JPS6180968A - Picture signal processor - Google Patents

Abstract

PURPOSE:To sharpen correctly the not only a character image part but also a halftone image part by selecting a different image emphasizing means in accordance with whether a notice picture element is in the character image part or the halftone image part. CONSTITUTION:An analog picture signal 22 from an image sensor 21 is converted to a digital picture signal 24 of 6 its and 64 gradations by an A/D converter 23. This digital picture signal 24 is supplied successively by one picture element each to an image data extracting part 25, and in this part, an image data of a notice picture element and an image data of its peripheral picture element are latched once and provided to an image state discriminating circuit 26. The discriminating circuit 26 discriminates from these picture element data whether the notice picture element is in a character image part or a halftone image part, its result is supplied to a multiplexer 41, and an output of the first or the second image emphasizing circuit 27, 28 is fetched.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image signal processing device for performing appropriate image processing on an image information source containing a mixture of character images and halftone images. .

"Prior Art" Image processing devices that read image information on a document and record or display it perform strong sub-processing on the read image.
This prevents deterioration in the reproducibility of line drawings. As such image sharpening processing, a method using a spatial frequency filter is generally used.

FIG. 11 is an example of a spatial frequency filter.

This spatial frequency filter is applied in a cross shape to a group of pixels on the document 10 as shown in FIG. The pixels are a(i, j-1), a(i-1
, J), a(i+L J), a(i, j+1). At this time, the filter constant of the pixel of interest a(i, j) for determining the filter characteristics is set to 1+
4D (D is a constant) and the filter constants for the four surrounding pixels are each -D, the pixel of interest a'' (i, j) after the sharpening process can be calculated using the following formula.

a'' (i, j) = (1 + 40) a (i, j) - D (
a (i, j-1) + a (i-1, j) + a (
i+1. J)+a (i, j+1))...
...(1) ``Problems to be solved by the invention'' However, such spatial frequency filters are originally set to sharpen character images, so they are used to avoid problems such as photographs or halftone dots in the manuscript. When there are halftone images whose density changes smoothly, there is a drawback that the sharpening effect on these parts is small, and on the contrary, the noise components contained in these images are amplified. This is because the high frequency components are mainly emphasized for character images, even though they exist in the relatively low spatial frequencies that make up the halftone image, meaninglessly amplifying the noise components present in these high frequency regions. This was due to the fact that he ended up doing it.

In view of the above circumstances, an object of the present invention is to provide an image signal processing device that can appropriately sharpen not only the character image portion but also the halftone image portion.

``Means for Solving the Problems'' In the present invention, as shown in principle in FIG. A first image enhancement means 11 that enhances an image using image data D1 belonging to a first area, and when this pixel of interest belongs to a halftone image part, the first area and at least a part thereof different second
The image signal processing device is provided with a second image enhancing means 12 that enhances the image using the image data D2 of the peripheral pixels belonging to the area. Here, the first area is set closer to the pixel of interest than the second area, but
These may partially overlap. The image signal processing device may include an image state determining means for determining whether the pixel of interest belongs to a character image portion or a halftone image portion, and may also include an image state setting means such as an external switch. Alternatively, the image state determination result may be set externally.

"Example" The present invention will be described in detail with reference to Examples below.

FIG. 2 schematically shows the image signal processing device of this embodiment. The image sensor 21 of this device is connected to the original 10
(See FIG. 12) is scanned in a plane and an analog image signal 22 is output.

, to/D converter 23 converts this analog image signal 22 into a 6-bit, ie, 64-gradation digital image signal 24. The digital image signal 24 is supplied pixel by pixel to the image data extraction section 25. The image data extraction unit 25 includes an image state determination circuit 26 and first and second image enhancement circuits 2.
The necessary image data groups 31 to 33 for 7.28 are extracted and supplied to them.

FIG. 3 shows the main parts of this image data extraction section 25. The image data extraction unit 25 extracts four line memos.
J 35+ ~35. a series circuit consisting of a latch circuit 36. , ~3615.36°1~36□1.
363. ~363s, 36. ,~36. ,．． 36.1
It is equipped with a series circuit consisting of ~36,5.

