1-α) x ² + αx, 0 ≦ x <0.5;

S _c (x) =-2 (1-α) x ² + (4-3α) × x + α−1, 0.5 ≦ x <1.

The vertical interpolation calculation module calculates interpolated pixel data from two sampling input pixels according to the scaling factor output of the control unit. After the vertical interpolation procedure is finished, the resulting image data is sent to the horizontal interpolation module. The horizontal interpolation module then calculates the interpolated pixel data based on the resulting image output data after vertical interpolation according to the scaling factor output from the control unit. After completing the horizontal interpolation, the interpolated image data appears on the digital image display.

Another aspect of the present invention provides a method for adjusting the image quality of a digital display device. The method includes the following steps: First, a lookup table for storing the pre-calculated vertical and horizontal scaling factors of the interpolation function defined as Y (x) = S _c (x) × (BA) + A. Make The scaling function S _c (x) is

S _c (x) = 2 (1-α) x ² + αx, 0 ≦ x <0.5;

S _c (x) =-2 (1-α) x ² + (4-3α) × x + α−1, 0.5 ≦ x <1.

Is defined as

Then, the desired sharpness is selected, and the weighting coefficient α according to the desired sharpness is calculated. Then, the vertical scaling factor and the horizontal scaling factor are determined by looking up the lookup table according to the weighting coefficient α. Then, calculate vertically interpolated pixel data based on every two sampling input pixels from the source image according to the vertical scaling factor, and generate a vertically interpolated image output. Then, horizontally interpolated pixel data is calculated based on the vertically interpolated image output and a resultant interpolated image output is generated according to the horizontal scaling factor. Finally, the resulting horizontal interpolated image output is displayed on the screen after the source image is fully interpolated.

The present invention provides a control interface on a digital image display such as a liquid crystal display (LCD) to adjust the sharpness of the source image in accordance with the weighting coefficient α. The most significant difference between the present invention and the prior art is that the value of the weighting coefficient α can change dynamically according to the needs of the user. The control interface may be executed by hardware, software, or firmware in a manner known in the art.

The image quality of the resulting image output using conventional near or linear interpolation can be improved by modifying the interpolation function adopted by the prior art. Thus, the present invention derives the improved interpolation function from the above-mentioned equation (1). According to a preferred embodiment of the invention, the quadratic interpolation function can be derived by the following steps:

If the scaling function S _c (x) is set to S _c (x) = a × x ² + b × x + c,

For 0 ≦ x <0.5, S _c (x) must satisfy three conditions:

S _c (0) = 0; S _c (0.5) = 0.5; S _c '(0) = α

In the above, α represents a weighting coefficient according to the adjustment signal from the control interface, and has a range of 0 to 1. The scaling function is derived as follows:

S _c = 2 (1-α) x ² + αx

For 0.5≤x≤1, S _c (x) must satisfy three conditions:

S _c (1) = 1; S _c (0.5) = 0.5; S _c '(1) = α

Finally, you get the following scaling function:

S _c (x) =-2 (1-α) x ² + (4-3α) × x + α-1

In the above formula, α represents a weighting coefficient and has a range of 0 to 1. When α = 0, the smoothness of the interpolated image output is certainly improved. Moreover, the contrast of the interpolated image output decreases as the value of α increases. As such, the value of the interpolation factor according to the quadratic interpolation function is shown in FIG. 6.

After obtaining the modified interpolation function as mentioned above, the sharpness for the digital image can be changed dynamically according to the method of the present invention.

Step 1: A control interface is provided to select the sharpness desired by the user, and then the weighting coefficient α is calculated according to the user's selection.

Step 2: Sequentially compute the vertically interpolated pixel data according to the weighting coefficient α based on the two sampling input pixels from the source image according to the second order scaling function.

Step 3: Next, the horizontal interpolated pixel data is sequentially sequentially based on the interpolated image data output of Step 2 according to the second scaling function defined by Y (x) = S _c (x) × (BA) + A. Compute: where Y (x) represents the interpolated pixel value and S _c (x) represents the scaling function.

For convenience of operation and simplicity of circuit design, the scaling factor values may be precalculated according to the scaling function S _c (x) and stored in the lookup table.

