JPH0787566B2 - Video printer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video printer, and more particularly to a video printer which is suitable for a printer that produces gradation and has improved image quality.

[Conventional technology]

Γ correction on the conventional printer side is described in the literature (IEEE, CE-28, No. 3 P.
As shown in Fig. 6 of 228), the gamma correction circuit was installed before A / D conversion. With this method, the memory for the image signal has only one line, but when actually printing a moving image, one screen memory is required. In this case, the memory image needs to be re-monitored. Became an obstacle, so it was necessary to perform the inverse γ correction after D / A conversion.

[Problems to be solved by the invention]

In the above conventional technology, when the screen memory is provided, it is necessary to have one analog γ correction circuit for each of the input and the output. In this case, the γ-correction circuit is a non-linear circuit and has a large number of parts, and it is difficult to make the characteristics uniform. I was crying.

An object of the present invention is to provide a video printer of high image quality by accurately performing these γ correction and inverse γ correction by a simple method.

[Means for solving problems]

In order to achieve the above object, the present invention provides a video printer, which receives a video signal and obtains a halftone image of the video signal, in which the input video signal has more bits than the number of bits assigned to one pixel. A / D conversion means for converting into a digital signal by means of, a non-linear conversion means for performing a non-linear signal conversion with respect to the digital signal, and an image for storing the upper bits of the signal-converted digital signal as a digital signal after the non-linear conversion A memory, a print signal output means for outputting a digital signal stored in the image memory as a print signal, and an inverse of the non-linear signal conversion performed by the non-linear conversion means with respect to the digital signal stored in the image memory. Non-linear inverse conversion means for conversion, and the converted signal is converted into an analog signal and output
And a D / A conversion means.

[Action]

That is, after converting a video signal from analog to digital, the signal is nonlinearly converted. This can be easily achieved by the method of referring to the table, there is no variation like analog, and the parts are simple. However, since it is a digital operation, a signal loss occurs. To prevent this, use the quantization bit number of the A / D converter for printing.
The number of bits is larger than the number of bits, and nonlinear signal conversion is performed in a digital state. After that, signals of the number of bits required for printing are taken out and stored in memory or printed. By doing so, it becomes possible to prevent digit loss due to digital calculation. When the digitalized signal is stored in the image memory and output to the image monitor, the image can be correctly monitored by performing the reverse signal conversion digitally before the 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 mbit by the A / D converter 1. After that, conversion is performed by the γ-power nonlinear converter 2 by 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 a converted signal. The nbit signal output from 3 is the gradation control circuit 4
Sent to the memory head. On the other hand, the output of 3 is multiplied by 1 / γ by the non-linear inverse converter 5 using ROM etc., and then D / A
It is adapted to monitor both sides which have been sent to a monitor television or the like via the converter 6 and stored therein. In this case m>
When n is set, it is possible to prevent the digit loss due to the conversion of the γth power. The value of γ is 2.2 or more, which is the γ of a cathode ray tube. The reason why γ ≧ 2.2 is described below. FIG. 2 shows the relationship between the signal and the print density. That is, the brightness of light incident on the video camera is E ₀ (%), the output voltage of the video camera is Ev (%) (reflectance 1%),
It is quite difficult to achieve a concentration higher than this, and practically even 1.5 can be used. Looking at the value of Ev 'in the case of D = 1.5 in Fig. 2, it is found that γ = 1 Ev' = 20.8% γ = 2.2 Ev '= 3.16% γ = 2.64 Ev' = 1.58%, and γ = 1 At this time, 20% of Ev 'becomes a black area, which cannot be used even if it is discretized. For example 64
When controlling halftones by gradation, 64 × 0.2≈13, which means that 13 gradations are not used. If γ is increased to 2.2 or 2.64, almost all of them can be used. Table 1 shows the number of gradations displayed for each density in the case of 64 gradations. That is, it can be seen that by increasing γ, the number of gradations of D = 1.5 or more decreases and the range of D = 0 to 0.5 increases, and particularly the low density region can be expressed finely.

As for the value of γ, from Table 1, if γ = 2.2 or more, D = 1.5
The number of gradations described above is small, and when D = 0 to 0.5, the density can be expressed with almost twice the fineness as in the case of γ = 1.

In Fig. 1, after the A / D conversion, digital nonlinear conversion and inverse conversion are performed, but the same applies to the case where the analog conversion is performed before the A / D conversion and after the D / A conversion. The effect of can be expected. The advantages of performing digital are as follows.

1) The nonlinear conversion circuit is simple and no adjustment is required.

2) Converting in analog, it does not return to the original even if it is reversely converted, and it is accompanied by an error, but it returns to the original in digital.

3) γ can be changed freely by rewriting the ROM table,
You can also adjust the image.

FIG. 3 shows a case where Ev 'and D have a linear relationship.

(1) in Figure 3 (2) is In the case of, the relationship between Ev ′ and Ev corresponding to the first quadrant is shown. That is, the concentration that gives Ev ′ and Ev as shown by the curve (1) and Ev ′ have a linear relationship, and 0.5 ≧ D ≧ 0, 1.0 ≧ D ≧ 0.5, 1.
The number of gradations in each of the three ranges of 5 ≧ D ≧ 1.0 is equal to 21. When given as in (2), D and E
v ′ can be represented by three straight lines, and the number of gradations is D =
It becomes 32 at 0 to 0.5, 19 at D = 0.5 to 1, and 13 at D = 1.0 to 1.5.
That is, by giving D and Ev 'in the form of a straight line or a polygonal line, the number of gradations near the target density can be adjusted, and a high-quality print in which pseudo contours are not noticeable can be obtained.

〔The invention's effect〕

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 pseudo contours are hard to appear.

Also, since the input video signal is A / D converted with a number of bits larger than the number of bits assigned to one pixel, the upper bits of the quantized bit number after A / D conversion are stored in the image memory. It is possible to prevent digit cancellation during digital calculation, and to monitor an image correctly. As a result, higher quality print results can be obtained.

[Brief description of drawings]

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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toru Takei, Toru Takei, 4026, Kuji-cho, Hitachi, Hitachi, Ibaraki, Hitachi Research Laboratory, Hitachi, Ltd. (56) References JP-A-60-139080 (JP, A) JP-A-52 -142445 (JP, A)

Claims (2)

[Claims] 1. A video printer, which receives a video signal and obtains a halftone image of the image, converts the input video signal into a digital signal with a number of bits larger than the number of bits assigned to one pixel. / D conversion means, a non-linear conversion means for performing a non-linear signal conversion to the digital signal, an image memory for storing the upper bits of the signal-converted digital signal as a digital signal after nonlinear conversion, the image memory Print signal output means for outputting the stored digital signal as a print signal, and non-linear inverse conversion means for performing inverse conversion of the non-linear signal conversion performed by the non-linear conversion means on the digital signal stored in the image memory. And a D / A conversion means for converting the signal after the inverse conversion into an analog signal and outputting the analog signal. Printer. 2. The non-linear conversion means according to claim 1, wherein the non-linear signal conversion is a non-linear signal conversion in which the input is raised to the power of γ and the output is γ ≧ 2.2. And a video printer.