JPS6310981A - Video printer - Google Patents

Abstract

PURPOSE:To obtain a print difficult to have a pseudo-contour with a high picture quality by performing a non-linear signal conversion in the input part of a video signal. CONSTITUTION:The video signal is diverged to (m) bit by an A/D converter 1. Thereafter, the conversion is carried out by a non-linear converter 2 of gammath power according to a table reference system through a ROM table or the like. After the conversion, a high order (n) bit is stored in a picture memory 3 as a signal after the conversion. The signal of the (n) bit is fed to a memory head by a gradation control circuit 4. The output of the picture memory 3 is multiplied by the 1/gamma th power by a non-linear power inverter 5 using the ROM or the like, thereafter, via a D/A converter 6 to a monitor television or the like and a stored picture is monitored. In this case, if m > n, the digit fall of the data by the gamma th power conversion can be prevented. As the value of gamma, there may be above 2.2 of gamma of a cathode ray tube. Thereby, the print of the high picture quality invisible in the pseudo-contour can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video printer, and particularly to a video printer with improved image quality suitable for a printer that produces gradation.

[Conventional technology]

Conventionally, γ correction on the printer side is described in the literature (IEEE).

CE-28, P of Nα3, see Fig. 6 of 228)
As shown in , a γ correction circuit was provided before A/D conversion. In this method, the memory for the image signal is only for one line, but when actually printing a moving image, one screen memory is required.In this case, the memory image needs to be remonitored, and the gamma correction Therefore, it was necessary to perform inverse γ correction after D/A conversion.

[Problem that the invention seeks to solve]

In the conventional technology described above, when a screen memory is provided, it is necessary to have one analog γ correction circuit for each input and output. In this case, the γ correction circuit is a non-linear circuit with a large number of components, and it is difficult to make the characteristics uniform, and as long as the γ-corrected signal is restored to its original state by inverse γ correction, as long as it is done in analog, some errors will occur. It had become.

An object of the present invention is to provide a high-quality video printer by performing these gamma corrections and inverse gamma corrections in a simple manner and with high precision.

[Means for solving problems]

In order to achieve the above object, the present invention performs γ correction on the digital signal side, thereby solving the correction accuracy problem that occurs in analog systems and reducing the number of parts.

[Effect]

That is, after converting the video signal and analog to digital, the signal is converted nonlinearly. This can be easily achieved by referring to a table, and there is no variation unlike in analog systems, and each component is simplified.

However, since it is a digital calculation, signal loss occurs. To prevent this, the number of quantization bits of the A/D converter is made larger than the number of bits used for printing, nonlinear signal conversion is performed in the digital state, and then only the number of bits required for printing is performed. The signal is extracted and stored in memory or printed. In this way, it becomes possible to prevent a loss of digits due to digital calculations. Furthermore, when storing a digitized signal in an image memory and outputting it to an image monitor, the image can be correctly monitored by performing reverse signal conversion digitally before D/A conversion.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. That is, the video signal is discretized into mbits by the A/D converter 1. Thereafter, conversion is performed by the γ-power nonlinear converter 2 using a table reference method using a ROM table or the like. After conversion, the upper n bits are stored in the image memory 3 as the converted signal.The n-bit signal outputted from 63 is sent to the storage head by the gradation control circuit 4. on the other hand,
The output of 3 is converted to 1 by a nonlinear inverse transformer 5 using ROM etc.
After being multiplied by /γ, the signal is sent to a monitor television or the like via a D/A converter 6, so that the stored screen can be monitored. In this case, by setting m) to n, data loss due to conversion to the γ power can be prevented. Further, the value of γ is set to 2, which is the γ of a cathode ray tube, or 2 or more. The reason for setting γ≧2.2 will be described below.

FIG. 2 shows the relationship between the signal and print density. That is,
E is the brightness of the light incident on the video camera.

