JP2931328B2 - Image signal compression coding device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image signal compression encoding apparatus, and more particularly, to an image signal compression encoding apparatus that keeps a data amount of a compression-encoded image constant.

BACKGROUND ART When digital image data such as image data captured by an electronic still camera is stored in a memory,
In order to reduce the amount of data and the storage capacity of the memory, various types of compression encoding are performed. In particular, two-dimensional orthogonal transform coding is widely used because it can perform coding at a large compression rate and can suppress image distortion due to coding.

In such two-dimensional orthogonal transform coding, image data is divided into a predetermined number of blocks, and image data in each block is subjected to two-dimensional orthogonal transform. The orthogonally transformed image data, that is, the transform coefficient, is compared with a predetermined threshold, and a portion below the threshold is truncated (coefficient truncation).
Is performed. Next, quantization with a predetermined step width, that is, normalization is performed. This gives the value of the conversion factor,
That is, the dynamic range of the amplitude is suppressed.

The comparison with the threshold value and the normalization process are often performed simultaneously. That is, when the conversion coefficient is normalized by a predetermined normalization coefficient and the result is converted into an integer, the conversion coefficient having a value lower than the normalization coefficient becomes zero.

The normalized transform coefficients are then Huffman encoded and stored on a recording medium such as a memory card.

In such two-dimensional orthogonal transform coding, so-called fixed-length coding is performed so that the output of Huffman-coded AC component coded data is limited to stop at a predetermined data length. This fixed length is desirably performed with an optimal data amount according to the required image quality, the capacity of the recording medium, and the like.

However, in the conventional device, the fixed length data amount is set uniformly by a specific method, and the fixed length is thereby performed. Therefore, it is not possible to perform an appropriate fixed length. This sometimes caused the output buffer to overflow.

Aims of the present invention are to solve such a problem of the prior art and to provide an image signal compression encoding apparatus capable of appropriately performing fixed length of encoded data.

DISCLOSURE OF THE INVENTION According to the present invention, an image signal compression encoding apparatus that divides digital image data forming one screen into a plurality of blocks and performs two-dimensional orthogonal transform encoding on the image data of each block includes a plurality of blocks. Orthogonal transformation means for two-dimensional orthogonal transformation of digital image data divided into blocks, encoding means for encoding data orthogonally transformed by the orthogonal transformation means, and encoded data for each block output from the encoding means Encoding output control means for limiting the amount; and a normalization coefficient setting means for setting a normalization coefficient used in the encoding means, wherein the encoding output control means outputs the normalization coefficient from the normalization coefficient setting means. When input, the amount of encoded data is limited by a predetermined value, and when no normalization coefficient is input from the normalization coefficient setting means, The amount of encoded data is limited based on the activity of image data for each divided block.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a detailed description will be given of an embodiment of an image signal compression encoding apparatus according to the present invention with reference to the accompanying drawings.

FIG. 1 shows an embodiment of an image signal compression encoding apparatus according to the present invention.

This device has a memory controller 10. The memory controller 10 is connected to a memory 60, and reads out still image data for one frame captured by, for example, an electronic still camera from the memory 60. The output from the memory controller 10 is input to the blocking unit 12. Blocking unit 12
Is constituted by a frame buffer, image data input from the memory controller 10 and stored in the blocking unit 12 is divided into a plurality of blocks, read out for each block, and sent to the two-dimensional orthogonal transform unit 14. The two-dimensional orthogonal transform unit 14 performs two-dimensional orthogonal transform on the image data of each block. As the two-dimensional orthogonal transform, a known orthogonal transform such as a discrete cosine transform or a Hadamard transform is used.

The image data for each block subjected to the two-dimensional orthogonal transformation in the two-dimensional orthogonal transformation unit 14 is arranged vertically and horizontally, similarly to the pixel data for each block shown in FIG. 3, and lower-order data is arranged in the upper left part. , The higher-order data becomes in the lower right direction. DC component data is arranged at the upper left. The output of the two-dimensional orthogonal transformation unit 14 is normalized by a predetermined quantization step value, that is, a normalization coefficient α in a normalization unit (not shown), and is sent to the AC encoding unit 32 of the encoding unit 28.

The AC encoding unit 32 also receives the normalization coefficient α from the α determination unit 16.
Is entered. The α determination unit 16 determines whether the normalization coefficient α input from the α setting unit 18 is 0, and
Is not 0, it is sent to the AC encoding unit 32 and the fixed bit length unit 36. The α setting unit 18 sets a normalization coefficient α. The normalization coefficient α is data used by the fixed-length-lengthening unit 36 to lengthen the output data from the AC encoding unit 32 to a fixed length. The setting of the normalization coefficient α is performed based on the amount of coded data output, by predicting an optimum value by a predetermined method such as Newton's method, and performing such that the amount of coded data output converges to a target value. Will be Therefore, the normalization coefficient α
Is corrected by determining whether or not the amount of encoded data is close to a fixed length target value, as described later. The initial value of the normalization coefficient α may be a constant value, or an approximate value may be set each time.