Here, each of the line memories 351 to 354 is a type of delay memory that outputs parallel image data of 6 bits per pixel with a delay of one main scanning line, and each of the latch circuits 3611 to 365s outputs parallel image data of 6 bits per pixel. This is an element that latches image data one pixel at a time. The digital image signal 24 is supplied to the latch circuit 3611 located at the end of the first series circuit. Second
~ Latch circuits 3621, 363I, 36. 1 and 361 are line memories 351 to 35.1, respectively. The digital image signals 371 to 37. is being supplied.

Now, the latch outputs of each latch circuit 36,1 to 3655 are converted into image data 381. to 3855, and the latch output corresponding to the pixel of interest is an image signal 3633. In this case, the image data group 31 supplied to the image state determination circuit 26 consists of nine image data 3822 to 3822 shown in FIG.
384. It is composed of Nyoto.

The image state determination circuit 26 determines the maximum image density value DI4AX in the image data group 31 in these 3×3 image areas.
and the minimum value DI41!1 are detected, and the difference between them is compared with a predetermined darkness value βTH (!:).If it is larger than the threshold value 1TH, it is determined that the image data 3833 of the pixel of interest is part of a character image. , otherwise, it is determined that it is a halftone image.These can be expressed in the following equation.

DMAX DMIN > LH...Character image DMAX D)IIN ≦ITH...Halftone image Here, the threshold value βT)l is usually a value of about 10 to 15 for 8-bit image data. Become.

The discrimination principle of the image state discrimination circuit 26 as described above will be explained with reference to FIG. This figure shows the signal level (a degrees) for one line in a certain part of the original. In this figure, a signal level of "1" means that that part of the document is ideally white, and a signal level of "64" means that that part is ideally black. The signal level changes smoothly as a whole in the first half of the scan.

In these parts, the signal level changes in multiple stages,
It can be seen that this is a halftone image area. In the halftone image area, there is no significant difference in density between two adjacent points. Therefore, within the 3×3 image data group 31 to which the pixel of interest belongs, the difference DM A
If X D K I N is equal to or smaller than the threshold fTM, the image data 3833 of the pixel of interest has a strong tendency to belong to a halftone image.

On the other hand, in FIG. 5, there is a sharply cut waveform in the latter half of the scan. This portion is an edge portion of a line image such as a character, and is a typical character image area. In such a character image area, there is a high possibility that even two points that are close to each other will have a large difference in density. Therefore, 3×3 image data group 3
1, if the difference a x D ) l + 11 is larger than the threshold j2to, the image data 3 of the pixel of interest
833 has a strong tendency to belong to character images. The determination result of the image state determination circuit 26 is output as a determination result signal 39 and becomes a control signal for the multiplexer 41.

On the other hand, the first image enhancement circuit 27 has an image data group 32
The same nine image data 3822 as shown in FIG.
~381. is supplied. The first image enhancement circuit 27 is
It is equipped with a spatial frequency filter whose content is shown as an example in FIG. 6, which is illustrated in correspondence with FIG.
Image data 3822-38, 2.383. ~384
4 is multiplied by the coefficient "-0, 5" and the sum of these is calculated.

Based on this calculation result, the image data 3833 of the pixel of interest is emphasized. The output characteristics of the spatial frequency filter in this case are as shown in FIG. That is, since the image data of pixels adjacent to the pixel of interest is used in the filter calculation, high frequency components forming the character image are emphasized and these parts become sharp.

On the other hand, the second image enhancement circuit 28 receives nine image data 3 shown in FIG. 8 as a 5×5 image data group 33.
81. ~386. is supplied. These are data groups located further outside the image data shown in FIG. The second image enhancement circuit 28 includes a spatial frequency filter as shown in FIG. 9, which is illustrated in correspondence with FIG. 8, as an example. The output of this spatial frequency filter is similar to the first image enhancement circuit 27, and the output of each image data 3811 to 385s
It is the total value multiplied by the coefficient. Since this second image enhancement circuit 28 uses pixels further away from the pixel of interest for filter calculation, the area of the halftone image or photographic image constituting the halftone image is selectively enhanced.

