KR20030072338A - Faster Transforms Using Scaled Terms, Early aborts, and Precision Refinements - Google Patents

Abstract

A fast transformation using a plurality of scaled terms, initial stop and precision subdivision is disclosed. Discrete transforms are divided into sub-transformations that are independently calculated using a plurality of scaling terms for the transform constants. Scaling effects on the transform coefficients may be selectively processed by appropriately scaling quantization values or any comparison values. The possible need to perform corrective action is detected based on testing the incremental calculation of the transform coefficients. Then, corrective action is performed. Corrective action includes subdividing the incremental calculation to obtain additional precision and / or stopping the incremental calculation when the resulting number is satisfactory.

Description

Faster Transforms Using Scaled Terms, Early aborts, and Precision Refinements}

The conversion of data from one domain (eg sampled data) to another domain (frequency space) is used in many signal and / or image processing applications. Such transformations are used in a variety of applications including, but not limited to, feature identification and / or extraction, signal correction, data compression, and data embedding / watermarking.

In data processing, data is typically represented as a sample discrete function. Discrete representations may be made deterministically or statistically. In the deterministic representation the point characteristic of the data is taken into account, while in the statistical representation the average characteristic of the data is specified. For example, in the art, it is known to use discrete cosine transform for data compression. In the specific examples mentioned in this specification, the terms image and image processing will be used. However, one of ordinary skill in the art will recognize that the present invention is not limited to image processing but can be used to process different kinds of data such as voice data, scientific data, image data, and the like.

In a digital image processing system, digital image signals are first formed by dividing a two-dimensional image into a grid. Each picture element in a grid, ie a pixel, is associated with a number of visual properties, such as brightness or color. These properties are converted to numbers. The digital image signal is then formed by assembling the numbers associated with each element in the image into a sequence that can be interpreted at the digital image signal receiver.

If too much data is provided to real applications that use the data, data compression is desirable in many data processing processes. Often, compression is used in the communication link, reducing the transmission time or the bandwidth required. Similarly, compression is also desirable in image storage systems, such as digital printers and copiers, in which "pages" of documents to be printed are temporarily stored in memory. The amount of media space in which image data is stored can be substantially reduced due to compression. In general, the scanned image (ie, the electronic representation of the hardcopy document) is often a desirable target for cursor compression.

Signal and image processing frequently requires converting input data into transform coefficients for analysis purposes. Often, only quantized versions of the coefficients are required (eg JPEG / MPEG data compression or audio / video compression). Many such applications need to be performed quickly in real time, such as generating JPEG data for high speed printers. Most of these transformations require effective implementations for real time and / or high speed execution regardless of whether compression is used as part of the data processing.

There is a burden in the data signal processing industry to find a high-speed way to perform digital signal processing most effectively and quickly. As in the field of compression, very active and competitive research is being conducted in the field of high-speed conversion implementation. The researchers made various attempts to improve the strength of the hardware to implement the transform by using the properties found in the transform and inverse transform.

One such technique is ISO 10918-1 JPEG International Standard / ITU-T Recommendation T.81. The draft JPEG standard is duplicated in Pennebaker and Mitchell ("JP: still image data compression standard" (New York, Van Northland Reinhold, 1993) and is referred to herein. In addition to the compression methods defined in the JPEG standard, other known data compression standards are Discrete Cosine Transform (DCT) coding, and images compressed using DCT coding are decompressed using an inverse transform known as inverse DCT (IDCT). A general reference to DCT is the "Discrete Cosine Transform" by Rao and Yip (New York, Academic Publishers, 1990), and is referred to herein. It is supposed to be familiar with the contents.

If still images represent a storage problem for computer users and others, it is clear that the video storage problem is much more serious because a full video video requires up to 60 images per second of the displayed video picture. Thus, video compression techniques have been the subject of further development and standard activities. Two important standards are the ISO 11172 MPEG International Standard and the ITU-T Recommendation H.261. Both of these standards rely in part on DCT coding and IDCT coding.

Two-dimensional discrete cosine transform is a pair of the formula to convert N _{1 ×} N ₂ number Arrays Another array of numbers N _{1 ×} N _2. The first array typically represents a rectangular N × N array of spatially determined component values that form the digital image. Since each pixel is associated with several of its elements, one element pixel is considered below for simplicity. However, it is obvious to those skilled in the art to expand to multiple element pixels. The second arrangement is an arrangement of discrete cosine transform coefficients representing the picture in the frequency domain. The method of representing an image with the coefficients of the frequency component is a special case of the discrete Fourier transform. Discrete Fourier Transform is a discrete version of the traditional mathematical Fourier transform in which any periodic waveform can be represented as the sum of sine and cosine waveforms of different frequencies and amplitudes. Thus, a discrete cosine transform, such as a Fourier transform, is a transform that transforms a signal in the time domain into a signal in the frequency domain or vice versa. All DCT multiplications are real. This lowers the number of multiplications required compared to the Discrete Fourier Transform. In most imaging cases, most of the signal energy is at low frequencies, which appears in the upper left part of the DCT. The lower right part shows a higher frequency, which is small enough to not cause visual distortion and can be ignored.

There are two basic discrete cosine transform equations. The first basic equation is a forward discrete cosine transform that transforms pixel values into discrete cosine transform coefficients. The second basic equation is the inverse discrete cosine transform that transforms the discrete cosine transform coefficients back to pixel values. Most applications of discrete cosine transform for images use an 8x8 array, so the N value is eight. Assuming that N is 8 when performing the transformation, f (i, j) is the pixel array values, and F (u, v) is the value of the discrete cosine transform coefficients, the two-dimensional discrete cosine transform formula is same.

Where x and y are spatial coordinates in the spatial domain (0,1,2 ... 7), u, v are coordinates in the transform domain (0,1,2 ... 7) and u = C _u = 1 / if 0 Otherwise 1, v = 0 if C _v = 1 / And 1 otherwise. The separable nature of the two-dimensional DCT is developed by performing a one-dimensional DCT on eight columns and then performing a one-dimensional DCT on the eight rows of the result. Several high-speed algorithms are available for calculating an eight-point one-dimensional DCT.

As mentioned above, the DCT part of the compressor consists of two main parts.

