JP2833666B2 - Image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to an image processing apparatus, and more particularly, to an image processing apparatus capable of correcting recording density unevenness that occurs when binary data is recorded.

[Prior art]

2. Description of the Related Art Conventionally, in a binary recording apparatus, a method of adjusting driving energy for each recording pixel has been used as a means for correcting recording density unevenness occurring for each recording pixel. In digital copiers and the like, multi-valued data is stored in advance.
In consideration of recording density unevenness that may occur when binarizing, multivalued data is corrected in advance and binarized.

[Problems to be solved by the invention]

However, in a binary recording device such as a thermal head or an ink jet printer, semi-fixed adjustment is required for each of thousands of linear recording elements, so that correction of recording density unevenness can be realized at low cost. It has the drawback that it cannot be used, and in copiers and the like, it is integrated with the recording device and image reading device. For example, when reading the same image and recording it simultaneously with multiple recording devices, multi-valued data However, it was not possible to correct the density unevenness of each recording apparatus even if correction was applied to the recording apparatus. SUMMARY An advantage of some aspects of the invention is to provide an image processing apparatus that corrects recording density unevenness that occurs when binary data is recorded, with a simple configuration. .

Means and Action for Solving the Problems

In order to achieve the above object, an image processing apparatus according to the present invention comprises: an arithmetic unit for obtaining an average density value of binary data of a plurality of pixels around a pixel of interest already binarized; and an average density obtained by the arithmetic unit. Correction means for correcting the value according to the characteristics of the recording element; binarization means for binarizing the image data of the pixel of interest in accordance with the average density value corrected by the correction means; And an error distribution means for distributing a binarization error generated in the binarization processing to image data of a non-binarized pixel around the target pixel. In order to achieve the above object, an image processing apparatus according to the present invention comprises: an arithmetic unit for obtaining an average density value of binary data of a plurality of pixels around a pixel of interest already binarized; A binarizing unit that binarizes the image data of the pixel of interest in accordance with the average density value;
Correction means for correcting a binarization error generated at the time of the value conversion processing in accordance with the characteristics of the printing element;
Error distributing means for distributing the binarization error to the image data of the non-binarized pixels around the target pixel. Further, in order to achieve the above object, the image processing apparatus according to the present invention comprises: an arithmetic unit for obtaining an average density value of binary data of a plurality of pixels around a pixel of interest already binarized;
Correction means for correcting the image data of the pixel of interest to which the binarization error generated in the binarization processing of the pixel for which the binarization processing has been performed is distributed according to the characteristics of the recording element; A binarizing unit for performing a binarizing process on the image data of the pixel in accordance with the average density value obtained by the calculating unit, and a binarizing error generated at the time of the binarizing process by the binarizing unit; And an error distributing means for distributing the image data of the pixels of the non-binarized processing.