The AC encoding unit 32 further receives the normalization coefficient α from the α calculation unit 44. α calculating unit 44 is a total activity calculating unit
A normalization coefficient α is set based on the total activity calculated in 26.

The image data for each block output from the blocking unit 12 is also sent to the block activity calculation unit 20. The block activity calculation unit 20 calculates the activity of each block, that is, the degree to which the block contains image data of high frequency components. The activity of a block is obtained by adding the absolute value of the difference between each pixel data constituting the block and the average value of these pixel data.

The activity for each block output from the block activity calculation unit 20 is the total activity calculation unit.
26 and output to the bit allocation calculation unit 40.

The total activity calculation unit 26 adds the activity for each block sent from the block activity calculation unit 20, and calculates the total value of the activities. The total activity calculator 26 outputs the total value of the activities to the bit allocation calculator 40.

The AC encoding unit 32 converts the AC component of the transform coefficient, which is scanned and input in a zigzag manner as shown in FIG.
Normalization is performed using the normalization coefficient α sent from 44, and encoding is performed. Since the AC component of the conversion coefficient is often continuous with zeros, a continuous amount of data of zero value, that is, a zero run length is detected, and a zero run length and a non-zero amplitude are obtained.
Performs dimensional Huffman coding. The output from the AC encoding unit 32 is sent to the fixed-length unit 36.

On the other hand, the DC component of the image data for each block output from the blocking unit 12 is sent to the DC coding unit 30 of the coding unit 28, and is subjected to Huffman coding in the DC coding unit 30. The DC encoded data output from the DC encoding unit 30 is sent to the output buffer 38.

The bit allocation calculation unit 40 calculates the coded bits allocated to each block using the activity value for each block transmitted from the block activity calculation unit 20 and the total value of the activities transmitted from the total activity calculation unit 26. The coded bits allocated to each block are two-dimensional Huffman coded for each block, and determine how far the data output from the low-frequency component should be cut off, that is, how many bits of the coded data are output. This is the specified number of bits. The coded bits allocated by the bit allocation calculation unit 40 are used for fixed length in the fixed length unit 36 when the normalization coefficient α is not input from the α determination unit 16.

The coded bit bit B1 allocated to each block is given by, for example, the following equation.

bit B1 = {(act b / act t) × bit [flag]} + {Carry Over} (1) In the above equation, bit [flag] represents the total number of bits of the entire image of the AC code. This is the number of bits assigned to the entire image of the AC code composed of a plurality of blocks. That is, when two-dimensional Huffman-encoded data for each block is output in order from the low-frequency component,
This is the number of bits indicating how many bits are to be assigned to the AC code for the entire image when data output is terminated at a predetermined number of bits. The amount of data that is compression-encoded and output is determined by the number of bits.

act b is an activity for each block. act
t represents the total activity, and is the total value of the activities of the block. Therefore, ｛(act b / act
t) × bit [flag]} allocates the number of bits allocated to the entire AC code according to the ratio of the activity of each block to the total value of the activity of the block.

{Carry Over} represents carry-over bits from the previous block, and as will be described later, coded bit bits to be distributed.
This is the number of bits carried over from the block immediately before the block for which B1 is to be obtained, that is, the number of unused bits that have been allocated to the previous block. The bit allocation may be performed without considering the carry-over bit {Carry Over}.

The coded bits bit B1 allocated to each block and output from the bit allocation calculation unit 40 are sent to the fixed length unit 36.

If the normalization coefficient α is input, the fixed length
There is no fixed length based on activity in 36. However, the bit allocation (Bit B) of each block is fixed to the maximum value so that the output buffer 38 does not overflow. Therefore, the AC coded data is output to the output buffer 38 within a range not exceeding the maximum value.

The AC coded data for each block, the number of bits of which is limited by the fixed length unit 36, is input to the output buffer 38. The output buffer 38 stores DC encoded data having a fixed code length and AC encoded data having a limited number of bits, and these data are sent to the gate 42. Gate 42
Temporarily accumulates the data sent from the output buffer 38,
These data are transmitted to the memory card 50 through the connector 44 according to the gate enable signal from the control unit 22. Thus, data is recorded on the memory card 50.

Note that a recording medium such as a magnetic disk or an optical disk may be used as the recording medium in addition to the memory card 50.

