JPS5825768A - Picture signal processing device - Google Patents

Abstract

PURPOSE:To eliminate the influence of jitter and to reduce the gradation error, by making the phase different by 180 deg. between saw tooth waves in raster-scanned even lines and odd lines to extract a pulse width modulated digital signal. CONSTITUTION:A signal (i) is supplied to a line counter 12 in every one line for original scanning, and logical ''1'' is generated for an odd line, and logical ''0'' is generated for an even line. A signal (n) (or m) is supplied to a saw tooth wave generator 4 from a frequency divider 3 through an AND circuit 14' (or 14) in accordance with the odd line (or even line), and a saw tooth wave (b) (or b') is supplied to a comparator 1. Since saw tooth waves (b) and b' are different in phase by 180 deg., gradation levels of picture elements in odd lines and even lines are extracted with phases shited from each other by 180 deg.. Even if jitter is includ ed at the rise of the saw tooth wave (b) or b', it is hardly apparent as hard copy recording.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image signal processing device, particularly an image signal processing device that extracts a pulse width modulated signal by comparing an analog image signal resulting from raster scanning of an II quantity with a sawtooth wave signal. 1. For example, the phase of the above-mentioned choppy wave is made to be x8/* between even-numbered scanning lines and odd-numbered scanning lines.

The present invention relates to an image signal processing device that extracts a digital signal corresponding to the pulse width of an obtained pulse width modulation signal.

The signal level of the anurg signal as a result of raster scanning the image is compared with, for example, the linearly increasing dark value level, the pulse width corresponding to the gradation of the S image is extracted, and the pulse 'Ili is digitized. A conversion to a digital signal with a transmission signal S is carried out. These digital signals are then stored in a storage device and can be sent to the server as needed.
It is used to make hard copies using printers, etc. However, if the linearly increasing threshold level is a sawtooth wave, if there is undesired jitter at the falling edge of the sawtooth wave, the gradation will contain an error. In order to prevent this problem, we will use the patent publication No. 54-2230.
As shown in Japanese Patent No. 4, it is known to use a triangular wave as the linearly increasing threshold level. However, in this case, the increasing slope portion and the decreasing slope portion of the triangular wave are compared with the signal level of the analog signal described above.

For this reason, compared to the number of gradation steps obtained when a sawtooth wave with the same peak value is used as the threshold.

If a triangular wave is used as a threshold value, another problem arises in that only half the number of stages can be obtained.

The present invention attempts to solve this problem.

Even if jitter is included at the falling point of the sawtooth wave used as a threshold, l! The iI ticket is phase-shifted by 180° to the floor III.
The above problem is solved by taking into consideration that the influence of the jitter does not appear excessively by extracting the jitter. This will be explained below with reference to the drawings.

FIG. 1 shows a mode of extracting a pulse width modulation signal when a sawtooth wave is used as a threshold value, FIG. The figure shows an embodiment of the present invention, and FIG. 4 shows a time chart for explaining the operation of the structure shown in FIG.

In the case shown in FIG. 1, an analog image signal obtained by scanning an image in a rask shape is supplied as a signal S to a filter l. On the other hand, Crotta oscillation! ! The output d of 2 provides a trailing signal to address signal generator 5 to generate address #, and also provides a write pulse to memory 6. That is, the output of comparator l (logic [lJ or rO
J)! Control is performed to write into the memory 6. The output d of the coarse clock oscillator 2 is frequency-divided by the 1 frequency divider 3 as shown in the time chart at the bottom of FIG.
13 is supplied to a sawtooth wave generator W4 to generate a sawtooth signal &, and the sawtooth signal number is supplied to a comparator l as a threshold signal. As a result, the image signal S and the sawtooth signal S are compared by the inverter l, and the inverter 1 generates the indicated output /, as shown in reduced scale in the middle and lower parts of the illustrated time chart in FIG. In other words, a pulse width modulated signal f corresponding to the signal level of the #image signal is generated and sent to the frequency divider 3 by 9.
For example, when the signal I is sampled once during one sawtooth wave period and written into the memory 6, the signal I is sampled once during one sawtooth wave period and written into the memory 6.
The pulse width-varied signal f is written into the memory 6 in the form of an 8-bit signal corresponding to the pulse width, as shown at the bottom of the time chart shown in FIG. Therefore, the gradation level of the lli vote is as shown in FIG.

