JPH0468769A - Video printer - Google Patents

Abstract

PURPOSE:To print out a picture onto recording paper whose carrier density is constant without a distorted picture by detecting a horizontal scanning frequency of an input video signal so as to vary a sampling frequency of an A/D converter circuit. CONSTITUTION:A horizontal scanning frequency detection circuit 7 detects a horizontal scanning frequency and A/D conversion is applied by using a sampling frequency corresponding to the detected horizontal scanning frequency. For example, in the case of the horizontal scanning frequency of 15kHz corresponding to the NTSC system, A/D conversion is applied by using a sampling frequency the same as that for a conventional system, and in the case of a personal computer signal of 31kHz, A/D conversion with a double sampling frequency is applied. Thus, a picture without distortion is printed out by keeping the carrier density of recording paper constant.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a video printer that prints images from images from televisions, VTRs, and the like.

<Prior Art> Generally, in a video printer compatible with NTSC video signals, the horizontal scanning frequency is 15.
If a video signal different from 73 kHz is input and printing is performed as it is, a distorted image will be printed in which so-called roundness is not maintained.

<Problem to be solved by the invention> For this reason, in conventional video printers, the horizontal frequency is
If it is not possible to capture and print a computer signal that is different from the TSC method, or if printing is based on such a computer signal, the image may be is corrected so that it is not distorted.

However, this method of correcting the image so that it does not become distorted by writing to or reading from the image memory has a disadvantage in that the configuration is complicated.

The present invention has been made in view of the above points, and uses a relatively simple configuration to prevent printed images from being distorted even when a video signal has a horizontal scanning frequency different from that of the NTSC system. 'The purpose is to

Means for Solving the Problems> In order to achieve the above-mentioned object, the present invention is configured as follows.

That is, the present invention provides A/D conversion for an input video signal.
Equipped with a /D conversion circuit, printing is performed on recording paper with a constant conveyance density by controlling the energization of the thermal head based on the video signal data converted from A/D by this A/D conversion circuit. The video printer is provided with a detection means for detecting the horizontal scanning frequency of the input video signal, and a sampling frequency variable means for varying the sampling frequency of the A/D conversion circuit based on the output of the detection means.

Effect> According to the above configuration, since the horizontal scanning frequency of the input video signal is detected and the sampling frequency of the A/D conversion circuit is varied to correspond to the horizontal scanning frequency,
For example, if the horizontal scanning frequency of the input video signal is higher than the horizontal scanning frequency of the NTSC system, by increasing the sampling frequency, it is possible to print on recording paper with a constant conveyance density; however, the image can be printed without distortion. Become.

<Example> Hereinafter, an example of the present invention will be described in detail in section L) with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

In the same figure, ■ is an A/D conversion circuit that A/D converts each color signal of R, G, and B as an input video signal corresponding to a still image, in accordance with a sampling clock described later. The conversion circuit 11 (for example, the horizontal scanning frequency of the NTSC system from a video camera is 15.
R, G, H decoded 73kHz video signal
color signal or higher than the NTSC horizontal scanning frequency from the computer), for example, R9G at 31kHz.
, H color signals are input.

Reference numeral 2 denotes a print processing circuit that controls the energization of the thermal head 3 and prints based on the color signal data A/D converted by the A/D conversion circuit l. . gradation printing is performed on recording paper that is conveyed at a speed of 1/2 mm).

Reference numeral 5 denotes a control circuit that controls each section and constitutes sampling frequency variable means 6, which will be described later.

In the video printer of this embodiment, even if the RlG and B signals from a personal computer have a horizontal scanning frequency different from the NTSC system, the image printed on the recording paper will not be distorted and the so-called roundness can be maintained. It is configured as follows.

That is, this video printer includes a horizontal scanning frequency detection circuit 7 that detects the horizontal scanning frequency of an input video signal based on a synchronization signal corresponding to an input color signal, and a horizontal scanning frequency detection circuit 7 that detects a horizontal scanning frequency of an input video signal based on a synchronization signal corresponding to an input color signal. , and sampling frequency variable means 6 for varying the sampling frequency of the A/D conversion circuit l.

The sampling frequency variable means 6 includes a control circuit 5 that outputs divided data corresponding to the detected horizontal scanning frequency based on the output of the horizontal scanning frequency detection circuit 7, and a control circuit 5 that outputs divided data corresponding to the detected horizontal scanning frequency based on the output of the horizontal scanning frequency detection circuit 7. The sampling clock generation circuit 8 outputs a sampling clock obtained by dividing the basic clock by dividing the basic clock to the A/D conversion circuit 1. The frequency will be A/D converted.

Here, the principle of correcting image distortion according to the present invention will be explained based on FIG. 2.

Figure 2 (A) is a diagram of a perfect circular original image, Figure 2 (B) is a diagram showing the relationship between the original image and two types of sampling clocks when the horizontal scanning period is constant, and Figure 2 ( C) is a diagram showing a printed image when A/D conversion is performed at each sampling clock.

As shown in FIG. 2, the sampling clock l
Assuming that the horizontal scanning period is sampled at 512 clocks by A/D conversion and a 512-dot thermal head is used, as shown by the solid line in FIG. 2(C),
The image will be printed as a perfect circle without distortion.

On the other hand, sampling clock 2 with a frequency of 1/2 of sampling clock 1: Therefore, A/D conversion is performed,
When sampling the horizontal scanning period with 256 clocks,
Since only 256 dots of data are input to the thermal head, a distorted vertically elongated image as shown in FIG. 2(C) is obtained.

Therefore, as explained in the above-mentioned prior art,
If a video signal different from this horizontal scanning frequency is input to a video printer whose horizontal scanning frequency is compatible with the NTSC system's 15°73kHz, and the image is printed by A/D conversion in the same way as with the NTSC system video signal, The resulting image will be printed as a distorted image whose roundness is not maintained.

Therefore, in the present invention, as shown in FIG.
A horizontal scanning frequency is detected by a horizontal scanning frequency detection circuit 7, and A/D conversion is performed at a sampling frequency corresponding to the detected horizontal scanning frequency.

For example, in the case of a horizontal scanning frequency of 15kHz compatible with the NTC system, A/D conversion is performed at the same sampling frequency as before, and in the case of a 31kHz personal computer signal, A/D conversion is performed at twice the sampling frequency. /D conversion, and by keeping the conveyance density of the recording paper constant, a distortion-free image is printed.

Furthermore, in this embodiment, a distortion adjustment means 1O consisting of a volume is provided, and if there is distortion in the printed image, the sampling frequency can be further varied and finely adjusted using this volume.

<Effects of the Invention> As described above, according to the present invention, the horizontal scanning frequency of the input video signal is detected and the sampling frequency of the A/D conversion circuit is varied. When the scanning frequency is higher than the horizontal scanning frequency of the NTSC system, by increasing the sampling frequency, images can be printed without distortion on recording paper with a constant conveyance density.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a diagram for explaining the correction principle of the present invention. l...A/D conversion circuit, 3...thermal head, 6
... Sampling frequency variable means, 7... Horizontal scanning frequency detection circuit. FIG. 1 (Block diagram of one embodiment of the present invention)

Claims (1)

[Claims] (1) A/D conversion circuit that A/D converts the input video signal (
1), and based on the video signal data A/D converted by the A/D conversion circuit (1), the thermal head (3)
A video printer that prints on recording paper with a constant conveyance density by controlling energization of the video printer includes: a detection means (7) for detecting the horizontal scanning frequency of the input video signal; A video printer comprising sampling frequency variable means (6) for varying the sampling frequency of the A/D conversion circuit (1) based on the output.