FR2509560A1 - COLOR DECODING DEVICE - Google Patents

Abstract

Device for color decoding a NTSC video signal of a computer capable of representing three different visualisations in one signal R.G.B. (red, green, blue). The invention is characterized by a differentiated decoding of said three visualisation modes and a deep logic analysis of the video signal. Particularly, one of the decodings utilizes a sampling of informations at a frequency equal to the fourteenth of the base frequency of the video signal alternatively on two distinct series of four bits. Another decoding is characterized by a variable position and frequency sampling according to the configuration of the video signal, said sampling frequency being able to go up to half the base frequency of the video signal.

Description

The subject of the present invention is a decoding device which, from a video signal coming from a computer and designed to produce certain images in the NTSC color television system in use in the United States of America, makes it possible to recreate similar images on signals
RGB (red, green and blue) which can be used directly (for example on a "PERITEL" socket in France) or directly recoded into SECi or PAL.

This video signal allows in NTSC to produce three different types of display: a 24-line text screen of 40 characters (7x8 dots matrix) 1 a high resolution color screen of 280x192 dots (6 colors possible), a low resolution color screen of 40x48 dots (16 colors possible).

The existing devices are content with sampling the video information at constant frequency and position independently of the viewing modes that this signal can represent. The sampling frequency is then a compromise between these different viewing modes and the result is then very approximate.
The invention is characterized by a differentiated decoding of the display nodes and the simple sampling at constant frequency and position is replaced by an advanced logical analysis of the information conveyed by the video signal.

This invention makes it possible to find the three visualizations on R.V.B. and add the following extensions to it: in text mode, you can choose the color of the text page from 15 colors by program from the computer; in low resolution mode, the few visible imperfections in NTSC (burrs, uneven dot sizes have been removed; in high resolution mode you can choose by program to keep the visualization produced in NTSC or to access some extensions: nine different colors on the same image, choice of each of these colors p @ rmi 16, possibility of preserving the precision of the black and white images.

The invention uses the following signals from the computer: 4 clocks H1, H2, H3, H4: H2, H3, H4 being respectively half, quarter and fourteenth of the base frequency
H1 (for example H1 = 14.318 MHz); video signal (VID), composite synchronization (SYNC); 2 signals indicating the display mode (TEXT and HR); an 8-bit data bus and a 16-bit address bus 2 input-output signals (DEV and 10).

The signal processing begins with a deworming and synchronization of the signals H2, H3, H4 and VID which are carried out by loading these signals into registers at the frequency Hî. Then, the elementary information is spread by compassing the video signal to the using a shift register transmitting 8 bits in parallel at the frequency H1, bits named B1 to B8 in the following, the first shifted bit appearing in B8, then in B7, etc ...

This information is then used in three different ways corresponding to each of the three viewing modes.

Low resolution mode: when R5gF is at 1 and HIE at O, sampling at frequency H4 is performed alternately of bits B2 to B5 (when H3 is at O) and bits B4 to B7 (when H3 is at 1).

Text mode: when TEX = 0, bit 31 is directed to the "select" of a 4-channel multiplexer to the inputs of which the signals corresponding to black are applied on one side and the other 4 of the bits previously loaded in a memory and corresponding to the color chosen for the text page from the computer "buses" (addresses, data and input-output).

High resolution mode: when TEXT = 1 and HR = I, the information used are bits B1, B2, B4, B6 and B8. The invention uses a flip-flop system with write authorization, the common clock being H2, authorization pending during the configuration of bits B1, B2, B4, B6 and B8 (fig. 2). This system makes it possible to obtain 4 signals which are distributed over the address and reading input inputs of two 4x4 bit registers, making it possible to obtain 8 color information of 4 bits previously loaded in these registers, therefore programmable from the computer. A parallel system allows these registers to be replaced by predefined color information when the computer is turned on (fig.4).

The signals from text decoding, low resolution and high resolution are multiplexed to a common 4-bit output entering a resistor matrix allowing 16 colors to be obtained on one output.
RGB conforms to the "PERITEL" standard.

FIG. 1 represents an exemplary embodiment of a circuit for filtering and synchronizing the signals, decoding in low resolution mode and multiplexing the 4 output bits of l. low and high resolution.

FIG. 2 gives an example of an analysis of the video signal in high resolution mode.

Figure 3 provides an example circuit for storing high resolution color information.

FIG. 4 gives an example of a circuit decoding the text mode and determining the predefined high resolution color information.

FIG. 5 provides an exemplary embodiment of an output circuit on an 11PERlTEL "socket.

This set of figures completely describes a practical embodiment of this invention, it being understood that it is not limiting as to its mode of implementation and the applications that can be made of it.

The function references of the circuits used are: 1: 74LS174, 2: 74LS164, 3: 74LS398, 4:? 4LS258A, 5: 74LS378 6: 74LS379, 7: 74LS175, 8: 74LS379, 9: 74L3170, 10: 74LS170 11: 74LS51, 12: 74LS158, 13: 74LS273, 14: 74LS258A, 15: 74LS244, 74LS10 for "NAND" doors, 74LS86 for "OR EXCLUSIVE" doors; diodes D1 and D2 are of the 1N4148 type, diode D3 is a 2.7V zener diode.

Claims (3)

1 Color decoding device for the video signal of a  computer characterized in that it includes three available  electronic decoding devices corresponding to  three display modes (24 lines of 40 characters  res, 40X48 stitches in 16 colors, 280X192 stitches in 6  colors), the election of the appropriate device being  made by the two signals GEXT and HR taken on the card  mother of the computer. 2 Device according to claim 1 characterized by the  only from 6 consecutive outputs of a register  at start-up, it alternately samples the 4 pre  and the last 4 trips at an equal frequency  at the fourteenth of the frequency of the register clock  shifted. 3 Device according to claims 1 or 2 characterized  by the fact that from the eight consecutive outings  a shift register, denoted B1 to B8 (the first  shifted bit appearing in B8, then B7 ...), it uses  bits B1, B2, B4, 36, B8 and stores them in four  series of registers at a frequency equal to half  of the shifter frequency, three of these series of  registers awaiting write authorizations depend  dantes of the configuration of bits B1, B2, B4, B6 and B8  (fig. 2).