【Example】

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus according to the present embodiment. In the figure, binary data input from the outside is an adder
According to 17, the multi-level level, that is, “0” for “0”,
In the case of "1", it is converted to "255" and, at the same time, error correction data described later is added. After the timing is adjusted by the D flip-flop (F / F) 12, the comparator 13
Is binarized again. This binarized data is DF / F
7 and input to RAM2 for line delay, RAM2, DF / F5,6
, And are input to an average density calculation ROM 8 described later. The output of the RAM 2 is input to the RAM 1 for delaying one line, and is delayed and held by the RAMs 1, DF / F 3, and 4, and is input to the average density calculation ROM 8. As a result, the average concentration calculation RO
In M8, it is possible to simultaneously refer to seven binarized data adjacent to the target pixel to be binarized and already binarized. Then, values of “0” to “255” are output as an average density based on these seven pieces of binary data. The above-mentioned average density is obtained by the product sum of the weight coefficient shown in the following figure and the already binarized binary data. That is, DF / F
When only the output of 7, DF / F5 is “1”, the average density is obtained as 75 + 60 = 135. This average density indicates a visual density level represented by the binarized data around the target pixel. here,
If the plurality of printing elements corresponding to the above seven pixels can perform dot printing uniformly, the above-mentioned average density matches the visual density level. The mean concentration and the qualifying concentration level of the are different. Therefore, the feature of the present embodiment is that the average density obtained by the above-described calculation is corrected based on the non-uniformity data in the non-uniform portion of the recording element, and the corrected average density is binarized. It is to be input to the comparator 13 as a threshold value.
That is, if the recording element characteristics near the pixel of interest are light (the dot size is small), the value is corrected to a value smaller than the average density 135 obtained by the above-described calculation, and the result is binarized as a binarization threshold. Then, it becomes easy to output the recording signal as “1”, and as a result, the number of dots around the target pixel increases,
Recording can be performed at a visually desired density. On the other hand, when the characteristics of the recording element in the vicinity of the pixel of interest are high (the dot size is large), on the contrary, the average value 135 is made larger to reduce the occurrence of a recording signal as "1". The number of recording dots per unit area can be reduced, and the same recording density as described above can be visually expressed. Next, the above-described binarization error correction will be described. Subtractor
11 is the input data and the binarization threshold (average density)
Find the difference between This value is the difference between the input data and the surrounding average density, and this difference is added to the input data to be binarized next, and the input data is stored. In this embodiment,
The generated binarization error is divided into two by the distributor 14, one of which is input to the RAM 15 which holds the delay of one line in order to correct the input data of the next line, and the other is input to the adder 16, that is, After the error generated one line before is added by the adder 16, the adder 17 corrects the input data for errors. The above processing is repeated for each pixel, and the recording density unevenness occurring for each pixel can be corrected while the input data is stored as the average density. Here, the above average value correction will be described in more detail with reference to FIG. FIG. 2 is a diagram showing conversion characteristics stored in advance in the average value conversion ROM 9 shown in FIG. L1 ~ for each pixel
The average value is converted according to one of the seven levels of L7. In other words, when the density is high according to the density unevenness of the recording element, L5, L6, and L7 are selected according to the level, and when the density is low, L3, L2, and L1 are selected. I do. Which conversion characteristic is selected for each pixel is determined by the correction value memory 10.
The memory 10 stores the 3-bit data representing the levels L1 to L7 to be selected for each pixel in an average value conversion RO.
Output to the address of M9. The characteristics of each pixel are set automatically by a method input by a service person or by reading an output image. The above conversion characteristics are not limited to the linear characteristics shown in FIG. 2, but may be non-linear. Also, the number of levels is 7 to 64
Increasing the level allows more accurate unevenness correction. As described above, according to the present embodiment, the binary data is converted into multi-valued data, and when the multi-valued data is binarized again, the unevenness of the recording element is corrected. The recording density unevenness correction can be performed, and the same binary data can be recorded by a plurality of printing apparatuses with the unevenness corrected at the same time, and the apparatus can be realized at low cost.

[Other embodiments]

