CN102088538B - Bit rate control circuit and method for image compression - Google Patents

Abstract

The present invention relates to a bit rate control circuit for image compression, comprising a compression unit, an R value estimation unit, and an LQF value estimation unit. The compression unit is used to perform a first compression on an image according to a preset linear quantization parameter (LQF _ini ) to obtain an initial pixel bit number (bpp _ini ) and an initial zero coefficient number (R _ini ). The R value estimation unit estimates a target zero coefficient number (R _target ) after quantization according to the initial pixel bit number and a target pixel bit number (bpp _target ). The LQF value estimation unit estimates a required target linear quantization parameter (LQF _target ) according to the target zero coefficient number (R _target ). The LQF _target can be used to perform a second compression on the image to obtain a compressed image corresponding to the target pixel bit number.

Description

Image compression bit rate control circuit and method

technical field

The present invention relates to image compression techniques, and more particularly to bit rate control techniques for image compression.

Background technique

The image compression technology can effectively reduce the memory capacity occupied by an original image, so as to effectively reduce the storage space while maintaining the image content. Generally speaking, however, the compression rate of an image varies with the complexity of its content. Therefore, the size of the memory space of the compressed image will change. However, for the application of digital cameras, in addition to reducing the memory space in static image compression, it is also hoped that the size of the compressed images is roughly the same, and does not change too much with the complexity of the image content.

In order to keep the image at about a fixed size, the bit rate control of still image compression is very important, so that the file size of the photo will not change too much with the content variation, so that the user can know the remaining storage space more effectively Take a few photos.

The content of US Patent No. 5594554 discloses that the quantization table (Quantization Table) that should be set for the second compression is calculated by using the file size obtained for the first time after image compression and a previously obtained mathematical model. However, the accuracy of the mathematical model used in this method will be different for different images. Moreover, the calculations used are more complicated, especially the use of exponential calculations.

US Patent No. 5677689 discloses that the quantization table for the second compression is calculated by using the activity metric obtained from the first compression and the previously obtained mathematical model. However, this method can only make the second compressed file smaller than the first one, and there is no way to adjust the file size upwards.

A parameter ρ is also proposed in the prior art, which is defined as the ratio of the number of zero coefficients (R) to all coefficients (T) after quantization. This parameter ρ can be associated with the compressed archive size.

Contents of the invention

The present invention provides a bit rate control circuit and method for image compression, which can simply estimate the target linear quantization parameter (LQF _target ) of the second compression as the basis for the second compression, so as to maintain an image file close to the target size.

An embodiment of the present invention provides a bit rate control circuit for image compression, including a compression unit, an R value estimation unit, and an LQF value estimation unit. A bit rate control circuit for image compression, including a compression unit, an R value estimation unit, and an LQF value estimation unit. The compression unit is used to compress an image for the first time according to a preset linear quantization parameter (LQF _ini ) to obtain an initial number of pixel bits (bpp _ini ) and an initial number of zero coefficients (R _ini ). The R value estimating unit estimates a target number of zero coefficients (R _target ) after quantization according to the initial number of pixel bits and a target number of pixel bits (bpp _target ). The LQF value estimating unit estimates a required target linear quantization parameter (LQF _target ) according to the target number of zero coefficients (R _target ). The LQF _target can be used to perform a second compression on the image to obtain a compressed image corresponding to the number of bits of the target pixel.

According to an embodiment, in the aforementioned image compression bit rate control circuit, for example, the R value estimating unit is based on a linear relationship between a coordinate point and a common origin of the bpp _ini and the R _ini , and the The bpp _target estimates the desired R _target .

According to an embodiment, in the aforementioned image compression bit rate control circuit, for example, the coordinates of the pixel bit number and the zero coefficient number of the common origin are zero and the total coefficient number T.

According to an embodiment, in the aforementioned bit rate control circuit for video compression, for example, the LQF value estimating unit obtains the LQF _target corresponding to the R _target according to a numerical relationship between the R value and the LQF.

According to an embodiment, in the aforementioned bit rate control circuit for video compression, for example, the numerical relationship between the R value and the LQF is included in the first compression performed by the compression unit, and simultaneously counts a number corresponding to a plurality of LQF values. A set R _set is provided to the LQF value estimation unit to calculate the LQF _target corresponding to the R _target by linear interpolation.

