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WO2005084033A1 - Diffusion d'erreur appliquee a la reduction de la dimension d'echantillon de video numerique - Google Patents

Diffusion d'erreur appliquee a la reduction de la dimension d'echantillon de video numerique Download PDF

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Publication number
WO2005084033A1
WO2005084033A1 PCT/US2004/022785 US2004022785W WO2005084033A1 WO 2005084033 A1 WO2005084033 A1 WO 2005084033A1 US 2004022785 W US2004022785 W US 2004022785W WO 2005084033 A1 WO2005084033 A1 WO 2005084033A1
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WIPO (PCT)
Prior art keywords
pixel sample
bits
sample size
digital video
quantization error
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Ceased
Application number
PCT/US2004/022785
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English (en)
Inventor
Michael Wilson Bruns
James Torpin Whittlesey
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Thomson Licensing SAS
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Thomson Licensing SAS
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/80—Details of filtering operations specially adapted for video compression, e.g. for pixel interpolation

Definitions

  • the present invention generally relates to digital video and, more particularly, to an error diffusion method and apparatus for digital video sample size reduction that prevents visual artifacts.
  • a video signal In digital video processing or transmission, it is common for a video signal to be conveyed between functional blocks with different inherent sample sizes.
  • a signal may be carried by a serial digital interface (e.g. SMPTE 292M) with 10-bit sample size to be compressed by an MPEG-2 encoder with an 8-bit sample size.
  • the default method to reduce the sample size at the interface to the encoder is to truncate the least significant bits of each sample.
  • the difference between the value of the original sample and the truncated sample is a form of quantization error. For some images, especially shallow ramps of color or brightness, truncation can result in an objectionable contouring or banding visual artifact.
  • the resulting field of sample values is not locally constant as with the truncation technique, but includes a modulation such that the reduced-size sample values averaged over the local region in the image are approximately equal to the original sample values before the reduction of sample size.
  • Conventional approaches directed to correcting contouring in digital images include random dither, ordered dither, and probabilistic dither. A random dither is added to the image before truncating the least significant bits of each sample. This makes fine detail harder or impossible to see (reduced spatial resolution) but it does cause the local average color after sample size reduction to be the same as in the original image which is the desired result.
  • the disadvantages of this approach are that it adds random noise to the image and it requires a random number generator in its implementation.
  • An ordered dither is a repeating two-dimensional pattern of dither values applied to the image before truncating the least significant bits of each sample.
  • This technique has the disadvantage of creating bands of a common dither pattern that may be as objectionable as the color bands that the technique is working to prevent.
  • Probabilistic dither covered by U.S. Patent No. 5,404,427 (hereinafter the "'427 Patent"), entitled “Video Signal Processing with Added Probabilistic Dither", issued on April 4, 1995, does not modify the original image before sample size reduction but rather increments the brightness and color values of certain pixels according to a random function with probability equal to the fraction that is truncated from the original sample.
  • the present invention is directed to an error diffusion method and apparatus for digital video with reduced sample size.
  • the error diffusion technique of the present invention is adapted to digital video to compensate for the loss in dynamic range when the sample size is reduced.
  • the resulting images are much less likely to exhibit banding or contouring artifacts compared to, e.g., a simple truncation technique.
  • the present invention is less complex and less expensive to implement than for example, the Probabilistic Dither approach described above, and does not require a random number generator as does the Probabilistic Dither approach.
  • an error diffusing method for processing a digital video having an original pixel sample size of m bits and a target pixel sample size of n bits, wherein m > n.
  • the method includes the step of distributing a quantization error calculated with respect to at least one previously processed pixel sample to only at least one subsequently processed pixel sample, the quantization error corresponding to at least one error diffusion function.
  • an error diffusing apparatus for processing a digital video having an original pixel sample size of m bits and a target pixel sample size of n bits, wherein m > n.
  • the apparatus includes means for accumulating quantization errors, the quantization errors corresponding to at least one error diffusion function.
  • the apparatus further includes means for distributing the quantization errors such that a quantization error calculated with respect to at least one previously processed pixel sample is distributed to only at least one subsequently processed pixel sample.
  • an error diffusing method for processing a digital video having an original pixel sample size of m bits and a target pixel sample size of n bits, where m > n.
  • the method includes the step of performing error diffusion with respect to the digital video using a set of coefficient values for distributing quantization error among pixel samples of the digital video that have yet to be processed, the set containing exactly one coefficient value equal to unity and the rest of the coefficient values equal to zero.
