JPH0428111B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to an improvement in a character signal conversion circuit for converting a character signal into an NTSC signal. [Technical background of the invention and its problems] In recent years, with the spread of personal computers, color character signals (three signals of R, G, and B) output from these computers have been transmitted to general television receivers. It is often done to supply and display the data. However, television receivers use the NTSC system, which limits the signal band to 4.5MHz or less, so high character signals with a bandwidth of 7MHz or more cannot be directly supplied to the television receiver. It is impossible to display it. Therefore, in the past, for example, as shown in Figure 1,
An NTSC conversion circuit is provided to convert character signals. That is, the three signals RS of R, G, and B output from the personal computer 1,
GS and BS are first connected to delay circuits 2a, 2b, and
2c, where the pixel width is expanded in the horizontal and vertical directions, and then the signal is converted by the signal conversion circuit 3 to produce the R-Y, BY, Y signals RS', BY', Create YS. Of the above-mentioned signals, the R-Y and B-Y signals RS' and BS' are passed through low-pass filters 4a and 4b with a cutoff frequency of 500 kHz, respectively, and then balanced modulation circuits 5a and 4b.
5b, amplitude modulates the 3.58MHz sine wave in circuits 5a and 5b, and sends the modulated output to synthesis circuit 6.
Thereafter, a superimposing circuit 7 superimposes the synthesized output on the luminance signal YS' from the signal converting circuit 3, and the output is supplied to a television receiver (not shown). However, this conventional conversion circuit has the following drawbacks. () Since the pixel width of the character signals RS, GB, and BS is expanded by delay circuits 2a, 2b, and 2c to make it compatible with the NTSC system, the display resolution deteriorates and fine characters cannot be displayed clearly. I can't. () In general, character signals have higher frequency components in the vertical direction than frequency components in the horizontal direction, so even if the pixel widths in each of the horizontal and vertical directions are expanded, they cannot be passed through the low-pass filters 4a and 4b. As a result, the signal level in the vertical direction becomes significantly lower than that in the horizontal direction. As a result, the characters become extremely unnatural, with thin vertical lines and only emphasized horizontal lines. This is extremely undesirable, especially when displaying a graph or the like, since almost no vertical lines are displayed. On the other hand, in order to emphasize the vertical direction, it has been proposed to pass the character signal through an IH delay line, but in such a circuit, for example, in the case of characters that are not continuous in the vertical direction, such as dots, the effect is was not obtained, and it was still not possible to obtain a clear display. [Object of the Invention] An object of the present invention is to provide a character signal conversion circuit that can display a clear display with uniform brightness regardless of the direction of vertical and horizontal bright lines or the form of characters. [Summary of the Invention] In order to achieve the above object, the present invention expands the pixel width of a character signal to match the NTSC signal, and for each pixel of the character signal with the expanded pixel width, A pixel string including a plurality of pixels located before and after each is extracted, and among the pixels constituting this pixel string, a pixel with a specific signal level, for example, a pixel of "1", is arranged in an isolated state. At least determine whether the pixel is in the first state, the second state exists every other pixel, or the third state exists continuously, and based on this determination result, the pixel is The signal level is set to a predetermined second level in the second state, and the signal level is set to a predetermined second level in the second state.
In the above state, the level is variably set to a first level higher than the second level, and in the third state, at least a third level lower than the second level is variably set. [Embodiment of the Invention] FIG. 2 is a circuit configuration diagram of a signal level control circuit which is a main part of a character signal conversion circuit in an embodiment of the present invention.
This is provided in place of a, 2b, and 2c. Note that a signal level control circuit is provided for each of the R, G, and B signals RS, GS, and BS, but since each circuit has the same configuration, only one of them is shown in FIG. This signal level control circuit includes a delay circuit 11 that expands the pixel width of a character signal (for example, an R signal RS) in the horizontal direction, and a delayed character signal RDS output from this delay circuit 11 that is synchronized with a clock signal CK for each pixel. and a 5-bit shift register 12 for shifting and inputting, and this shift register 12.
a determination circuit 13 to which the parallel outputs of are supplied, and a latch circuit 1 that latches the determination output of this determination circuit 13
4 and a signal level variable circuit 15. The judgment circuit 13 is composed of a read-only memory, and guides the parallel output from the shift register 12 as an address signal, and outputs the judgment value stored in the storage area designated by this address signal to the corresponding terminal D ₁ . , D ₂ , D ₃ , and D ₄ . Here, the storage contents of the ROM are set as shown in the following table.

【table】

〔Effect of the invention〕

As described in detail above, the present invention extracts, for each character of a delayed character signal, a pixel string including a plurality of pixels located before and after this pixel, and identifies a The arrangement state of pixels with a signal level of , for example, pixels of "1", is the first state that exists in isolation, the second state that exists every other pixel, or the arrangement state that exists continuously. According to the result of this determination, the signal level of the pixel is set to a predetermined second level in the second state, and to a predetermined second level in the first state. The first level is higher than the first level, and in the third state, the third level is lower than the second level. Therefore, according to the present invention, it is possible to provide a character signal conversion circuit that can provide a clear display with uniform brightness regardless of the direction of vertical and horizontal bright lines or the form of characters.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional character signal conversion circuit, FIG. 2 is a circuit diagram showing the main part configuration of a character signal conversion circuit according to an embodiment of the present invention, and FIG. 3 is the circuit shown in FIG. FIG. 3 is a signal waveform diagram for use in explaining the action of FIG. 11...Delay circuit, 12...Shift register,
13...Determination circuit (ROM), 14...Latch circuit, 15...Signal level variable circuit, 16...Logic circuit.

Claims (1)

[Scope of Claims] 1. In a character signal conversion circuit that converts a character signal into an NTSC signal, means for enlarging each pixel of the character signal to a time width compatible with the NTSC signal, and each of the character signals output from this means. For each pixel, a pixel string including a plurality of pixels located before and after the pixel is extracted, and among the pixels composing this pixel string, an array state of pixels having a specific signal level exists in isolation. means for at least determining whether the first state is present at every other pixel, the second state is present at every other pixel, or the third state is continuously present; The signal level of the pixel is set to a predetermined second level in the second state.
a first level higher than the second level in the first state, and a third level lower than the second level in the third state. A character signal conversion circuit comprising level variable means.