Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
1999-01-22
2001-11-27
Luu, Matthew (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S605000
Reexamination Certificate
active
06323872
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for converting the representation of a video image between two coding systems. More specifically, the invention relates to a process that makes it possible to convert the representation of a video image between two coding systems in which the two respective sets of parameters are deduced from one another by means of a matrix transformation.
The invention can be applied, for example, to the conversion of images between the RGB and YCbCr standards.
2. Description of the Related Art
When an image is sent through a network, for example of the Internet type, the image can be compressed by an algorithm in accordance with ITU standard H261. The image is coded according to the YCbCr coding system (Y=luminance, Cr=the difference between the red component and the luminance, Cb=the difference between the blue component and the luminance) defined in recommendation 601 of the CCIR (International Radio Consultative Committee). When the image is retrieved in an operating system, for example of the “WINDOWS” type, the image is coded according to the RGB standard (R=red, G=green, B=blue). The two sets of parameters of the two coding systems are deduced from one another by means of a matrix transformation. Thus, the conversion of the parameters from one coding system to the other requires, for each pixel of the image, a number of calculations that are very costly in terms of machine time.
SUMMARY OF THE INVENTION
A first object of the invention is to offer a process for converting the representation of a video image between two coding systems that reduces the number of processing operations during the conversion of the image.
This object is achieved because of the fact that the process for converting the representation of a video image between two coding systems with the aid of two respective sets of parameters, each of which sets of parameters is deduced from the other by means of a matrix transformation, is characterized in that it comprises:
a step comprised of selecting, for each parameter in the set to be converted from the first coding system to the second coding system, a breakdown in the parameters of the second coding system representing the value of the parameter in the matrix transformation, and
a step comprised of adding the breakdowns of each of the parameters to be converted.
According to another characteristic of the process, each of the parameters of the two coding systems have ranges of authorized values, and the conversion process includes a step comprised of clipping the values of the parameters to be converted and/or the values of the converted parameters that are outside the corresponding ranges of authorized values.
According to still another characteristic of the process, each breakdown in the parameters of the second coding system is selected by addressing a stored conversion table with the aid of the input value of the parameter in question.
According to yet another characteristic of the process, the addition operation is followed by a step for shifting and reorganizing the result.
According to still another characteristic, the breakdowns in the parameters of the second coding system are constituted by words having the same bit size, the values of the parameters of the second coding system of the breakdown being located in adjacent bit ranges and possibly being separated by at least one protection bit for preventing the propagation of the carry resulting from the additions.
According to another characteristic of the process, the values of the parameters of the second coding system of the breakdown have bit sizes greater than the sizes of the coded values at the end of the conversion, both in the low-order bits for increasing the precision of the calculations and in the high-order bits for accommodating the overflow. The step comprised of adding the breakdowns of each of the parameters to be converted is followed by a step comprised of extracting the bit ranges representing the values of the parameters of the second coding system, in order to eliminate the precision bits, the carry bits and the overflow bits.
According to another characteristic of the process, the process for converting the representation of a video image between two coding systems is used to convert an image from the RGB standard to the YCbCr standard and vice versa.
According to another characteristic, the process for converting the representation of a video image between two coding systems comprises a step for clipping the values of the parameters of the breakdown constituting the converted parameter, the clipping step being comprised of replacing the values that are lower than the lower limit of the range of authorized values with the lower limit value, and of replacing the values that are higher than the upper limit of the range of authorized values with the upper limit value.
According to another characteristic, the clipping step is carried out either directly in the conversion tables or by a program.
According to another characteristic, each breakdown is constituted by a 32-bit word, each conversion table associated with a parameter to be converted (R, G, B), respectively (Y, Cr, Cb) comprising at least 256 words or breakdowns corresponding to the possible values of the parameters to be converted.
According to another characteristic, for the conversion of the parameters (R, G, B) into parameters (Y, Cr, Cb), the breakdowns of the parameters (R, G, B) each comprise a first range of N
1
bits representing the corresponding value of the parameter (Y), or luminance, a second range of N
2
bits representing the corresponding value of the parameter (Cb), or the difference between the luminance and the blue chrominance, and a third range of N
3
bits representing the value corresponding to the parameter (Cr) or the difference between the luminance and the red chrominance.
According to another characteristic, all of the ranges comprise additional bits for increasing precision.
According to another characteristic, for the conversion of the parameters (Y, Cr, Cb) into parameters (R, G, B), the breakdowns of the parameters (Y, Cr, Cb) comprise a range of M
1
bits representing the corresponding value of the parameter (R), or the color red, a range of M
2
bits representing the corresponding value of the parameter (B), or the color blue, and a range of M
3
bits representing the corresponding value of the parameter (G), or the color green, each of the bit ranges representing values of the parameters R and B comprising 1 bit provided for protection against the propagation of the carry, all of the ranges having at least 1 bit for increasing precision and 1 overflow bit.
REFERENCES:
patent: 5124688 (1992-06-01), Rumball
patent: 5150206 (1992-09-01), Roberts
patent: 5504821 (1996-04-01), Kanamori et al.
patent: 5510852 (1996-04-01), Shyu
patent: 5541658 (1996-07-01), Ishiwata
patent: 5841422 (1998-11-01), Shyu
patent: 0551773 (1993-07-01), None
patent: 0680223 (1995-11-01), None
patent: 2670593 (1992-06-01), None
Bull S.A.
Havan Thu-Thao
Luu Matthew
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