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EP0982708B1 - Method and apparatus for processing video pictures, in particular for large area flicker effect reduction - Google Patents

Method and apparatus for processing video pictures, in particular for large area flicker effect reduction Download PDF

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Publication number
EP0982708B1
EP0982708B1 EP99115651A EP99115651A EP0982708B1 EP 0982708 B1 EP0982708 B1 EP 0982708B1 EP 99115651 A EP99115651 A EP 99115651A EP 99115651 A EP99115651 A EP 99115651A EP 0982708 B1 EP0982708 B1 EP 0982708B1
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German (de)
French (fr)
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EP0982708A1 (en
Inventor
Carlos Correa
Rainer Zwing
Sebastien Weitbruch
Gangolf Hirtz
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THOMSON LICENSING
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Thomson Licensing SAS
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    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007Display of intermediate tones
    • G09G3/2018Display of intermediate tones by time modulation using two or more time intervals
    • G09G3/2022Display of intermediate tones by time modulation using two or more time intervals using sub-frames
    • G09G3/2033Display of intermediate tones by time modulation using two or more time intervals using sub-frames with splitting one or more sub-frames corresponding to the most significant bits into two or more sub-frames
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007Display of intermediate tones
    • G09G3/2018Display of intermediate tones by time modulation using two or more time intervals
    • G09G3/2022Display of intermediate tones by time modulation using two or more time intervals using sub-frames
    • G09G3/2029Display of intermediate tones by time modulation using two or more time intervals using sub-frames the sub-frames having non-binary weights
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00Control of display operating conditions
    • G09G2320/02Improving the quality of display appearance
    • G09G2320/0247Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00Control of display operating conditions
    • G09G2320/02Improving the quality of display appearance
    • G09G2320/0266Reduction of sub-frame artefacts
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007Display of intermediate tones
    • G09G3/2018Display of intermediate tones by time modulation using two or more time intervals
    • G09G3/2022Display of intermediate tones by time modulation using two or more time intervals using sub-frames
    • G09G3/204Display of intermediate tones by time modulation using two or more time intervals using sub-frames the sub-frames being organized in consecutive sub-frame groups
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/28Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels

Definitions

  • the invention relates to a method and apparatus for processing video pictures, in particular for large area flicker effect reduction.
  • the invention is closely related to a kind of video processing for improving the picture quality of pictures which are displayed on matrix displays like plasma display panels (PDP), display devices with digital micro mirror arrays (DMD)and all kind of displays based on the principle of duty cycle modulation (pulse width modulation) of light emission.
  • PDP plasma display panels
  • DMD digital micro mirror arrays
  • plasma display panels are known for many years, plasma displays are encountering a growing interest from TV manufacturers. Indeed, this technology now makes it possible to achieve flat colour panels of large size and with limited depths without any viewing angle constraints.
  • the size of the displays may be much larger than the classical CRT picture tubes would have ever been allowed.
  • a plasma display panel utilises a matrix array of discharge cells which could only be switched ON or OFF. Also unlike a CRT or LCD in which grey levels are expressed by analogue control of the light emission, in a PDP the grey level is controlled by modulating the number of light pulses per frame. This time-modulation will be integrated by the eye over a period corresponding to the eye time response.
  • this time-modulation repeats itself, with a base frequency equal to the frame frequency of the displayed video norm.
  • a light emission with base frequency of 50 Hz introduces large area flicker, which can be eliminated by field repetition in 100Hz CRT TV receivers.
  • the duty cycle of light emission in PDPs is ⁇ 50% for middle grey. This reduces the amplitude of the 50Hz frequency component in the spectrum, and thus large area flicker artefact, but due to the larger size of PDPs, with a larger viewing angle, even a reduced large area flicker becomes objectionable in terms of picture quality.
  • the present trend of increasing size and brightness of PDPs will also contribute to aggravate this problem in the future.
  • a tone display and apparatus is known in which it is proposed to divide at least one of the sub-fields in a multiple-bit binary sub-field code into at least two smaller sub-fields wherein at least one other sub-field is positioned between the two smaller sub-fields for improving the picture quality.
  • JP-A-05-127612 shows a method for increasing the field frequency by grouping of sub-fields in two consecutive groups.
  • the starting times of the two groups are adjusted so that light generation takes place in a time raster corresponding to the doubling of the field frequency.
  • This adjustment is done by using constant length sub-fields apart from so-called normal-bit sub-fields which have a length of twice a nonnormal-bit subfield, where the length T is determined by the number of sub-fields and the field length in time.
  • the reduction of the large area effect is made by utilising an optimised sub-field organisation for the frame period.
  • the sub-fields in a frame period are organised in two consecutive groups, and the starting times of the two sub-field groups are adjusted to a time raster of 10 ms in the case of a video standard with 50Hz frame repetition rate by adding a first blanking period of a first dedicated length behind the last sub-field of the first sub-field group and a second blanking period of a second dedicated length behind the last sub-field of the second sub-field group; and by a specific coding it is achieved that to a value of a pixel a code word is assigned which distributes the active sub-field periods over the two sub-field groups.
  • the frame period will be divided in 8 lighting periods which are also very often referred to sub-fields, each one corresponding to one of the 8 bits.
  • the grey level 92 will also very often referred to sub-fields, each one corresponding to one of the 8 bits.
  • the grey level 92 will thus have the corresponding digital code word %1011100.
  • the sub-fields may consist of a number of small pulses with equal amplitude and equal duration. Without motion, the eye of the observer will integrate over about a frame period all the sub-periods and will have the impression of the right grey level. The above-mentioned sub-field organisation is shown in Fig. 1 .
  • FIG. 2 An example of a commonly used sub-field organisation for 60Hz video standards is shown in Fig. 2 .
  • the sub-field number has been increased to 12 sub-fields SF.
  • the relative duration of the sub-fields are given in Fig. 2 .
  • the lighting phase has a relative duration of 255 relative time units.
  • the value of 255 has been selected in order to be able to continue using the above mentioned 8 bit representation of the luminance level or RGB data which is being used for PDPs.
  • the seven most significant sub-fields have a relative duration of 32 relative time units.
  • the relative duration of a sub-field is often referred to the 'weight' of a sub-field, the expression will also be used hereinafter.
  • each sub-field SF there is a small time period in which no light is emitted. This time period is used for the addressing of the corresponding plasma cells. After the last sub-field a longer time period where no light is emitted is added. This time period corresponds to the vertical blanking period of the video standard. The implementation of such a vertical blanking period is necessary in order to be able to handle non-standard video signals generated in VCR's or video games, etc.
  • a digital representation of the grey level 92 in this sub-field organisation is e.g. 000001111100.
  • This figure is a 12 bit binary number corresponding to the 12 sub-fields. It will be used to control the lighting pulses for the corresponding pixel during a frame period. It should be noted, that there exist a few other possible 12 bit code words for the same grey level, due to the fact that there are seven sub-fields width identical weight.
  • Fig. 3 a new sub-field organisation according to the invention is shown for 50Hz video standards.
  • the frame period for 60Hz video standards is 16.6ms and for 50Hz 20ms and thus larger for 50Hz video standards. This allows for the addressing of more sub-fields in 50Hz video standards.
  • the number of sub-fields has been increased to 14. This does not cause extra costs since the added time to the frame period is greater than the added number of sub-fields: (20.0/16.6) > (14/12).
  • the sub-fields are structured in two separate sub-field groups G1, G2.
  • One vertical frame blanking period has been replaced by two vertical frame blanking periods VFB1, VFB2, one at the end of the frame period and the other between the two sub-field groups.
  • the 2 sub-field groups are identical in terms of the six most significant sub-fields and different in terms of the least significant sub-field.
  • the weight of the least significant sub-field is small and does not introduce significant large area flicker, and this is the reason why it is not necessary that they are also identical.
  • a sub-field coding process that distributes luminance weight of a given pixel value symmetrically over the 2 sub-field groups is also applied.
  • a small difference in luminance weight between the 2 sub-field groups means a small 50 Hz luminance frequency component, and thus small levels of large area flicker.
  • For the sub-field coding process there is no need of a complicated calculation.
  • a corresponding table where the code words for the 256 different grey levels/pixel values are stored can be used.
  • the first component, 3 (87 mod 4) is the component which is to be coded by the least significant sub-fields of the two sub-field groups.
  • the second and third component which must be multiples of 4 (because of the fact that the six most significant sub-fields in both groups have weights which are multiples of four) are made as equal as possible. If they cannot be made equal, as this is the case with 87 , the second component, to be coded with the sub-fields of group 1, should be made greater by 4.
  • 44 is to be coded with the sub-fields of group G1, and 40 is to be coded with the sub-fields of group 2.
  • the difference in weight between the two sub-field groups is never greater than 5.
  • a second example will be explained with grey level/pixel value 92 .
  • FIG. 4 An apparatus according to the invention is shown in Fig. 4 .
  • the apparatus may be integrated together with the PDP matrix display. It could also be in a separate box which is to be connected with the plasma display panel.
  • Reference no. 10 denotes the whole apparatus.
  • the video signal is fed to the apparatus via the input line V in .
  • Reference no. 11 video processing unit wherein the video signal is digitalized and Y,U, V data is produced.
  • interlace video standards require a previous conversion, here.
  • an YUV/RGB data conversion will be made in this unit as the PDPs work with RGB data.
  • the generated RGB data is forwarded to the sub-field coding unit 12. Therein, to each RGB pixel value the corresponding code word will be selected from a table 13.
  • These code words are forwarded to the frame memory in addressing unit 14 of the PDP 10. With these data the addressing unit 14 controls the plasma display 15.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
  • Transforming Electric Information Into Light Information (AREA)

