JP3385652B2 - Digital image data quantizer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantization apparatus for adaptively quantizing each pixel data of a digital image signal. 2. Description of the Related Art It is known to compress or expand the data amount of a digital image signal by quantizing each pixel data of the digital image signal. For example, 8
By quantizing one bit of pixel data into pixel data of a smaller number of bits, the data amount can be compressed. More specifically, the ADRC proposed by the applicant of the present application
In (encoding adapted to dynamic range), image data is converted into a block structure, and each pixel data of the image data is quantized by a quantization step width adapted to the dynamic range of the block (Japanese Patent Laid-Open No. 61-1449).
No. 89). In conventional quantization, when original data is quantized to a smaller number of bits, adaptive quantization is performed so that data generated by quantization (referred to as quantized data) does not lose fidelity to the original data. It has been proposed to do so. For example, as one method of adaptive quantization, the applicant of the present invention has proposed a method of quantizing data with respect to a time variation of an original signal in addition to a quantization error as disclosed in Japanese Patent Application No. 4-343402. Has been proposed in consideration of the time variation of the image and the inclination with respect to the past surrounding pixels. This quantizer has a difference between a quantization error, a change in the original signal in the time direction and that of the quantized data, a change in the time direction between the original signal and a past spatially shifted pixel, and An error between the quantized data and that of the quantized data is obtained, and an evaluation value is obtained by multiplying each error by a weight coefficient. This evaluation value is obtained for each of a plurality of quantized data candidates, and the candidate with the smallest value is selected as the optimal quantized data. In the quantizers and other adaptive quantizers proposed above, when considering changes in the spatial direction and / or the temporal direction, for example, the upper side of the pixel to be quantized is considered. And the left pixel.
When the input image data is divided into blocks and adaptive quantization is performed, the upper left and left reference pixels and their quantized data do not exist for the pixel at the upper left corner of the block. Therefore, quantization has been performed assuming appropriate values as the values of the reference pixel and its quantized data. As an example, the value of the right pixel is temporarily used as the value of the left pixel, and the value of the lower pixel is temporarily used as the value of the upper pixel. [0007] Even when the next pixel is quantized, adaptive quantization is similarly performed with reference to the left and upper pixels and the respective quantized data. In this way, the influence of the quantization performed with reference to the first upper left corner quantization data also affects the second and subsequent quantizations. as a result,
The influence of the quantization of the first pixel has an influence on the quantization of the entire block. As a result, there is a problem that the output image tends to flow from the upper left to the lower right. Accordingly, an object of the present invention is to provide a digital image signal quantizing apparatus which solves the above-mentioned problems by preparing a plurality of reference start pixels in a block. According to a first aspect of the present invention, there is provided a quantization apparatus for quantizing each pixel data of digital image data, wherein the digital image data is converted into data having a block configuration including a plurality of pixels. Blocking means for conversion, and a pixel at a predetermined position connected to the blocking means
Starting from the data, all pixel data in the block are applied in order.
First and second adaptive quantization means for応量Ko of, first
And one selection means for selecting a quantization output of the second adaptive quantizing means, in respect quantized output of the first and second adaptive quantization unit, to select the quantized output of the hand a, Ri Do and control means for controlling the selection means, the first
And each of the second adaptive quantizer, block
Pixel data of the first quantization data candidate and the
Quantum obtained by shifting the 1 quantized data candidate upward by 1 bit
The quantized data candidate and the first quantized data candidate are
At least one of the bit-shifted quantized data candidates
It forms a deviation or the other of the second quantized data candidate live, first
And for each of the second quantized data candidates
The fidelity of digital image data to temporal changes
Generates a first evaluation value that becomes smaller as the value becomes higher, and spatially shifts.
The higher the fidelity of the position
And generates a second evaluation value of the first and second evaluation values.
An addition value is obtained, and among the first and second quantized data candidates,
Quantizes the quantized data candidates with the smaller added value
A first and a second adaptation.
The quantizing means includes a pixel for starting adaptive quantization in the block.
