EP1638068A1 - Procédé et dispositif pour générer des codes de sous-trames - Google Patents

Procédé et dispositif pour générer des codes de sous-trames Download PDF

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Publication number
EP1638068A1
EP1638068A1 EP05108347A EP05108347A EP1638068A1 EP 1638068 A1 EP1638068 A1 EP 1638068A1 EP 05108347 A EP05108347 A EP 05108347A EP 05108347 A EP05108347 A EP 05108347A EP 1638068 A1 EP1638068 A1 EP 1638068A1
Authority
EP
European Patent Office
Prior art keywords
look
luminance
codes
video
subfield
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05108347A
Other languages
German (de)
English (en)
Inventor
Sebastien Weitbruch
Carlos Correa
Cedric Thebault
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thomson Licensing SAS
Original Assignee
Thomson Licensing SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from EP04292221A external-priority patent/EP1638067A1/fr
Application filed by Thomson Licensing SAS filed Critical Thomson Licensing SAS
Priority to EP05108347A priority Critical patent/EP1638068A1/fr
Publication of EP1638068A1 publication Critical patent/EP1638068A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control 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
    • G09G3/22—Control 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
    • G09G3/28—Control 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
    • G09G3/288—Control 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 using AC panels
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/0271—Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
    • G09G2320/0276—Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/0285—Improving the quality of display appearance using tables for spatial correction of display data
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/06—Adjustment of display parameters
    • G09G2320/0673—Adjustment of display parameters for control of gamma adjustment, e.g. selecting another gamma curve
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2360/00—Aspects of the architecture of display systems
    • G09G2360/16—Calculation or use of calculated indices related to luminance levels in display data
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control 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
    • G09G3/2007—Display of intermediate tones
    • G09G3/2018—Display of intermediate tones by time modulation using two or more time intervals
    • G09G3/2022—Display of intermediate tones by time modulation using two or more time intervals using sub-frames
    • G09G3/2029—Display of intermediate tones by time modulation using two or more time intervals using sub-frames the sub-frames having non-binary weights