Description

  • The invention relates to a method and apparatus for processing video pictures, in particular for large area flicker effect reduction.
  • More specifically the invention is closely related to a kind of video processing for improving the picture quality of pictures which are displayed on matrix displays like plasma display panels (PDP), display devices with digital micro mirror arrays (DMD)and all kind of displays based on the principle of duty cycle modulation (pulse width modulation) of light emission.
  • Background
  • Although plasma display panels are known for many years, plasma displays are encountering a growing interest from TV manufacturers. Indeed, this technology now makes it possible to achieve flat colour panels of large size and with limited depths without any viewing angle constraints. The size of the displays may be much larger than the classical CRT picture tubes would have ever been allowed.
  • Referring to the latest generation of European TV sets, a lot of work has been made to improve its picture quality. Consequently, there is a strong demand, that a TV set built in a new technology like the plasma display technology has to provide a picture so good or better than the old standard TV technology.
  • A plasma display panel utilises a matrix array of discharge cells which could only be switched ON or OFF. Also unlike a CRT or LCD in which grey levels are expressed by analogue control of the light emission, in a PDP the grey level is controlled by modulating the number of light pulses per frame. This time-modulation will be integrated by the eye over a period corresponding to the eye time response.
  • For static pictures, this time-modulation, repeats itself, with a base frequency equal to the frame frequency of the displayed video norm. As known from the CRT-technology, a light emission with base frequency of 50 Hz, introduces large area flicker, which can be eliminated by field repetition in 100Hz CRT TV receivers.
  • Contrary to the CRTs, where the duty cycle of light emission is very short, the duty cycle of light emission in PDPs is ~50% for middle grey. This reduces the amplitude of the 50Hz frequency component in the spectrum, and thus large area flicker artefact, but due to the larger size of PDPs, with a larger viewing angle, even a reduced large area flicker becomes objectionable in terms of picture quality. The present trend of increasing size and brightness of PDPs, will also contribute to aggravate this problem in the future.
  • From US-A-5 187 578 a tone display and apparatus is known in which it is proposed to divide at least one of the sub-fields in a multiple-bit binary sub-field code into at least two smaller sub-fields wherein at least one other sub-field is positioned between the two smaller sub-fields for improving the picture quality. In one embodiment it is proposed to double the complete set of sub-fields according to the standard 8 bit binary code in a frame period.
  • JP-A-05-127612 shows a method for increasing the field frequency by grouping of sub-fields in two consecutive groups. In the method the starting times of the two groups are adjusted so that light generation takes place in a time raster corresponding to the doubling of the field frequency. This adjustment is done by using constant length sub-fields apart from so-called normal-bit sub-fields which have a length of twice a nonnormal-bit subfield, where the length T is determined by the number of sub-fields and the field length in time.
  • Invention
  • Therefore, it is an object of the present invention to disclose a method and an apparatus which reduces the large area flicker artefact in PDPs in particular for 50Hz video norms, without incurring extra costs similar to those required by 100Hz TV receivers in a more flexible way.
  • This object is achieved by the measures claimed in claims 1 and 8.
  • According to the claimed solution in claim 1, the reduction of the large area effect is made by utilising an optimised sub-field organisation for the frame period. The sub-fields in a frame period are organised in two consecutive groups, and the starting times of the two sub-field groups are adjusted to a time raster of 10 ms in the case of a video standard with 50Hz frame repetition rate by adding a first blanking period of a first dedicated length behind the last sub-field of the first sub-field group and a second blanking period of a second dedicated length behind the last sub-field of the second sub-field group; and by a specific coding it is achieved that to a value of a pixel a code word is assigned which distributes the active sub-field periods over the two sub-field groups.
  • This solution has the effect that the 50Hz frequency component is substantially reduced compared to a sub-field organisation where only one sub-field group is used. The repetition of 50Hz heavy lighting periods is substituted by a repetition of 100Hz small lighting periods. By using this method virtually no extra costs are added, except for a slight increase in the PDP control complexity.
  • Advantageously, additional embodiments of the inventive method are disclosed in the respective dependent claims. The use of identical structures for the two sub-field groups (for the most significant sub-fields) helps to make sure that the two lighting periods have similar characteristics (see claim 2). The weight of the least significant sub-fields is small and does not introduce significant large area flicker. This is the reason why it is not required that the least significant sub-fields are identical for the two sub-field groups.
  • Advantageous embodiments for the apparatus disclosed in claim 8 are apparent from the dependent claims 9 to 10.
  • Drawings
  • Exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description.
  • In the figures:
  • Fig. 1
    shows an illustration for explaining the sub-field concept of a PDP;
    Fig. 2
    shows a typical sub-field organisation used for 60Hz video standards;
    Fig. 3
    shows a new sub-field organisation for 50Hz video standards; and
    Fig. 4
    shows a block diagram of the apparatus according to the invention.
