JPH078004B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image by dot recording, and in particular, one pixel is input as binary image data to form one picture element from a plurality of pixels. The present invention relates to an image forming apparatus that forms an image using a pixel as a unit of density.

2. Description of the Related Art Conventionally, image forming apparatuses that perform dot recording according to input image information have been known.

When halftone reproduction is performed in such an apparatus, a technique generally called a dither method is used, and the density of an image is represented by changing the number of dots recorded per unit area. However, the halftone reproduction by the dither method has various problems such as the disturbance of the edges of the image and the generation of moire, and the circuit requires a memory and a comparator for storing the dither pattern.

Further, when the input data is binary image data, there is a drawback that recording at a plurality of density levels cannot be performed.

The present invention has been made in view of the above points. Even if the input data is image data of 1 pixel binary, 1
The present invention provides an image forming apparatus capable of forming an image having excellent gradation by forming two picture elements and forming an image with one picture element as a unit of density.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 (a) shows a part of an image having a binary level of 1 pixel white and black obtained by reading an original image at a resolution of 8 lines / mm. This is shown in FIG. 1 (b). As described above, it is divided as a picture element including a pixel set in a 2 × 2 unit area. Of the four pixels forming this picture element, for example, the number of black level pixels is counted, and the count value is assigned to each picture element as the density rank number. Then, this rank number is stored as image information of each picture element. That is, assuming that the black level image data is 1, each pixel in FIG. 1 (a) is binarized as shown in FIG. 1 (c). A value obtained by adding the numerical values of the respective pixels in one picture element is as shown in FIG. 1D, and this value is stored as the density rank number.

In this way, one picture element composed of 2 × 2 pixels is stored in a 3-bit binary number as a rank number from 0 to 4. FIG. 2 shows an example of a circuit configuration for performing the above storage operation.

A binary video signal serially output line by line from an output device equipped with an image pickup device such as a CCD has four buffer memories 1, 2, 3 each having a capacity of at least one line in units of one line. , 4 are sequentially stored in time series. Here, when the video signals are written in the buffer memories 1 and 2, the video signals are read from the buffer memories 3 and 4, and the read and write operations are alternately performed with the buffer memories 1 and 2, 3 and 4 as a set. The memory read signal 25 and the Mamori write signal 26 for switching the write / read operation are output by the control circuit 5 in synchronization with the video signal, and the timing is set. The address counter 6 is a circuit for generating a storage address 24 of a video signal which is pixel data.

Writing video signals to the buffer memory is 1 → 2 → 3
The reading is performed for each line in the order of .fwdarw.4, but the reading is performed simultaneously for two lines for each set of the buffer memories 1 and 2 and the buffer memories 3 and 4. For example, when a video signal is written in the buffer memories 3 and 4, the buffer memories 1 and 2 are simultaneously read. The binary counter 7 divides the video signal read from the buffer memory into 2 bits each, and the bit counters 8 and 9 are black level pixels.
Is counted for each line, and the output is added by the adder 12 every 2 bits.
Is output to. On the other hand, when writing is being performed in the buffer memories 1 and 2, it is similarly read from the buffer memories 3 and 4. Therefore, the adders 12 and 13 output, for example, the number of black level pixels out of 2 × 2 pixels as the density rank number of 3 bits. In the multiplexer 14, two lines of the original pixel data, that is, every line of the image memory 15, the adders 12 and 13 are selected and stored in the image memory 15 as image information as shown in FIG. .

FIG. 3 shows the image memory 15 of FIG. 2 in the LED printer.
FIG. 4 is a drive and brightness modulation circuit diagram of an LED array in which a plurality of LED light emitting elements are arranged in a row in an output unit that performs an image recording operation based on the image information read from FIG. As shown in FIG. 1 (d), the stored image information is stored in parallel in the memory 15 by 3 bits each.
Is read out, input to the D / A converter 40, and the voltage value according to the pixel density rank number is output to the line L2. This is shown in FIG. In FIG. 4, L2 indicates a voltage value when the density rank number of each picture element changes in the order of 3 → 2 → 3 → 1 → 0 → 2 → 4. S ₀ , S ₁ , ... are minute LEDs
Synchronized with the memory read clock φ _R for each picture element by the element selection pulse, the analog switches AS1, AS2 ,.
Is turned on and the LED elements LD1, LD2, ...

Next, how the brightness of the LED element is modulated will be described. Now
The analog switch AS1 is turned on LD1 is selected by the signal S _1. At this time, since S ₁ is summer "1", the transistor Q1 is turned off and has, to the transistor Q2 in response to the value of the data bus DB of three bits carrying the image density data data is the D / A A base bias is applied according to the output voltage of the converter 40 to control the current flowing through the LED element LD1. On the other hand, the data on the data bus DB is "0""0""0"
At this time, the output voltage of the D / A converter is 0 V, and almost no emitter current flows through the transistor Q2, so the LED element LD1 is turned off and nothing is printed.

As shown above, the dot printing of the picture elements exposed by the LED elements is as shown in FIG. 5, and the lighting amount of each LED element changes according to the data (0-4) stored in the data bus DB. Since the exposure amount of the photoconductor is different, images having different densities can be obtained. Incidentally, when the LED elements LD1 is not selected, S ₁ is "0",
Therefore, the transistor Q1 is turned on, the base of the transistor Q2 becomes "0", and the LED element LD1 does not light. In this embodiment, DB has 3 gradations and 5 gradations, but it is needless to say that by increasing the number of DB bits, more subtle brightness modulation can be performed and the effect is great.

Although the electrostatic recording method using the LED element has been described in the present embodiment, the present invention relates to an ink jet printer that performs recording by intensity modulation of a laser beam printer that performs dot recording with a laser beam or ink droplets. Ink drop control can also be used. Further, the density-ranked signal may be directly supplied to the printer without passing through the memory.

Effect As described above, according to the present invention, even if the input data is binary image data of one pixel, one picture element is composed of a plurality of pixels and one picture element is used as a density unit to form an image. As a result, an image with excellent gradation can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the number of density ranks, FIG. 2 is a circuit diagram for assigning density ranks, FIG. 3 is a circuit diagram of an example of a recording unit, and FIG.
FIG. 5 is a time chart showing the output state of each signal, and FIG. 5 is a diagram showing the density of recording dots. 1 to 4 are buffer memories, 12 and 13 are adders, 15 is an image memory, and 40 is a D / A. The converters LD1 to LD4 are LED elements.

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Claims (1)

[Claims] 1. An input unit for inputting binary image data representing a binary state of white and black for one pixel, and one picture element from binary image data of a plurality of pixels input by the input unit. A counting unit configured to count the number of black pixel data in the binary image data of pixels in the pixel, and a storage unit that stores the number of black pixel data in the pixel counted by the counting unit. A D / A conversion unit for converting the number of black pixel data in the picture element from the storage unit into analog data; and forming an image by using the analog data from the D / A conversion unit as a density unit of one picture element. And an image forming unit for forming the image forming apparatus.