The first part is to transform the highly correlated image data into weak correlation coefficients using DCT transform, and the second part is to perform quantization on the coefficients to reduce the bit rate for transmission or storage. However, enormous calculations are required in performing DCT. For example, in order to process an eight-dimensional one-dimensional DCT, currently known fast algorithms require 13 multiplications and 29 additions. In the paper "A FAST DCT-SQ schema for images" (Trans. IEICE, Vol. E-71, No. 11, pp 1095-1097, nov. 1988), Y.Arai, T. Agui and M. Nakajima have many We proposed that the DCT multiplication of can be formulated as a scaling multipliers for the DCT coefficients. The DCT after the multipliers are factored out is called the scaled DCT. The scaled DCT is orthogonal or no longer normalized, while the scaled factors can be recovered in a subsequent quantization process. Arai et al. Have demonstrated in their paper that only five multiplications and 29 additions are required to process an 8-point scaled DCT. As mentioned above, the image is divided into rectangular blocks of 8x8 pixels, 16x16 pixels or 32x32 pixels. Each block is often processed by a one-dimensional DCT in a row-to-column, followed by a row-to-column. On the other hand, different block sizes are selected for compression due to different types of input and different quality requirements on the decompressed data.

Scaled terms are used to replace multiple constants, such as cosine terms, in a discrete cosine transform (DCT) with the most number of additions / subtractions. However, the scaled terms are only approximations of the constants in the equation. Thus, to reduce the number of operations, some errors are acceptable to maintain precision limited to a fixed number of bits. If the numbers in the result are farther from the decision boundary (eg threshold or quantization boundary) than the maximum allowable error, the result will not be affected by the estimate. However, during incremental calculations, the numbers of the result can be determined to require additional precision. The original input values are no longer available in registers, and cycles related to cache misses and memory delays can be imposed by refetching the original input values from memory. The old-fashioned option is to perform an inverse transform on the values (e.g. IDCT) and then perform a higher precision forward transform (e.g. FDCT, sometimes just DCT). This tricky approach is a waste of computation.

In general, however, research has generally focused on specific techniques, such as those described above using DCT coding to provide the desired degree of compression. However, in certain circumstances other transforms may be used that provide certain advantages. For example, in the DCT compression coding method described above, the input image is divided into a number of uniform blocks and a two-dimensional discrete cosine transform function is applied to each block to transform the data sample into a set of transform coefficients to remove spatial redundancy. do. However, high compressibility can be achieved, but a faint or obvious blocking effect can occur. In addition, the vector quantization method used by the compression system may be advantageous due to the high compression rate. On the other hand, the sub-band method can reduce the blocking effect that occurs at high data compression rates. Discrete wavelet transform (DWT) or sub-band coding (SBC) methods encode, for example, signals based on time and frequency components. As such, these conversion methods can be useful for analyzing non-stop signals and have the advantage that they can be designed to take into account the characteristics of the human visual system (HVS) for image analysis.

There is a need to provide a method and apparatus for providing fast conversion calculations that can reduce software execution time and reduce hardware requirements by using early stop and precision improvements to save process cycles.

FIELD OF THE INVENTION The present invention relates generally to data processing, and more particularly to fast transformations utilizing multiple scaled terms, early aborts, and precision refinements.

1 illustrates a typical image compression system.

2 shows a block diagram of a JPEG encoder.

3 shows a flowchart of the present invention.

4 shows a flowchart of a method for finding a simultaneous representation of a first reference C1, or a second reference C2.

FIG. 5 shows a flow chart for providing high speed conversion using corrective action to provide fast conversion calculation and reduced execution time.

6 shows a flow diagram of a stopping method according to the present invention which demonstrates stopping the continuous iteration of the transform coefficient calculation process.

7 illustrates testing at least one incrementally calculated number.

8 is a flowchart of a refinement method according to the present invention.

9 shows a flowchart of a first method of generating a submatrix.

FIG. 10 is a flow diagram illustrating a second method for generating a submatrix when _d D ₀ is non-reversible.

11 shows a printer according to the invention.

12 illustrates a data analysis system in accordance with the present invention.

13 illustrates another data analysis system in accordance with the present invention.

In order to overcome the aforementioned limitations of the prior art, and to overcome other limitations that become apparent upon reading and understanding the present specification, the present invention discloses a fast transform that uses multiple scaling terms, initial stops, and precision subdivisions.

The present invention solves the above-mentioned problems by dividing the discrete transform equation into a sub-conversion that can be calculated independently using the scaling term for the conversion constants. It also finds an optimal representation of the scaling terms for binary operations. The final calculation enables high speed calculations, reducing software execution time and reducing hardware requirements. Moreover, one skilled in the art will recognize that inverse transformations can often be implemented using the same method, and therefore, in general, the same number of operations are used. In addition, the present invention solves the aforementioned problems by reducing the number of multiplications by using scaling terms for the conversion constants. After scaling, the constant terms are replaced by a series of small linear shifts and additions because the constants are approximated as a 2-squared sum after only a few additions. Those skilled in the art will appreciate throughout this specification that the term "matrix" is used to encompass not only its traditional mathematical meaning, but also all hardware and software systems that can be represented equally as mathematical matrices in analysis. In addition, the present invention detects when to perform a corrective action according to the calculation test of the incremental calculation of the conversion constants, performs corrective actions, and refines the incremental calculation and / or results to obtain additional precision. If the number is too small, the above-mentioned problems are solved by stopping the incremental calculation.

The method according to the principles of the present invention comprises arranging transform equations into at least one collection having at least two conversion constants, and substantially uniform between at least two conversion constants in the at least one set. Independently scaling the at least two transform constants of each set using a scaling term to maintain a ratio. The method also includes representing each scaled discrete cosine transform constants as an estimate of discrete cosine transform constants approximated by a 2-squares sum.

Other embodiments of the method according to the principles of the present invention have alternative or optional additional features. One feature of the present invention is that the method includes dividing the data into at least one block and converting the block into transform data using scaled transform equations.

Another feature of the present invention is to transform the block into transform data by performing matrix multiplication on the discrete cosine transform equations based on binary arithmetic operations using estimates of the scaled discrete cosine change constants.

Another feature of the present invention is that the scaled term is selected according to a predetermined cost function.

Another feature of the present invention includes selecting a scaling term such that the largest error for any transform coefficient of the selected cost function is not greater than its respective predetermined error rate.

Another feature of the invention includes selecting a scaling term such that the predetermined cost function has an error that is less than or equal to the predetermined error rate.

Another feature of the present invention includes selecting a scaling term such that the predetermined cost function is such that each of the associated selected conversion constants is less than or equal to their respective predetermined error rate.

It is another feature of the present invention to select a scaling term and expression for the conversion constants such that the predetermined cost function has a system of binary representations with all of the conversion constants in the set having a predetermined characteristic.