Definitions

  • the present invention relates to a method for generating subfield codes for pictures displayed on a display device like plasma display panels (PDPs) or display devices wherein the grey level of the pixels of the pictures displayed by the display device is obtained by modulating the number of light pulses per frame or sustain pulses (PWM for Pulse Width Modulation). It also relates to an apparatus for implementing said method.
  • a display device like plasma display panels (PDPs) or display devices wherein the grey level of the pixels of the pictures displayed by the display device is obtained by modulating the number of light pulses per frame or sustain pulses (PWM for Pulse Width Modulation). It also relates to an apparatus for implementing said method.
  • PDPs plasma display panels
  • PWM Pulse Width Modulation
  • a plasma display panel is constituted by two insulating plates sealed together to form a space filled with gas. Ribs are provided inside the space to form a matrix array of discharge cells which could only be "ON” or “OFF". Also, unlike other displays such as CRT (Color ray tube) or LCD (Liquid Crystal Display) in which grey levels are expressed by analogue control of the light emission, a PDP controls the grey level by modulating the number of light pulses per frame. These light pulses are known as sustain pulses. The time-modulation will be integrated by the eye over a period corresponding to the eye time response.
  • each subfield SF corresponds to one of the 8 bits as shown in figure 1.
  • each subfield SF is a period of time comprising :
  • a priming pulse P may be used at the beginning of the frame period. Such priming makes a pre-excitation of the plasma cell to prepare the cells for homogeneous writing of each subfield.
  • PDPs require use of a Peak White Enhancement (PWE) circuit, which controls peak white level as a function of average image power.
  • PWE Peak White Enhancement
  • the number of peak white sustain pulses is adapted to said average picture power and the sustain pulses can not be neatly divided amongst the subfields as mentioned above.
  • grayscale inversions means that, under certain circumstances, a video level N+1 could be darker than a video level N leading in disturbing grayscale non-linearity.
  • the problem of level inversion can be easily explained by the means of one example.
  • the following table 1 gives the number of sustain pulses per subfield for a frame comprising 12 subfields with the following weights 1 2 3 5 8 13 19 25 32 40 49 58 and for the following APL (Average Power level) values 0%, 20%, 40%, 60%, 80% and 100%.
  • APL Average Power level
  • the video level 6 (111000000000) corresponds to 3 sustain pulses (1+1+1) and 3 writing operations.
  • the video level 7 (010100000000) will also correspond to 3 sustain pulses (1+2) but with only 2 writing operations.
  • the video level 6 Since each writing operation brings an emission of light (around 20% of a sustain cycle), the video level 6 will be lighter than the video level 7. The apparition of such inversions will depend on the APL level so that a change in the contrast, luminance or picture content will introduce new non-linearity in the grayscale portrayal.
  • Figure 1 shows the behavior of the luminance model for each codeword used for displaying the video levels 0 to 255.
  • the curve shows a lot of grayscale inversions, plateaus (same luminance for two consecutive video levels) and non-linearities.
  • table 2 shows that there is already some codewords having equal luminance model like the rows corresponding to numbers 1 and 2 or the rows corresponding to numbers 5 and 6. Furthermore, some grayscale inversions are already observed like between the rows corresponding to numbers 3 and 4. Therefore, a reordering and modification of this table is mandatory.
  • the next step of the Metacode concept disclosed in EP 1 353 315 consists in a reordering of the codes in order to suppress inversion as well as plateaus.
  • new codes called luminance codes or metacodes are selected. Table 3 illustrates this principle:
  • the present invention is about the codedrop principle.
  • the problem encountered for implementing this method is that it requires a huge amount of memory.
  • the Look up table (LUT) presented in Table 5 represents the implementation of a codedrop concept suppressing in the displayed process the levels 2, 6, 8, 9, 11, 12, 13.
  • the invention relates to a method for generating subfield codes for video levels in pictures displayed on a display device wherein the video levels is obtained by modulating the number of light pulses per frame or sustain pulses, said method comprising the following steps:
  • the offset value associated to a video level n n>0, equals to the difference between the luminance code associated to the video level n and the luminance code associated to the video level n-1.
  • the invention relates also to an apparatus for performing the above-mentioned method, wherein said apparatus includes a picture average power measuring circuit, a memory storing said first look-up table, a memory interface unit for reading the first look-up table associated to the measured average power value, a computation unit for generating the second look-up from the first look-up table, a load unit for loading said second look-up table into a transcoding unit used for mapping video levels to luminance codes and a subfield coding unit for mapping luminance codes to subfield codes.
  • FIG. 2 shows a circuit arrangement for coding the video levels into subfield codes.
  • Transcoding LUTs 10 are used for mapping video levels into luminance codes.
  • a transcoding LUT is associated to each APL value, and if need be, to each color component and each display mode.
  • These transcoding LUTs are stored in an external memory. As previously mentioned, the size of this external memory must be 4,5 Mbit for 256 video levels with 3 colors and 3 display modes.
  • These transcoding LUTs 10 are used by a transcoding block 11 for mapping the video levels into luminance codes. These luminance codes are then mapped to subfield codes by a subfield coding block 12.
  • the LUTs used for mapping the video levels into luminance codes are offset LUTs as shown in Figure 3.
  • an offset value is stored for each video level instead of a luminance code.
  • This offset value for a video level n (referenced Offset(n)) is the difference between the luminance code associated to the video level n (referenced LC(n)) and the luminance code associated to the video level n-1 (referenced LC(n-1)).
  • the offset value associated to the video level 0 is 0.
  • the offset value do not need to be coded on 8 bits. For example, they are coded on 4 bits, the first bit representing the sign and the three other bits representing the offset amplitude.
  • the offset value is comprised between -7 and +7.
  • This offset values are used by a computation block 21 for generating the transcoding LUT to be loaded in the transcoding block 11.
  • a transcoding LUT is regenerated at each frame by using the offset LUT associated to the APL value measured for this frame.
  • Another advantage of this method is that the bandwidth required for loading the transcoding LUT generated by the computation block 21 is reduced.
  • the data to be loaded in the transcoding block 11 are only 368 bits (92x4) instead of 2048 bits (256x8). It can be very advantageous when the load operation is carried out during the vertical blanking.
  • FIG. 4 A possible implementation of the inventive method is illustrated by Figure 4. All the processing blocks (video degamma, subfield coding, serial parallel conversion, controller) are included in a plasma display controller 30, that in most cases is an ASIC. All the look-up tables data is stored on an external memory 31 (EPROM or FLASH) that can be read bit sequentially by the controller 30. In normal operation, at the end of every frame, a new offset LUT data has to be downloaded by the controller 30 depending on the APL value that have been computed during the active part of the video based on R, G and B signals. The APL value is computed in an APL measurement block 32 inside the controller 30.
  • Each refresh operation of the offset LUT inside the controller 30 is based on three blocks: a memory interface 33 that simply reads at a specific address inside the external memory 31 a certain amount of bits corresponding to the offset values associated to the APL value measured by the block 32, a computation block 34 (equivalent to the block 21 of Figure 3) that builds up the transcoding LUT to be stored inside the controller 30 and finally a loading block 35 in charge of loading the specific transcoding LUT.
  • the look-up tables stored in the external memory 31 are transferred to the memory interface 33 by using pins SCLK and SDATA of the memory 31 at the end of each frame during the vertical blanking. Indeed, it takes a complete active frame to compute the APL level required to load the right LUTs and it is not allowed to change the content of any LUT during the displaying of active part, otherwise the pictures will lost their homogeneity. Once the new APL value has been determined, the controller 30 requests the required data from the memory 31 and loads the required look-up table data in the memory interface 33.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Power Engineering (AREA)
  • Plasma & Fusion (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
EP05108347A 2004-09-15 2005-09-12 Procédé et dispositif pour générer des codes de sous-trames Withdrawn EP1638068A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP05108347A EP1638068A1 (fr) 2004-09-15 2005-09-12 Procédé et dispositif pour générer des codes de sous-trames

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP04292221A EP1638067A1 (fr) 2004-09-15 2004-09-15 Procédé et dispositif pour générer des codes de sous-trames
EP05108347A EP1638068A1 (fr) 2004-09-15 2005-09-12 Procédé et dispositif pour générer des codes de sous-trames

Publications (1)

Publication Number Publication Date
EP1638068A1 true EP1638068A1 (fr) 2006-03-22

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EP05108347A Withdrawn EP1638068A1 (fr) 2004-09-15 2005-09-12 Procédé et dispositif pour générer des codes de sous-trames

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1250696A2 (fr) 2000-01-26 2002-10-23 Thomson Licensing S.A. Procede de traitement d'images video en vue de l'affichage sur un dispositif d'affichage
EP1353315A1 (fr) 2002-04-11 2003-10-15 Thomson Licensing S.A. Procédé et dispositif d'amélioration de la résolution en niveau de gris d'un dispositif d'affichage d'images

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1250696A2 (fr) 2000-01-26 2002-10-23 Thomson Licensing S.A. Procede de traitement d'images video en vue de l'affichage sur un dispositif d'affichage
EP1353315A1 (fr) 2002-04-11 2003-10-15 Thomson Licensing S.A. Procédé et dispositif d'amélioration de la résolution en niveau de gris d'un dispositif d'affichage d'images

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