JPS6052166A - Binary-coding display method of picture signal - Google Patents

Abstract

PURPOSE:To attain binary intermediate tone display without granular noise by introducing regularity to a dither signal to be added to a picture signal level. CONSTITUTION:A longitudinal axis is an amplitude of a dither signal and a lateral axis represents a picture element step and a1, a2, a3- are uniform random numbers. The polarity of the dither signal is inverted at each picture element and one uniform random number is given at one positive/negative cycle of the polarity. Since the polarity of a random number of the dither signal is inverted at a prescribed pitch, the periodicity is added at random. Thus, in adding the random number of the polarity inversion type to an original signal and binary-coding the original signal, since the regularity by the pitch frequency is introduced, the effect suppressing granular noise is generated. Thus, the binary intermediate the display without granular noise is attained in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for binarizing and displaying image signals capable of expressing halftones.

Conventional configuration and its problems Conventionally, there are various algorithms for binary halftone display methods. Among these, the simplest method is:
A so-called random dither method is known in which a random number is added to the image signal level and binarized at a certain threshold. This principle will be explained using FIG. 1. In FIG. 1, 1o is an adder and 11 is a comparator.

If (m, n) are the coordinates of the original image data in the original image,
The signal f'm,n obtained by adding the original image data fm,n and the random number am,n in the adder 10 is added to the comparator 11, and this becomes the threshold TKU and becomes f'm.If n≧T, the output data, n is set to 1, and if f'm,n<T, q output data m,n is determined to be 0. As shown in FIG. 2, this binarization determination method is as follows: random numbers Cm, n'Fr: original image data fm
, n by the comparator 11 to obtain output data Gm,n similar to the method of determining whether the data cm,n is 1 or O. In the case of the above method, the random number Cm, nid added to the original image data is called a dither signal. The simplest method is to use -disturbance numbers for the dither signals Cnl and H. However, this method has the disadvantage of conspicuous granular noise. That is, in general, binary halftone display requires a certain degree of randomness in order to follow changes in the image, but on the other hand, the randomness generates visual grain noise and deteriorates the image quality.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned drawbacks, and an object of the present invention is to provide a binary display method for image signals that enables binary halftone display without grainy noise. In order to achieve the above object, the present invention inverts the polarity of the pixel signal level of each pixel for each pixel step, so that the polarity is positive or negative.
This is a binarization display method of an image signal in which a signal that gives one random value per cycle is added and binarization processing is performed.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Visual graininess depends on low frequency components in the spatial frequency domain. Therefore, in order to suppress this graininess, the present invention introduces regularity to the dither signal added to the image signal level. This regularity suppresses noise components in the low frequency range.

FIG. 3 is a one-dimensional diagram showing the dither signal of the present invention.
The vertical axis shows the amplitude of the dither signal, and the horizontal axis shows the pixel step. ('11 a2, "s...") is a uniform random number. The polarity of this dither signal is inverted one pixel step at a time. Also, one uniform random number is given in one cycle of positive and negative polarity. FIG. 4 is a diagram showing the dither signal of the present invention in two dimensions, and shows the two-dimensional plane coordinates of the original image data (
m, n) is also inverted one pixel step at a time in both m and n directions, and one uniform random number is given in one cycle of positive and negative polarity.

(bll b21 bs...) is a uniform random number.

FIG. 5 is a circuit diagram for implementing the present invention. Assuming that the coordinates of the original image are m and n, the synchronized clock d of the pixels in the m direction is passed through the flip-flop circuit 21 and the signal f whose frequency has been lowered is inputted to the counter 20.
The output g of 0 is input to the ROM 23 as an address.

The synchronized clock e of the pixel in the n direction is passed through the flip-flop circuit 22, and the signal whose frequency is lowered is similarly input to the address line of the ROM 23. The ROM 23 stores in advance a uniform random number, and a random number is generated for every two pixels in the m direction and the n direction according to the address determined by the output g' of the counter 20 and the signal. Addition and subtraction between the output data C of the ROM 23 and the original image data C is performed by an adder/subtractor 24, and the switching between addition and subtraction is performed by the output signal 1 of the exclusive OR circuit 26 of the signals f and h. The comparator 25 compares the output signal of the adder/subtracter 24 with the threshold value e, and outputs the output signal P.
It determines whether the signal is on or off and converts it into a binary value.

The dither signals illustrated in FIGS. 3 and 4 differ from conventional random numbers in that the polarity of the random numbers is inverted at two fixed pitches. As explained in Figure 5, if such polarity-inverted random numbers are added to the original signal and binarized, regularity due to pitch frequency is introduced compared to the conventional simple U/Dum dither method. This produces the effect of suppressing granular noise. In other words, if we believe in spatial frequency, the noise components due to random numbers will be concentrated near the pitch frequency of polarity reversal, and the low frequency components of the noise distribution will be moved to the high frequency side, resulting in a visual noise smoothing effect. .

Effects of the Invention As described above, the present invention adds a signal whose polarity is reversed at each pixel step to the pixel signal level of each pixel and gives one random value in one cycle of positive or negative polarity, and then performs binarization processing on this signal. With the binarization display method of an image signal, it is possible to display a halftone display without grainy noise using a binarization code.

[Brief explanation of the drawing]

1 and 2 are block diagrams of a signal processing system for performing the conventional binary halftone display method, respectively. 4 is a two-dimensional diagram showing the dither signal in the binarized halftone display method according to the present invention, and FIG. 6 is a diagram showing the circuit system for implementing the binarized display method according to the present invention. It is a block diagram showing an example. 20...Counter, 21.22...Flip-flop circuit, 23...ROM, 24...
...Adder/subtractor, 25...Comparator, 26.
...Exclusive OR circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure C Sui, 71 43 Figure 4

Claims (1)

[Claims] Binarization of image signals characterized by adding a signal whose polarity is reversed for each pixel step and giving one random value in one cycle of positive or negative polarity to the pixel signal level of each pixel, and then performing a binarization process. Display method.