Another feature of the invention is that the cost function minimizes the number of add operations.

Another feature of the invention is that the cost function minimizes the worst case of the addition operation.

Another feature of the invention is that the selected characteristic comprises a minimum number of common two-squared terms.

It is another feature of the present invention to select the scaling term and expression for the transform constants such that all of the transform constants for the set have a simultaneous binary expression with a minimum number of common two-squared terms, so that the binary arithmetic shift is more than the multiplication operation. It is implemented when it is efficient.

Another feature of the present invention is that the selected characteristic includes a non-zero two-squared term that is maximally grouped.

Another feature of the present invention is that selecting a scaling term for the transformation constants such that all of the transformation constants for the set have a system of binary expressions with a non-zero power of two, which is the largest grouping, is more efficient with multiplication using small integers. This is implemented when it is more desirable than multiplication using large numbers.

Another feature of the invention is that the coefficients in the two-squared polynomial representing the constants are not zero.

Another feature of the present invention is that the bit position value determines a two-squared term.

Another feature of the invention is that maximizing a nonzero zero-squared population comprises: a) setting the first variable to the i th element in the block, and b) initializing the second variable to the value 2. C) initializing the bitmask to binary 3, and d) the i th element represented by the first variable is equal to 2 ⁿ + 2 ^n-1 = 2 ^{n +} 1-2 ^n-1 . Analyzing the bits to determine if they are candidate representations for reordering them, and e) performing an efficient power of 2 given by 2 ⁿ + 2 ^n-1 = 2 ^{n +} 1-2 ^n-1 Encoding the i th element by adding the second variable to the first variable, f) obtaining a new representation and incrementing the first variable to the i + 1 th element, g ) Bit shifting the bit mask and the second variable to the left, and h) step d to g. And finding all the representations of the constants scaled by the copying step.

Another feature of the invention further includes the step of shifting the mask bits to the left after checking whether the first variable matching the mask bits is set, thereby inserting 0 to the right to insert 2 ^n. + 2 ^n-1 = 2 ^{n + 1-2} Increase the power of 2 used to reorder ^n-1 .

Another feature of the invention is that the set represents a disjoint set of transforms of partial calculation.

Another feature of the present invention is that the set does not represent a disjoint set of transforms of partial calculation.

Another feature of the invention is that the method further comprises selecting an independent scaling term for each of the transform arithmetic units of the at least one set.

The method according to the principles of the present invention comprises the steps of: testing at least one number calculated from the incremental calculation of the conversion coefficients during the conversion, determining whether to perform a correction according to the test result, and determining that the correction is necessary And performing a corrective action at the time.

Other embodiments of the method according to the principles of the present invention include alternative or optional additional features. One feature of the present invention includes the step of detecting whether the determining step yields a conversion statement with an accuracy that the incremental calculation of the conversion factor cannot tolerate, and wherein the performing of the corrective action subdivides at least one number. It is to include a step.

Another feature of the present invention is that the transformation includes a transformation matrix and the subdivision includes applying a segmentation matrix to increase the precision of the incremental calculation of the transformation constant.

Another feature of the invention is that the submatrix comprises I + _d D _{m + 1} D _m ⁻¹ .

Another feature of the invention is that the method further comprises generating at least one submatrix based on the estimated conversion constants.

Another feature of the invention is that the step of generating at least one submatrix is performed offline or at initialization.

Another feature of the invention is that generating the submatrices includes recognizing that the approximation is invertible, generating the submatrices given by I + _d D _{m + 1} D _m ⁻¹ , and efficiently calculating Structuring the transformation for

In another aspect of the present invention, generating a sub-matrix includes recognizing that it is impossible to recover the nth column of a transform matrix to generate the transform, and generating a pseudo inverse of a part of the transform matrix. And calculating an approximation of the at least one submatrice using the pseudo inverse of the transform matrix.

Another feature of the present invention is that the approximation of the submatrices is I + _d D ₁ It will include.

Another feature of the invention is the step of determining whether to perform corrective action further comprises the step of determining whether an error caused by terminating the incremental calculation is tolerable and the step of performing the corrective action comprises Stopping the incremental calculation.

Another feature of the present invention is that the incremental calculation ends when it is determined that the incremental calculation will yield a number expected within the selected range.

Another feature of the invention is that the number expected within the selected range includes a conversion factor that satisfies the precision requirements.

Another feature of the invention is that the incremental calculation ends when it is determined that the subdivision of the conversion coefficient does not change the result.

Another feature of the invention is that after examining the relative magnitude of the result of the incremental calculation, the subdivision of the conversion coefficient changes the result when the intermediate value of at least one conversion coefficient is small compared to the intermediate value of another conversion coefficient. It is judged not to be.

Another feature of the invention is that after examining the magnitude of the result of at least one incremental calculation, it is determined that the subdivision of the conversion coefficient does not change the result when at least one intermediate value of the conversion coefficient is less than a predetermined threshold. Will be.

Another feature of the invention is characterized in that the determining step further comprises the step of determining that the conversion coefficient will be within zero of the predetermined range and the step of performing the corrective action comprises stopping the incremental calculation of the conversion coefficient. will be.

According to another embodiment of the present invention, a data compression system is provided. The data compression system includes a transformer-transformations for applying a linear transformation to correlate data into transform coefficients using transform equations, preparing the transform equations into at least one set having at least two transform constants; Scaling the at least two conversion constants of each set independently using a scaling term to maintain a substantially uniform ratio between the at least two conversion constants in the at least one set, wherein the scaling term is selected And a quantizer for quantizing the transform data into quantum data by reducing the number of bits needed to represent the transform coefficients.

According to another embodiment of the present invention, a printer is provided. The printer includes a memory for storing the image data, a processor for processing the image data to provide a compressed print stream output, and a printhead drive circuit for controlling the printhead to generate printouts of the image data. And the processor applies a linear transform to correlate the data into transform coefficients using the transform equations, the transform equations comprising: preparing the transform equations into at least one set having at least two transform constants; Scaling the at least two transformation constants of each set independently using a scaling term to maintain a substantially uniform ratio between the at least two transformation constants in the set, wherein the scaling term is a predetermined cost function Is selected according to.

According to another embodiment of the present invention, an article of manufacture is provided. The article of manufacture comprises a computer readable program storage medium, the medium comprising the steps of preparing the conversion equations into at least one set having at least two conversion constants and substantially between the at least two conversion constants in the at least one set. Independently scaling the at least two conversion constants of each set using a scaling term to maintain a uniform ratio, wherein the scaling term is executed by a computer to perform a method selected according to a predetermined cost function. It is a practical implementation of one director's program instructions.