    Exemplary embodiments
  • In the field of video processing is an 8-bit representation of a luminance level very common. In this case each level will be represented by a combination of the following 8 bits: 2 0 = 1 , 2 1 = 2 , 2 2 = 4 , 2 3 = 8 , 2 4 = 16 , 2 5 = 32 , 2 6 = 64 , 2 7 = 128
    Figure imgb0001
  • To realise such a coding scheme with the PDP technology, the frame period will be divided in 8 lighting periods which are also very often referred to sub-fields, each one corresponding to one of the 8 bits. The duration of the light pulse for the bit 21 = 2 is the double of that for the bit 20 = 1. With a combination of these 8 sub-periods, we are able to build said 256 different grey levels. E.g. the grey level 92 will also very often referred to sub-fields, each one corresponding to one of the 8 bits. The duration of the light pulse for the bit 21 = 2 is the double of that for the bit 20 = 1. With a combination of these 8 sub-periods, we are able to build said 256 different grey levels. E.g. the grey level 92 will thus have the corresponding digital code word %1011100. It should be appreciated, that the sub-fields may consist of a number of small pulses with equal amplitude and equal duration. Without motion, the eye of the observer will integrate over about a frame period all the sub-periods and will have the impression of the right grey level. The above-mentioned sub-field organisation is shown in Fig. 1.
  • Most of the developments for PDPs have been made for 60Hz video standards, like NTSC. For these video standards it has been found that a refined sub-field organisation should better be used to avoid artefacts and improve picture quality.
  • An example of a commonly used sub-field organisation for 60Hz video standards is shown in Fig. 2. The sub-field number has been increased to 12 sub-fields SF. The relative duration of the sub-fields are given in Fig. 2. When all sub-fields are activated, the lighting phase has a relative duration of 255 relative time units. The value of 255 has been selected in order to be able to continue using the above mentioned 8 bit representation of the luminance level or RGB data which is being used for PDPs. The seven most significant sub-fields have a relative duration of 32 relative time units. In the field of PDP technology, the relative duration of a sub-field is often referred to the 'weight' of a sub-field, the expression will also be used hereinafter. Between each sub-field SF, there is a small time period in which no light is emitted. This time period is used for the addressing of the corresponding plasma cells. After the last sub-field a longer time period where no light is emitted is added. This time period corresponds to the vertical blanking period of the video standard. The implementation of such a vertical blanking period is necessary in order to be able to handle non-standard video signals generated in VCR's or video games, etc.
  • A digital representation of the grey level 92 in this sub-field organisation is e.g. 000001111100. This figure is a 12 bit binary number corresponding to the 12 sub-fields. It will be used to control the lighting pulses for the corresponding pixel during a frame period. It should be noted, that there exist a few other possible 12 bit code words for the same grey level, due to the fact that there are seven sub-fields width identical weight.
  • In Fig. 3 a new sub-field organisation according to the invention is shown for 50Hz video standards. The frame period for 60Hz video standards is 16.6ms and for 50Hz 20ms and thus larger for 50Hz video standards. This allows for the addressing of more sub-fields in 50Hz video standards. In the example shown in Fig. 3 the number of sub-fields has been increased to 14. This does not cause extra costs since the added time to the frame period is greater than the added number of sub-fields: (20.0/16.6) > (14/12).
  • The sub-fields are structured in two separate sub-field groups G1, G2.
  • One vertical frame blanking period has been replaced by two vertical frame blanking periods VFB1, VFB2, one at the end of the frame period and the other between the two sub-field groups.
  • The 2 sub-field groups are identical in terms of the six most significant sub-fields and different in terms of the least significant sub-field. The weight of the least significant sub-field is small and does not introduce significant large area flicker, and this is the reason why it is not necessary that they are also identical.
  • For large area flicker effect reduction a sub-field coding process that distributes luminance weight of a given pixel value symmetrically over the 2 sub-field groups is also applied. A small difference in luminance weight between the 2 sub-field groups, means a small 50 Hz luminance frequency component, and thus small levels of large area flicker. For the sub-field coding process there is no need of a complicated calculation. A corresponding table where the code words for the 256 different grey levels/pixel values are stored can be used.
  • The coding process can best be explained with an example. Consider the grey level/pixel value 87. This number can be written in the following form: 87 = 3 + 44 + 40
    Figure imgb0002
  • 87 has been split in three components. The first component, 3 = (87 mod 4) is the component which is to be coded by the least significant sub-fields of the two sub-field groups. The second and third component, which must be multiples of 4 (because of the fact that the six most significant sub-fields in both groups have weights which are multiples of four) are made as equal as possible. If they cannot be made equal, as this is the case with 87, the second component, to be coded with the sub-fields of group 1, should be made greater by 4. In the example, 44 is to be coded with the sub-fields of group G1, and 40 is to be coded with the sub-fields of group 2. Using these rules, the final code is: 87 ̲ = 1 ̲ * 1 + 1 ̲ * 4 + 0 ̲ * 8 + 1 ̲ * 16 + 1 ̲ * 24 + 0 ̲ * 32 + 0 ̲ * 40 1 ̲ * 2 + 0 ̲ * 4 + 0 ̲ * 8 + 1 ̲ * 16 + 1 ̲ * 24 + 0 ̲ * 32 + 0 ̲ * 40
    Figure imgb0003