With reference to FIG. 7, the figure shows the value of the scaling factor according to the method of the present invention using ten sampling input pixels. From the illustration of Figure 7, the advantages of the present invention are evident. The interpolated image output according to the present invention can improve or preserve image clarity and is thus superior to conventional linear interpolation. Compared with the conventional near method, interpolation image output according to the present invention can also reduce contrast noise. Furthermore, by providing the adjustable weighting coefficient α, the present invention can save the cost of installing a separate circuit for adjusting the sharpness.

The interpolation function derived as described above may be executed by hardware. The interpolation function 1 can be simplified and modified as follows:

Y (x) = S _c (x) × (BA) + A. ---------(2).

According to the interpolation function (2), the circuit design for computing the interpolated pixel data is shown in FIG. The circuit consists of only two adders and one multiplier.

Since the interpolation function is performed based on Cartesian coordinates, the interpolation procedure first performs vertical interpolation and then horizontal interpolation based on the source image. The general structure of the image scaler is shown in FIG. With reference to FIG. 9, the user can select the sharpness from the control interface 90 to adjust the sharpness on the source image. In response to the user's selection, an adjustment signal 96 is generated and input to the control unit 92. The control interface 90 may be executed by software, hardware, or firmware.

Since the interpolation procedure is to perform vertical interpolation first, the sampling input pixels A and B are read sequentially from lines A and B of the source image, and are input to the vertical interpolation calculation module 91. The vertical interpolation calculation module 91 calculates the interpolated pixel data Y (x) according to the interpolation function (2). The scaling function S _c (x) is then obtained from the control unit 92.

The control unit 92 determines the vertical scaling factor by looking up the lookup table according to the adjustment signal 96, and then outputs the vertical scaling factor S _c _ v to the vertical interpolation calculation module 91. After finishing the vertical interpolation procedure, the resulting interpolated image is sent to the horizontal interpolation calculation module 93 via the delay module.

The horizontal interpolation calculation module 93 calculates the interpolated pixel data Y (x) based on the interpolated image output as the result of the vertical interpolation calculation module 91 according to the interpolation function (2). The horizontal scaling factor S _c _ h is input from the control unit 92. The horizontal scaling factor is also calculated by looking up the lookup table 103. Finally, the resulting interpolated image data is output to the display after finishing the interpolation procedure.

The control unit 92 can be seen more clearly from FIG. 10. The control unit 92 can calculate the horizontal and vertical scaling factors of S _c (x) by looking up the lookup table 103. After the user selects the sharpness for the image output, the weighting coefficient α representing the selectivity is input to the scaling factor calculation module 104 to be calculated according to the scaling function S _c (x). The weighting coefficient α has a value between 0 and 1. The scaling factor calculation module 104 may be executed by firmware. The scaling function for the quadratic interpolation function is:

S _c (x) = 2 (1-α) x ² + αx, 0 ≦ x <0.5;

S _c (x) =-2 (1-α) x ² + (4-3α) × x + α−1, 0.5 ≦ x <1.

The precalculated data of the quadratic scaling function may be stored in the lookup table 103. As a result, the scaling factor can be easily found by the indication of the weighting coefficient α and the position of the interpolated pixel x. The lookup table 103 may be implemented in Synchronous Random Access Memory (SRAM).

The position of the interpolated pixel x may be calculated by the scaling controller 105 in accordance with the vertical scaling signal 102 and the horizontal scaling signal 101. Since the scaling factor of the corresponding pixel has been stored in was pre-calculated lookup table 103, the interpolated pixels x horizontal scaling factor value of S _c _h and the value of the vertical scaling factor S _c _v is simply a lookup table (103) You can find out by looking for it. As such, using the lookup table 103 and the scaling factor calculation module 104, the circuit design can be simplified. Moreover, since the present invention can provide better sharpness, it does not require additional circuitry for sharpness adjustment.

In summary, the apparatus and method of the present invention can improve the quality of a digital image by providing an adjustable weighting factor for the quadratic interpolation function. As a result, the present invention can reduce contrast noise while preserving or improving image clarity due to the output of the desired image. The present invention can also improve the smoothness in the edge region. Moreover, the present invention can control the desired sharpness without installing additional circuitry.