Position and the direction to select pixel data in the block are different.
And each of the first and second adaptive quantization means
In addition, the added value generated for all the pixels in the block
The total of the totaled first and second evaluation values is supplied to the control means.
Control means for controlling the first and second adaptive quantization means
Of the quantized outputs, the sum of the first and second evaluation values is better.
Ri person to select a small, Rukoto to control the selection means
And a digital image data quantizing device characterized by the following. There are provided at least two adaptive quantization circuits having different reference start pixels. In each adaptive quantization circuit, the fidelity to the original data is evaluated, and an evaluation value is formed for each pixel. This evaluation value is integrated over one block, and the output data with the smaller integrated value is selected. This can avoid the above-described problem that occurs when the start pixel is fixed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a quantization device according to the present invention will be described. To facilitate understanding of the present invention, an adaptive quantization device proposed by the present applicant will be described first. FIG. 1 schematically shows a system in which a quantizer is used. An input image 1 is subdivided into a number of blocks by a blocking circuit 2. In units of each block,
The encoder 3 performs an encoding process. The encoder 3 is, for example, the above-described ADRC encoder, and includes a quantization device 5 therein. The encoded output of the encoder 3 is supplied to the recording or communication system 4. The present invention relates to the quantization device 5. FIG. 2A shows conventional quantization. This quantization outputs quantized data that minimizes the quantization error of the following equation. Q = | (Yt−Xt) | (1) Here, Xt represents the input signal level at time t, and Yt is the level of the quantized output of Xt. As shown in FIG. 2A, when attention is paid to a level region having two quantization step widths, an input signal indicated by a white dot is included in the upper region at time t-1, and the code signal in the upper region is displayed. Occurs, and the value indicated by the central arrow is restored. At the next time t, since the input signal is included in the lower region, a code signal in the lower region is generated. Further, at time t + 1, since the input signal is included in the upper region, a code signal in the upper region is generated. Although the change in the level of the actual input signal is small, the level of the input signal changes near the boundary of the level range in the quantization characteristic. As shown in FIG. Although the level of the input signal is constant, the level may change due to noise, quantization error, or the like. Therefore, when such a problem occurs in a stationary portion such as a background, there is a problem that visual deterioration is conspicuous. FIG. 2B is a diagram for solving such a problem.
4 illustrates the quantization disclosed in the earlier application. FIG. 2A
A in the time direction of the input signal which varies with time
Find the slope of Further, the respective slopes of the changes B and C in the time direction of the quantized data are obtained. The change B is a change in the quantized data candidate obtained in the same manner as in the related art, and the change C
Is a change to a candidate that has been incremented by one from the quantized data at time t. Of the changes B and C, the change C is the change A
Therefore, the quantized data candidate causing the change C is selected as the normal quantized data at the time t. The evaluation value Q in the time direction is obtained by the following equation. Q = | (Yt-Yt-1)-(Xt-Xt-1) | (2) In the above evaluation of the change in the time direction, the change of the pixel at the same position between one frame is checked. ing. In addition to this, the change in the time direction at the spatially shifted position is also examined. As shown in FIG. 3, when attention is paid to the pixel X, the change in the time direction is examined using the pixel b above X and the pixel d to the left of X. That is, the evaluation value in this case is represented by the following equation. Q = | (Yt−b′t−1) − (Xt−bt−1) | (3) b′t−1 is quantized data of bt−1. Q = | (Yt-d't-1)-(Xt-dt-1) | (4) d't-1 is the quantized data of dt-1. The overall evaluation value Q is calculated by multiplying each of the above-described evaluation values including the same quantization error (Equation 1) by a weighting factor. Q = α | (Yt−Yt−1) − (Xt−Xt−1) | + β | (Yt−Xt) | + γ | (Yt−b′t−1) − (Xt−bt−1) | + γ | (Yt-d't-1) - (Xt-dt-1) | ··· (5) [0018] the quantized data Yt ⁰ to the evaluation value Q was similarly to the conventional quantization, 1 bit this The quantized data Yt ^H shifted to the larger direction and the quantized data Yt ^L shifted to the smaller one bit are calculated respectively, and the quantized data candidate with the smallest evaluation value is selected as the final output. . The above is the quantization algorithm of the quantization device proposed earlier. FIG. 4 shows the overall configuration of the quantization device. A digital video signal is supplied to an input terminal 11. In this video signal, each pixel data is 8-bit data. Current frame memory 1