According to another embodiment of the present invention, a data analysis system is provided. The data analysis system prepares the transform equations into at least one set having at least two transform constants and maintains the at least two transforms of each set in order to maintain a substantially uniform ratio between the at least two transform constants in the at least one set. Transformations formed by scaling the constants independently using a scaling term, the scaling term being selected according to a predetermined cost function, and applying a transformation to perform a linear transformation to correlate the data into a transformation coefficient. It includes a converter.

The foregoing and other advantages and features characterizing the invention are specifically specified in the claims appended hereto. However, for a better understanding of the advantages and advantages achievable by using the present invention and the present invention, reference should be made to the drawings and description of the invention, illustrating specific examples of the device according to the present invention.

In the following description of the embodiments, reference is made to the drawings, which form a part of this specification, which shows by way of example specific embodiments in which the invention has been practiced. It will be appreciated that other embodiments may be utilized as structural changes may be made without departing from the scope of the present invention.

The present invention provides a fast transformation using multiple scaled terms. The transform is divided into sub-transformations that are independently calculated using the scaled terms for the transform constants. Find the optimal representation of scaled terms for binary arithmetic. This method enables fast conversion calculations, reduces software run time and reduces hardware requirements. In accordance with the present invention, the discrete transforms used in signal and image processing employ so-called basic functions that set the transform structure and form the basis for allowing the transform to be computed into two or more subsets. Then, a cost function for fast implementation of the transform is used to find the optimal representation of the fundamental coefficients in the calculation.

1 illustrates a typical image compression system 100. The data compression system comprises three closely coupled components: (a) transducer 120, (b) quantizer 130, and (c) optional entropy encoder 140. Compression is achieved by decorating the image data, quantizing the resulting transform coefficients and, if desired, applying a linear transform to entropy code the quantized values. Various linear transformation techniques have been developed, including discrete Fourier transforms (DFTs), discrete cosine transforms (DCTs), discrete waveform transforms (DWTs), and other transforms with different pros and cons.

Quantizer 130 merely reduces the number of bits needed to store them by reducing the precision of the transformed coefficients. Because this is a many-to-one mapping, it is a lossy process and an important source of compression in the encoder. Quantization can be performed for each individual coefficient, which is known as Scalar Quantization (SQ). Quantization can also be performed on a set of coefficients, which is called vector quantization (VQ). Depending on the problem encountered, uniform and non-uniform quantizers can be used.

Optional entropy encoder 140 further compresses the quantized values losslessly to provide better compression overall. This will use the model to accurately determine the probabilities for each of the quantized values and calculate the appropriate code based on these probabilities so that the output code stream result will be smaller than the input stream. Although simple run-length encoding (RLE) has proved to be very useful for applications requiring high speed execution, the most commonly used entropy encoders are Huffman encoders and operational encoders.

The term "image transformation" commonly refers to the unitary matrices class used to represent an image. This means that images can be transformed into alternate representations using these matrices. These transforms form the basis of transform coding. Transform coding is the process by which coefficients from a transform are coded for transmission.

Signal x is a function that maps each integer from 0..n-1 to a complex number. Take a line of sampled or pixelated image with samples or pixels evenly spaced. The "orthogonal basis" of this set of (x) Function set, where y ¹ z to be. The conversion of (x) represented by F (y) is It becomes This type of transformation is used in many signal and image processing applications to extract information from the original signal. One example of a transform is the Discrete Fourier Transform (DFT), where b _y (x) = exp (2pixy / n). A related example is the Discrete Cosine Transform (DCT), where b _y (x) = cos (2pxy / n). Another example is a waveform transform, where b _y (x) is a particular scaled and offset version of the mother waveform function. (See Ingrid Daubechies, Ten Lectures on Wavelets, Society for Industrial & Applied Mathematics, (May 1992).)

We will now demonstrate the rationale for independent scaling operations by showing a mathematical basis that allows us to scale without destroying the structure of the transform. Transform It is defined as Consider cases where b _y (x) is made such that this transformation can be divided into two or more disjoint sums regardless of the structure of (x) (described below). (The term "disjoint" when used in this specification with reference to a set of equations means that there is no conversion factor in common between the equations of two separate sets of equations.) For example, b (x) _2y In the case of even symmetry and b (x) _{2y + 1} is odd symmetry, any (x) can be written specifying (x) = _e (x) + _o (x). Where _e (x) is even (symmetrical with respect to zero), _o (x) is radix (asymmetrical with respect to zero), to be. This allows the transformation to be written as

2 shows a block diagram of a JPEG encoder 100. In FIG. 2, digital image data 110 is divided 112 into 8 × 8 pixel blocks. Then, a discrete cosine transform (DCT) for each block is calculated (120). Discrete cosine transform helps to separate data into different parts (or spectrum sub-bands) of importance (eg, importance to the visual quality of an image). DCT is similar to the Discrete Fourier Transform, transforming a signal from the spatial domain into the frequency domain.

Quantizer 130 rounds off DCT coefficients according to the quantization matrix. This step yields the "loss" characteristic of JPEG, but allows for a large compression ratio. There is a tradeoff between image quality and quantization. Large quantization step sizes result in unacceptable image distortion. This effect is similar to generating large distortions by quantizing the Fourier series coefficients too coarsely. On the other hand, fine quantization lowers the compression rate. The problem is how to quantize the DCT coefficients most efficiently. Due to the inherent high frequency roll-off of people's vision, high frequencies play a less important role than low frequencies. This allows JPEG to use a much larger step size for high frequency coefficients, thereby producing no noticeable image distortion. The quantizer coefficient output is then encoded by optional entropy encoder 140 to produce a compressed data stream 150 into an output file. The entropy encoder is not an option in the case of JPEG, but in other similar data compression systems it can be designed without the CPU cycles required for the entropy encoder.

However, as described below, there is a need to provide a method and apparatus for performing discrete cosine transform by reducing multiplication steps to increase the throughput of encoder 100. As described below, the method according to the present invention reduces the multiplication in the knuckle formula by scaling the coefficient matrix. Each separable subgroup is scaled separately from other sets. Within each set, the remaining multiplications are replaced by simple shifts and additions. Scaling terms are selected according to various cost functions. The preferred embodiment uses a cost function that reduces the number of additions and reduces the worst number of additions. However, those skilled in the art will understand that alternative cost functions may be selected depending on how many errors are allowed per coefficient. Moreover, those skilled in the art will understand that inverse DCT (IDCT) can be implemented using the same method so that the same number of operations are used.