The data output from the output buffer 38 is also sent to the code counter 24. The code counter 24 counts the code amount of the data sent from the output buffer 38. The output of the code counter 24 is sent to the control unit 22.

The control unit 22 is a control unit that controls the operation of each unit of the apparatus through a signal line (not shown). The α setting unit 18 calculates the normalization coefficient α by a predetermined method as described above. The control unit 22 requests the α setting unit 18 to create a normalization coefficient α. The control unit 22 also controls the fixed length lengthening unit 36 according to the determination from the α determination unit 16.

 The operation of the present apparatus will be described with reference to the flow chart of FIG.

First, the DC code amount, that is, the number of bits allocated to DC encoded data is calculated (100).

The normalization coefficient α is input from the α setting unit 18 to the control unit 22,
The control unit 22 transfers the normalization coefficient α to the α determination unit 16 of the encoder 28 (102). The α determination unit 16 determines whether the normalization coefficient α input from the α setting unit 18 is 0 (10
Four). When the normalization coefficient α is 0, that is, the α setting unit 1
If the normalization coefficient α has not been sent from 8, the DC component is encoded by the DC encoding unit 30 (130). Next, a block bit allocation is created by the bit allocation calculation unit 40 of the encoder 28 (132). The α calculating unit 44 creates a normalization coefficient α according to the data from the total activity calculating unit, and thereby the AC component is encoded by the AC encoding unit 32 (134). The coded AC component data is sent to the fixed length
Then, the length is fixed by the block bit allocation from the bit allocation calculation unit 40 (136). It is determined whether encoding has been completed for all blocks (138), and if not completed, the process returns to step. This process ends when encoding is completed for all blocks.

If it is determined in step 104 that the normalization coefficient α input from the α setting unit 18 is not 0, that is, if the normalization coefficient α is sent from the α setting unit 18, Normalization is performed using the normalized coefficient α.
In this case, the DC component of the block sent from the blocking unit 12 to the DC encoding unit 30 is encoded (step 11).
0), sent to the output buffer 38. Next, the AC component of the transform coefficient is sent from the two-dimensional orthogonal transform unit 14 to the AC encoding unit 32, where encoding is performed.
Encoding is performed using the normalization coefficient α sent to the encoding unit 32. At this time, the bit allocation value in the fixed length lengthening unit 36 is fixed to a predetermined constant value regardless of the value of the activity (step 112). The fixed length data is accumulated in the output buffer 38, and the data amount is counted by the code counter 24.

It is determined whether or not the coding of the DC component and the coding of the AC component have been completed for all blocks (step 114). If not completed, the process returns to step 110, and the coding of the DC component and the coding of the AC component have been completed. Repeat the encoding. When the coding of the DC component and the coding of the AC component are completed for all the blocks, the data amount counted by the code counter 24 is calculated by the control unit.
The control unit 22 determines whether or not the code amount is sufficiently close to the target value of the fixed length (step 11).
8). As the target value, a predetermined number of bits is set in advance as a code amount to be assigned to the data of one encoded image.

If the code amount exceeds the target value or is not close to the target value, the α setting unit 18 newly adds a normalization coefficient α
Is calculated (step 120). After that, returning to step 102, the normalization coefficient α is input again from the α setting unit 18, and α
The data is transferred to the determination unit 16 (102).

If the code amount from the code counter 24 does not exceed the target value and is sufficiently close to the target value, the control unit 22 sends a gate enable signal to the gate 42 (122), and the code stored in the output buffer 38. The converted data is sent to the memory card 50 through the connector 44 (124). As a result, the encoded data is recorded on the memory card 50.

According to the present embodiment, it is determined whether or not the normalization coefficient α has been input to the encoder 28 from the α setting unit 18, and if it has been input, the encoded data amount is limited thereby,
It is determined that the obtained code amount is close to the target value and output from the gate. If the obtained code amount exceeds the target value or is not close to the target value,
More suitable α is set in the α setting unit 18 and the α determination unit
Sent to 16. Therefore, since the optimum normalization coefficient α is obtained and the fixed length can be obtained by using the optimum normalization coefficient α, appropriate compression can be performed according to the required image quality, the capacity of the memory card 50, and the like.

Since the normalization coefficient α set as the optimum value is set outside the encoder 28, it can be used for compression encoding of other image data.

Further, even when the normalization coefficient α is input from the α setting unit 18, since the fixed length is performed by the coded bit bit B1 calculated in the bit distribution calculating unit 40 inside the encoder, the output buffer 38 never overflows.

In the above embodiment, the encoded data output from the fixed-length section 36 is stored in the output buffer 38, and is output to the gate 42 by the gate enable signal from the control section 22. Output buffer in the converter 28
An output buffer may be provided at the gate 42 without providing the 38. In this case, the code amount of the coded data counted by the code counter 24 is determined by the control unit 22, and if it is close to the target value, each block is coded using the normalization coefficient α at that time. , The encoded data may be output to the output buffer.