The method and apparatus for interpolating a digital image of the present invention can flexibly adjust the sharpness of an image because the image quality of the digital image can be adjusted by dynamically adjusting a weighting factor required for the second interpolation function. In addition, the circuit design can be simplified to reduce the manufacturing cost.

The present invention has been described with respect to the described embodiments, which are not intended or intended to be limiting. Various modifications and combinations of the embodiments described in addition to the embodiments of the invention will be apparent to those skilled in the art with respect to the above description. It is therefore intended that the appended claims cover such modifications or embodiments.

Claims (8)

Control interface means for generating an adjustment signal in accordance with the selected sharpness; A scaling factor calculation module coupled to the control interface means for calculating a value of a weighting factor in accordance with the adjustment signal; A control unit connected to the scaling factor calculation module for determining a vertical scaling factor and a horizontal scaling factor by finding a lookup table according to the weighting factor, wherein the lookup table is Y (x) = S _c (x) × (BA) + Stores the pre-calculated vertical scaling factor and the horizontal scaling factor of the interpolation function Y (x) defined by A, wherein the scaling function S _c (x) is Sc (x) = 2 (1-α) x² + αx, 0 ≦ x <0.5 Sc (x) =-2 (1-α) x² + (4-3α) × x + α−1, 0.5 ≦ x <1 And A and B represent two sampling input pixels closest to the interpolated pixel, x represents the position of the interpolation pixel with respect to A, and α represents a weighting factor; A vertical interpolation calculation module coupled to the control unit to calculate vertically interpolated pixel data based on every two input pixels coming from the source image according to the vertical scaling factor coming from the control unit and to calculate a vertical interpolated result; A horizontal interpolation calculation module coupled to the control unit for calculating horizontal interpolated pixel data based on the vertical interpolated result, and for calculating the resulting interpolated image data according to the horizontal scaling factor from the control unit; And Display means for displaying the resulting interpolated image data on a screen; Apparatus for interpolating a digital image according to the selected sharpness, characterized in that consisting of. An apparatus for interpolating a digital image according to a selected sharpness according to claim 1, wherein said weighting coefficient α has a range of 0-1. The digital image interpolation according to the selected sharpness of claim 1, wherein the vertical interpolation module and the horizontal interpolation module are operated by Y (x) = S _c (x) × (BA) + A. Device for An apparatus for interpolating a digital image according to a selected sharpness according to claim 1, wherein said control interface means can be implemented in software, hardware or firmware. The method of claim 1 wherein the apparatus for interpolating a digital image in accordance with the selected sharpness, characterized in that the scaling function S _c (x) that can be executed by firmware. Create a lookup table to store the precalculated vertical and horizontal scaling factors of the interpolated function defined by Y (x) = S _c (x) × (BA) + A, wherein the scaling function S _c ( x) is S _c (x) = 2 (1-α) x ² + αx, where 0 ≦ x <0.5 and S _c (x) =-2 (1-α) x ² + (4-3α) × x + α-1, defined as 0.5≤x <1, A and B represent input pixels closest to the interpolated pixel, x represents the position of the interpolated pixel relative to the position of A, and α represents a weighting factor; Selecting a desired sharpness and calculating a weighting coefficient α according to the desired selectivity; Determine a vertical scaling factor and a horizontal scaling factor by finding the lookup table according to the weighting coefficient α; Calculating vertically interpolated pixel data based on every two input pixels emanating from a source image according to the vertical scaling factor to yield a vertically interpolated result; Calculate a horizontal interpolated pixel based on the vertical interpolated result and calculate the resulting interpolated image data according to the horizontal scaling factor; And Presenting the horizontal interpolated result on the screen after the source image is interpolated; A method for interpolating a digital image according to a desired sharpness, characterized in that it comprises a step. 7. The digital according to the requested sharpness of claim 6, wherein the horizontal interpolated value and the vertical interpolated value are performed by an interpolation function Y (x) = S _c (x) × (BA) + A. Method for interpolating an image. 7. A method according to claim 6, wherein the weighting coefficient α has a range of 0-1.