JPH048088A - Offset sampling signal interpolation device - Google Patents

Abstract

PURPOSE:To prevent production of deterioration in a picture due to loopback distortion by selecting an interpolation means in response to the correlation between a picture element group comprising picture elements located around the interpolation picture element and plural other picture element group located around the picture element group and a distribution range of each level in plural picture elements. CONSTITUTION:A maximum value and a minimum value in a group phi detected by a maximum value minimum value detection circuit 16 are fed to a distribution range detection circuit 19. The distribution range detection circuit 19 calculates the distribution range of a picture element data and gives it to a comparator 18. The comparator 18 compares the above distribution range with a prescribed reference value Kc and when the distribution range is larger, an interpolation output from a 1st switch 5 is outputted. When the reference value is larger, an interpolation output from a 2-dimension interpolation circuit 3 is outputted by switching control of a 2nd switch 17. The optimum interpolation processing is implemented by selecting the interpolation circuits 1-3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an interpolation device for offset-sampled image signals, etc.

(Prior Art) A method called offset sampling has been known as a method for compressing bandwidth or reducing the amount of information when recording and transmitting various information signals such as image signals.

In the two-dimensional case, this offset sampling refers to the horizontal direction (X direction) and vertical direction (X direction) as shown in Figure 5.
The sampling interval (Tx, Ty) is set to twice the pixel interval (Hx, Hy) in the original signal, and the vertically adjacent sampling points are separated from each other by half the sampling interval (T x / 2). By performing such offset sampling, the transmission band can widen the spatial frequency components in the horizontal or vertical direction relative to the spatial frequencies in the diagonal direction, as shown in FIG. In addition, when displaying or printing out the offset sampled image signal as described above, interpolation is performed to interpolate the pixels between each sampling point (interpolated pixels) from the adjacent pixels, as shown in Figure 7. processing is required. This interpolation process functions as a spatial filter that passes the frequency components in the shaded area shown in Figure 6 and blocks the frequency components in the area including the turning point A.This interpolation process is based on sampling theory. Above, it is positioned as a post-filter.

By the way, offset sampling as described above is
This is a very effective method if the pre-filter before sampling is applied correctly, that is, if the band is sufficiently limited, but for example, due to hardware constraints, the pre-filter cannot be applied sufficiently. If the pre-filter is not applied sufficiently in order to widen the transmission band or to widen the transmission band, a problem of image deterioration due to generation of aliasing distortion may occur.

That is, if the prefilter is insufficient, the offset
When sampling is performed, the horizontal high-frequency components of the original signal are folded back as vertical high-frequency components as shown in Figure 8(a), and the vertical high-frequency components are folded back as shown in Figure 8(b). The components are folded back as high-frequency components in the horizontal direction.

For this purpose, for example, an image including a straight line portion as shown in FIG. 9(a) may be offset and synthesized as shown in FIG. Even if the above-mentioned interpolation processing is performed on the sampling signal, the aliasing distortion cannot be completely removed because the high-frequency components in the original signal cannot be separated from the high-frequency components due to aliasing. As a result, significant image deterioration occurs in the output image, such as uneven shading or blurring in straight line portions, as shown in FIG.

Therefore, in the past, a technique called an adaptive interpolation method was generally known as a technique for reducing the occurrence of aliasing distortion as described above.

This adaptive interpolation method determines whether it is better to interpolate from pixels in the horizontal direction or pixels in the vertical direction when performing interpolation processing on sampled image signals. Alternatively, it is detected whether it is better to perform interpolation using all surrounding pixels, and depending on this detection result, selectively select each spatial filter having the characteristics shown in FIGS. 10(a) to (C), for example. This method is used to remove unnecessary aliasing components. In this case, if the interpolated pixels are pixels forming a straight line in the horizontal direction, a filter having characteristics that allows more frequency components in the horizontal direction to pass, as shown in FIG. 10(a), should be used. Filters (removes) vertical frequency components including aliasing components.

(Problems to be Solved by the Invention) In the above-described adaptive interpolation method, the performance of the interpolation device is determined by the accuracy with which it is determined which interpolation method to use for interpolation.

That is, when there is a high probability that an erroneous determination will occur, there is a problem in that performing interpolation processing based on the erroneous determination not only reduces the original signal component but also increases aliasing distortion.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to accurately detect the "tendency" of peripheral images around interpolated pixels to prevent the occurrence of aliasing distortion. It is an object of the present invention to provide an interpolation device for offset sampling signals that can prevent offset sampling signals.