  • FIG. 1 is a diagram illustrating a partially processed image to which the present invention may be applied, according to an illustrative embodiment of the present invention
  • FIG. 2 is a diagram illustrating diffusion coefficient values relating the to the
  • FIG. 3 is a diagram illustrating simplified error diffusion coefficient values for digital video, according to an illustrative embodiment of the present invention
  • FIG. 4 is a block diagram illustrating an error diffusion apparatus for digital video, according to an illustrative embodiment of the present invention
  • FIG. 5 is a flow diagram illustrating an error diffusion method for digital video, according to an illustrative embodiment of the present invention
  • FIG. 6 is a diagram illustrating an 11-bit data set with 8 bits over the decimal and 3 under, to which the present invention may be applied, according to an illustrative embodiment of the present invention
  • FIG. 7 is a diagram illustrating a modified version of the sample data set from FIG.
  • FIG. 8A is a diagram illustrating a shallow ramp reduced to 6 bit RGB samples with no error diffusion in which banding artifacts are visible
  • FIG. 8B is a diagram illustrating a modified version of the shallow ramp reduced to 6 bit RGB samples with error diffusion to eliminate banding artifacts according to an illustrative embodiment of the present invention.
  • DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an error diffusion method and apparatus for digital video with reduced sample size. It is to be understood that the present invention may be implemented in various forms of hardware, software, firmware, special purpose processors, or a combination thereof. Preferably, the present invention is implemented as a combination of hardware and software.
  • the software is preferably implemented as an application program tangibly embodied on a program storage device.
  • the application program may be uploaded to, and executed by, a machine comprising any suitable architecture.
  • the machine is implemented on a computer platform having hardware such as one or more central processing units (CPU), a random access memory (RAM), and input/output (I/O) interface(s).
  • the computer platform also includes an operating system and microinstruction code.
  • the various processes and functions described herein may either be part of the microinstruction code or part of the application program (or a combination thereof) that is executed via the operating system.
  • various other peripheral devices may be connected to the computer platform such as an additional data storage device and a printing device.
  • the present invention may be implemented in hardware circuits within an application specific integrated circuit (ASIC) or a programmable logic device (PLD) such as a field programmable gate array (FPGA).
  • ASIC application specific integrated circuit
  • PLD programmable logic device
  • FPGA field programmable gate array
  • color images are comprised of three or more components, any of which may be expressed in any of a number of color spaces such as, for example, YCbCr, CYMK, RGB, and so forth.
  • error diffusion is applied separately and independently to each component.
  • some color spaces such as YCbCr support sub-sampled chroma, and that the error diffusion technique and the present invention are also applicable in this case.
  • the original pixel sample size is not mentioned and is implied to be infinite, i.e., an analog value with infinite dynamic range.
  • the error diffusion technique is inherently numerical, so it is reasonable to assume that m has some finite, practical value.
  • the target sample size in the original description is 1 bit as the algorithm is originally proposed as a greyscale algorithm for bi-level devices, such as a printed page.
  • the Spatial Greyscale algorithm is disclosed as being applicable to devices that allow several brightness levels at each pixel instead of only two.
  • Error diffusion operates on raster-based images, which means that they are expressed in terms of a two-dimensional array of color and brightness values arranged on a uniform grid. Processing proceeds along one line of samples from first to last, then proceeds to the next line, and so on until the entire image is processed. For example, consider the partially processed image in FIG. 1.
  • FIG. 1 is a diagram illustrating a partially processing image 100 to which the present invention may be applied, according to an illustrative embodiment of the present invention.
  • processing proceeds from left to right, top to bottom. Pixels marked by " ⁇ ” are already processed, pixels marked by "P' are currently processed, and pixels marked by "(7 have not yet been processed. Processing includes dividing the original m-bit sample(s) at P by 2 m'n , and keeping the integer part of the quotient as the final value(s) for P. 2 m'n'1 is added to P before the division to give rounding rather than truncation.
  • the quantization error ⁇ from the division is then expressed in terms of the original sample value and may be positive or negative.
  • the value of the quantization error ⁇ is expressed with m bits but its magnitude is less than 2 m'n .
  • ⁇ P m - (P n x 2 m -" )
  • FIG. 3 is a diagram illustrating simplified error diffusion coefficient values 300 for digital video, according to an illustrative embodiment of the present invention.
  • the coefficient set 300 of FIG. 3 has the advantages of not requiring the addressing of pixels on the next line, which can complicate practical implementations, and the resulting pixel values can be stored within the original sample size m of the source image.
  • the disadvantage of the simplified coefficient set 300 is a greater possibility of objectionable textures and patterns to be visible in the processed image, similar to those problems observed with the random or ordered dither technique.