It is converted into a digital signal with nine gradations from #1 to #9.

As shown in Figure i1, the pulse variation related signal extracting means using a sawtooth wave as a threshold signal has a relatively simple configuration and can divide the number of gradation steps as described above! It has the advantage that a large number of stations can be taken in accordance with the ratio of branching in #3. However, if jitter is included at the falling point of the sawtooth wave generated by the sawtooth wave generator 4, it will directly give an error to the pulse width of the pulse width modulation signal. 0 for this
As mentioned at the beginning of this specification, using a triangular wave as the threshold signal is considered, but this involves problems such as the number of gradations that can be extracted is about half.

Fig. 3 shows the configuration of an embodiment of the present invention that solves the above-mentioned problems.
k # # p d * a # / corresponds to Figure 21, 10 is the timing control circuit, 11 is the lead/
A write control circuit, 12 is a line counter that counts raster scan lines (in the illustrated case, it is a binary counter), and 13 is an OR circuit.

14 and 14' represent AND circuits, and 15 represents a NOT circuit, respectively. Also, the signal d r IB * in FIG.
%s...corresponds to the signal waveform shown in FIG.

A signal i is supplied to a line counter 12 for each l line that scans the image, and the twin counter 12 generates a logic rlJ corresponding to an odd numbered line in the illustrated case and a logic output corresponding to an even numbered H line. rOJ is generated. Therefore, corresponding to the odd-numbered lines, the signal signal from the frequency division Wh3 is supplied to the p sawtooth wave generator 4 via the AND circuit 14', and the sawtooth wave shown in FIG. 4 is supplied to the frequency generator l.

On the other hand, corresponding to the even-numbered lines, the signal part from the frequency dividing IB3 is supplied to the sawtooth wave generator 4 via the AND circuit 14, and the signal part is supplied to the sawtooth wave generator 4 through the AND circuit 14, and the signal part is supplied to the sawtooth wave generator 4, which generates a 180° phase with respect to the sawtooth wave as shown in FIG. The shifted sawtooth wave is the comparator l
supplied to therefore.

As shown in the bottom row of FIG. For example, even if jitter is included at the falling edge of the sawtooth wave or b', the presence of the jitter will be almost eliminated when output as a hard/pure recording. It becomes almost invisible and allows you to obtain smooth recorded images.

As described above, according to the present invention, it is possible to provide an image signal processing apparatus that uses a sawtooth wave signal as a threshold signal and can obtain a hard copy or the like in a manner in which the influence of jitter is practically invisible.

[Brief explanation of drawings]

Figure 1 shows how to extract a pulse width modulated signal using a sawtooth waveform as a threshold, and the 5tF2 diagram is 54
? 1 is an explanatory diagram illustrating the number of gradation levels obtained by the illustrated extracting means; 3 is an explanatory diagram illustrating the configuration of an embodiment of the present invention; 5
Figures +-4 show time charts for explaining the operation of the configuration shown in Figure 3. In the figure, 1 is a comparator and 2 is a clock oscillator. 3 is a branching unit, 4 is a sawtooth wave generator, 5 is an address signal generator, 6 is a memory, and 12 is a line counter. Patent applicant: Alps Electric Co., Ltd. Patent attorney Mori 1) Hiroshi # 1 eye, 2 eyes, 3 eyes

Claims (1)

[Claims] A pulse width modulation signal is extracted by comparing the signal level of an analog image signal obtained by raster scanning an image with the signal level of a sawtooth signal. In an image signal processing device that performs modulation, a plurality of mutually adjacent scanning lines scanned in a raster pattern are regarded as one group, and the above-mentioned saw is applied to each analog image signal corresponding to each scanning line belonging to the one group. An image signal processing device characterized in that sawtooth wave signals obtained by shifting the phase of the wave signals are associated with each other, and a digital signal corresponding to the pulse width is extracted from each obtained pulse width modulated signal.