JPH01254071A - Picture processor - Google Patents

Abstract

PURPOSE:To obtain a picture with excellent gradation and simple processing by converting an input picture data into a high density data, binarizing it and outputting the input picture data in a multi-value level based on the result. CONSTITUTION:A picture data read by an input sensor 11 is converted into a digital signal by an A/D converter 12 and the signal is subject to correction and adjustment processing such as shading correction and contrast adjustment. Then a picture element density conversion circuit (I) 14 converts the data into a data with a picture element density finer than the input picture element density and a binarizing circuit 15 applies binarizing processing in the main scanning direction by a double density. Then a picture element density conversion circuit (II) 16 applies conversion restoring the binarized data with high density into a multi-value data with output picture element density of a multi-value printer 17. Thus, it is possible to express the input picture data in a multi-value level based on the simple binarizing processing.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image processing device such as a digital printer and a digital facsimile that digitally handles images.
In particular, the present invention relates to an image processing device capable of reproducing halftone images.

[Conventional technology]

Traditionally, this type of device uses two methods, such as the dither method and the error diffusion method.
A halftone image is reproduced by binarizing input image data using a digitization method and recording the processed binary data by turning dots on and off using a binary printer.

[Problem that the invention seeks to solve]

However, this type of device can only express 2 levels.
Since there are only steps, it was not possible to reproduce a good halftone image.

However, with the development of printer technology in recent years, the dot on/off
In addition to the off state, printers that can express intermediate levels have been developed. This type of printer is called a ternary printer if it can take one intermediate level, and a quaternary printer if it can take two intermediate levels.

However, in this type of multilevel printer, in order to convert input image data into multilevel levels, multiple types of dither threshold values are used, or even when simply ternarizing, two types of threshold values are required. The disadvantage is that the processing method becomes complicated.

[Means and operations for solving the problem] According to the present invention, an input means for inputting image data, a conversion means for converting the input image data into a pixel density finer than the input pixel density, and the above conversion means and a binarization means for binarizing the image data converted into high-density Gansanji = Toushi; It outputs image data at multiple levels.

This makes it possible to express input image data at a multilevel level based on simple binarization processing.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. Image data read by an input sensor 11 such as a CCD is converted into a digital signal by an A/D converter 12.

For example, if an A/D converter for 8-bit conversion is used, 256
This allows for gradation expression. In this embodiment, it is assumed that the image data represents the density of the original image. This signal is subjected to correction processing such as shading correction and contrast adjustment in the correction circuit 13. Next, the pixel density conversion circuit (1) 14 converts the data into data with a pixel density finer than the input pixel density. For example, in order to convert to double density in the main scanning direction, pixels in the main scanning direction may be read out twice and sent to post-processing. Next, the binarization circuit 15 is a circuit that performs binarization using an error diffusion method, and this process performs binarization processing at twice the density in the main scanning direction compared to normal. Note that the binarization circuit 15 may be a circuit that simply performs binarization using a threshold value, or a circuit that uses a dither threshold value.

Next, in the pixel density conversion circuit (II) 16, 2
Conversion is performed to convert the digitized data back to multi-value data of the output pixel density of the multi-value printer.

This process converts area gradation (a method of expressing gradation by turning on/off dots) into gray gradation. This result is outputted by the multilevel printer 17 to form an image.

FIG. 2 is a diagram showing the flow of processing in the block diagram of FIG. Figure 2 (a) shows the input pixel density]
) ij (i, j are integers) indicates one pixel of input image data. Figure 2 (b) shows the pixel density after high-density processing in density conversion (1) 14, where one pixel is divided into the main scanning direction (
It is divided into two equal parts in the i direction) to double the density and contain the same data. Here, you may enter interpolated data instead of the same data. 2() and 2) show the results of binarization in the binarization circuit 15, in which dot on/off is determined for each double-density pixel. Figure 2 (d) shows density conversion (II)
This is the output result of 16. The binarization results in Figure 2 (...) are divided into two-pixel units, and the case where both pixels are dot-on is shown in B.
Lack, if only one side is on, G
r a y, when both dots are off, wh i
It is a 3-valued version with te binding. In other words, this result is output by the multilevel printer 17. For example, in an inkjet printer, a large area of ink is used for Black, a small area of ink is used for GrayO, and Wh
At the time of ite, control is performed so that ink is not applied.

Furthermore, as shown in FIG. 2 (11), one pixel of input image data can be expressed in multiple levels even if a binary printer outputs only the dot on/off signal as it is.

FIG. 3 shows an embodiment of the density conversion circuit (1) 16. The input signal DIJ is read and written to a FIFO memory (first-in-first-out) 31 using a clock φ1 from a clock generator 32. Also, from the clock generator, a clock φ2 is sent to the binarization circuit 15.
is given. Here, φ2=2φ1, which is a twice as high frequency clock. As a result, the binarization process is performed with twice as many clocks, and the pixel density in the main scanning direction is isometrically doubled.

FIG. 4 is a block diagram of the binarization circuit 15 based on the error diffusion method.