  • the simplified coefficient set 300 of FIG. 3 is directed to one part of the present invention. Another part of the present invention deals with the problem of a regular pattern of sample values appearing in the processed image when the source image is a noise-free, shallow ramp of brightness or color. Computer generated images tend to have this characteristic. Avoiding the regular pattern of sample values is the reason for adopting a random function in the probabilistic dither algorithm of the '427
  • A A prev + P m - P n x2 m-n
  • a and A pr ⁇ V are recognized as the quantization error from the current pixel at P and that of the previous pixel, respectively.
  • the term in parentheses includes the distribution of the previous quantization error into the current pixel.
  • the term in square braces is the division operation.
  • A is also recognized in this equation as performing an accumulator function.
  • the result of the error diffusion algorithm is the modulation of the pixel values in the processed image.
  • the exact position of a particular modulation is not important. In fact, it is desired that the modulation be irregular from line to line to avoid regular patterns of sample values.
  • the method of the present invention avoids a regular pattern of modulation by not clearing the accumulator value from one raster line to the next. This means that each line of error diffusion begins with a quasi-random seed value that resulted from the accumulation of processing of the previous line.
  • FIG. 4 is a block diagram illustrating an error diffusion apparatus 400 for digital video, according to an illustrative embodiment of the present invention.
  • FIG. 5 is a flow diagram illustrating an error diffusion method for digital video, according to an illustrative embodiment of the present invention.
  • An image such as, e.g., a frame or field image 401 is input to a raster scanner 410.
  • the output of the raster scanner 410 (raster-based digital image 402) is input to a color component demultiplexor 420.
  • the output of the demultiplexer 420 includes three or more color components such as, but not limited to, R, G, B, or Y, CB, CR, or Y, U, V, and so forth.
  • the output of the demultiplexor 420 includes serialized sample streams 403, which are applied to an error diffusion module 430.
  • the method of FIG. 5 is performed by the error diffusion module 430.
  • the output of the error diffusion module 430 is applied to a color component multiplexor 440.
  • the output of the color component multiplexor is applied to a raster generator 450 which, in turn, outputs a frame or field image 404 corresponding to image 401 such that image 404 exhibits less or no banding or contouring artifacts compared to, for example, a simple truncation technique.
  • a description will now be given of the steps performed by the error diffusion module 430 corresponding to FIG. 5 with respect to a given digital video having an original pixel sample size of m bits and a target pixel sample size of n bits, where m > n.
  • an accumulator value A corresponding to the original pixel sample size of m bits, is set to zero (0) (step 505).
  • the accumulator value A may be considered as the cumulative quantization error for previously processed samples to be applied to the pixel sample that is currently being processed.
  • the next pixel sample Pm to be processed (which is the currently processed pixel sample at step 515), having the original pixel sample size of m bits, is retrieved (step 510).
  • an accumulator value A pr ⁇ V for the previously processed pixel is added to that pixel sample (e.g., the next sample Pm retrieved at step 510) (step 515), and a rounding operation is performed on the sum (step 520). For example, 2 ⁇ m ⁇ 1) is added to the sum of Pm and the accumulator value A pr ⁇ vto effect rounding.
  • a truncation operation is then performed on the resultant value (i.e., the sum of Pm and A prev and 2 (m" ⁇ ",) ) from step 520 (step 525). For example, the resultant value is divided by 2 (m" ⁇ ) to effect truncation.
  • the integer of the resultant value of step 525 is calculated to obtain a sample pixel Pn having the target pixel sample size of n bits (step 527).
  • the sample Pn is sent to the next process (e.g., color component multiplexing) (step 530).
  • the error of the pixel sample Pm is added to the accumulator value A (step 535).
  • the error is as follows: (Pm + A pr ⁇ V ) - (Pn * 2 ⁇ m ⁇ n) ).
  • a restriction is imposed on the error diffusion method such that the accumulator value A is not reset on the line or frame boundaries (step 540).
  • the method then returns to step 510 to retrieve the next pixel sample Pm for
  • FIG. 6 is a diagram illustrating an 11 -bit data set 600 with 8 bits over the decimal and 3 under, to which the present invention may be applied, according to an illustrative embodiment of the present invention.
  • FIG. 7 is a diagram illustrating a modified version 700 of the sample data set 600 from FIG. 6 reduced to 8 bits with error diffusion, according to an illustrative embodiment of the present invention.
  • a TEXAS INSTRUMENTS DLP cinema projector was used to display the image onto a 24-foot wide screen. The projector was specially modified to not perform internally any image resizing and to display the center 1280 x 1024 pixels of the image. Error diffusion was shown to eliminate banding and contouring artifacts in several different shallow ramps of brightness and color.
  • a quality CRT monitor is also a suitable device for evaluating banding artifacts because high resolution is not required.
  • FIG. 8A is a diagram illustrating a shallow ramp 800 with 6 bit RGB samples with no error diffusion
  • FIG. 8B is a diagram illustrating a modified version 850 of the shallow ramp 800 with 6 bit RGB samples with error diffusion according to an illustrative embodiment of the present invention.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Image Processing (AREA)