The output characteristic of the spatial frequency filter in this case is the 10th [D
It will look like the one shown below. Since the gain in the high frequency portion is relatively reduced in this way, it is possible to compensate for the deterioration in image quality of the halftone image without amplifying the noise component.

Now, the multiplexer 41 shown in FIG. to select one of these. and image signal 45
This is then sent to a subsequent recording section or display section (not shown). Here, the image signal 43 from the first image enhancement circuit 27 is selected by the image state discriminating circuit 26.
is a state in which the pixel of interest is determined to be a character image, and the image signal 44 by the second image enhancement circuit 28 is selected in a state in which the image state discrimination circuit 26 is determined to be a halftone image in this pixel of interest. . Image signal 43 by multiplexer 41
．． The selection operation of 44 is performed for each pixel, which enables fine control of image enhancement.

In the embodiment described above, the image condition is determined by the image condition determination circuit 26, but the image signal processing circuit may be provided with a switch for indicating the image condition, and the image enhancement for character images and the intermediate The one for toned images may be specified each time. Such a switch is not limited to simply indicating a switching point on a document-by-document basis or in the sub-scanning direction, but may also be a complex instruction means that causes a specific area of the document to be subjected to a specific filter process.

Furthermore, in the embodiment, the image data of the first region and that of the second region are made independent from each other except for the image data of the pixel of interest, but image data in which these partially overlap may be used. Of course. Furthermore, in the embodiment, image sharpening was controlled by determining the image state of each pixel, but it is also possible to extend and apply the determination result for one pixel of interest to a predetermined image area including this pixel of interest. This simplifies image processing.

"Effects of the Invention" As explained above, according to the present invention, different filters are applied to the character image part and the halftone image part, so it is possible to set the spatial frequencies to be emphasized to the optimum values. can. Therefore, it is possible to create a three-dimensional effect in the image, especially in the halftone image portion, and it is possible to reduce noise and improve image quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of the present invention, and FIGS. 2 to 10 are for explaining an embodiment of the present invention. Of these, FIG. 2 shows an outline of the image signal processing device. 3 is a block diagram embodying the main parts of the image data extraction section, FIG. 4 is an explanatory diagram showing the arrangement structure of the image data group 31, and FIG. 5 is a main scanning diagram when reading a document. A waveform diagram showing changes in signal level on the line, Figure 6 is
7 is a characteristic diagram of this spatial frequency filter, FIG. 8 is a block diagram showing the arrangement structure of the image data group 33, and FIG. 9 is a block diagram showing the arrangement structure of the image data group 33. A block diagram of a spatial frequency filter used in the image enhancement circuit 28, FIG. 10 is a characteristic diagram of the latter spatial frequency filter, FIG. 11 is a block diagram of a conventional spatial frequency filter uniformly used, and FIG. The figure is an explanatory diagram showing the relationship between the spatial frequency filter shown in FIG. 11 and the document. 11...First image enhancement means, 12...
- Second image enhancement means, 25... Image data extraction unit, 26... Image state determination circuit, 27... First image enhancement circuit, 28...・・・
-Second image enhancement circuit. Applicant Fuji Xerox Co., Ltd. Agent Patent Attorney Ume Yamauchi
Figure 1 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] 1. When the pixel of interest, which is the pixel to be processed, belongs to a portion of a character image composed of characters or line drawings, an image belonging to the first region among the surrounding pixels located around this pixel; a first image enhancing means for emphasizing an image of a pixel of interest using data; The second area has a different area.
and second image enhancement means for enhancing an image of the pixel of interest using image data of the peripheral pixels belonging to the area. 2. Claim 1, characterized in that the first region is set closer to the pixel of interest than the second region.
Image signal processing method described in section. 3. The image according to claim 1, wherein the first region does not overlap with the second region and is set closer to the pixel of interest than the second region. Signal processing method. 4. The image signal processing device according to claim 1, further comprising image state determining means for determining whether the pixel of interest belongs to a character image portion or a halftone image portion. 5. The image according to claim 1, further comprising image state setting means capable of externally setting whether the pixel of interest belongs to a character image portion or a halftone image portion. Signal processing device.