3 shows a flow chart 200 of the present invention. In FIG. 3, the transformation is divided into at least one sub-transformation having at least two constants (210). The term "sub-transformation" as used herein refers to a set of equations used to generate a subset of transform terms (the subset includes all of the transform terms or less than the total number of transform terms). Next, the conversion constants for each set are independently scaled using the scaling terms to maintain a substantially uniform ratio between the conversion constants in the set, and the scaling terms are selected according to a predetermined cost function (220). The result is a transform for block transform. The data is divided into at least one block (230). Thereafter, the block is transformed into transformed data using a transform equation (240). Traditional systems will perform steps 210 and 220 offline. However, for algorithms specified at runtime, such as JPEG 200, these steps will be performed automatically during the program initialization phase. Referring to quantizer 130 of FIG. 1, transform data is quantized by integrating scaling into quantization. This is described in Integer Cosine Transform (ICT) (for example, Pang et al., "A self-timed chip for image coding" IEEE trans, Circuit system for Video Tech., Vol. 9, no. 6,1999, (see pp.856-860), where each coefficient is scaled by the same value in all equations, the ICT method does not provide the same computational advantages as the method described above.

Selecting a scaling term for the constants is performed using a cost function that indicates the needs of the target system. Several parameters for this cost function have been identified for fast conversion. The actual cost function used may include one or a combination of the following cost functions.

The first cost function is that the largest error on any transform coefficient i.e., F (x) is not greater than P%, where P is chosen by the algorithm designer. In the following examples, P is 1.

The second cost function is that the more important conversion constants chosen by the algorithm designer are not greater than the P _important % error. In the example below, the error of the low frequency terms is less than 0.1%.

The third cost function is divided into two criteria, C1 and C2, which apply to different systems. That is, one is generally chosen to satisfy either the criteria C1 or C2. The reference C1 may be applied to an implementation where shift is more efficient than multiplication (eg, software or firmware). The reference C2 can be applied to implementations where multiplications employing small integers are more desirable than multiplications employing larger integers (eg, software implementations where multiplications beyond a certain number of bits use more overall precision or are important). Specific examples are given to illustrate these two criteria. Both criteria can be used together.

According to the first criterion C1, all scaled integer basis multipliers appearing in the same sum (in the case of FDCT, the constants C ₁ to C ₇ , C _k = cos (kp / 16)) are the minimum number It should contain a simultaneous binary representation with a common power of two. In other words, the set of 2-squared terms that span all representations in the set should be as small as possible. Real constants can be approximated by rational numbers, that is, integer ratios. The word "representation" as used herein in connection with the scaled constant of the transformation refers to the manner in which these integer ratios of molecules are calculated as the sum and / or difference of the power of two powers.

For example, in FDCT, transformations can be divided into three sets of equations:

The notation used in these formulas is taken from the Pannebaker book. Ss Proportional to Thus, the constants in set 3 must include simultaneous binary representations with a minimum number of common power terms, but their simultaneous representations are not related to those used in the constants in set 2. A specific example of set 3 is given by

All of these representations have an error of less than 1% per coefficient. In this example, the common set of two power terms is {2 ⁵ , 2 ³ , 2 ¹ , 2 ⁰ }, as shown in the equation above. These expressions can be expressed in terms of polynomials for two by multiplying each two power term by one or zero. In other words,

Effectively minimizing the number of these terms is as follows. Equations of set 3 can be calculated by grouping these powers of two. In the structure in which the reference C1 is used, since addition and shift take less cycles than multiplication, the equations of set 3 can be regarded as matrix operations as follows.

This adds up to shifts and performs a total of 28 operations. If A = d _25- d ₃₄ and B = d ₀₇ + d ₁₆ is calculated first, the equation is:

In the case of pre-calculation, this is 24 cycles. Also, if we eliminate the 2 ⁰ term, the error for C ₅ rises to about 3%, but the total number of operations is reduced to 20. On most multiprocessors, multiplication requires one or more cycles (between 4 and 11 cycles). The calculation of the odd-numbered coefficients of the fast DCT described above is an initial step to sum and differences. Note that we use 11 additions and 4 multiplications except calculations.

According to a second criterion C2, the same must (e. G., The same set of set of the above-described 1, 2, 3) all the scaled integer base multiplier represented in, for example, in the case of FDCT C ₁ to C ₇ are one possible aggregate Must contain simultaneous binary representations with nonzero clustered zero terms. In other words, the difference between the largest power of two and the smallest power of two should be as small as possible. An example of a grouped expression is as follows. 28 = 2 ⁵ -2 ² and 28 = 2 ⁴ +2 ³ +2 ² . In the first example, the power of 2 is spread by 5-2 = 3, and in the second example the power of 2 is spread by 4-2 = 2. This would make the second expression of 28 more grouped than the first. The advantages are as follows. That is, assume that all constants in the set have an expression such that the smallest power of 2 is 2 ² . This means that there is two bits of precision that can be picked up in quantization and scaling in the calculation, and effectively, we do not have to perform shifts for the trailing zeros by dividing all constants by 2 ² . .

The additional magnitude represented by the trailing zeros may be a number prior to quantization if necessary, e.g., if one at the end within one of the representations needs to be "obtained" for the precision of making the quantization decision. Can be reintroduced into (Please refer to the example proposed under the above-mentioned C1 that it is possible to discard ²⁰ wherein.)

4 shows a flowchart 300 of a method for finding a system of representations for a second reference C2 using the following conditions.

2 ⁿ + 2 ^n-1 = 2 ^{n +} 1-2 ^n-1 (5)

First, "num" is set to the "repcount" -1st element of the array "reps" (step 310). The current coefficient of representation for a given number is "repcount". The variable "add" is initialized to 2 (step 312). The bitmask is initialized to binary 0 ... 011 (step 314).

The bits are examined to determine whether both bits of the " number " that match the mask bits are set (340). Otherwise (342), the mask is shifted one by one 350, inserting zeros to the right and "addition" are shifted to the left one by one to increase the power of two used for realignment in Equation (5) above. If both bits of the "number" matching the mask bits have been set (344), this bit pattern "number" is a candidate representation for performing the reordering of terms using the condition (5) described above. Then, "number" encodes the expression by adding "addition" to "number" to change the power of 2 given by the equation shown in condition (5). (346). This provides faster speed and more efficient storage than the obsolete method (e.g., doing exhaustive searches on expressions and storing all the values of 0, +1, -1 separately). A new expression is obtained and the "expression coefficient" is set to "expression coefficient" +1 (348). The mask is shifted left one by one (350).