According to an embodiment, in the aforementioned bit rate control circuit for image compression, for example, the LQF value is a multiple of the LQF _ini .

According to an embodiment, in the aforementioned image compression bit rate control circuit, for example, the LQF values include LQF _ini /4, LQF _ini /2, LQF _ini /1, LQF _ini *2, LQF _ini *4.

According to an embodiment, in the aforementioned image compression bit rate control circuit, for example, the R value estimating unit and the LQF value estimating unit are integrated into a computing unit.

According to an embodiment, in the aforementioned image compression bit rate control circuit, for example, the compression unit further performs the second compression on the image according to the LQF _target to obtain the compressed image.

According to an embodiment, the aforementioned image compression bit rate control circuit, for example, further includes another compression unit for performing the second compression according to the LQF _target .

According to an embodiment, in the aforementioned image compression bit rate control circuit, for example, the image is a static image.

Another embodiment of the present invention proposes a bit rate control method for image compression, including performing quantization processing on an image according to a preset quantization table and a preset linear quantization parameter, so as to perform a first compression on the image ; Obtain an initial number of pixel bits (bpp _ini ) and an initial number of zero coefficients (R _ini ) through the first compression; a target pixel bit required according to the initial number of pixel bits (bpp _ini ) number (bpp _target ) to estimate a target number of zero coefficients (R _target ); estimate a target linear quantization parameter (LQF _target ) according to the R _target ; and perform a second compression on the image according to the LQF _target to obtain A compressed image corresponding to the target pixel number of bits.

According to an embodiment, in the aforementioned bit rate control method for image compression, for example, the step of estimating the target number of zero coefficients (R _target ) includes: a coordinate point and a coordinate point according to the bpp _ini and the R _ini A linear relationship between the common origin, the bpp _target is used to estimate the desired R _target

According to an embodiment, in the aforementioned bit rate control method for image compression, for example, the coordinates of the pixel bit number and the zero coefficient number of the common origin are zero and the total coefficient number T.

According to an embodiment, in the aforementioned bit rate control method for video compression, for example, the step of estimating the target linear quantization parameter (LQF _target ) includes: according to a numerical relationship between the R value and the LQF, to obtain the corresponding The LQF _target of the R _target .

According to an embodiment, in the aforementioned bit rate control method for image compression, for example, the numerical relationship between the R value and the LQF is included in the first compression, and a group of R _sets corresponding to a plurality of LQF values are counted at the same time , to provide the LQF _target corresponding to the R _target calculated by linear interpolation in the step of estimating the LQF value.

According to an embodiment, in the aforementioned bit rate control method for image compression, for example, the LQF value is a multiple of the LQF _ini .

According to an embodiment, in the aforementioned bit rate control method for image compression, for example, the LQF values include LQF _ini /4, LQF _ini /2, LQF _ini /1, LQF _ini *2, LQF _ini *4.

According to an embodiment, in the aforementioned bit rate control method for image compression, for example, the numerical relationship between the R value and the LQF is a relationship curve obtained by pre-statistics.

According to an embodiment, in the aforementioned bit rate control method for image compression, for example, the image is a static image.

The above description is only an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention, it can be implemented according to the contents of the description, and in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable , the following preferred embodiments are specifically cited below, and are described in detail as follows in conjunction with the accompanying drawings.

Description of drawings

FIG. 1 is a schematic diagram of the standard compression process of JPEG.

FIG. 2 is a schematic diagram illustrating the relationship between the number of pixel bits (bpp) and the parameter ρ according to an embodiment of the present invention.

FIG. 3 shows a schematic diagram of the relationship between parameter ρ and NQF.

FIG. 4 is a schematic block diagram of a bit rate control circuit for image compression according to an embodiment of the present invention.

FIG. 5 is a schematic flowchart of a bit rate control method for image compression according to an embodiment of the present invention.

FIG. 6 is a schematic flowchart of a bit rate control method for image compression according to an embodiment of the present invention.