In order to achieve this object, the present invention provides a correlation between a pixel group made up of pixels located around the interpolated pixel and a plurality of other pixel groups located around this pixel group, and the interpolated pixel. An interpolation device for offset sampling signals, comprising a selection means for selecting one of the outputs of each of the interpolation means according to the distribution range of each level in a plurality of pixels located around the pixel; It provides:

(Function) According to the present invention configured as described above, the degree of correlation between a pixel group composed of pixels located around an interpolated pixel and a plurality of other pixel groups located around this pixel group is determined. By selecting the interpolation means accordingly, it is possible to perform interpolation processing based on the result of accurately determining the "tendency" around the interpolation pixel.

Thereby, it is possible to prevent the occurrence of aliasing distortion due to the conventional erroneous determination, and it is possible to prevent the occurrence of image deterioration due to the aliasing distortion.

In addition, in the present invention, the "trend" of changes in patterns, etc. around the interpolated pixel is detected by detecting the level distribution range of each pixel data, and the level changes around the interpolated pixel according to the detection result. When there are few pixels, interpolation output based on all surrounding pixels of the interpolation pixel is outputted in a single order, thereby making it possible to realize interpolation processing in which false determinations are less likely to occur.

(Embodiment) Hereinafter, a preferred embodiment of the offset sampling device according to the present invention will be described in detail with reference to FIGS. 1 to 4.

FIG. 1 is a block diagram showing the configuration of the interpolation device of this embodiment,
FIG. 2 is a layout diagram of each pixel used to detect a "tendency" around the interpolation pixel in this embodiment.

In this embodiment, it is detected whether the interpolation pixel should be interpolated starting from pixels in the horizontal direction, starting from pixels in the vertical direction, or using all surrounding pixels. Therefore, not only an adjacent pixel group φ consisting of four pixels A(φ) to D(φ) adjacent to the interpolation pixel in the horizontal and vertical directions, but also four pixels each including one pixel of each pixel in this group φ The degree of correlation between each of these groups φ to 4 is detected using peripheral pixel groups 1 to 4 consisting of the following.

That is, A/D (analog-digital) not shown.
Each pixel data of the group φ of predetermined bits (for example, 12 bits) outputted from a converter etc. is supplied to a horizontal interpolation circuit 1, a vertical interpolation circuit 2, and a two-dimensional interpolation circuit 3, respectively. Ru. In the horizontal interpolation circuit 1, each pixel data (A, B,
C.

Based on D), the value of the interpolated pixel is calculated by performing an interpolation calculation, for example, (B+D)/2. Similarly, the vertical interpolation circuit 2 calculates the value of the interpolated pixel by performing an interpolation operation, for example (A+C)/2, based on each pixel data of the supplied group φ. Further, in the two-dimensional interpolation circuit 3, based on each pixel data of the supplied group φ,
+C+D)/4 is performed to calculate the value of the interpolated pixel.

The interpolated pixel data calculated as described above are supplied to first switches 5 whose switching is controlled by an interpolation means selection circuit 4, which will be described later.

Furthermore, each pixel data of the group φ is stored in the binarization circuit 1.
Binarized at 0, the first to fourth correlation calculation circuits 6
．． 7.8.9 respectively.

Here, each of the binarization circuits 10 converts each supplied pixel data into an average value (threshold value) supplied from an average value calculation circuit 11 that sequentially determines the threshold value according to the pixel data of the group φ. The data is binarized accordingly. Further, the average value calculation circuit 11 supplies threshold data sequentially determined according to the pixel data of the group φ to the binarization circuit 10 and other binarization circuits 12, 13, 14, and 15, which will be described later. do. That is, the average value calculation circuit 11 in this embodiment has the maximum value and minimum value of each pixel data in the group φ detected by the maximum value/minimum value detection circuit 16 to which each pixel data of the group φ is supplied. values are supplied, and the average value of these maximum and minimum values is used as the threshold value.

On the other hand, the first correlation calculation circuit 6 includes the group 1.
Each pixel data is binarized and supplied to a binarization circuit 12, and this first correlation degree calculation circuit 6 converts the supplied pixel data (binarized data) of group φ and pixel data of group 1. The degree of correlation between these groups is calculated based on (binarized data). Similarly, the second to fourth correlation calculation circuits 7 to 9 include groups 2 to 4.
Each pixel data of
The third correlation calculation circuit 8 calculates the correlation between group φ and group 3, and the fourth correlation calculation circuit 9 calculates the correlation between group φ and group 4. Calculate degree. The calculated outputs P(1) to P(4) from each of these correlation degree calculation circuits are supplied to the interpolation means selection circuit 4, respectively.