Shifting is performed until a predetermined maximum number "maxmask" is reached (370). If the predetermined maximum number has not been reached, the routine is repeated with a new "expression coefficient" value such that "number" is set to a new representation. Otherwise (374), the routine ends.

By the way the representations are coded in the program, the program stores whether the coefficients in a polynomial of power of two (see equation (4), for example) are not zero, that is, +1 is stored as all "1" bits. And 0 tracks if it is stored as a "0" bit. The power of two in the polynomial is encoded at the bit position. For example, bit 0 (most right) corresponds to 2 ⁰ . Since the program does not distinguish between + 1s, you may wonder how the program tracks expressions. Because the mask scans the outer side of the integer representation and the representation change from 2 ⁿ + 2 ^n-1 to 2 ^{n +} 1-2 ^n-1 shifts only the power of 2 to the left in the polynomial representation (that is, used in the representation Since only a power of 2 is increased), a power of 2 cannot be shifted so that a power of 2 with a + 1 multiplier is added to the same power of 2 with a-1 multiplier. Thus, since knowledge of the original integer, combined with the integer stored in the "expression" described above, is sufficient to uniquely determine the representation, it is sufficient to track only the multiplier that is not zero.

As noted above, the present invention also works for transforms where the terms are not properly separated into disjoint equation sets, as FDCT (and IDCT) can be separated into the sets 1,2, and 3 described above. do. As mentioned above, the term "disjoint" when used herein in connection with a set of equations means that there is no conversion constant common between the equations in the two disjoint equation sets. In the case where the binary representation of powers of 2 described above is used for constants, by choosing a set of equations for the transform arbitrarily or according to some cost function, and by selecting independent scaling terms for the constants in each set, The speed improvement can still be achieved by grouping a power of 2 for the conversion constant expression. You will want a criterion to find a representation for the coefficients of any set of equations. This works especially well when the transform is divided into these sets because the transform constants are grouped into sets of disjoint equations.

The following is an example of using FDCT with different groupings.

Now, the scaling term of the set 6 can be obtained, and a system of expressions for C ₁ , C ₃ , C ₄ , C ₅ , C ₇ for performing the three calculations of the set can be found. Then, different scaling terms for set (8) and simultaneous expressions for C ₁ , C ₃ , C ₅ , C ₇ for these formulas can be found, which are used for the calculation of set (6). The expressions are very different.

FIG. 5 shows a flow diagram 300 for providing faster conversion using corrective action to quickly perform conversion calculations and reduce execution time. At least one number from an incremental calculation using transform constants in the transform is tested 310. Then, based on the testing result, it is determined when to perform a corrective action (320). If it is determined that the corrective action is to be performed, the corrective action is performed (330).

When each _d D _k adds at least one additional bit precision to the conversion performed by D, a first example of refinement occurs. The second example is a conversion vector Occurs when at least one element is assumed to be very small, so that the entire row of _d D _k is approximated to zero, allowing the calculation of at least one element of F to be skipped.

In a first example, if all D _k are invertible, that is, D _k D _k ^-1 = D _k ^-1 D _k = 1, identity matrix (one from the upper left to the lower right diagonal is 1 and the remainder is 0) Is often the matrix D In this case, it can be written as follows.

(Where I is the identity matrix). That is, an additional step of precision is provided by performing one or more transform steps on the transformed coefficients. Using this additional step, the conversion of adding precision is the first embodiment of the subdivision provided in the present invention, since it saves performance for both IDCT and subsequent DCT. The matrix for (I + _d D _{m + 1} D _m ⁻¹ ) can be calculated _first as matrix R _{m + 1} , There is a single-step transform for.

The second example of the subdivision requires a different approach. Consider a specific example in which the two-dimensional transformation has already been performed with high precision in the first dimension, FD ¹ , _d D ₀ has the eighth row 0, and _d D ₁ = D- _d D ₀ . Then _d D ₀ is not invertible. That is, there is no way to restore the original 8-th column of the FD ¹ from the _{d D 0} FD ¹ (This is to find out the FD ¹ from the _d D ₀ FD ¹ can be regarded as a seven formula are eight known formula According to the fact that they are present). However, if an assumption is made for ^one of eight columns of FD ¹ , the other seven columns can be estimated from _d D ₀ FD ¹ , subject to the assumption for the eighth column. Since the higher-numbered conversion values tend to be less important in real images than the lower-numbered conversion values, it is reasonable to assume that the eighth column contains small elements that can be approximated to zero. do. D _{d 0} can then be treated as an 8 x 7 matrix (ignoring rows of 0), and as known in the literature, a pseudo-inverse matrix, Is identified as follows.

Here, an eighth row of zeros has been inserted for the assumed eighth coefficients. This gives an 8x8 approximation for _d D ₀ ^-1 , so we = (I + ` _d D ₁ ) Can be approximated.

This approximate subdivision is the second embodiment of the subdivision according to the invention, which saves the cycle of IDCT and thus DCT as in the first example.

When the calculation result is predicted to be too small, a stop procedure will be used to determine when the calculation can be completed before completion of the calculation to save cycles, so that the calculation result will be quantized to zero. One example of a break procedure application is shown in the above example, where at least one small transform coefficient is not calculated, which is basically equivalent to setting the corresponding row or rows of the transformation matrix to zero. Another example is to stop the calculation by limiting the precision when it is predicted that the additional conversion precision provides negligible additional information for the conversion values, for example when the calculation result is expected to be small. An alternative method involves testing the magnitude of the sum and / or difference for some of the inputs to the transform. For example, in the case of FDCT, the following equation calculates the second transform coefficient.

Where d ₀₇₃₄ = s _07- s ₃₄ and d ₁₆₂₅ = s _16- s ₂₅ , which are described in the PENbaker and Mitchell textbooks. It can be tested whether the magnitude of these values affects subsequent processing of the conversion coefficient. In this example, if S (2) is less than the magnitude of Q / 2 (Q is the quantization value of S (2)), S (2) will be quantized to zero. This translates to a test that d ₀₇₃ is smaller than Q / (2C ₂ ) in size and d ₁₆₂ is smaller than Q / (2C ₆ ) in size. If this test is met, the calculation for S (2) can be stopped and S (2) is set to zero, its quantization value. This way of testing the sum and / or difference of input values can be extended to all equations of the FDCT.