Next, another embodiment of the present invention will be described below with reference to the accompanying drawings. In this embodiment, the same processing as described above is performed on a binarization error, and a schematic configuration thereof is shown in FIG. In FIG. 3, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. As described above, the generated binarization error is the difference between the binarized data and the average density, and the large positive error means that the input data to be corrected is recorded in the recording dot "1". It means that it is easily priced. Therefore, when the recording element in the vicinity of the target pixel is light (when the dot is small), a predetermined value is added to the output value from the subtractor 9, and as a result, the input data is converted in the (+) direction. When the recording element is dark, a predetermined value is subtracted from the output value from the subtractor 9, and as a result, the input data is converted in the (-) direction. FIG. 4 is a diagram showing conversion characteristics of data written in the error conversion ROM 19 shown in FIG. As in the above-described embodiment, the correction data for each pixel is read from the correction memory 10 and input to the address terminal of the error conversion ROM 19. Then, by selecting the conversion characteristics shown in FIG. 4 for each pixel, density unevenness correction can be performed. As described above, by increasing the conversion characteristic to a level of 7 to 63, more accurate unevenness correction can be performed.
It goes without saying that the characteristics are not limited to those shown in FIG. <Modification> The same processing can be performed after error correction of input data. An embodiment in this case will be described below with reference to FIG. First, after the input binary data is assigned to “0” and “255”, when the binary error correction is performed, “−255” to “5” are obtained.
12 ". Accordingly, if the input data is corrected in the (+) direction, the recording dot "1" is easily binarized when the recording element is light. On the contrary, if the recording element is dark, the recording dot "1" is corrected in the (-) direction. The dot "1" is reduced, and both can be recorded at a uniform density. Although the embodiment has been described in the case of a single color, in a color printing apparatus capable of printing in four colors of C, Y, M, and K, it goes without saying that the processing is performed for each color and each printing element. In the embodiment, the average density is calculated from seven pixels adjacent to the pixel of interest. However, if this area is made wider, smoother unevenness correction can be performed. Further, the input binary signal is converted to "0" and "25" having an 8-bit width.
The processing is performed after converting to "5". If the number of bits is reduced to "0" and "16", hardware can be realized at lower cost. If the bit width is increased to "0" and "1024", finer and more precise control becomes possible. In this case, it goes without saying that the processing is performed by normalizing the maximum density to “16” or “1024” in the average density calculation ROM 8.

【The invention's effect】

As described above, according to the present invention, it is possible to correct recording density unevenness that occurs when binary data is recorded, with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing a configuration of an image processing apparatus according to this embodiment, FIG. 2 is a diagram showing conversion characteristics in this embodiment, and FIG. 3 is a configuration of an image processing apparatus in another embodiment. FIG. 4 is a diagram showing a conversion characteristic in another embodiment, and FIG. 5 is a diagram showing a modification of the image processing apparatus in the embodiment. In the figure, 1,2,15 ... delay RAM, 3-7,12 ... DF / F, 8 ...
Average density calculation ROM, 9 average value conversion ROM, 10 correction value memory, 11 subtractor, 13 comparator, 14 distributor
16, 17 ... adder, 18 ... printer.

Claims (3)

(57) [Claims] A calculating means for calculating an average density value of binary data of a plurality of pixels around a pixel of interest which has already been binarized; and correcting the average density value obtained by the calculating means in accordance with the characteristics of a printing element. Correction means; binarization means for binarizing image data of a pixel of interest in accordance with the average density value corrected by the correction means; binary generated at the time of the binarization processing by the binarization means An image processing apparatus, comprising: an error distribution unit that distributes a binarization error to image data of pixels of a non-binarized process around a target pixel. 2. A calculating means for calculating an average density value of binary data of a plurality of pixels around a pixel of interest already binarized, and converting the image data of the pixel of interest into two in accordance with the average density value obtained by the calculating means. A binarizing unit for performing a binarizing process; a correcting unit for correcting a binarization error generated at the time of the binarizing process of the binarizing unit in accordance with a characteristic of a printing element; An image processing apparatus, comprising: an error distribution unit that distributes a binarization error to image data of non-binarized pixels around a target pixel. 3. A calculating means for calculating an average density value of binary data of a plurality of pixels around a pixel of interest which has already been binarized, and a binary value generated at the time of binarizing a pixel which has already been binarized. Correction means for correcting the image data of the pixel of interest to which the quantization error is distributed according to the characteristics of the recording element; and correcting the image data of the pixel of interest corrected by the correction means according to the average density value obtained by the arithmetic means. Binary processing 2
A binarization unit; and an error distribution unit that distributes a binarization error generated in the binarization process of the binarization unit to image data of a non-binarized pixel around a pixel of interest. Image processing apparatus.