JP2797019B2 - Video printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial application field> The present invention relates to a video printer that prints from an image such as a television or a VTR.

<Conventional technology> Generally, in a video printer that supports an NTSC video signal, if a video signal whose horizontal scanning frequency is different from the NTSC system's 15.73 kHz is input and printing is performed as it is, the so-called circularity is maintained. It will be printed as a distorted image that does not drip.

<Problem to be Solved by the Invention> For this reason, in a conventional video printer, the horizontal frequency is
When printing cannot be performed by capturing a PC signal that is different from the NTSC system, or in the case of printing based on such a PC signal, when the PC signal is loaded into the image memory or read, the image Is corrected so as not to be distorted.

However, such a method of correcting the image so as not to be distorted by writing or reading to or from the image memory has a disadvantage that the configuration becomes complicated.

The present invention has been made in view of the above points,
An object of the present invention is to prevent a printed image from being distorted even with a video signal having a relatively simple configuration and a horizontal scanning frequency different from that of the NTSC system.

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

That is, the present invention provides an A / D converter for A / D converting an input video signal.
A video printer that has a conversion circuit and prints on recording paper with a constant transport density by controlling the energization of the thermal head based on the video signal data A / D converted by the A / D conversion circuit. A detecting means for detecting a horizontal scanning frequency of the input video signal, and a sampling frequency varying means for varying a sampling frequency of the A / D conversion circuit according to the horizontal scanning frequency based on an output of the detecting means. Are provided.

<Operation> According to the above configuration, the horizontal scanning frequency of the input video signal is detected, and the sampling frequency of the A / D conversion circuit is varied so as to correspond to the horizontal scanning frequency.
For example, when the horizontal scanning frequency of the input video signal is higher than the horizontal scanning frequency of the NTSC system, an image can be printed on recording paper having a constant transport density without distortion.

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

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

In FIG. 1, reference numeral 1 denotes an A / D conversion circuit that performs A / D conversion of each of R, G, and B color signals as input video signals corresponding to a still image in accordance with a sampling clock described later.
For example, the D conversion circuit 1 outputs an R, G, B color signal obtained by decoding a 15.73 kHz video signal, which is an NTSC horizontal scanning frequency from a video camera, or an NTSC horizontal scanning frequency from a personal computer. High, for example, R, G at 31 kHz,
The B color signal is input.

Reference numeral 2 denotes a print processing circuit which controls printing of the thermal head 3 based on the color signal data A / D converted by the A / D conversion circuit 1 to perform printing. ,
The color signal data of G and B are color-converted into complementary color signal data of yellow, magenta, and cyan, and the power supply to the thermal head 3 is controlled by the complementary color signal data. mm) to perform gradation printing on the recording paper conveyed in (mm).

Reference numeral 5 denotes a control circuit that controls each unit and constitutes a sampling frequency varying unit 6 described later.

In the video printer of this embodiment, the image printed on the recording paper is not distorted even with R, G, B signals from a personal computer having a horizontal scanning frequency different from the NTSC system, so-called,
The following configuration is used to maintain roundness.

That is, in this video printer, a horizontal scanning frequency detection circuit 7 for detecting a horizontal scanning frequency of an input video signal based on a synchronization signal corresponding to an input color signal, and A based on an output to the detection circuit 7 And a sampling frequency varying means 6 for varying the sampling frequency of the / D conversion circuit 1.

The sampling frequency varying means 6 includes a control circuit 5 that outputs frequency-divided data corresponding to the detected horizontal scanning frequency based on an output of the horizontal scanning frequency detection circuit 7 and a frequency-divided data from the control circuit 5. And a sampling clock generating circuit 8 for outputting a sampling clock obtained by dividing the basic clock to the A / D conversion circuit 1, whereby each of the R, G, B color signals is sampled in accordance with the horizontal scanning frequency. A / D conversion is performed at the frequency.

Here, the principle of correcting image distortion according to the present invention will be described with reference to FIG.

FIG. 2 (A) is a diagram of an original image of a perfect circle, FIG. 2 (B) is a diagram showing the relationship between the original image and two types of sampling clocks when the horizontal scanning period is fixed, and FIG. FIG. 3C is a diagram illustrating a printed image when A / D conversion is performed at each sampling clock.

As shown in FIG. 2, assuming that A / D conversion is performed by the sampling clock 1 and the horizontal scanning period is sampled by 512 clocks and a thermal head of 512 dots is used, a solid line in FIG. 2C is used. As shown, the image is printed in a perfect circle without distortion.

On the other hand, when the A / D conversion is performed by the sampling clock 2 having a frequency half the sampling clock 1 and the horizontal scanning period is sampled by 256 clocks, only 256 dots of data are input to the thermal head. This results in a distorted vertically long image shown in FIG.

Therefore, as described in the above-described prior art, a video signal whose horizontal scanning frequency is different from this horizontal scanning frequency is input to a video printer corresponding to 15.73 kHz of the NTSC system, and the same as in the case of the NTSC system video signal. When the image is printed after A / D conversion, the image is printed as a distorted image in which the roundness is not maintained.

Therefore, in the present invention, as shown in FIG. 1, the horizontal scanning frequency is detected by the horizontal scanning frequency detecting circuit 7, and A / D conversion is performed at a sampling frequency corresponding to the detected horizontal scanning frequency. ing.

For example, in the case of a horizontal scanning frequency corresponding to the NTSC system of 15 kHz, A / D conversion is performed at the same sampling frequency as in the past, and in the case of a PC signal of 31 kHz, the A / D conversion is performed at twice the sampling frequency. Conversion is performed, and printing is performed with an image having no distortion by keeping the conveyance density of the recording paper constant.

Further, in this embodiment, a distortion adjusting means 10 made of a volume is provided, and when the printed image has a distortion, the sampling frequency can be further varied by the volume to make fine adjustment.

<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 according to the horizontal scanning frequency. For example, if the horizontal scanning frequency of the input video signal is NT
When the horizontal scanning frequency is higher than that of the SC system, by increasing the sampling frequency, an image can be printed on recording paper having a constant transport density without distortion.

[Brief description of the drawings]

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

Claims (1)

(57) [Claims] An A / D conversion circuit (1) for A / D converting an input video signal, and a thermal head based on the video signal data A / D converted by the A / D conversion circuit (1). In a video printer that prints on a recording sheet having a constant transport density by controlling the energization of (3), a detection unit (7) for detecting a horizontal scanning frequency of the input video signal; A video printer, comprising: a sampling frequency varying means (6) for varying a sampling frequency of the A / D conversion circuit (1) according to the horizontal scanning frequency based on the output of (7).