    or 87 = 45 + 42
    Figure imgb0004
    45 = 1 + 4 + 16 + 24
    Figure imgb0005
    42 = 2 + 16 + 24
    Figure imgb0006
    or 87 = 00110010011011.
    Figure imgb0007
  • With this coding process, the difference in weight between the two sub-field groups is never greater than 5.
  • A second example will be explained with grey level/pixel value 92. 92 = 0 + 48 + 44 92 ̲ = 0 ̲ * 1 + 0 ̲ * 4 + 1 ̲ * 8 + 1 ̲ * 16 + 1 ̲ * 24 + 0 ̲ * 32 + 0 ̲ * 40 0 ̲ * 2 + 1 ̲ * 4 + 0 ̲ * 8 + 1 ̲ * 16 + 1 ̲ * 24 + 0 ̲ * 32 + 0 ̲ * 40
    Figure imgb0008

    or 92 = 48 + 44
    Figure imgb0009
    48 = 8 + 16 + 24
    Figure imgb0010
    44 = 4 + 16 + 24
    Figure imgb0011

    or 92 = 00110100011100.
    Figure imgb0012
  • An apparatus according to the invention is shown in Fig. 4. The apparatus may be integrated together with the PDP matrix display. It could also be in a separate box which is to be connected with the plasma display panel. Reference no. 10 denotes the whole apparatus. The video signal is fed to the apparatus via the input line Vin. Reference no. 11 video processing unit, wherein the video signal is digitalized and Y,U, V data is produced. As plasma displays are addressed in progressive scan mode, interlace video standards require a previous conversion, here. For interlace - progressive scan conversion many solutions are known in the art which can be used here. Also, an YUV/RGB data conversion will be made in this unit as the PDPs work with RGB data. The generated RGB data is forwarded to the sub-field coding unit 12. Therein, to each RGB pixel value the corresponding code word will be selected from a table 13. These code words are forwarded to the frame memory in addressing unit 14 of the PDP 10. With these data the addressing unit 14 controls the plasma display 15.
  • For 60Hz video norms the large area flicker effect is not so disturbing as for 50Hz video standards. While the invention has been explained for 50Hz video norms it is apparent, that it can also be used to improve the picture quality of 60Hz video norms.
  • The blocks shown in Fig. 4 can be implemented with appropriate computer programs rather than with hardware components.
  • The invention is not restricted to the disclosed embodiments. Various modifications are possible and are considered to fall within the scope of the claims. E.g. the number and weights of the used sub-fields can vary from implementation to implementation.
  • All kinds of displays which are controlled by using different a PWM like control for grey-level variation can be used in connection with this invention.