100: DCT unit

102: Coefficient quantization unit

104: Huffman coding unit

200: Compression unit

202: R value estimation unit

204: LQF value estimation unit

206: Compression unit

S100～S108: steps

S200～S206: steps

Detailed ways

In order to further explain the technical means and effects of the present invention to achieve the intended purpose of the invention, below in conjunction with the accompanying drawings and preferred embodiments, the specific implementation of the bit rate control circuit and method for image compression proposed according to the present invention, Structure, characteristic and effect thereof are as follows in detail.

Based on the concept of the parameter ρ, the present invention can compress images according to a predetermined file size. It also provides a simple and fairly accurate bit rate control method for still images, such as JPEG. A number of embodiments are given below to illustrate the present invention. However, the invention is not limited to the various exemplary embodiments presented. In addition, the examples mentioned can also be properly combined with each other.

FIG. 1 is a schematic diagram of the standard compression process of JPEG. Referring to Fig. 1, after the digital image data is input, after being converted by a discrete cosine transform (Discrete Cosine Transform, DCT) unit 100, the DCT coefficients will be quantized by the coefficient quantization unit 102 according to the quantization table (Quantization Table) Q[i] (Quantization) to obtain quantitative results. After the quantization result is encoded by the Huffman Coding unit 104, a standard bit string can be obtained, that is, a JPEG stream.

Generally, the processing unit of the DCT unit 100 is an operation in units of 8×8 pixel blocks, and there is a quantization table Q[i] for its 64 converted coefficients to record the quantization coefficients corresponding to each position.

Generally speaking, the quantization table Q[i] is obtained, for example, by a set of preset quantization tables combined with a linear quantization parameter (Linear Quantization Factor, LQF). For example, the preset quantization table is {Q _default [i], i: 0~63}, and the quantization table used for compression takes the accuracy of 1/512 as an example, and Q[i] is:

(1) Q[i]=min(255, max(1, (Qdefault[i]*LQF+256)/512))

Wherein, both Q[i] and Q _default [i] are integers between 1 and 255. LQF is used to scale the preset quantization table linearly. This example has an accuracy of 1/512. The following embodiments assume that the LQF accuracy is 1/512 unless otherwise mentioned. In addition, as known to those skilled in the art, the corresponding preset quantization tables of Y and Cb/Cr are usually different.

Then, before the present invention proposes a method for processing the scaling ratio of the image compression, further research is conducted on the aforementioned parameter ρ. The parameter ρ is defined as the ratio of the number R of zero coefficients after quantization to the total number T of coefficients (ρ=R/T).

It should be noted here that the R values mentioned in the following description all represent the number R of zero coefficients after quantization, which may correspond to different characteristics of bit rates for different compression methods. Take an image in JPEG format as the experiment and explanation below. Of course, after the verification of multiple different images, the characteristics described can be deduced as general characteristics, which are not different for different images.

For an image, the number T of compression coefficients is a fixed value, but the number R of compressed zero coefficients varies with the content of the image. Therefore, since the parameter ρ is defined as ρ=R/T, it will be related to the size of the image file. FIG. 2 is a schematic diagram illustrating the relationship between the number of pixel bits (bpp) and the parameter ρ according to an embodiment of the present invention. Referring to FIG. 2 , the horizontal axis is the parameter ρ and the vertical axis is bpp (bits per pixel). The number of bits here is the encoding data of quantized coefficients after DCT, excluding JPEG file header data (header). From the distribution of bpp corresponding to parameter ρ, it can be observed that bpp and ρ present a nearly linear relationship. When ρ is small, for example, at 0.7, although the slope of the relationship line is slightly gentle, it is still close to a straight line relationship. Therefore, bpp and ρ described by straight lines still maintain acceptable accuracy. This linear relationship is useful for making predictions. It can also be observed that when ρ approaches 1, bpp approaches 0. Therefore, for any graph, when the coordinates of any set of ρ ₀ and bpp ₀ are known, the connection between (ρ ₀ , bpp ₀ ) and (1, 0) can be used as the relationship between bpp and ρ in the graph forecast reference line.

Furthermore, since T is a constant for an image, after a correction of T, the prediction reference line is equivalent to any known set of R ₀ and bpp ₀ , by (R ₀ , bpp ₀ ) and The connecting line of (T, 0) is used as the prediction reference straight line of the relationship between bpp and R in the figure. Between ρ and R is only an algebraic replacement of fixed multiples. However, in actual processing, R replaces ρ to simplify the calculation processing of hardware or software, and an embodiment thereof will be described later.

