DE4435394A1 - Video signal processor - Google Patents

Abstract

The present invention relates to video signal processors, for example video character generators, which perform anti-aliasing. According to the present invention, there is provided a video signal processor in which signals representing images are subjected to anti-aliasing before display, the generator including means for 1) subjecting such signals to a first, relatively slow anti-aliasing process to produce relatively high quality images and 2) subjecting such signals to a second, relatively fast anti-aliasing process to produce relatively lower quality images; and means for selecting between the first and second processes. This allows a desired balance between operating speed and image quality to be achieved. <IMAGE>

Description

The invention relates to video signal processors, e.g. B. Video character generators
In television studios, character generators are used to generate character signals that are superimposed on a television signal to display an image on a television receiver. In order to reproduce high quality text, the so-called anti-aliasing technique is used to digitally filter the signal representing each character before use. However, this can result in a slower processing speed than is desired in certain applications.

According to the invention, a video signal processor is featured see where signals representing images before the Be subjected to an anti-aliasing effect, the processor having means to 1) such Signals a first, relatively slow anti-aliasing process subject to images of relatively high quality generate, and 2) these signals a second, relative rapid anti-aliasing process to submit to images to produce relatively lower quality, as well Facilities to switch between the first and second process select.

The video signal processor is preferably a video character generator, and the images reproducing signals indicate preferably characters or other graphic representations again.  

The invention is illustrated below with a single Drawing, for example, explains a block diagram of an example video signal generator using of the invention.

The block diagram of the drawing is a video signal generator, such as that from Aston Electronic Designs Ltd., 123/127 Deepcut Bridge Road, Deepcut, Camberley, Surrey GU16 6SD, England is manufactured under the name "motif".

Images to be played back are held in a double frame memory arrangement 1 , which consists of a pair of 32 bit field memories A and B, which enables direct cutting during a program and enable effects to be carried out between two pages. The memory arrangement is constructed in such a way that they supply both fields of the image to a motion interpolator 2 at the same time. This interpolates horizontally by taking a weighted sum of three neighboring pixels of the current line and vertically by taking a weighted sum of the corresponding pixel values from the current line of the current field and the line on each side (in the other field). By changing the weights, the resulting output signal brings an image on the output side to sub-pixel (horizontal) or sub-TV lines (vertical) accuracy. In this way, inserts can be run through uniformly at any speed.

The output signal of the motion interpolator 2 is passed for output to a conventional D / A converter (DAC) and to an analog processing output stage 3 and a conventional digital output processing stage 4 .

A separate 32 bit state image memory 5 holds a full color state image for the operator to view.

The playback construction described above is controlled by a playback processor 6 which is implemented using bit disk components. The generator is controlled by a 68030 microprocessor 7 together with a math coprocessor that handles 16 Mb of memory, including font cage memory, disk memory, and connections to the operator and external peripherals.

In practice, the base frame of the generator comprises three rack space units and is 530 mm deep. It has a vertical counter mother plate, in which four "Double Euro Cards" 280 mm deep on the front and another two "Double Euro Cards" are inserted on the back. The four front cards include: the video signal output, memory array 1 , playback processor 6, and central processor. The two rear cards provide the driver and video / synchronization input and output sockets, the parallel and serial interfaces, the network interface and the keyboard input.

The electronics unit also includes one energy source, two Standard disk drives (one 127 Mb hard disc and one 3.5 ′ ′ floppy disk drive), plus an optional 44 Mb Syquest plate drive with removable plates, one Synchronizing pulse generator (SPG) / keyer and digital serial and parallel outputs to CCIR recommondations 601 and 656. Two "video grab" options are also available available, one to take pictures in GBR or Y / Pb / Pr plus Key to enter the other in 601 parallel and serial Formats.

A keyboard 8 is provided and up to 10 keyboards can be "daisy-chained" using a 75 ohm standard video cable up to a maximum of 300 m from the base frame.

Video outputs are intended for both editing and transmission. The editing output of a keyer 9 is provided as a GBR, while the transmission can be configured either for GBR or for Y / Pb / Pr plus key.

Separate, time-controlled synchronization outputs from an external synchronization source or derived from the internal synchronization pulse generator are also available for editing and transfer see. Two parallel interfaces are together with two intelligent serial interfaces provided for electronic newsroom use cases for RS232 or RS422 operation can be configured. A parallel Centronics interface can be connected to a printer to print out tables of contents etc. A network factory interface can be up to eight nodes or up to 64 Handle nodes with external hardware. Based on ARCNET allows the network to separate sheet files, sheets, Transfer images, logos and fonts between machines become.

An optional "genlock" color SPG / coding 10 and coupler 11 arrangement provides two keyed outputs (one with a protective bypass), two coded outputs, two mixed synchronization inputs with broadcasting quality (if "genlocked", ie if on an external output signal) keyed) and a YC (S) output. An optional digital output for CCIR Recommondations 601 and 656 is available in two versions: only parallel (transmission and key), and parallel and serial. The "Video Grab" option is available for input signals from GBR-Y / Pb / Pr plus key sources or for digital parallel / series format.