In this embodiment, the correlation degree P (N) is calculated by each of the correlation degree calculation circuits 7 to 9 as follows: P(N)=A(φ)■
A(N) + B(φ)■B(N) +C(φ) O
C(N) + D(φ) [phase] D(N) (N=1.
2, 3.4) It is performed based on the formula:

Furthermore, in the above equation, the calculation of X and Y follows the calculation rules as shown in the table below.

The correlation degree calculation output P (N) as described above is supplied to the interpolation means selection circuit 4, and this interpolation means selection circuit 4 selects the group φ that has the highest correlation degree based on the supplied output P (N). The group is detected, and a selection signal for selecting a predetermined interpolation method according to the detection result is supplied to the first switch 5.

The first switch 5 selectively supplies one of the interpolation outputs from the interpolation circuits specified by the selection signal to the second switch 17.

Further, the interpolation output from the two-dimensional interpolation circuit 3 is supplied to this second switch 17.
is controlled by the comparison output of the comparator 18 to selectively output the interpolation output from the two-dimensional interpolation circuit 3 or the interpolation output from the first switch 5.

That is, the maximum value and minimum value within the group φ detected by the maximum value/minimum value detection circuit 16 are detected by the distribution range detection circuit 1.
The distribution range detection circuit 19 calculates the difference between the maximum value and the minimum value, that is, the distribution range (for example, contrast) of the pixel data, and supplies it to the comparator 18.

Then, the comparator 18 compares the distribution range (biased position) with a predetermined reference value Kc, and if the distribution range is larger, that is, if there is a level change in brightness, color, etc. greater than a predetermined value around the interpolation pixel, If it exists, the interpolation output from the first switch 5 is output, and when the reference value is larger, that is, when there is little change around the interpolation pixel, the interpolation output from the two-dimensional interpolation circuit 3 is output. The switching of the second switch 17 is controlled as follows.

Note that the reference value Kc may be variably set, for example, while monitoring the interpolation output.

Next, to explain the operation of the interpolation device configured as described above, as shown in FIG.
), the difference between these values, that is, the above distribution range, and a predetermined reference value Kc are compared (step 2). If the reference value is larger, the interpolation output of the two-dimensional interpolation circuit is output (step 3).

On the other hand, if the above distribution range is larger than the predetermined reference value Kc, those with large correlations in the horizontal direction and those with large correlations in the vertical direction are calculated from each calculated output P (N) of each correlation calculation circuit. Step 4), and determine whether they are substantially equal (Step 5).

As a result, if they are equal, it is impossible to determine whether it is better to interpolate from pixels in the horizontal direction or pixels in the vertical direction, and the output of the two-dimensional interpolation circuit 3 is sent to the switch 5. A selection signal to be outputted from is output (step 3).

In addition, if they are not equal, determine the magnitude of the horizontal correlation degree and the vertical correlation degree (Step 6), and if the horizontal correlation degree is large, it is better to interpolate from the horizontal pixel. If the correlation in the vertical direction is large, the interpolation pixel is selected from the pixel in the vertical direction. It is determined that interpolation is better, and a selection signal is outputted to cause the output of the vertical interpolation circuit 2 to be output from the switch 5 (step 8).

In this way, in this embodiment, since the degree of correlation between the adjacent pixel group including the pixels adjacent to the interpolated pixel and the surrounding pixel group is detected, it is possible to determine whether it is better to interpolate the interpolated pixel starting from the horizontal pixel. , it is possible to accurately determine whether it is better to perform interpolation starting from pixels in the vertical direction or using all surrounding pixels.

Then, based on such accurate judgment, by selecting adjacent pixels to be used in calculations when calculating interpolation and interpolation pixels from data of adjacent pixels, that is, selecting interpolation circuits 1 to 3. Optimal interpolation processing can be performed.

Therefore, in this embodiment, aliasing distortion due to the above-mentioned erroneous determination hardly occurs, thereby making it possible to prevent image deterioration due to aliasing distortion.

Furthermore, as a result of simulation experiments conducted by the present applicant, it has been found that the probability of occurrence of an erroneous determination according to this embodiment is extremely small compared to the conventional method.

Furthermore, in the above-mentioned embodiment, by binarizing each pixel data supplied to each correlation degree comparison circuit,
Arithmetic processing in these circuits can be simplified,
As a result, processing speed can be increased and hardware can be downsized.