Abstract

L'invention porte sur un procédé de diffusion d'erreur afin de traiter une vidéo numérique possédant une dimension d'échantillon de pixel originale de m bits, m > n. Ce procédé consiste à distribuer une erreur de quantification calculée en fonction d'au moins un échantillon de pixel préalablement traité uniquement à au moins un échantillon de pixel ultérieurement traité, l'erreur de quantification correspondant à au moins une fonction de diffusion d'erreur.
PCT/US2004/022785 2004-02-04 2004-07-15 Diffusion d'erreur appliquee a la reduction de la dimension d'echantillon de video numerique Ceased WO2005084033A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US54188704P 2004-02-04 2004-02-04
US60/541,887 2004-02-04

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WO2005084033A1 true WO2005084033A1 (fr) 2005-09-09

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1901279A3 (fr) * 2006-09-18 2009-11-18 Samsung Electronics Co., Ltd Appareil et procédé d'amélioration des qualités de mouvement et d'images fixes de sortie dans un terminal de communication mobile

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0706165A1 (fr) * 1994-09-30 1996-04-10 Texas Instruments Incorporated Filtre pour la diffusion d'erreur
US6069609A (en) * 1995-04-17 2000-05-30 Fujitsu Limited Image processor using both dither and error diffusion to produce halftone images with less flicker and patterns
US6271936B1 (en) * 1998-12-11 2001-08-07 Eastman Kodak Company Combining error diffusion, dithering and over-modulation for smooth multilevel printing
US20030071831A1 (en) * 2000-08-30 2003-04-17 Beuker Rob Anne Matrix display device with multiple line addressing

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0706165A1 (fr) * 1994-09-30 1996-04-10 Texas Instruments Incorporated Filtre pour la diffusion d'erreur
US6069609A (en) * 1995-04-17 2000-05-30 Fujitsu Limited Image processor using both dither and error diffusion to produce halftone images with less flicker and patterns
US6271936B1 (en) * 1998-12-11 2001-08-07 Eastman Kodak Company Combining error diffusion, dithering and over-modulation for smooth multilevel printing
US20030071831A1 (en) * 2000-08-30 2003-04-17 Beuker Rob Anne Matrix display device with multiple line addressing

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1901279A3 (fr) * 2006-09-18 2009-11-18 Samsung Electronics Co., Ltd Appareil et procédé d'amélioration des qualités de mouvement et d'images fixes de sortie dans un terminal de communication mobile
US7729552B2 (en) 2006-09-18 2010-06-01 Samsung Electronics Co., Ltd Apparatus and method for improving qualities of motion and still images to be output in a mobile communication terminal

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