Characters (or other graphic data) to be processed and / or reproduced by the system are entered on the keyboard 8 , or are remotely entered into the system by the parallel, serial or network interface into the system via an input / output unit 12 . The character generator reproduces the characters (or graphic data) in anti-aliasing form in order to eliminate visual aliasing effects, such as "staircasing" along diagonal lines. This is done to control the intensity of the pixels that define the characters, more precisely than just "on" or "off". Suitably, the intensity of each pixel can be selected from 256 available intensity levels.

The perceived character quality can be mainly due to two criteria are assessed: the "smoothness" of all lines and curves in the sign (e.g. lack of "stair formation"), and the visual stability of the sign (e.g. lack of Field flickering). The generator can therefore Effect aliasing between individual scan lines, to avoid visual flickering caused by the Interlace image repeat process can occur through which creates a TV picture.

The method by which the anti-aliasing effect is carried out is the main factor affecting the quality of the output Character controls. However, as previously described, requires a higher level of anti-aliasing effect longer Processing times.

A standard anti-aliasing technique is to make the required character larger than required, e.g. B. twice as large as the final size), but without forming an anti-aliasing effect. This main non-anti-aliasing character is then processed to the required size by going through a two-dimensional filter. According to the example of the invention, the 68030 processor 7 changes the characteristics of the filter to be used by the character generator in accordance with the required reduction ratio of the master character to the required height, so that different qualities of the characters and thus different processing speeds can be selected by the user. For example, the user can choose between high quality characters with a relatively low processing speed and low quality characters with a relatively high processing speed.

To do this, the generator must at least have two processing techniques available. Two processes  processing techniques, the different processing speeds skills and signs of different qualities are now described, for example:

In a first, relatively slow technique, a two-dimensional Gaussian filter used to image reduce and produce a high quality sign. Takes a reduction ratio R according to the height and width of the Main character to the anti-aliasing character is a two-dimensional Gaussian filter the size of N pixels (Width) by M lines (height) used to make a weighted Generate sum over a range of the main character. Of the Value of this weighted sum at a particular point used to adjust the intensity of the relevant pixel in the Generate anti-aliasing characters. The filter is every R Pixels and R lines are applied to the main character to make up the generate required anti-aliasing character size.

In particular, the weighted sum W for a pixel on Point (x, y) in the anti-aliasing character calculated as follows:

in which:
F _{(x, y) is} the filter weight for a deviation (x, y) (note that (0,0) is the center of the filter); and
M _{(x, y) is} the pixel value or the intensity in the main character at the position (x, y). M _{(x, y)} can only have the value 0 or 1, which indicates "off" or "on".

Typically the following limits apply:

N, M R

to ensure that all major pixels are scanned become, and

M N

to help reduce interlaced flicker adorn.

The Gaussian filter weight F at x pixels and y lines from The center of the filter can be calculated from:

F _{(x, y)} = ke⁻ ^{(π d) ²}

in which:
k is a scale constant used to control the total filter weight;
e the base of the natural log, and
d the distance from the center of the filter to the position at x pixels and scaled by a constant c
y lines from the center of the filter, which is given by:

k is a scale constant.

Different line qualities and different ver Working speeds can be changed by changing the above Constants R, M, N, k and c can be effected.

A second, relatively faster technique (which is typically provides a reduced quality) is a variant of first technique and uses a flat filter instead of one Gaussian filter. In this case, each filter weight has the same constant value f, d. H.:

F _{(x, y)} = f

With this technique, the values for M and N are typical less than the equivalent values using the first technique.

The operator can e.g. B. by using the keyboard 8 choose between these techniques or alternatively between other techniques to achieve a desired balance between processing speed and character quality.

Claims (10)

1. A video signal processor, in which signals representing images are subjected to anti-aliasing processing before reproduction, characterized by means for subjecting these signals to first, relatively slow anti-aliasing processing and for the reproduction of images of relatively high quality and subjecting these signals to second, relatively fast, anti-aliasing processing to produce relatively low quality images for display and means to choose between the first and second processing. 2. Processor according to claim 1, characterized in that the first anti-aliasing processing to receive the images defining data with a resolution greater than that with of which they are to be reproduced and the processing of the received data for generating the images for the Playback includes. 3. Processor according to claim 2, characterized in that the first anti-aliasing processing is the application of a first filter on the received data. 4. Processor according to claim 3, characterized in that the anti-aliasing processing the determination of the intensity a pixel of an image for display by calculation the sum of the products the intensity of each relevant Place one in the received data and value this position includes a suitable first filter function.   5. Processor according to claim 4, characterized in that the first filter function is a Gaussian filter function. 6. Processor according to one of claims 1-5, characterized in that the second anti-aliasing processing the reception of the Data defining data with a resolution greater than the one with which they are to be reproduced and the Processing the received data to generate the images includes for playback. 7. Processor according to claim 6, characterized in that the second anti-aliasing processing is applying one second filter on the received data. 8. The processor according to claim 7, characterized in that determining the intensity of a pixel of an image Reproduction by calculating the sum of the products of the Intensity of each relevant point in the data received and the value of a suitable one for this position Filter function includes. 9. Processor according to claim 8, characterized in that the filter function is a constant value for all digits. 10. Processor according to one of claims 1-9, characterized in that he is a video character generator and that the pictures representative signals representations of characters or other graphic illustrations.