Claims (10)

  1. Method of processing video pictures, in particular for large area flicker effect reduction, the video picture consisting of pixels, the pixels being digitally coded, the digital code word determining the length of the time period during which the corresponding pixel of a display is activated, wherein to each bit of a digital code word a certain activation duration is assigned, hereinafter called sub-field (SF), the sum of the durations of the sub-fields (SF) according to a given code word determining the length of the time period during which the corresponding pixel is activated, the sub-fields (SF) of a pixel are organised in two consecutive groups (G1, G2), and that to a value of a pixel a code word is assigned which distributes the active sub-field periods over the two sub-field groups (G1, G2), characterised in that for the generation of the code word which is assigned to the pixel value the pixel value is split in three components, the first one being the pixel value modulus the number 4, and the second and third component which are multiples of the number 4, being made as equal as possible, and wherein the first component is coded with the least significant sub-fields (SF) of both groups (G1, G2) and the second component with the sub-fields (SF) other than the least significant sub-field of the first group (G1) and the third component with the sub-fields other than the least significant sub-field of the second group (G2) wherein the the following sub-field organisation is used for 50 Hz video norms like PAL and SECAM;
    the frame period is sub-divided in 14 sub-fields (SF), when the maximum activation period of a pixel during a frame period has a relative duration of 256 time units, then the sub-fields (SF) of the first group (G1) have the following duration: Sub-field number Duration/relative time units 1 1 2 4 3 8 4 16 5 24 6 32 7 40
    and the sub-fields (SF) of the second group (G2) have the following durations: Sub-field number Duration/relative time units 1 2 2 4 3 8 4 16 5 24 6 32 7 40
  2. Method according to claim 1, wherein the number of sub-fields in the two sub-field groups (G1, G2) is identical.
  3. Method according to claim 2, wherein each of the sub-fields of the two sub-field groups (G1, G2) is identical in weight except for a number of least significant sub-fields.
  4. Method according to one of claims 1 to 3, wherein the last sub-field (SF) of the first group (G1) is separated from the first sub-field (SF) of the second group (G2) by a certain amount of time.
  5. Method according to one of claims 1 to 4, wherein the vertical blanking period (VFB) of the video frame is subdivided in two parts, the first one (VFB1) being located between the last sub-field of the first group (G1) and the first sub-field of the second group (G2) and the second one (VFB2) being located between the last sub-field of the second group (G2) and the first sub-field of the next frame period.
  6. Method according to one of the claims 1 to 5, wherein for 50 Hz video norms, like PAL, SECAM where a frame period lasts 20 ms, the first sub-field of the second group (G2) starts 10 ms after the beginning of the frame period.
  7. Method according to one of claims 1 to 6, wherein if the second and third component cannot be made equal, the second component should be made greater by the number 4 than the third component.
  8. Apparatus for processing video pictures, in particular for large area flicker effect reduction, the video pictures consisting of pixels, the pixels being digitally coded, the digital code word determining the length of the time period during which the corresponding pixel of a display is activated, wherein to each bit of a digital code word a certain activation duration corresponds, hereinafter called sub-field (SF), the sum of the activation durations according to a given code word determines the length of the time period during which the corresponding pixel is activated in one frame period, a sub-field organisation is being used in which the sub-fields (SF) of a pixel are divided in two consecutive groups (G1, G2), and characterised by sub-field coding means (12, 13) being adapted for assigning a given pixel value a code word which distributes the active sub-field periods equally over the two sub-field groups (G1, G2), wherein the sub-field coding means comprise a code table in which for all possible pixel values the corresponding code word is stored that was coded according to the method according to one of claims 1 to 7.
  9. Apparatus according to claim 8, the apparatus comprising a matrix display.
  10. Apparatus according to claim 9, the apparatus comprising a plasma display.
EP99115651A 1998-08-19 1999-08-07 Method and apparatus for processing video pictures, in particular for large area flicker effect reduction Expired - Lifetime EP0982708B1 (en)

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EP98115607A EP0982707A1 (en) 1998-08-19 1998-08-19 Method and apparatus for processing video pictures, in particular for large area flicker effect reduction
EP98115607 1998-08-19
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