Method and circuit configuration for producing a sequence of...

Television – Format conversion – Line doublers type

Reexamination Certificate

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Details

C348S452000

Reexamination Certificate

active

06262774

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for converting an input image sequence composed of line-interlaced half-frames at a first repetition frequency to an output image sequence composed of progressive images at a second repetition frequency, which is twice the first. The invention also relates to a circuit configuration for such a conversion.
In order to produce a television picture which is as free of flicker as possible, previous solution approaches are based on the conversion of the signal which is transmitted at the transmitter end and contains line-interlaced fields at a field repetition frequency of 50 or 60 Hz to a field sequence at a field repetition frequency of 100 or 120 Hz, respectively. Such a conversion is described, for example, in European published patent application EP 0 727 904 A2. Other methods provide for the conversion to an image sequence composed of progressive images at a frame refresh rate of 50 or 60 Hz, in which case the progressive images contain the entire number of lines. That method is described, for example, in European published patent application EP 0 679 022 A2.
Flicker effects are still perceptible both with field sequences at 100/120 Hz and with progressive image sequences at 50/60 Hz. In the former case, the edge flickering is admittedly reduced, but it is not completely corrected. Furthermore, line wandering may still occur. In the latter method, the large-area flickering is not completely surpressed.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and a circuit for producing a sequence of progressive images, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provide for improved freedom from flickering.
With the foregoing and other objects in view there is provided, in accordance with the invention, an image conversion method, which comprises:
receiving an input image sequence composed of line-interlaced fields at a first repetition frequency;
converting the input image sequence to an output image sequence composed of progressive images at a second repetition frequency double the first repetition frequency; by
producing from the input image sequence an intermediate image sequence composed of line-interlaced fields at the second repetition frequency;
filtering the fields in the intermediate image sequence and the fields in the input image sequence and producing therefrom the progressive images of the output image sequence.
The frame refresh rate of the progressive images according to the invention is twice the input frequency, that is to say 100 or 120 Hz. As a consequence, edge and large-area flickering are located outside the spectrum that is responsible for the human eye perceiving flickering, and are no longer perceptible by the human eye. The picture is thus virtually completely flicker-free.
The conversion to the intermediate image sequence and to the intermediate video signal with line-interlaced fields at twice the input field frequency is known per se. Appropriate circuitry implementations are thus commercially available. The conversion step originating from the to progressive images at twice the repetition frequency requires only relatively simple filter operations, such as median filtering, but, in particular, no additional image storage complexity. Movement information which can possibly be used is already available from the known conversion method to the intermediate image sequence, and can be adopted for the subsequent progressive conversion.
In accordance with an added feature of the invention, the progressive images in the output image sequence are formed with lines in a first raster position and lines in a second raster position, and successive fields of the intermediate image sequence are each formed only with lines in a different raster position.
In accordance with an additional feature of the invention, in each case one image in the intermediate image sequence and in the output image sequence can be assigned to a movement phase of one of the images in the input image sequence and in each case one further image in the intermediate image sequence and in the output image sequence can be assigned to a further movement phase located between these movement phases, in that the lines of an image in the intermediate image sequence are transferred into the lines in the corresponding raster position in the respective image in the output image sequence of the same movement phase, and in that one of the pixels in the lines in the other raster position of this image in the output image sequence is obtained by means of filtering to which, on the input side, at least one pixel in a line (which is adjacent in terms of position to the pixel to be produced) in the image of the same movement phase in the intermediate image sequence is supplied as well as a pixel at a point which corresponds in terms of position to the pixel to be produced in that image of the input image sequence which, in the movement phase, is closest to the image of the output image sequence.
In accordance with another feature of the invention, each of the image sequences is split into one image sequence having a high signal element containing high-frequency image elements and having a low signal element containing low-frequency image elements, and those pixels are weighted from the input image sequence that are in the same raster position in comparison to the pixel to be produced more highly on the input side for the high signal element in the filtering if movement is found as compared to when no movement is found.
In accordance with a preferred embodiment of the invention, the filtering is median filtering.
In accordance with again an added feature of the invention, the median filtering step comprises supplying a first pixel to a median filter for the high signal element, the first pixel being taken from the field assigned to the intermediate image sequence in the movement phase on the line positionally adjacent to the pixel to be produced from the output image, taking a second pixel from the field in the input image sequence closest to the image of the output image sequence in the movement phase, from a point positionally corresponding to the pixel to be produced, together with the second pixel, if no movement is found, and a fixed value, if movement is found.
With the above and other objects in view there is provided, in accordance with the invention, a circuit configuration for converting an input image sequence composed of line-interlaced fields at a first repetition frequency to an output image sequence composed of progressive images, comprising:
an input receiving an input video signal of an input image sequence composed of line-interlaced fields at a first repetition frequency;
a converter connected to the input for converting the input video signal into an intermediate video signal including an intermediate image sequence composed of line-interlaced fields at a second repetition frequency; and
an output device connected to the converter for producing from the input video signal and the intermediate video signal an output video signal with an output image sequence composed of progressive images.
In accordance with a concomitant feature of the invention, the converter comprises a first image memory receiving the input video signal and outputting a first video signal at a double frame refresh rate, and a second image memory connected to receive from the first image memory the first video signal and outputting a second video signal delayed by one field relative to the first video signal, an intermediate video signal generator having an input connected to the first image memory and the second image memory for generating from the first and second video signals the intermediate video signal, and wherein the output device for producing the output video signal has an input connected an output of the first and second image memories and to an output of the generator.
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