(Vector or matrix A range-by-term range check for the elements of Are not all negative, and -T <F <T (where T's are not negative and satisfying the test for F) It's not clear how to turn it into enough to satisfy the test for. DCT employs both positive and negative operations, which suffers from the fact that it breaks the order-by-term alignment in the equation. Specifically, - < < end < < I can not say that means.

Thus, abort is concerned with terminating computational precision when it is expected that additional transform precision will have an acceptable or negligible effect on subsequent processing operations (eg, quantization or comparison) results. For example, the coefficient of DCT may be scaled by an integer and approximated by the sum of powers of two. In the case of radix terms, one example of these approximations is as follows.

We write (using the above notation):

Also, as discussed above, all of the aforementioned matrices and their sequential sums are invertible. now, If <<, that is, If the j th element of is very small in size, j (32 _d D ₀ F) must be small. Otherwise, j ((8 _d D ₁ +2 _d D ₂ + _d D ₃ ) F) will not cancel it, to make the final result small. The relative size of the calculation results can be checked. For one intermediate precision, if one transformed value is smaller than the other values, or smaller than any predetermined threshold, subsequent refinements to the transform value can be stopped.

6 shows a flowchart 400 of a stop method of stopping further repeating the transform calculation process in accordance with the present invention. In FIG. 6, at least one incrementally calculated number is tested 410. If certain criteria are met, further calculations are stopped (420). Incremental calculation of transform coefficients can be stopped when errors that occur due to interruption of incremental calculations are acceptable. For example, the incremental calculation may be terminated when it is determined that the incremental calculation will yield a predicted number within a predetermined range, for example a conversion factor that satisfies the precision requirements. Alternatively, the transform coefficient incremental calculation may be stopped if the transform coefficient is within a predetermined range of zero.

7 is a flowchart 500 of at least one incrementally calculated number of tests. In FIG. 7, an incremental calculation is tested 510 to determine when the subdivision of the transform coefficient will not change the result. This test can be performed in at least two ways, as shown in FIG. 7. After examining the relative magnitude of the incremental calculation result, when the intermediate value of the at least one transform coefficient is smaller than the intermediate value of another transform coefficient, it may be determined that the subdivision of the transform coefficient does not change the result (520). . Alternatively, after checking the relative magnitude of the incremental calculation result, when the intermediate value of the at least one conversion factor is less than the predetermined threshold value, it may be determined that the subdivision for the conversion factor does not change the result (530). ).

8 is a flowchart 600 of a subdivision method in accordance with the present invention. First, a determination is made whether the transformation needs better precision (610). The transform is a transform matrix, and the submatrices can be used to increase the precision of the incremental calculation of the transform coefficients. If more precision is needed, the submatrix is applied to the transformation (620). Subdivision matrices are generated at offline or initialization time and are based on estimated conversion constants.

9 is a flowchart 700 of a first method for generating a subdivision matrix. First, it is recognized that the approximation transformation is reversible (710). A subdivision matrix given by I + _d D _{m + 1} D _m ⁻¹ is generated 720. Then, the transform is structured 730 for efficient computation.

However, as discussed above, _d D ₀ is a non-reversible back, it is not possible to restore the original 8-th column of the FD ¹ FD ₀ D from _d ^1. FIG. 10 is a flowchart 800 illustrating a second method of generating a subdivision matrix when _d D ₀ is non-reversible. First, it is recognized that recovery of the nth column of the transformation matrix for generating the transformation is impossible (810). A pseudo inverse of the transform matrix portion is calculated (820). An approximation of the subdivision matrix is then generated 830 using the pseudo inverse of the transformation matrix. The approximation of the subdivision matrix is I + _d D ₁ Is made of.

11 shows a block diagram 400 of a printer 420 in accordance with the present invention. In FIG. 11, the printer 420 receives image data 412 from the host processor 410. The image data 412 is provided to the memory 430, which may be configured with an 8 × 8 block sample. The 8 × 8 block sample is processed by a processor 440, such as a raster image processor. The raster image processor 440 provides the printhead drive circuit 450 with a compressed print stream representing image data. The printhead drive circuit 450 then controls the printhead 460 to produce an output 470 of image data.

The process described with reference to FIGS. 1-4 is tangibly embodied in a computer readable medium or carrier 490 or other storage or data communications devices, such as one or more fixed and / or removable data storage devices shown in FIG. 11. Can be. A computer program is loaded into memory 492 to execute processor 440 of FIG. The computer program includes instructions that, when read and executed by the processor of FIG. 11, cause the processor 440 to perform the steps necessary to carry out the steps or elements of the present invention.

12 illustrates a data analysis system 500 in accordance with the present invention. In FIG. 12, converter 510 generates transform data 524 using transform equation 520. Transformation equation 520 is divided into at least one sub-transformation with at least two conversion constants. At least two or more transform constants of each set are scaled independently with a scaling term to maintain a substantially equal ratio between at least two or more constants in at least one set, wherein the scaling term is selected according to a predetermined cost function. The transform data 524 can then be selectively quantized by the quantizer 530. The quantization value of quantizer 530 is adjusted to reflect the scaling term used for each coefficient.

13 illustrates another data analysis system 600 in accordance with the present invention. In FIG. 13, converter 610 receives data block 612 to be analyzed. The converter 610 generates the conversion data 624 using the conversion equation 620. Transformation equation 620 is divided into at least one sub-transformation with at least two conversion constants. At least two or more transform constants of each set are scaled independently with a scaling term to maintain a substantially equal ratio between at least two or more constants in at least one set, wherein the scaling term is selected according to a predetermined cost function. The transform data 624 is then compared to the scaled comparison values in the comparator 630.