2 and the previous frame memory 13 are connected in series, the current frame memory 12 outputs the pixel signal Xt of the current frame, and the previous frame memory 13 outputs the pixel signal Xt-1 of the previous frame at the same position. The pixel signal Xt is supplied to the quantization circuit 14. The quantization circuit 14 performs quantization as in the related art,
The median value Yt ⁰ , the upper data Yt ^{H obtained} by increasing the median value by +1 and the lower data Yt ^L obtained by deducting the median value by −1 are generated. Output signals of these quantization circuits 14 are used as evaluation value generation circuits 15, 1
6, 17 respectively. Also, the quantization circuit 14
, That is, quantized data candidates are supplied to the selector 18. The selector 18 is controlled by a control signal from a determination circuit 19, and outputs quantized data to an output terminal 20 thereof. This quantized data is supplied to the memory 21. From the memory 21, the quantized data Y of the previous frame
t-1 occurs. Quantized data Yt-1 of the previous frame
Is supplied to the evaluation value generation circuits 15, 16 and 17. The evaluation value generation circuit 15 outputs the upper data Yt ^H
An evaluation value Q ^H of will be generated in accordance with equation (5). ^{That, Q H = α | (Yt} H -Yt-1) - (Xt-Xt-1) | + β | (Yt H -Xt) | + γ | (Yt H -b't-1) - (Xt-bt -1) | + γ | (Yt H -d't-1) - (Xt-dt-1) | ··· (6) [0023] evaluation value generation circuit 16, the evaluation value Q of the median Yt ^{0 0} is generated according to equation 5. ^{That, Q 0 = α | (Yt} 0 -Yt-1) - (Xt-Xt-1) | + β | (Yt 0 -Xt) | + γ | (Yt 0 -b't-1) - (Xt-bt -1) | + γ | (Yt 0 -d't-1) - (Xt-dt-1) | ··· (7) [0024] evaluation value generation circuit 17, the lower data Yt ^L
An evaluation value Q ^L of will be generated in accordance with equation (5). ^{That, Q L = α | (Yt} L -Yt-1) - (Xt-Xt-1) | + β | (Yt L -Xt) | + γ | (Yt L -b't-1) - (Xt-bt -1) | + γ | (Yt L -d't-1) - (Xt-dt-1) | ··· (8) [0025] the evaluation value Q ^H, Q ⁰ and Q ^L is the determination circuit 19 , And the determination circuit 19 determines the minimum of these values, and the selector 18 selects a quantized data candidate corresponding to the determined evaluation value. The output terminal takes out the quantized data Yt. Next, an embodiment of the present invention will be described with reference to FIG. A digital image signal is supplied to an input terminal indicated by reference numeral 31, and the data in the raster scanning order is converted into, for example, a (4 × 4) block structure by a blocking circuit 32. FIG. 6 shows this block, x1
X16 is pixel data in the block. Adaptive quantizing circuits 33a, 33b, 33c and 33d are connected in parallel to the blocking circuit 32. Adaptive quantization circuits 33a, 33b, 33c, 33d
Performs adaptive quantization of 16 pixels in a block in order from different start pixels. In this example, the adaptive quantization circuit 33a
Uses x1 as a start pixel and quantizes pixel data in a block in the order shown by the arrow in FIG. The adaptive quantization circuit 33b quantizes the pixels in the block starting from x4. The adaptive quantization circuit 33c quantizes the pixels in the block with x13 as the start pixel, and the adaptive quantization circuit 33d quantizes the pixels in the block with x16 as the start pixel. Output signals of the adaptive quantization circuits 33a to 33d are supplied to a selection circuit 34,
One quantized output selected by the selection circuit 34 is generated at the output terminal 35. These adaptive quantization circuits 33a-33
As d, the one shown in FIG. 4 described above as an example can be used. Of course, the adaptive quantization circuit may have another configuration. In the adaptive quantization circuits 33a to 33d, as described above, the evaluation value Q is obtained, and the quantization output which is estimated to be the best is thereby selected. Each adaptive quantization circuit 3
In 3A～33d, evaluation value used to determine the quantized output of the pixels in the block (i.e., in the adaptive quantization circuit described above, the minimum value in the ^{Q H, Q 0, Q L} ) aggregate The signals are supplied to the circuits 36a to 36d, respectively. The tallying circuits 36a to 36d tally evaluation values for 16 pixels generated in one block, and generate a total thereof. Outputs of the tally circuits 36a to 36d are supplied to the determination circuit 37. The judgment circuit 37 includes totaling circuits 36a to 36d.