Next, the present invention goes on to find the linkage relationship that can be used to control the bit rate. FIG. 3 shows a schematic diagram of the relationship between the parameter ρ and NQF, where NQF represents the normalized LQF, that is, NQF (normalized quantization factor)=LQF/512. Referring to Fig. 3, the relationship between parameter ρ and NQF is a smooth curve, that is, the relationship between ρ and LQF is also a smooth curve. Although this curve cannot be described by a simple mathematical formula, it can be described by numerical analysis. In other words, the curve of the parameter ρ and NQF can be described by multiple reference points, and the line-taking points can be estimated by interpolation (for example, linear interpolation).

Judging from the relationship between Figure 2 and Figure 3, bpp can correspond to LQF, and the curve in Figure 3 can generally be completed through statistics first. However, the points of this curve can also be obtained by statistics during the first compression, and the method will be described later. Moreover, the present invention also analyzes the same parameters for different images, and then determines that the characteristics in FIG. 2 and FIG. 3 are generalized characteristics, and there will be no obvious difference due to different image contents. Therefore, the control of bpp can be adjusted by proper LQF. After the image is compressed again, a bpp close to the desired target can be achieved.

FIG. 4 is a schematic block diagram of a bit rate control circuit for image compression according to an embodiment of the present invention. Referring to FIG. 4 , the bit rate control circuit for image compression includes a compression unit 200 , an R value estimation unit 202 , and an LQF value estimation unit 204 . The compression unit 200 quantizes an image according to a preset quantization table and a linear quantization parameter. That is, the compression unit 200 performs a first image compression according to a preset linear quantization parameter (LQF _ini ) to obtain an initial number of pixel bits (bpp _ini ) and an initial number of zero coefficients (R _ini ). The R value estimating unit 202 estimates a target number of zero coefficients (R _target ) after quantization according to the initial number of pixel bits (bpp _ini ) and a desired number of target pixel bits (bpp _target ). The LQF value estimating unit 204 estimates a required target linear quantization parameter (LQF _target ) according to the R _target obtained by the R value estimating unit 202 . The LQF _target can be used to perform a second compression on the image to a compression unit 206 , which is then input to the compression unit 200 for the second image compression, and the LQF _ini is replaced by the LQF _target .

Here, the LQF value estimating unit 204 estimates the desired LQF _target according to the relationship in FIG. 3 . In order to establish the curve data as shown in FIG. 3 , a set of data points is needed to describe the curve numerically. In other words, it requires a set of R _set composed of multiple different R values, and different R values correspond to a set of LQF _set including multiple different LQFs. The general direct way is to count multiple numerical points on a set of LQF _sets to count the corresponding multiple R numerical points. These R value points can be obtained, for example, through multiple quantizations in advance.

However, the present invention, for example, proposes an easier way to obtain a desired set of R _set , which can simultaneously perform statistics to obtain a set of curve data points when the compression unit 200 performs the first compression. In other words, R _set does not need to be quantized multiple times to obtain it. For example, the quantization method of rounding is to count the number of DCT coefficients x[i] and quantization coefficients Q[i] corresponding to the selected LQF points.

For example, first obtain x'[i] according to formula (2),

(2) x'[i]=sign(x[i])*int((abs(x[i])+Q[i]/2)/Q[i]),

Among them, sign() is a sign function, abs() is an absolute value function, and int() is an integer function. Then the quantization result is zero is equal to (abs(x[i])+Q[i]/2)/Q[i]<1, that is, abs(x[i])/Q[i]<1/2 , the value of abs(x[i])/Q[i] would have been obtained during the quantization process during the compression process. Also, Q[i]/2 added to the latter term is a general rounding method, but it is only one method. The added Q[i]/2 can also be other values, such as Q[i]/4, which is not a condition of rounding. The selection of LQF _set is, for example, the five statistical points of LQF _set = {LQF _ini /4, LQF _ini /2, LQF _ini /1, LQF _ini *2, LQF _ini *4}, and the corresponding R _set can be used as follows A simple comparison of sizes yields:

