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Patent Searching and Data


Title:
METHOD OF DISPLAYING A SEQUENCE OF IMAGES FROM A DIGITAL VIDEOCAMERA
Document Type and Number:
WIPO Patent Application WO/1998/000966
Kind Code:
A1
Abstract:
Method for rapid FM-halftoning of pictures where all possible values in the picture correspond to a halftone plate, in which the halftone dots are maximally scattered. If the picture that is to be halftoned contains 256 different tone values, thus 256 halftone plates are pre-calculated, all constituted only by ones and zeros, that together build a halftoning volume. At the halftoning itself no comparison is then executed, but the choice to set a certain position in the picture or not is instead solved by a table-look-up method. The value of the input picture gives index in the table (that is which halftone plate that is to be used) and then the value from the corresponding position in the halftone plate is copied into the output picture.

Inventors:
KRUSE BJOERN (SE)
NILSSON FREDRIK (SE)
Application Number:
PCT/SE1997/001180
Publication Date:
January 08, 1998
Filing Date:
June 30, 1997
Export Citation:
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Assignee:
FORSKARPATENT I LINKOEPING AB (SE)
KRUSE BJOERN (SE)
NILSSON FREDRIK (SE)
International Classes:
H04N1/405; (IPC1-7): H04N1/40; H04N1/405
Foreign References:
US5463720A1995-10-31
EP0647058A21995-04-05
EP0639023A11995-02-15
EP0642258A21995-03-08
JPH0879547A1996-03-22
US5111310A1992-05-05
Other References:
PROCEEDINGS OF THE IEEE, Volume 76, No. 1, 1998, (New York), ROBERT A. ULICHNEY, "Dittering with Blue Noise", pages 56-79.
Attorney, Agent or Firm:
Berglund, Erik (Linkļæ½ping, SE)
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Claims:
Claims
1. FMhalftoning method, characterized in the use of precalculated halftone plates, which to their number correspond to the number of possible tone values in the picture that is to be halftoned and that into the halftoned picture is copied the value from the corresponding position in the halftone plate. FMhalftoning method according to claim 1 , characterized in that the precalculated halftone plates are correlated, that is show similar halftone patterns so that soft tone transitions also will be soft in the halftoned picture FMhalftoning method according to claim 1 or 2, characterized in that one already at the calculation of the halftone plates compensates for the dot gain at printing FMhalftoning method according to claim.
2. or 3, characterized in that at the calculation of the precalculated halftone plates one starts from one and the same matrix (of desired size) with white noise, and for each desired tone value a threshold value is used on this that gives the desired relationship between halftone dots and background, whereafter the halftone dots are resorted so that they become maximally scattered within the frame of what the requirement, that the halftone plates are to be correlated, allows Halftoning method according to claim 2 or 3, characterized in that one calculates a number of halftone plates that are a number of tone values apart, whereafter one interpolates the intermediate halftone plates by matching together halftone dots that are close to each other in the two plates and allowing one dot step by step to approach the other one FMhalftoning method according to claim 2 or 3, characterized in that in order to avoid unfavorable interferences between picture and halftone one requires that the local mean value does not deviate more than a given constant level.
Description:
M et h o d of displaying a sequence of images from a digital videocamera.

At FM-halftoning of pictures where it is required that the time used for halftoning is as short as possible, one is today generally obliged to use methods that use threshold matrixes.

Halftoning with this method is based on a comparing of values in the picture that is to be halftoned with values in the threshold matrix Depending on the result of the comparison the corresponding position in the binary representation of the picture will be set to zero or one The threshold matrix is repeatedly placed over the picture, edge to edge with itself, so that the entire picture can be halftoned.

At the halftoning of tint plates, that is areas where the value of the input picture is constant, one wishes the halftone dots to be maximally scattered and that the relation to the background shall correspond to the value of the input picture When threshold matrix methods are used the first criteria will not be possible to fulfill for all possible values in the input picture If for instance a comparison between a value in the picture and a corresponding value in the threshold matrix results in the value in the output picture being set to one, this position will always remain in value one for all tint plates with higher values This results, if good quality is to be obtained, in a comparatively long processing time

In order to achieve a faster halftoning method, one allows, in accordance with the invention, all possible values in the input picture to correspond to a halftone plate, in which the halftone dots are maximally scattered. If the picture that we are to halftone contains 256 different tone values, our method will thus use 256 pre-calculated halftone plates, all constituted only by ones and zeros, that together build a halftoning volume. At the halftoning itself one does no longer have to execute any comparison. The choice to set a certain position in the output picture or not is instead solved by a table-look-up method The value of the input picture gives index in the table (that is which halftone plate that is to be used) and then the value from the corresponding position in the halftone plate is copied into the output picture.

In conventional threshold matrix halftoning, a matrix with values between 0 and 255 would instead be used Our method is thus more memory requiring, in this case 32 times as much memory is required, but the method is very simple to implement in hardware once the halftone plates have been calculated Furthermore, it can be mentioned that already at the calculation of the halftone plates the dot gain at printing can be compensated for and a printable original directly obtained

The halftone plates In order to obtain a good result it is important that at least (regarding tone value) proximate tint plates are correlated, that is show similar halftone patterns, so that soft tone transitions in the original also will be soft in the halftoned picture There must thus be a continuity in the halftoning volume This is solved in one of the following ways

Alternative 1 Generate a matrix (of desired size) with white noise, allow this to serve as a starting picture for the calculation of all the halftone plates In order to compute a halftone plate for a certain tone value, set a threshold value for the matrix that gives the desired relation between halftone dots and background Thereafter the halftone dots are re-sorted so that they become maximally scattered In the same manner all halftone plates that are to be part of the volume are calculated

Alternative 2 Calculate two halftone plates that are a number of tone values apart according to alternative 1 Interpolate thereafter the intermediate halftone plates This is done by matching together halftone dots that are close to each other in the two plates and allowing one of the dots step by step to approach the second one Intermediate halftone plates thus obtain halftone dots that lie somewhere on the way between two halftone dots matched together The remaining part of the volume is filled out in the same way

Alternative 3 At the generation of a halftoned picture, in unfavorable cases, interferences may occur between picture and halftone At the emergence of such cases a correction of the

given value of the basic algorithm can be executed for instance by requiring that the local mean value does not deviate more than a given constant level.

An example of the invented method is in the enclosed drawings shown as Fig. 1, while the result of a halftoning in accordance with the invention is shown in Fig. 2, where in particular the soft transitions in the gray tones can be noted In Fig 1 is illustrated how at halftoning by table-look-up 255 pre-calculated halftone plates are used with a binary halftone plate for each value