(%), and the output voltage of the video camera is Ev (%) (reflectance of 1%), and it is quite difficult to achieve a higher density than this, so even 1.5 can be used in practice. In Fig. 2, the value of Ev' when D=1.5 is y=I Ev'=20.8% γ=2.2 EV'=3.16%y=2.64
Ev' = 1.58%, and when γ = 1, E
20% of ν' becomes a black area and cannot be used even if it is discretized. For example, when controlling the intermediate tone with 64 gradations, it becomes 64 x O, 2 valves 13, and 13g! The counterfeit portion will not be used. If γ is increased to 2.2 or 2.64, most of the results can be used.6 Table 1 shows the Vll tone that occurs for each density in the case of 64 gradations, that is, by increasing γ.

It can be seen that the number of gradations above D=1.5 decreases, and increases between D=O and 0.5, making it possible to express particularly low density regions finely.

Table 1 From Table 1, if γ = 2.2 or more, then D =
The number of gradations of 1.5 or more is also small, and when D=O to 0.5, the density can be approximately twice as fine as when γ=1.

In Figure 1, after A/D conversion, digital nonlinear conversion,
Although inverse conversion is performed, similar effects can be expected when nonlinear conversion is performed in the analog signal state before A/D conversion and after D/A conversion. The advantages of digital implementation are shown below.

1) The nonlinear conversion circuit is simple and does not require adjustment.

2) In analog, even when converted and inversely converted, it does not completely return to its original state and is accompanied by an error, but in digital it returns to its original state.

3) γ can be changed freely by rewriting the ROM table, and can also be adjusted using images.

Figure 3 shows a case where Ev' and D are in a linear relationship.

In FIG. 3, (1) and (2) show the relationship between Ev' and Ev corresponding to the first quadrant. In other words, there is a linear relationship between Ev' and the concentration where Ev is given as shown in curve m (1), and Ev' is 0.5
≧D≧0.1.0≧D≧0.5, 1.5≧D≧1.0
The number of gradations within each of the three ranges is equal to 21. Also, when given as in (2), D and Ev'
can be drawn by three straight lines, and the number of gradations is D=O~
0.5 is 32. D=0.5-1 and 19. D=1.0~1
．． 5 becomes 13. That is, by giving D and Ev' in the form of a straight line or a broken line, the number of gradations near the target density can be adjusted, and a high-quality print in which false contours are not noticeable can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the density of the print can be made fine with a simple circuit, and there is an effect that it is possible to provide a print with high image quality and in which false axis outlines are less likely to appear.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIGS. 2 and 3 are diagrams showing the relationship between a video signal and print density. 1...A/D converter, 2...Nonlinear converter, 3...
- Image memory, 4...Nm control circuit, 5... Nonlinear inverse transformer. 6...D/A converter.

Claims (1)

[Claims] 1. A video printer that inputs a video signal and prints a halftone image thereof, which performs nonlinear signal conversion at the input portion of the video signal. . 2. A video printer according to claim 1, wherein the nonlinear signal conversion is a conversion in which an input signal raised to the γ power is used as an output signal, and γ is equal to or larger than 2.2. 3. In a video printer that receives a video signal and prints a halftone image, converts the video signal into a digital signal with a bit number equal to or greater than the number of signal bits of the gradation expressed in the print. A video printer characterized in that the digital signal is subjected to non-linear signal conversion and then made equal to the number of gradation bits expressed in a print. 4. A video printer according to claim 3, characterized in that the nonlinear signal conversion is a conversion in which an input signal raised to the power of γ is used as an output signal, and γ is equal to or larger than 2.2. . 5. In claim 1 or 3, the printer is provided with a screen memory, the output of the memory is converted into a digital signal for obtaining a print, and the printer is converted into an analog signal through a separate D/A converter. A video printer that performs inverse conversion of the nonlinear signal conversion performed at the entrance and outputs the result to a monitor television or the like. 6. In claim 1 or 3, a screen memory is provided, and after non-linear signal conversion, the screen memory stores the output, the output of the screen memory is used as a signal for obtaining a print, and a separate A video printer characterized in that the output of the double-sided memory is subjected to an inverse conversion of the nonlinear signal conversion performed previously, and then converted to an analog signal through a D/A converter and output to a monitor television or the like.