TONE CONTROL DEVICE IN MONOCHROMATIC TONE DISPLAY APPARATUS

Abstract: In a tone control device in a monochromatic tone display apparatus, when an intensity signal and at least one of the R, G and B signals is active, an AND gate (17) generates a maximum tone level signal. A selector/adder having OR gates (13, 14, 15) and resistors (R13, R14, R15) receives the maximum tone level signal and the R, G and B signals. When the maximum tone level signal is inactive, the selector/adder generates a tone level signal in response to the active state of the R, G and B signals. When the maximum tone level signal is active and all the R, G and B signals are inactive, the selector/adder generates a minimum tone level voltage. However, when the maximum tone level signal and at least one of the R, G and B signals is active, the selector/adder generates a maximum tone level voltage.

Description: The present invention relates to a tone display control device for producing a monochromatic tone level voltage. A monochromatic tone system is defined as a system for producing a pseudocolor display by using a monochromatic display. Tone levels are determined in correspondence with respective colors, and tone differences are expressed on the monochromatic display by utilizing tone level differences. For example, one-bit I (intensity) data is added to the 3-bit data of R·G·B to represent 8 colors and to format the 4-bit data of I·R·G·B which can express 16 tones corresponding to 16 colors. When the 4-bit data is displayed on the monochromatic display, the 4-bit data can display a maximum of 16 tones. In other words, 16 tone levels are given in correspondence with 16 colors. The I bit is set at logic "0" in the normal mode, and at logic "1" in an emphasizing mode. Assume that the 4-bit data of I·R·G·B is weighted to provide a color code C = I x 8 + R x 4 + G x 2 + B , and that numbers 0 through 15 are given by Cs, respectively. The smaller the color code is, the lower the tone level. The larger the color code, the higher the note level. According to the above-described system, however, since the difference between the adjacent tone levels is small, the difference cannot be easily identified. In addition, since the I bit among the I, R, G and B bits has the maximum weight coefficient, the screen is darkened as a whole when the I bit is rarely enabled. Prior art document US-A-4 236 175 describes a monochromatic picture display device comprising a converter circuit. This converter circuit has three inputs to each one of which a bivalent color signal R, G and B is supplied, for converting these bivalent color signals into a monochromatic signal appearing at an output thereof, having an amplitude which is different for each color combination. An adder circuit and a non-linear circuit coupled to the adder circuit provide a plurality of increased amplitudes of the monochromatic signal for color signal combinations corresponding to the lowest amplitude, differing from zero, of the monochromatic signal. The combination of a sum signal and a correction signal is formed from the bivalent color signals, wherein the color differences are derived from the sum signal and the correction signal ensures a basic luminance. In this monochromatic picture display device original colors remain recognizable by choosing a suitable luminance ratio, and colors having a low brightness are displayed with a sufficient degree of visibility. It is an object of the present invention to provide a monochromatic tone display apparatus wherein the conventional 16 tones are compressed to 9 tones to increase the difference between each two adjacent tone levels. To solve this object the present invention provides a tone display control device as stated in claim 1. In a tone display control device according to the present invention, when the I bit is set at logic "0", eight color codes represented by the 3-bit data of R·G·B are respectively assigned to eight tone levels. However, when the I bit is set at logic "1", the maximum tone level is assigned to the color code irrespective of the logic state of the 3-bit data of R·G·B. 16 colors can be expressed by a total of 9 tone levels. Therefore, since the difference between each two adjacent tone levels can be increased, the difference can be easily identified. Even if the I bit is rarely set at logic "1", the screen will not be darkened. The present invention provides the following effects: 1) Since the difference between each two adjacent tone levels is increased, the display contents can be easily recognized; 2) Even if the I bit is rarely set at logic "1", the screen will not be darkened; and 3) Since the difference between the tone levels for the I bit of logic "1" and for the I bit of logic "0" is increased, the primary function (i.e., an emphasizing function) of the I bit can be properly performed. Other objects and features of the present invention will be apparent from the following description taken in connection with the accompanying drawings, in which: Fig. 1 is a diagrammatic representation showing the relationship between the color codes, the tone levels and the I, R, G and B bits in a conventional 16-tone system; Fig. 2 is a diagrammatic representation showing the relationship between the color codes, the tone levels and the I, R, G and B bits in a 9-tone system according to the present invention; and Fig. 3 is a block diagram of a monochromatic tone display apparatus according to an embodiment of the present invention. Fig. 2 is a diagrammatic representation showing the relationship between the color codes, the tone levels and the I, R, G and B bits in a 9-tone system. In this embodiment, when an intensity (I) bit is set at logic "0", eight color codes represented by the 3-bit data of R·G·B are assigned to eight tone levels, respectively. However, when the I bit is set at logic "1", the maximum level is assigned to the color code irrespective of the 3-bit data of R·G·B. The color codes are assigned with a total of 9 tone levels. When the I bit is set at logic "1" and all the R, G and B bits are set at logic "0", the color code consisting of the 4-bit data of I·R·G·B is assigned to the minimum level in the same manner as the 4-bit data of all "0"s. As a comparison, the relationship between the color codes, the tone levels and the I, R, G and B bits in the 16-tone system is diagrammatically illustrated in Fig. 1. Fig. 3 is a block diagram of a monochromatic tone display apparatus according to an embodiment of the present invention. A horizontal synchronizing signal (HSYNC) and a vertical synchronizing signal (VSYNC) generated from a display controller (not shown) are supplied to a non-exclusive OR gate 11. The I bit (the intensity signal) is supplied to one input terminal of an AND gate 17. The R, G and B signals are supplied to an OR gate 18 and one input terminal of each of the OR gates 13, 14 and 15. An output signal from the OR gate 18 is supplied to the other input terminal of the AND gate 17 and a buffer 16. An output signal from the AND gate 17 is supplied to a buffer 12 and the other input terminal of each of the OR gates 13, 14 and 15. The buffer 12, the OR gates 13, 14 and 15, and the buffer 16 are commonly connected to an amplifier 19 through corresponding resistors R12, R13, R14, R15 and R16. An output terminal of the non-exclusive OR gate 11 is connected to output terminals of the gates 13 through 15 and the buffers 12 and 16. At the same time, the non-exclusive OR gate 11 is also connected to a power source voltage VCC through the resistor R11, and grounded through resistor R17. The buffers 12 and 16 are arranged to synchronize with propagation delay times of the gates 13 through 15. When one of the HSYNC and VSYNC signals is set at logic "1", the OR gate 11 generates a logic "0" signal. When one of the R, G or B signals is set at logic "1", the OR gate 18 generates an output signal of logic "1". This output signal is supplied to the other input terminal of the AND gate 17. When the I signal is set at logic "1", the AND gate 17 generates, through the buffer 12, a signal indicating that the tone is of the maximum level. The OR gate 13 generates a signal indicating, similarly, that the R signal is of the maximum level, the OR gate 14 generates a signal indicating that the G signal is of the maximum level, the OR gate 15 generates a signal indicating that the B signal is of the maximum level, and the buffer 16 generates a signal indicating that one of the R, G and B signals is present. The resistor R11 constitutes a pull-up resistor; R12 through R16, open collector resistors for the buffer 12, the OR gates 13 through 15, and the buffer 16; and R17, a pull-down resistor. These resistors constitute an adder from which the total voltage from the active resistors is applied to the amplifier 19. According to the experimental results of this application, the following resistances are preferable: R11 = 220 ohms R12 = 820 ohms R13 = 220 ohms R14 = 470 ohms R15 = 910 ohms R16 = 470 ohms R17 = 240 ohms The operation of the monochromatic tone display apparatus having the arrangement described above will be described in detail with reference to Figs. 2 and 3. As shown in Fig. 2, assume all the I, R, G and B bits are set at logic "0". When the HSYNC or VSYNC signal supplied from the display controller (not shown) is set at logic "1", an output signal from the OR gate 11 is set at logic "0". An output potential at the amplifier 19 is the ground potential. As shown in Fig. 2, the tone level signal is of the minimum level. When only the B signal is set at logic "1", the resistors R15 and R16 are active. A total voltage from the resistors R15 and R16 is applied to the amplifier 19. Furthermore, when only the G signal is set at logic "1", the resistors R14 and R16 are active. The total resistance of the resistors R14 and R16 is smaller than that of the resistors R15 and R16, so that the total voltage from the resistors R14 and R16 is higher than that of the resistors R15 and R16. Similarly, when the R, G and B signals are set at logic "1", the resistors R13, R14 and R15 are active. The total voltage from the resistors R13 through R16 is applied to the amplifier 19. As shown in Fig. 2, the tone level is increased in a stepwise manner. When the I bit is set at logic "1" and all the R, G and B bits are set at logic "0", an output from the OR gate 18 is set at logic "0", and an output from the AND gate 17 is set at logic "0" accordingly. Therefore, since all the resistors R12 through R16 are inactive, the tone level is of the minimum level, as shown in Fig. 2. When the I bit is set at logic "1" and one or all of the R, G and B bits are set at logic "1", an output signal from the AND gate 17 is, likewise, set at logic "1". Consequently the resistor R12 is active. The signal of logic "1" from the AND gate 17 is supplied to the OR gates 13, 14 and 15, and their outputs are set at logic "1" irrespective of the logic levels of the R, G and B signals. As a result, all the resistors R13 through R16 are active. The maximum total voltage from the resistors R12 through R16 is always applied to the amplifier 19 so that the tone level is kept at the maximum level, as shown in Fig. 2.