In addition, in this embodiment, by detecting the distribution range of each pixel in the group φ, a "trend J" of changes around the interpolated pixel is detected, and according to this detection result, there is little change around the interpolated pixel. In the above two-dimensional interpolation circuit 3
By outputting the interpolation output from the first place, it is possible to realize interpolation processing with fewer erroneous determinations. Note that the operation of detecting the "trend" of changes in patterns, etc. around the interpolation pixel and the operation of detecting the degree of correlation may be performed simultaneously in parallel or serially.

Incidentally, in the above embodiment, each group is composed of four pixels, but the present invention is not limited to this. For example, as shown in FIG. 4, each group is composed of more pixels (in this case, It is also possible to configure it with 12 pixels (12 pixels), so that more accurate "trend" determination can be made.

Note that in the above embodiment, two-dimensional offset and
Although the case of sampling has been described, it goes without saying that the present invention may be applied to an interpolation device when offset sampling is performed on a three-dimensional image such as a moving image.

Further, in the above-described embodiment, each of the interpolation circuits 1 to 3 uses only four pixels adjacent to the interpolation pixel for calculation and obtains the interpolation pixel by 1, but surrounding pixels may also be used for this calculation.

Further, in the above embodiment, each pixel data is binarized, but the present invention is not limited to binary conversion, and may be multi-valued depending on the required processing speed. Of course.

Furthermore, although the second switch 17 is particularly provided in the above-described embodiment, the present invention is not limited to such a configuration; for example, the comparison output of the comparator 18 may be supplied to the interpolation means selection circuit 4. The selection signal may be generated by

(Effects of the Invention) As is clear from the above description, according to the present invention, it is possible to select an optimal interpolation means from a plurality of interpolation means for calculating and interpolating interpolation pixels from an offset sampled signal. , since the decision is made based on the correlation between multiple pixel groups consisting of pixels located around this interpolated pixel, it is difficult to determine whether it is better to interpolate from pixels in the horizontal direction or from pixels in the vertical direction. It is possible to accurately determine whether it is better to perform interpolation or to interpolate using all surrounding pixels. Therefore, according to the present invention, it is possible to prevent the occurrence of aliasing distortion due to the above-described erroneous determination, and thereby it is possible to prevent image deterioration due to aliasing distortion.

In addition, in the present invention, the level distribution range of each pixel data around the interpolated pixel is detected, and according to the detection result, if there is little change around the interpolated pixel, all pixel data around the interpolated pixel is By outputting the interpolation output based on the first position, it is possible to realize interpolation processing with fewer erroneous determinations.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment according to the present invention,
2(a) and 2(b) are pixel arrangement diagrams showing the relationship between interpolated pixels and adjacent pixel groups and surrounding pixel groups, FIG. 3 is a flowchart showing the operation of the embodiment shown in FIG. 1, and FIG. 4 is a pixel arrangement diagram showing other relationships between interpolated pixels and adjacent pixel groups and peripheral pixel groups, Figure 5 is a diagram showing a two-dimensional offset sampling structure, and Figure 6 is a diagram of the band that can be transmitted by offset sampling. Figure 7 is a diagram showing the spatial frequency spectrum; Figure 7 is a diagram schematically showing the interpolation operation for restoring the original signal from sampling data;
Figures (a) and (b) are diagrams showing the spatial frequency spectrum of aliasing components, Figure 9 is a diagram showing an example of occurrence of aliasing distortion, and Figure 10 is a diagram showing an example of occurrence of aliasing distortion.
Figures (a) to (c) are characteristic diagrams of the interpolation circuit. 2... Vertical interpolation circuit, 3... Two-dimensional interpolation circuit, 4... Interpolation means selection circuit (selection means), 5... Switch, 6.7, 8.9... Correlation degree calculation Circuits, 10.12.1
3.14.15...Binarization circuit, 11...Threshold value determination circuit, 10...Distribution range detection circuit. Patent applicant: Canon Corporation 1...Horizontal interpolation circuit, V5 (branch) Lee Yunfee (removable 1)
pan) L: 9t, Fig. 7 Byonyamamoto / (d) (,,b) ○ ・ ・ ・ ○

Claims (1)

[Claims] A plurality of interpolation means that interpolate each other, and a degree of correlation between a pixel group composed of pixels located around the interpolated pixel and a plurality of other pixel groups located around this pixel group. and a selection means for selecting one of the outputs of each of the interpolation means according to the distribution range of each level in a plurality of pixels located around the interpolation pixel. Interpolator.