R _ini ＝{x[i] meets the quantity of abs(x[i])/Q[i]<1/2}

R _LQFini/2 ＝{x[i] meets abs(x[i])/Q[i]＜1/4 quantity}

R _LQFini/4 ＝{x[i] meets abs(x[i])/Q[i]＜1/8 quantity}

R _LQFini*2 ＝{x[i] meets the number of abs(x[i])/Q[i]<1}

R _LQFini*4 ＝{x[i] conforms to the number of abs(x[i])/Q[i]<2}

That is to say, in the whole process, for example, an initial LQF _ini is used to perform the first JPEG compression to obtain bpp _ini and R _ini . Then use (bpp _ini , R _ini ) and (0, T) to form a straight line according to the characteristics in Figure 2, and then substitute bpp _target to get R _target . In addition, in addition to R _ini , the quantization parameters can be obtained from the coefficients after DCT in the first JPEG compression, which are LQFini/2, LQFini/4, LQFini*2, and LQFini*4 relative R _LQFini/2 , R _{LQFini/ 4} , R _LQFini*2 , and R _LQFini*4 . The LQF _set is {LQF _ini /4, LQF _ini /2, LQF _ini , LQF _ini *2, LQF _ini *4}, and the corresponding R _set is {R _LQFini/4 , R _LQFini/2 , R _ini , R _LQFini*2 , R _LQFini*4 }. R _set was obtained in the aforementioned statistical manner.

Next, an estimate of the LQF _target can be obtained by interpolation (eg, linear interpolation). For example, R ₁ and R ₂ closest to R _target can be found from R _set first, and then the corresponding LQF ₁ and LQF ₂ can be found to connect (R ₁ , LQF ₁ ) and (R ₂ , LQF ₂ ) straight line. Then, substitute R _target into the straight line to get LQF _target . Finally, use the LQF _target to compress the original image a second time to get the final result.

The following is an example process of bit rate control for JPEG 422 compression for a 4064x2704 image using the above method. Firstly, it is desired to obtain a bit rate of bpp _target =3, and its compressed initial value LQF _ini =96. For example, the first compression can obtain bpp _ini =2.429, R _ini =18108052, and with LQF _set ={LQF _ini /4, LQF _ini /2, LQF _ini , LQF _ini *2, LQF _ini *4}={24, 48, 96, 192, 384} correspond to R _set = {14688698, 16739607, 18108052, 19161683, 19980455}. Next, substitute 3 of bpp _target into the straight line connected by (2.429, 18108052) and (0, T=21978112) to obtain R _target =17198293. Then, it can be seen from the analysis that the R _target is between 16739607 and 18108052 corresponding to LQF=48 and LQF=96. Then substitute R _target into the straight line connected by (16739607, 48) and (18108052, 96) to obtain LQF _target = 64, which is the estimated value of the bit rate corresponding to bpp _target = 3.

Finally, LQF _ini =96 is replaced by LQF _target =64 for the second compression to obtain bpp=3.01137, and the error between it and bpp _target =3 is only 0.38%. In this way, in a simple way, the image can be compressed close to the bpp _target , which includes reducing and increasing the size of the image file, and maintaining it close to the bpp _target .

The above LQF _target describes the curve with five points. However, if the scope and accuracy of quantization parameters are to be increased, R _set can also be increased by R _LQFini*8 or R _LQFini/8 , for example. That is to say, more reference points can describe the curve more accurately. In addition, in order to increase the interpolation accuracy of the LQF _target , for example, the linear interpolation method can be changed to a polynomial interpolation method to estimate the LQF _target more accurately. In yet another embodiment, in order to increase the precision of the quantization parameters, the precision of the LQF can also be increased, for example, set to 1/1024.

FIG. 5 is a schematic flowchart of a bit rate control method for image compression according to an embodiment of the present invention. Referring to FIG. 5 , the bit rate control method for image compression includes step S100 to perform a first compression on an image with LQF _ini . The first compression is to quantize the image according to a preset quantization table Q _ini [i] and a preset linear quantization parameter LQF _ini . During one compression, an initial pixel bit number (bpp _ini ) and an initial pixel bit number (R _ini ) are also calculated. In step S102, statistics of R _set are also made for the predetermined LQF _set during the first compression. In step S104 , R value estimation is performed again, which includes estimating a target number of zero coefficients after quantization (R _target ) according to a desired number of target pixel bits (bpp _target ). In step S106, LQF value estimation is performed, which includes a target linear quantization parameter (LQF _target ) required for estimation according to the R _target . In step S108, a second compression is performed on the image with the LQF _target .

