GB2090506A

GB2090506A - Video colour graphics apparatus

Info

Publication number: GB2090506A
Application number: GB8036245A
Authority: GB
Original assignee: British Broadcasting Corp
Current assignee: British Broadcasting Corp
Priority date: 1980-11-12
Filing date: 1980-11-12
Publication date: 1982-07-07
Also published as: GB2090506B

Abstract

n-bit code numbers in a picture store 11 are read out synchronously with television waveforms to a "palette" 17 (programmable look-up table) and digital-to-analogue converters 18R, G, B to provide video signals for a picture whose elements are individually given their colours by the stored n-bit numbers. A keyboard 22, graphics tablet 24 and control unit 20 enable an artist to set up the contents of the store 11 to draw the desired picture. In order to allow a modification to the picture to be tested, a flag bit store 12 can have flag bits set to "1" for those elements which are to be in a new colour defined by an n-bit code written into a register 26. When a signal on input 34 is "1" each "1" flag bit causes a selector 16 to pass the register code to pass to the palette 17 in place of the corresponding code in the picture store 11. When the artist is satisfied with the modification, the unit 20 writes the code in the register 26 into all n-bit locations in the store 11 corresponding to "1" flag bits, which are reset to "0". <IMAGE>

Description

SPECIFICATION Video colour graphics apparatus The present invention relates to video colour graphics apparatus of the type wherein orbit code numbers are stored individually for each picture element of a video picture and the code numbers are synchronously decoded to determine the colours assigned to the picture elements by generating video signals for the different colours. Such apparatus is of considerably utility in setting up title pages, diagrams, cartoons and picture material in general made up of coloured lines and block areas. A small value of n gives a good palette of colours (e.g. n = 3 yields 23 = 8 different colours) and the colours can be userdefinable.The user can be provided with input devices such as a keyboard and/or a light pen type of graphics tablet and can "draw'' the desired picture while examining what he is generating on a colour monitor.

Whether the input means for the code number memory are entirely hardware based or (as will generally be preferred) utilize much software, the basis of operation is the same.

Pictures are drawn" by changing the numbers in the individual locations corresponding to the picture elements and the basis of operation can be referred to as an electronic version of "painting by numbers".

It has been appreciated that one practical difficulty arises when an artist, having overwritten information in the store by creating a new line or area in a given colour, decides that he wishes to reverse the process and reconsider his action. In general, in existing systems the overwritten numbers cannot be restored unless a complete record of the previous picture has been made.

With a view to overcoming this problem there is now provided apparatus as set out in claim 1 below, to which reference should now be made.

In the preferred embodiment of the invention there is a single flag bit only per picture element since the addition of 1 bit to n bits yields substantially benefits at small extra expense. The invention may be extended to use more than 1 flag bit, allowing the artist to test two, or even more, different modifications to the picture before committing himself to the change. However, assuming n to be small it becomes uneconomic to add more than one or two flag bits and it will be better to duplicate the complete memory to store the new picture and the old picture.

The flag bits can be in an additional memory but are preferably included in words individual to the picture elements, each word comprising the aforesaid n bits and the flag bit(s) and any other required bits, e.g. parity bits or bits defining special control functions.

One simple example is to use a 4-bit wide memory with a capacity of say 256k words to store n = 3 bits plus 1 flag bit.

An embodiment of the invention will now be described by way of example, with reference to the sole Figure of the accompanying drawing which is a block circuit diagram.

The apparatus comprises a memory 10 shown as divided into an bit picture store 11 and a 1-bit flag store 12 although, as already explained, the bits and flag bits need not be in physically separate storage.

The contents of the memory are read out in known manner under the control of scanning logic 14 synchronised to the television scanning waveforms to read out the ambits at correct picture element rate. The bits are normally routed by an n bit data selector 16 to a programmable look-up table 17 which is designated the palette because its function is to define the colours associated with the different bit codes. For each such code there is output a predetermined group of three numbers, e.g. 8-bit numbers, specifying the R, G and B components of the colour for the corresponding picture element. The 8-bit numbers are converted to analogue voltages by respective digital-to-analogue converters 1 8R, 1 8G and 1 8B whose outputs constitute R, G and B video signals.

The contents of the memory 10 and the programming of the palette 17 are under the control of the user by way of control hardware/software, called the control unit 20. The control unit is provided with input devices such as a keyboard 22 and graphics tablet 24 and may be employed to alter the programming of the palette by rewriting the 8-bit numbers assigned therein to the different decodes. The main function of the control unit 20 is to write new numbers in selected locations of the memory 10 and it is arranged in known manner that such writing does not interfere with the synchronous read-out under control of the scanning logic 14. For example the memory 10 can be arranged in blocks accessed in sequence by the logic 14 while the control unit 20 is only allowed access to blocks not currently accessed by the logic 14.