``Image data D1'' is weighted by adding a value obtained by multiplying the error data εij generated in the already processed image data stored in the error buffer memory 46 by a predetermined weighting coefficient akl by the generator 44 and the adder 41 is added.

becomes.

An example of the weighting coefficient αkl is shown in FIG.

Next, the correction data D'ij is compared with a threshold value T in a binarization circuit, and if it is above the threshold value, it is 1, and if it is below the threshold value, it is O.
outputs the signal yij.

νj corresponds to a binary signal that determines dot on/off. This binary data is sent to the density conversion circuit (I[)t6.

On the other hand, the subtracter 45 calculates the correction data yIj and the output yIJO difference t1j. This difference operation is yij =
When it is 1, the maximum data Dmax (for example, 255), y
When ij is 20, Dli is set as the minimum data Dmin (0).
Take the difference from j. This result is the error buffer memory 4
6 is written to pixel position 43. Pixel position 43 corresponds to the pixel position currently being processed. By sequentially repeating this operation, the binarization process using the error diffusion method is executed. FIG. 5(A) is a block diagram of the density conversion circuit (n) 16. 1 with data P of binary data yIj and latch 51
The pixel-delayed data Q is subjected to a logical operation to determine the multi-value level.

As shown in Figure 5 (b), when both P and Q are 0,
When o is 1 and either P or Q is 1, Xl is 1, P and Q
When both are 1, the output is obtained so that X2 becomes 1. Xo
When is 1, it is White, and when Xl is 1, it is Gray
, A ternary level is determined that is Black when X2 is 1. What makes this possible is A in Figure 5 (a).
ND circuit 52, EXOR circuit 53, NAND circuit 54
, and the output X2. Obtain X, , Xo.

Based on the outputs X2, Xl, and Xo, the multilevel printer 1
In step 7, multilevel recording is executed.

In this way, according to the above-described embodiment, by performing binarization processing using data with a higher density than the input pixel density, and then performing processing back to gray scale data depending on the number of dots,
Images with excellent resolution and gradation can be obtained.

Furthermore, even if the output yIJ shown in FIG. 4 is output as is using a binary printer, it is possible to express the input image data at a multilevel level, and it is possible to express the input image data at a multilevel level even when using a conventional binary printer. 9 This eliminates the need for laser beam printers and the like to control the laser emission time in several stages in order to express three or more values. In addition, inkjet printers no longer require controlling the degree of ink drop in several stages.

In the above-mentioned embodiment, the case where area gradation=shading gradation is shown.

This allows a printer that controls the size of a dot per pixel, such as a laser beam printer, or a printer that controls the size of an ink drop, to output an area that is variable and equal to the density level. For example, as shown in FIG. 8, when one pixel of Gray is output to a printer, it becomes area gradation and no error occurs.

On the other hand, some inkjet printers express multi-value levels by switching between a plurality of inks (dark ink and light ink). In this case, depending on the density of the ink used, there may be cases where the area gradation does not equal the light/dark gradation. In this case, the image data at the time of output will be shifted by the difference between (density data based on gradation) and (density data based on area gradation).

Therefore, it is necessary to use the difference as error data and re-diffuse the data into the error line buffer. Figure 7 is a block diagram of a circuit that corrects the error after density conversion. E2 = (density data based on gradation) - (density data based on area gradation) is added to the binarization error E1 by an adder 74 and then written into an error buffer memory 75. As mentioned above, the error E2 is for the pixel block of the binarization process,
Since it occurs every two pixels, there are two methods: adding it to one of the two pixels, and spreading it evenly to y2E2. This can be easily realized by adjusting the timing in hardware.

This makes it possible to correct errors between the output of the printer and the multi-value level value processed by the binarization circuit 71 even in a printer using light and dark ink.

In addition, in this embodiment, one input pixel is doubled and binarized, but it is also possible to triple the input pixel or divide one pixel into 2×2, using the same concept as in this embodiment, to create a multi-value level. Needless to say, it can be determined.

In order to simplify the explanation, this embodiment shows a case where there is only one input image data, but by using input image data of R2O and 83 colors, color image reproduction processing can also be easily realized.

Further, the binarization process is not limited to the error diffusion method, and other binarization methods can be used.

〔effect〕

As explained above, according to the present invention, input image data is converted into high-density data, the converted data is binarized, and based on the result, input image data is outputted at a multilevel level, so that the processing is simple. It becomes possible to obtain an image with excellent gradation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the processing flow of FIG. 1, and FIG. 3 is a block diagram showing details of pixel density conversion (1). Figure 4 is a block diagram showing details of the binarization circuit using the error diffusion method, Figure 5 is a block diagram showing details of pixel density conversion (n), and Figure 6 is a matrix that is the weighting coefficient of the error diffusion method. FIG. 7 is a block diagram of the second embodiment of the present invention, and FIG. 8 is a diagram showing area gradation=shading gradation.

Claims (1)

[Claims] An input means for inputting image data; a conversion means for converting the input image data into a pixel density finer than the input pixel density; An image processing device comprising: a binarization means for converting the image data into a multivalued image, and outputs the image data inputted by the input means at a multilevel level based on the binary result of the binarization means.