The foregoing description of the exemplary embodiments of the invention has been presented for the purposes of illustration and illustration. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

Claims (36)

Arranging the transform equations into at least one collection having at least two conversion constants, Independently scaling the at least two conversion constants of each set using a scaling term to maintain a substantially uniform ratio between the at least two conversion constants in the at least one set How to include. 2. The method of claim 1, wherein the scaling term is one of the at least one set of conversion constants. 2. The method of claim 1, wherein each conversion constant is represented by an estimate of a conversion constant approximated by a sum of powers of two. 2. The method of claim 1, further comprising separating data into at least one block and transforming the block using equations applied to maintain a substantially uniform ratio between at least two conversion constants in the at least one set. The method further comprises the step of converting. 5. The method of claim 1 or 4, wherein the scaling terms are selected according to a predetermined cost function. 6. The method of claim 5, further comprising determining a predetermined cost function by selecting the scaling term such that the largest error for any transform coefficient is not greater than a predetermined error rate. 6. The method of claim 5, further comprising determining the predetermined cost function by selecting the scaling term such that a predetermined conversion constant is less than or equal to a predetermined error rate. 6. The method of claim 5, further comprising determining a predetermined cost function by selecting a scaling term and a representation such that all of the transform constants of the set have simultaneous binary representations having predetermined characteristics. 9. The method of claim 8, wherein selecting a scaling term and a representation such that all of the transform constants in the set have a system of binary representations with a minimum number of common two-squared terms is implemented when the binary arithmetic shift is more efficient than the multiplication operation. 10. The system of claim 9, wherein all representations of scaled constants are a) setting a first variable to the i th element in the block; b) initializing the second variable to the value 2, c) initializing the bitmask to binary 3, d) analyzing the bits to determine whether the i th element represented by the first variable is a candidate representation for reordering terms using 2 ⁿ + 2 ^n-1 = 2 ^{n +} 1-2 ^n-1 Steps, e) adding the i th element by adding the second variable to the first variable in order to efficiently perform a power of 2 given by 2 ⁿ + 2 ^n-1 = 2 ^{n +} 1-2 ^n-1 Encoding, f) obtaining a new representation and incrementing the first variable to the i + 1 th element, g) shifting the bitmask and the second variable one bit to the left; h) repeating steps d through g Method found by the steps comprising. 11. The method of claim 10, further comprising: shifting the mask bits to the left after checking whether the first variable matching the mask bits is set, whereby zero is inserted to the right; and 2 ⁿ + 2 ⁿ Increasing the power of 2 used for reordering ^-1 = 2 ^{n +} 1-2 ^n-1 . 10. The method of claim 9, wherein the predetermined characteristic comprises maximum grouped non-zero two-squared terms. 13. The method of claim 12, wherein selecting a scaling term such that all of the transform constants in the set have a systemic binary representation with maximum non-zero powers of two powers, wherein the multiplication operation employing small integers employs larger integers. The method implemented when it is preferable to multiplication. 14. The method of claim 13, wherein the coefficients of the power of two powers of said constant representing non-zero are tracked. 15. The method of claim 14, wherein the value of the bit position determines the two-squared term. 14. The method of claim 13, wherein maximizing a group of nonzero powers of two a) setting a first variable to the i th element in the block; b) initializing the second variable to the value 2, c) initializing the bitmask to binary 3, d) analyzing the bits to determine whether the i th element represented by the first variable is a candidate representation for reordering terms using 2 ⁿ + 2 ^n-1 = 2 ^{n +} 1-2 ^n-1 Steps, e) adding the i th element by adding the second variable to the first variable in order to efficiently perform a power of 2 given by 2 ⁿ + 2 ^n-1 = 2 ^{n +} 1-2 ^n-1 Encoding, f) obtaining a new representation and incrementing the first variable to the i + 1 th element, g) shifting the bitmask and the second variable one bit to the left; h) finding all representations of the scaled constants by repeating steps d through g. 17. The method of claim 16, further comprising: shifting the mask bits to the left after checking whether the first variable matching the mask bits is set, thereby inserting 0 to the right; and 2 ⁿ + 2 ^n-1 = 2 ^{n + 1-2} increasing the power of 2 used for reordering ^n-1 . 2. The method of claim 1, wherein the set represents a disjoint set of transform equations of partial calculation. The method of claim 1, wherein the set does not represent a disjoint set of transform equations of a partial calculation. 20. The method of claim 19, further comprising selecting an independent scaling term for the transform constants in the at least one set. The method of claim 1, Testing at least one number resulting from the incremental calculation of the transform coefficients during the conversion, Determining whether to perform a corrective action based on the test result; Steps to perform correction if it is determined that correction is necessary How to include. 22. The method of claim 21, wherein determining whether to perform corrective action comprises detecting whether an incremental calculation of the transform coefficient yields transform coefficients with unacceptable precision and the performing step comprises the at least one number. Subdividing the method. 23. The method of claim 22, wherein the transformation comprises a transformation matrix and the subdivision step includes applying a subdivision matrix to increase the precision of the incremental calculation of the transformation constants. The method of claim 23, wherein the submatrices comprise I + _d D _{m + 1} D _m ⁻¹ . 22. The method of claim 21, further comprising generating at least one submatrix based on estimated conversion constants. 26. The method of claim 25, wherein generating at least one submatrix is performed offline or upon initialization. 26. The method of claim 25, wherein generating the at least one submatrix comprises: recognizing that the approximation is invertible, generating the submatrix given by I + _d D _{m + 1} D _m ^−1; Structuring the transformation for efficient computation. The method of claim 25, wherein generating the at least one submatrix Recognizing that the nth column of the transformation matrix for generating the transformation is impossible to recover; Calculating a pseudo inverse of a portion of the transform matrix; Generating an approximation to the at least one submatrix using the pseudo inverse of the transform matrix How to include. 29. The method of claim 28, wherein an approximation of the submatrices is I + _d D ₁ How to include. 22. The method of claim 21, wherein determining whether to perform corrective action further comprises determining whether an error resulting from terminating the incremental calculation is acceptable and performing the corrective action comprises incrementing the conversion coefficient. Stopping the calculation. 31. The method of claim 30, wherein the incremental calculation is terminated when a determination is made that the incremental calculation will yield a number expected within a predetermined range. 32. The method of claim 31 wherein the number expected within the predetermined range includes a conversion factor that meets precision requirements. 32. The method of claim 31, wherein the incremental calculation ends when it is determined that the subdivision of the conversion coefficient does not change the result. 34. The method of claim 33, wherein after examining the relative magnitude of the result of the incremental calculation, the subdivision of the conversion coefficient does not change the result when the intermediate value of the at least one transform coefficient is small compared to the intermediate value of another transform coefficient. How do you think? 34. The method of claim 33, wherein after examining the magnitude of the result of at least one incremental calculation, it is determined that the subdivision of the conversion coefficient does not change the result when at least one intermediate value of the conversion coefficient is smaller than a predetermined threshold value. Way. 22. The method of claim 21, wherein the determining step further comprises determining that the conversion coefficient is within zero of a predetermined range and wherein performing the corrective action comprises stopping the incremental calculation of the conversion coefficient. .