JPS6027463B2 - Low pixel density conversion device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides two
The present invention relates to a pixel density conversion device for value image information.

In this type of image transmission device, many attempts have been made to improve the efficiency of the transmission path by encoding the image information using the correlation and reducing the amount of signals to be transmitted.

In addition to this, if a pixel density conversion method is used in which the pixel density of the original image is converted to, for example, 1/4 of the image density on the transmitting side and then transmitted, the amount of transmitted signals can be further compressed to 1/4. To convert a binary image to a pixel density of 1'4,
2×2 pixels must be converted to 1 pixel, but 2×
For example, if there are two or more black pixels in two pixels, it becomes a black pixel,
The conventional method using majority voting, which converts pixels into white pixels in other cases, has the drawback that an original image including a white line as shown in FIG. 2 is filled with a completely black image as shown in FIG. In Figures 2 and 3, the large pixels separated by thick lines are low pixel density pixels, the small pixels separated by pongee lines are high pixel density pixels, and the four small pixels within the large pixel are 2 × 2 pixels. It is a pixel.
The same applies to FIGS. 4 and 5, which will be explained later. The purpose of the present invention is to perform narrowing processing to convert black pixels located at the boundary into white pixels based on the logic determined by the black and white arrangement of surrounding pixels, and then perform low pixel density conversion to eliminate such defects. An object of the present invention is to provide a low pixel density conversion device.

According to the present invention, since the original image is narrowed in advance and then subjected to low pixel density conversion, the narrow white area of the original image can be saved without being filled in.

FIG. 1 is a block diagram when the present invention is applied to the transmitting side of a facsimile transmission device.

On the transmission side shown in FIG. 1, a transmission original image 1 is converted into an electric pulse signal by a known photoelectric conversion circuit 2. As shown in FIG. The narrowing processing circuit 3 shaves the boundary points of the pattern, and the low pixel density conversion circuit 4 determines whether the corresponding high pixel density pixel is black or white based on a majority vote between high pixel density pixels, and converts the pixel density to low pixel density based on that determination. It is encoded by the encoding circuit 5 and sent to the transmission path. 6th
FIGS. 8 to 8 show examples of thinning processing performed on simple patterns.

The pattern on the left is the original pattern, and in the first step, the black pixels adjacent to the white pixels on the left and above are converted to white pixels to form the central pattern. In the second stage, among the black pixels in the center pattern, those adjacent to white pixels on the right and below are converted to white pixels, forming the right pattern. However, as shown in Figure 7, when converted to white pixels,
A black pixel in which the connection between black pixels is not preserved is not converted into a white pixel even if a white pixel is adjacent to the black pixel. FIG. 2 is an example of an original image to be transmitted.

FIG. 4 shows an image corresponding to the output of the narrowing processing circuit 3,
The narrowing process widens the width of the thin white area. Fifth
The figure shows an image corresponding to the output of the low pixel density conversion circuit 4, and because thinning processing was performed in advance, thin white areas are preserved without becoming black areas. FIG. 9 is an example of a narrowing processing circuit corresponding to FIG. 13. The output of the photoelectric conversion circuit 2 in FIG. 1 is taken into a +3-bit shift register 7, and whether the center pixel i of 3×3 pixels is the final point is determined by the skeleton ROM 8 using 8 neighboring points a to h. , if it is the final point, a signal k=1 is output. Here, n is the number of pixels on the - line, and the final point is a point that cannot be deleted because the connectivity of the image will not be preserved if the point is deleted. logical product i
- When d·f=1, since d≠0 and f≠0, both the left and above black pixels of black pixel i are black pixels, and i is not a boundary point between the left and above. Further, when the logical product k·i=1, the black pixel i is the final point because k is 0. Output i/d of OR circuit 13
・f+k・i are the left and upper boundary points, with those that are not the final point removed, and are input to the 3-bit shift register 10.

Similarly, shift register 10, skeleton, ROMI 1
, AND circuits 15, 25, and OR circuit 16 are used to delete right and lower boundary points that are not the final point. However, this final point includes the final point i=k・i determined by the skeleton ROM 8 and stored in the n+2 bit shift register 9, and the newly generated final point k'・i after deleting the left and upper boundary points. There are two ways. FIG. 10 shows an example of the skeleton ROMs 8 and 11.

Pixels a, b, c, and d are associated with the four bits of the high-order address, and pixels e, f, g, and h are associated with the four bits of the low-order address.
An x mark in the address section indicates a bit that can be either 0 or 1, a 0 mark at an intersection indicates that data k at that address is 0, and no mark indicates that it is 1. FIG. 11 is an example of a low fluorine density conversion circuit corresponding to FIG. 14.

The output of the thinning processing circuit 3 shown in FIG.
, b'', c'', and d'' are determined by the AND circuits 18 to 23 and the OR circuit 24, and if two or more of the four pixels are black, it is considered a black pixel, and otherwise, it is considered a white pixel. As described above, since the low pixel density conversion device according to the present invention first performs thinning processing before performing pixel low conversion, the distance between black pixels can be increased by one or two pixels, and thin white areas in the original image do not have to be filled in. It has its features.

The present invention has been described in detail above, but for the sake of simplicity, only the case where a black pixel at the boundary is converted to a white pixel has been described.

Depending on the original image to be sent, there may be many thin black lines and it may be better to convert the white pixels at the boundaries to black pixels. In this case, the black and white described above can be reversed.

[Brief explanation of drawings]

FIG. 1 is a block diagram when the present invention is applied to the sending side of a facsimile transmission device, and FIG. 2 is an example of an original transmission image.
Fig. 3 shows the pixel density converted using the conventional method, and Figs. 4 and 5 show the processing according to the present invention, and show the pixel density and pixel density corresponding to the outputs of the narrowing processing circuit and the low pixel density conversion circuit, respectively. 6 to 8 are examples of narrowing processing, FIG. 9 is an example of a narrowing processing circuit, FIG. 10 is an example of a structure of a skeleton ROM, and FIG. 11 is an example of a low pixel density conversion circuit. In the figure, 1... Original image to be sent, 2...
...Photoelectric conversion circuit, 3...Slimming processing circuit, 4.
...Low pixel density conversion circuit, 5... Encoding circuit, 6... Transmission side control circuit, 7, 10... Young+3 bit shift register, 8, 11... Skeleton R
OM, 9, 17"""h+2 bit shift register, 1
2, 14, 15, 18-23, 25...AND
Circuit, 13, 16, 24...OR circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11

Claims (1)

[Claims] 1. A means for sampling an image signal and converting it into a black and white binary image, and for a black pixel located at the boundary between white and black, when replacing the black pixel with a white pixel, the connection between surrounding black pixels is preserved. means for detecting whether the connection is preserved; means for converting a black pixel located at the boundary into a white pixel only when it is determined by the detecting means that the connection is preserved; and converting the converted signal into a white pixel; 1. A low pixel density conversion device, comprising means for converting into a sample value with a low sampling density.