Effects According to the present invention, the compression encoding apparatus sets a normalization coefficient α outside the encoder, and performs a fixed length using the normalization coefficient α. Since the normalization coefficient α is set outside the encoder, the normalization coefficient α can be used for compressing a plurality of image data. Moreover, since the upper limit of the encoded and output data is determined, the output buffer does not overflow.

Further, even when the normalization coefficient α is not supplied from outside the encoder, the fixed length can be made based on the activity of the block.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an image signal compression encoding apparatus according to the present invention, FIG. 2 is a flowchart showing the operation of the apparatus shown in FIG. 1, and FIG. FIG. 4 is a diagram showing an example, and FIG. 4 is a diagram showing the order of encoding AC components of transform coefficients. Description of Signs of Main Parts 14 Two-Dimensional Orthogonal Transformation Unit 16 α Determination Unit 18 α Setting Unit 20 Block Activity Calculation Unit 24 Code Counter 26 Total Activity Calculation Unit 28 Coding Unit 30 DC encoding unit 32 AC encoding unit 36 Fixed length unit 38 Output buffer 40 Bit allocation calculation unit 42 Gate 44 α calculation unit 50 Memory card

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kenji Moronaga 2-26-30 Nishiazabu, Minato-ku, Tokyo Fuji Photo Film Co., Ltd. (56) References JP-A-2-159185 (JP, A) JP JP-A-2-124690 (JP, A) JP-A-2-183668 (JP, A) JP-A-2-222386 (JP, A)

Claims (1)

(57) [Claims] 1. An image signal compression coding apparatus for dividing digital image data constituting one screen into a plurality of blocks and performing two-dimensional orthogonal transform coding on the image data of each block. And outputting a first normalization coefficient, and when a normalization coefficient creation request signal is received after the output of the first normalization coefficient, sets a second normalization coefficient based on the received request signal. A first normalization coefficient setting means for outputting the first normalization coefficient; and determining whether or not the first normalization coefficient from the first normalization coefficient setting means has been input. Outputs the input first normalization coefficient to
When it is determined that no input is made, the first normalization coefficient is not output, and when the second normalization coefficient is input from the first normalization coefficient setting means, the input second normalization coefficient is output. Normalizing coefficient determining means for outputting a normalizing coefficient of the following; orthogonal transforming means for performing a two-dimensional orthogonal transform on the digital image data divided into the plurality of blocks; The data orthogonally transformed by the transforming means is normalized and coded by the received third normalizing coefficient, and when the normalizing coefficient determining means outputs the first or second normalizing coefficient, Encoding means for normalizing and encoding the data orthogonally transformed by the orthogonal transformation means with the output first or second normalization coefficient; and a block for calculating an activity of image data for each of the divided blocks. Activity calculating means; coded data amount allocating means for calculating the coded data amount allocated to each block based on the activity for each block calculated by the block activity calculating means; The activity of each block is added to calculate a total value of the activities of the one screen, and the calculation used by the encoding means when the first normalization coefficient is not output from the normalization coefficient determination means. A second normalization coefficient setting means for setting and outputting the third normalization coefficient based on the obtained total value; and a case where the first or second normalization coefficient is output from the normalization coefficient determination means. The encoded data for each block output from the encoding means according to a predetermined value. If the first normalization coefficient is not output from the normalization coefficient determination means, the data is output from the coding means in accordance with the output from the coded data amount distribution means. Encoding output control means for limiting the amount of encoded data for each block; and encoding data for each block from the encoding means for which the amount of encoded data has been limited by the encoded output control means. Storage means for storing; code count means for counting the code amount of encoded data for each block from the storage means; receiving the data amount for each block counted by the code count means, and controlling the respective means. The normalization coefficient determining means determines that the first normalization coefficient has been input from the first normalization coefficient setting means. The input first normalization coefficient is sent to the encoding means and the encoding output control means, and the encoding means normalizes and encodes the received first normalization coefficient and encodes the encoded data. The encoded output control means sends the encoded output control means to the storage means by limiting the amount of encoded data for each block from the encoding means by a predetermined value, and sends the data to the storage means. Stores the transmitted coded data for each block, sends the stored coded data for each block to the code counting means, and the code counting means transmits the code of the transmitted coded data for each block. Counting the amount of data and sending the counted amount of data to the control means. The normalization coefficient generation request signal for performing a predetermined correction so that the code amount count value approaches the target value is determined if it is not sufficiently close to the target value. And transmitting the image data to the first normalization coefficient setting means.