JPS60130261A - Main scanning line density converting system - Google Patents

Abstract

PURPOSE:To attain density conversion to an original with high fidelity by connecting a low pass filter having a cut-off frequency being 1-1/2 of a clock frequency of an image sensor between the image sensor and a sample-and-hold circuit. CONSTITUTION:When a picture signal (a) is inputted to the low pass filter 5 having a cut-off frequency being 1-1/2 of the clock frequency of the image sensor 1, it output is a smooth waveform as shown in a signal (b). In applying the signal to the sample-and-hold circuit 2, a waveform (c) much closer to the original picture signal is obtained. This is effective to ensure the fidelity of the information of the original in converting the line density from N lines/mm. into M lines/mm. and interleaving (N-M)-bit at each N-bit.

Description

DETAILED DESCRIPTION OF THE INVENTION (8) Technical Field of the Invention The present invention relates to a main scanning line density conversion method for facsimile machines and the like.

(bl Technology Background In recent years, facsimile machines, etc.
The transmission speed is increased by reducing the image quality of the original to 7.7 lines/tbva and reading the rough areas at 3.85 lines/1111 lines. There is. For example, when transmitting after reducing to 3/4, that is, when converting the linear density from 16 lines/mi to 12 lines/mi, the conventional method uses 4 of the clock cycle applied to the image sensor (line sensor). A method was adopted in which the image signal was sampled using a sampling pulse with a cycle of /3.

(C1 Problems with the Prior Art Figure 1 is a block diagram for explaining such a conventional main scanning linear density conversion method, and Figure 2 (al is the output waveform of the image sensor in Figure 1; Figure 2 (bl
shows the output waveform of the sample bold circuit.

In both figures, optical information sent from the original through the optical system is input to an image sensor 1J which reads image information at a linear density of N lines/mm, where it is photoelectrically converted.

A clock signal with a frequency of f = 1/TnIlz is supplied to the image sensor 1, and in synchronization with this clock signal, an image signal 3 is sequentially output from 1 bit to 1 as shown in FIG. 2(a). Ru. This analog image signal 3 is input to the sample hold circuit 2, and the cotton density M to be converted is
1 /Tm llz (i.e. N of f
/M times), the peak values are sequentially sampled and held (Figure 2 (
b)).

However, in the conventional method of converting the linear density from N lines/mil+ to M lines/mil+, A in Fig. 2 fal.

Bits like those shown in B, C, and D are thinned out, and in addition, the peak value of each bit is sampled and held, resulting in an image signal that is quite different from the original image signal, and its fidelity may be affected. It had the disadvantage of being damaged.

(di Purpose of the Invention The purpose of the present invention was made in view of the above-mentioned conventional drawbacks,
The purpose of this invention is to provide a main scanning linear density conversion method that can obtain an image signal that is more faithful to the original information when converting the linear density. Serial analog image signals read by the image sensor and sequentially obtained from an image sensor driven by the clock frequency f are sampled at a frequency of M/H of the clock frequency f and converted into a linear density of M lines/dragon. This is achieved by providing a main scanning line density conversion method characterized in that the analog image signal is sampled after passing through a low-pass filter.

(fl　Embodiments of the invention Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a block diagram for explaining the main scanning line density conversion method of the present invention, and FIGS. 4(a) to (C1 are the output waveform of the image sensor in FIG. The output waveforms of the hold circuits are shown.

The difference between FIG. 3 and FIG. 1 is that a low-pass filter 5 is connected between the image sensor 1 and the → sample hold circuit 2, and the same parts as in FIG. 1 are given the same symbols. It is. The cutoff frequency of this low-pass filter 5 may be 1 to 1/2 of the clock frequency of the image sensor 1.

When an image signal similar to that shown in FIG. 1 (al) (waveform of FIG. 4 + al) is input to the low-pass filter 5, its output becomes a smooth waveform as shown in FIG. 4 (b), and the sample bold circuit 2 The output also has a waveform that is quite close to the original image signal (
Figure 4(C)). If this is N pieces/11tA to M pieces/y
sm to N bits (N-M
) It is the same as in the prior art that the signals are thinned out at the ratio of bits, but this effect is produced by smoothing both signals of the image sensor 1 by the low-pass filter 5 before that. The output of sample and hold circuit 2 is then converted to analog/
The signal is input to a digital converter (-V shown) and digitized.

(g) Effects of the Invention As explained in detail above, the main scanning linear density conversion method of the present invention connects a low-pass filter between the image sensor and the sample hold circuit, thereby making it possible to more faithfully reproduce the information in the original. This has the effect that a good image signal can be obtained.

[Brief explanation of drawings]

1 and 2 are block diagrams and waveform diagrams for explaining the conventional main scanning line density conversion method, and FIGS. 3 and 4 are block diagrams for explaining the main scanning line density conversion method of the present invention. FIG. 3 is a diagram and a waveform diagram. In the figure, ■ is an image sensor 2 is a sample Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] Serial analog image signals read at a linear density of N lines/number and sequentially obtained from an image sensor driven by a clock frequency r are calculated by M/N of the clock frequency f.
A main scanning linear density conversion method in which the analog image signal is sampled at a frequency of M lines/square and converted to a linear density of M lines/square, wherein the analog image signal is sampled after passing through a low-pass filter. Linear density conversion method.