The control unit can possess features such as are well known in microprocessor controlled video displays such as the ability to draw straight lines and curves between specified points, the ability to assign a code to all elements in a given area, and so on.

As so far described the apparatus is, with the exception of the flag store 12 and selector 16, conventional and need not be described in greater detail. The store 12 and selector 16 are used in conjunction with a working colour register 26 into which one of the bit codes can be entered by the operator via the keyboard 22 and control unit 20. This code may be the same as one of the codes already employed in the picture store 11 or can be a different one of the available 2" codes. The register 26 is connected to the second input port 16R of the data selector 16.The control signal on an input 28 which determines the state of the selector is provided by a NAND gate 30 having one input 32 connected to the output of the 1-bit flag store 12 and second input 34 to which a "Q" signal is applied (directly from a switch on the keyboard or from an output of the control unit 20) when it is desired to display the old picture as defined exclusively by the contents of the picture store 11. The "0" input forces the selector input 28 to "1" '' and the input port 16S which is connected to the picture store 11 is connected to the output port 16Q.

When it is desired to display the new picture the signal on the input 34 is switched to "1" and the selector input 28 follows the complement of the flag store output bits. For every picture element which is the same in the new picture as in the old, the corresponding flag bit is set to "0" which produces a "1" on the selector input 28 so that the port 16S is again connected to the output 16Q.

For every picture element which is to be changed, i.e. to the colour whose code is in the register 26, the corresponding flag bit is set to "1" which produces a "O" on the selector input 28. The selector then connects the second port 16R to the output port 1 6Q so that the code in the register 26 is routed to the palette 17 in place of the code in the picture store 11.

Before describing how the apparatus will be used by an artist it is pointed out that the functions of the control unit described above and below consist in writing data into and reading data from memory locations, whether these are the bit locations in the picture store 11, the 1-bit locations in the flag store 12, the bit location constituted by the register 26 or the registers in the programmable look-up table (palette) 17 which determine the output decodes. Accordingly it is superfluous to go into details of construction of the unit 20 which can be implemented conveniently by a microprocessor suitably programmed, whether by software or firmware.

In known apparatus the control unit would be employed to modify the picture by writing a new code directly into the relevant locations of the picture store 11. In using the apparatus in accordance with the invention, however, a different procedure is adopted. Firstly the code for the colour to be employed in the modification is written into the register 26 and the input 34 is set to "1". Then, instead of writing the new code directly into the relevant locations of the picture store 11, "1" bits are written into the corresponding locations of the flag store 12. The picture will change just as in the normal usage of the known apparatus but the old picture remains stored in the picture store 11 and the artist can at any time revert to the old picture by switching the signal on the input 34 to "O".

When the artist is satisfied with the modification and decides to commit himself to it, he issues a "replace" command via the keyboard 22 and the control unit 20 tests all flag bit locations and wherever there is a "1" bit it writes the code in the register 26 into the rr bit location in the picture store corresponding to the flag bit location in question. The flag bit is also reset to "O".

Many modifications to the apparatus are clearly possible. For example the selector 16 could be replaced by a three-channel selector downstream of the palette 17 in which case the register 26 would be replaced by three 8bit registers whose contents would be switched to the digital-to-analogue converters 18R, 18G, 18B in place of the outputs from the palette 17, in the presence of a "1" flag bit. It would then be possible to test modifications involving a colour not currently programmed into the palette, although it would naturally have to be programmed in before the modification could be accepted as a feature of the picture in the store 11.

Claims

1. Video colour graphics apparatus comprising memory means storing code numbers defining the colours of picture elements and storing corresponding flag bits, input means for writing in code numbers and flag bits, output means operable synchronously in relation to scanning waveforms to read out the code numbers and decode them to video signals, and modifying means responsive to a predetermined flag bit status to effect a predetermined modification of the video signals such that the corresponding picture element assumes a colour different from that defined by its stored code number.

2. Apparatus according to claim 1, wherein the output means comprise decoding means for decoding the code numbers and the modifying means comprise a register for storing a code number defining the said different colour, and a data selector responsive to the flag bits to route the code numbers from the memory means and the code number in the register selectively to the decoding means.

3. Apparatus according to claim 1, wherein the output means comprise decoding means for decoding the code numbers to digital video signals and digital-to-analogue converters and the modifying means comprise registers for storing a set of numbers defining the said different colour, and selector means responsive to the flag bits to route the num bers from the decoding means and from the registers selectively to the digital-to-analogue converters.

4. Apparatus according to claim 1, 2 or 3, wherein the input means are operable on command to modify each stored code number in the memory means which corresponds to the said flag bit status.