In the bit rate control method for image compression described above, step S102 is to simultaneously perform statistics during the first compression, so as to simplify the compression process. However, as a general principle, as long as the LQF _target corresponding to the R _target can be analyzed, the relationship curve between the two can be obtained in various ways, not limited to the way shown in FIG. 5 .

FIG. 6 is a schematic flowchart of a bit rate control method for image compression according to an embodiment of the present invention. Referring to FIG. 6 , step S200 performs a first compression on an image, wherein the first compression is to quantize the image according to a preset quantization table Q _ini [i] and a preset linear quantization parameter LQF _ini . During the compression, an initial pixel bit number (bpp _ini ) and an initial pixel bit number (R _ini ) are also calculated. Next step S202 is to estimate the R value, which includes estimating a target number of zero coefficients (R _target ) after quantization according to a desired number of target pixel bits (bpp _target ). Step S204 performs LQF value estimation, which includes a target linear quantization parameter (LQF _target ) required for estimation according to the R _target , for example, a curve data table for interpolation calculation of the LQF _target . In other words, the curve data table in step S204 can be obtained from pre-obtained data or, for example, by the method of step S102 in FIG. 5 , and is not limited to a specific method. Step S206 uses the LQF _target to perform a second compression on the image.

The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this field Those skilled in the art, without departing from the scope of the technical solution of the present invention, can use the technical content disclosed above to make some changes or modify equivalent embodiments with equivalent changes. Any simple modifications, equivalent changes and modifications made to the above embodiments by the technical essence still belong to the scope of the technical solutions of the present invention.

Claims (18)

1. the bit rate control circuit of an image compression is characterized in that it comprises:

One compression unit is used for according to a default equal interval quantizing parameter L QF _IniOne image is carried out the compression first time, count bpp to obtain an initial pixel bit _IniAn and initial zero coefficient number R _Ini

One R value evaluation unit, according to this initial pixel bit number and an object pixel bit count bpptarget estimate quantize after a target zero coefficient number R _Target, wherein the R value is zero coefficient number R value after representative quantizes; And

One LQF value evaluation unit is according to this target zero coefficient number R _Target, estimate the linear quantization parameter LQF of a needed target _Target, wherein the LQF value is to represent equal interval quantizing parameter L QF value;

The linear quantization parameter LQF of this target wherein _TargetCan be used for this image is carried out a for the second time compression, to obtain a compressing image that should object pixel bit number;

Wherein said R value evaluation unit is to count bpp according to this initial pixel bit _IniWith this initial zero coefficient number R _IniA coordinate points and the linear relationship between the common initial point, count bpp with this object pixel bit _TargetEstimate desired this target zero coefficient number R _Target

2. the bit rate control circuit of image compression according to claim 1 is characterized in that the pixel bit number of wherein said common initial point and the coordinate of zero coefficient number are zero and overall coefficient number T.

3. the bit rate control circuit of image compression according to claim 1, it is characterized in that wherein said LQF value evaluation unit is with respect to the numerical relation of described equal interval quantizing parameter L QF, to obtain should target zero coefficient number R according to zero coefficient number R value after the described quantification _TargetThe linear quantization parameter LQF of this target _Target

4. the bit rate control circuit of image compression according to claim 3, it is characterized in that zero coefficient number R value after the wherein said quantification is included in this compression unit with respect to this numerical relation of described equal interval quantizing parameter L QF and carries out during this compresses for the first time, add up simultaneously one group of zero coefficient number R of corresponding a plurality of equal interval quantizing parameter L QF values _Set, offering this LQF value evaluation unit, calculate should target zero coefficient number R by linear interpolation _TargetThe linear quantization parameter LQF of this target _Target

5. the bit rate control circuit of image compression according to claim 4 is characterized in that wherein said a plurality of equal interval quantizing parameter L QF value is with this default equal interval quantizing parameter L QF _IniThe value of a plurality of multiples.