, Ie, the minimum value in the sum of the evaluation values is detected, and a selection signal for identifying the adaptive quantization circuit corresponding to the detected minimum value is generated. This selection signal controls the selection circuit 34. Therefore, the quantized data generated at the output terminal 35 is data when quantized in the order from the start pixel such that the total sum of the evaluation values is minimized. According to the present invention, when quantizing blocked image data, the one having the best order of quantization in a block can be selectively formed. By referring to the left and upper pixels, it is possible to prevent an output image from flowing from the upper left.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block diagram of a digital image signal transmission system to which the present invention can be applied. FIG. 2 is a schematic diagram for explaining a conventional quantization method and a previously proposed quantization method. FIG. 3 is a schematic diagram for explaining a spatial arrangement of pixel signals. FIG. 4 is a block diagram showing a configuration of a previously proposed quantization device. FIG. 5 is a block diagram of one embodiment of the present invention. FIG. 6 is a schematic diagram for explaining a block configuration. FIG. 7 is a schematic diagram illustrating the order of quantization. [Description of Signs] 32 Blocking circuits 33a to 33d Adaptive quantization circuit 34 Selection circuit 37 Judgment circuit

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N ^7/ 24-7/68 H04N 1/41-1/419 H03M ^7/ 30-7/50

Claims (1)

(57) [Claim 1] A quantization apparatus for quantizing each pixel data of digital image data, wherein the digital image data is converted into data having a block configuration composed of a plurality of pixels. Blocking means, connected to the blocking means, and pixel data at a predetermined position
Start with , apply all pixel data in the above block in order
First and second adaptive quantization means for quantizing said selection means for selecting a quantization output of one of the first and second adaptive quantization means, said first and second adaptive quantization Seki <br/> to the quantization output of the reduction means, so as to select the quantization output of the hand, Ri Do and control means for controlling said selection means, said first and second adaptive quantization Each of the means performs a first quantization on the pixel data in the block.
Data candidate and the first quantization data candidate
Bit-shifted quantized data candidate and the first quantum
Data obtained by shifting the quantized data candidate downward by 1 bit
Second quantized data of at least one of the candidates
Data candidates and generate the first and second quantized data candidates.
And changes in the time direction of the digital image data.
Generates a first evaluation value that decreases as the fidelity of the
The fidelity of spatially shifted positions to changes in the time direction
A second evaluation value, which becomes smaller as the value becomes higher, is generated.
And an added value of the second evaluation value and the added value of the first and second quantized data candidates.
Quantized data candidates for which the calculated value is smaller are output as quantized outputs.
And the first and second adaptive quantization means are configured to select the block
The position of the pixel where adaptive quantization starts in the block
The direction in which the pixel data is selected is made different, and each of the first and second adaptive quantization means
The sum generated for all pixels in the block
The sum of the first and second evaluation values obtained by summing up the values is determined by the above control.
Means, wherein said control means controls said first and second
Among the quantization outputs of the adaptive quantization means, the first and second
So that the sum of the evaluation values of 2 is smaller ,
An apparatus for quantizing digital image data, comprising controlling a selection means .