Claims: A tone display control device for producing a monochromatic tone level voltage corresponding to R (red), G (green) and B (blue) signals, as well as to an I (intensity) signal, in synchronism with a horizontal synchronizing (HSYNC) signal and a vertical sync (VSYNC) signal, upon reception of the HSYNC, VSYNC, R, G, B and I signals, characterized by comprising: means (18, 17, 12, 13, 14, 15, R11, R12, R13, R14, R15, R17) for generating different tone level voltages in response to correspondingly different combinations of R, G, B signals, when at least one of the R, G, B signals is active, while the I signal is inactive, for generating a minimum tone level voltage when all the R, G and B signals are inactive, independent of whether the I signal is active or not, and for generating a maximum tone level when one or a combination of the R, G and B signals is active in combination with an active I signal. A tone display control device according to claim 1, characterized in that said generating means comprises: a first gate circuit (18) for receiving the R, G and B signals which are externally supplied thereto, and for producing a logical ORed signal of the R, G and B signals; a second gate circuit (17) in the form of an AND-gate which receives said I signal at a first input thereof and the logical ORed signal output from said first gate circuit (18) at a second input thereof, for generating a maximum tone level signal when at least one of an R, G or B signal is active and the I signal is active; third, fourth and fifth gate circuits (13, 14, 15) in the form of OR-gates which receive said R, G and B signals at a first input thereof, respectively, and said maximum tone level signal output from said second gate circuit (17) at a second input thereof, respectively; and resistors (R13, R14, R15), each of which has one end connected to said third, fourth and fifth gate circuits (13, 14, 15), respectively, and the other end connected to a power source voltage via a pull-up resistor (R11), said resistors constituting an adder and being arranged to generate said different monochromatic tone level voltages.

Inventors: NAKAMURA, NOBUTAKA C/O PATENT DIVISION
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1985
Main classification: G09G1
IPC codes: H04N5, G06F3, G09G1, G09G5