6. the bit rate control circuit of image compression according to claim 4 is characterized in that wherein said a plurality of equal interval quantizing parameter L QF value comprises described default equal interval quantizing parameter L QF _Ini/ 4, described default equal interval quantizing parameter L QF _Ini/ 2, described default equal interval quantizing parameter L QF _Ini/ 1, described default equal interval quantizing parameter L QF _Ini* 2, described default equal interval quantizing parameter L QF _Ini* 4.

7. the bit rate control circuit of image compression according to claim 1 is characterized in that wherein said R value evaluation unit and this LQF value evaluation unit are to be integrated in a computing unit.

8. the bit rate control circuit of image compression according to claim 1 is characterized in that wherein said compression unit is in addition according to the linear quantization parameter LQF of this target _TargetThis image is carried out this compress for the second time, to obtain this compressing image.

9. the bit rate control circuit of image compression according to claim 1 is characterized in that it also comprises another compression unit, is used for according to the linear quantization parameter LQF of this target _TargetCarrying out this compresses for the second time.

10. the bit rate control circuit of image compression according to claim 1 is characterized in that wherein said image is a static image.

11. the bit rate control method of an image compression is characterized in that it may further comprise the steps:

According to a default quantization table and a default equal interval quantizing parameter one image is done quantification treatment, this image is carried out a for the first time compression;

Compress for the first time by this, obtain an initial pixel bit and count bpp _IniAn and initial zero coefficient number R _Ini

Count bpp according to this initial pixel bit _IniA desired object pixel bit is counted bpp _TargetEstimate a target zero coefficient number R _Target

According to this target zero coefficient number R _TargetEstimate the linear quantization parameter LQF of a target _TargetAnd

According to the linear quantization parameter LQF of this target _TargetThis image is carried out a for the second time compression, to obtain a compressing image that should object pixel bit number;

Wherein estimate this target zero coefficient number R _TargetStep include: count bpp according to this initial pixel bit _IniWith this initial zero coefficient number R _IniA coordinate points and the linear relationship between the common initial point, count bpp with this object pixel bit _TargetEstimate desired this target zero coefficient number R _Target

12. the bit rate control method of image compression according to claim 11 is characterized in that the pixel bit number of wherein said common initial point and the coordinate of zero coefficient number are zero and overall coefficient number T.

13. the bit rate control method of image compression according to claim 11 is characterized in that wherein estimating the linear quantization parameter LQF of this target _TargetStep include: according to the numerical relation of zero coefficient number R value after quantizing with respect to equal interval quantizing parameter L QF, to obtain should target zero coefficient number R _TargetThe linear quantization parameter LQF of this target _Target

14. the bit rate control method of image compression according to claim 13, it is characterized in that zero coefficient number R value after the wherein said quantification is included in respect to this numerical relation of described equal interval quantizing parameter L QF carries out adding up simultaneously one group of zero coefficient number R of corresponding a plurality of equal interval quantizing parameter L QF values during this compresses for the first time _Set, calculate should target zero coefficient number R to be provided in this step of carrying out equal interval quantizing parameter L QF value estimation by linear interpolation _TargetThe linear quantization parameter LQF of this target _Target

15. the bit rate control method of image compression according to claim 14 is characterized in that wherein said a plurality of equal interval quantizing parameter L QF value is with default equal interval quantizing parameter L QF _IniThe value of a plurality of multiples.

16. the bit rate control method of image compression according to claim 14 is characterized in that wherein said a plurality of equal interval quantizing parameter L QF value comprises described default equal interval quantizing parameter L QF _Ini/ 4, described default equal interval quantizing parameter L QF _Ini/ 2, described default equal interval quantizing parameter L QF _Ini/ 1, described default equal interval quantizing parameter L QF _Ini* 2, described default equal interval quantizing parameter L QF _Ini* 4.

17. the bit rate control method of image compression according to claim 13 is characterized in that zero coefficient number R value is to add up in advance a relation curve that obtains with respect to this numerical relation of described equal interval quantizing parameter L QF value after the wherein said quantification.

18. the bit rate control method of image compression according to claim 11 is characterized in that wherein said image is a static image.

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