JP2552382B2 - Image signal compression coding device - Google Patents

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 temporarily stores image data forming one screen in a recording medium and then performs compression encoding. .

BACKGROUND ART When digital image data such as image data taken by a digital electronic still camera is stored in a memory, compression encoding by various methods is performed in order to reduce the data amount and the memory storage capacity. It is being appreciated. 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 a two-dimensional orthogonal transform coding, image data forming one screen is divided into a predetermined number of blocks on the screen, and the image data in each block of the divided screen is two-dimensional orthogonal. To be converted. The orthogonally transformed image data, that is, the transform coefficient, is compared with a predetermined threshold value, and the portion below the threshold value is truncated (coefficient truncation). As a result, the conversion factor below the threshold is
It is processed as 0 data. Next, the transform coefficient subjected to coefficient truncation is divided by a predetermined quantization step value, that is, a normalization coefficient, and quantization by a step width, that is, normalization is performed. This gives the value of the conversion factor,
That is, the dynamic range of the amplitude can be suppressed.

In such a two-dimensional orthogonal transform coding, when the above-mentioned normalization coefficient is normalized with a constant value and coded, the amount of coded data differs depending on the image data, and the data is recorded in the memory. It was inconvenient.

That is, when the data is normalized by using a certain normalization coefficient and coded, the amount of coded data in the image data including many high frequency (AC) components is large, and the low frequency (DC) is large.
The image data including many components has a small amount of encoded data. The difference in the amount of encoded data is 5 to
Since it can reach up to 10 times, it is inconvenient when recording in a fixed capacity memory.

Therefore, for example, one screen is divided into a plurality of blocks, the degree of inclusion of high-frequency components in the divided block-unit image data, so-called activity, is calculated, and the normalization coefficient is set for each block based on this. That is, the number of bits per pixel is set (bit allocation).

However, for example, when an image is recorded by a digital electronic still camera equipped with such an image signal compression encoding device, a main subject (for example, a person) is displayed on the screen.
If there is a high activity area around (background), the bit allocation at the time of image data compression is set to be high in that area. Therefore, the bit distribution in the area of the main subject located in the central portion of the screen becomes relatively low, and there is a problem that the image quality is deteriorated due to the compression processing of the image data.

The present invention has been made in view of such circumstances, and when the image data forming one screen is once stored in the memory and then compression-encoded, bit allocation is performed according to the area on the screen. An object is to provide an image signal compression encoding device that can be set.

DISCLOSURE OF THE INVENTION According to the present invention, digital image data constituting one screen is divided into a plurality of blocks on the screen, each block is subjected to two-dimensional orthogonal transformation, and the orthogonally transformed image data is given. An image signal compression encoding device for normalizing based on the normalization coefficient and encoding the normalized image data includes a first storage means for storing digital image data and a first storage means. Image reproducing means for displaying the read digital image data on the display screen, and area designating means for designating an area on the screen where the bit allocation should be increased during the image data compression processing among the images displayed on the display screen. And a block activity calculation means for calculating the activity for each block,
A total activity calculating means for calculating the total value of the block activities for one screen output from the block activity calculating means, and a first number for calculating the number of bits distributed to each area including the area designated by the area designating means.
Bit allocation calculation means, the number of bits calculated by the first bit allocation calculation means and distributed to each area, the activity for each block belonging to each area calculated by the block activity calculation means, and the total activity calculation means. Second bit allocation calculating means for calculating the number of bits allocated to each block belonging to each area based on the total value of the activity of each block unit, and the first bit allocation calculating means is the area designating means. The area designated by is weighted and calculated so that the bit allocation is higher than other areas.

Description of Embodiments Embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1A and 1B show the configuration of an embodiment of an image signal compression encoding apparatus according to the present invention.

This device has a blocking unit 12. The blocking unit 12 is composed of a frame buffer, and still image data for one frame captured by an electronic still camera is input through the input terminal 10 and stored. Blocking unit 12
The image data for one frame stored in is divided into a plurality of blocks, read in block units, and sent to the two-dimensional orthogonal transformation unit 14. The two-dimensional orthogonal transformation unit 14 performs two-dimensional orthogonal transformation on the image data input in block units. Well-known techniques such as discrete cosine transform and Hadamard transform are used as the two-dimensional orthogonal transform.

The image data in block units, which has been two-dimensionally orthogonally transformed by the two-dimensional orthogonal transformation unit 14, is arranged vertically and horizontally, low-order data is arranged in the upper left portion, and becomes higher-order data in the lower right direction. The output of the two-dimensional orthogonal transformation unit 14 is sent to the normalization unit 16.

The normalization unit 16 performs the normalization after performing the coefficient truncation on the image data that has been two-dimensionally orthogonally transformed by the two-dimensional orthogonal transformation unit 14 based on the setting output of the normalization coefficient setting unit 22, that is, the transformation coefficient. To do. The coefficient truncation is to compare the orthogonally transformed transform coefficient with a predetermined threshold value and to cut off a portion below the threshold value. The normalization is a product of a predetermined quantization step value, that is, the normalization coefficient α obtained from the quantization table 54 and the weighting coefficient T set by the parameter setting unit 52, for the conversion coefficient for which the coefficient rounding is performed. αT
Quantization is performed by dividing by. Normalization coefficient α
Is set by the normalization coefficient setting unit 26 on the basis of a value obtained by summing the activities in block units calculated by the total activity calculating unit 24, as will be described later.

The image data in block units 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 on a block-by-block basis, that is, the degree to which high-frequency component image data is included in the block.

The calculation of the activity B-act (i, j) in block units is performed by dividing the divided blocks into, for example, 8 blocks as shown in FIG.
If it consists of × 8 pixels, the pixel data is
Then (where i, j = 0 ... 7), the expression Is calculated by here, Is.

That is, according to this equation, 8 × 8 that form a block
The average value DC (i, j) of the pixel data is calculated, the absolute value of the difference between each pixel data and the average value DC (i, j) is added, and the activity B-act (i, j) in block units is calculated. Ask for.

If you use the above formula to find the activity,
Since (i, j) is obtained by adding each pixel data and dividing the added data by 64 which is the number of pixels of the block, it can be configured only by an adder and a shifter for shifting data. Also, B-act (i, j) is the obtained DC
It is calculated by the absolute value conversion circuit and the adder using (i, j). Therefore, a multiplier and a divider are not required in the calculation of activity B-act (i, j).

As described above, the block activity calculation unit 20
Calculates the activity B-act (i, j) in block units and outputs it to the total activity calculation unit 24. The total activity calculation unit 24 sends the activity B-act (i, j) in block units sent from the block activity calculation unit 20.
Is added to calculate the total value T-act of the activities. The total activity calculation unit 24 outputs the total value T-act of activities to the normalization coefficient setting unit 26, the bit factor calculation unit 44, and the bit allocation calculation unit 46.

The normalization coefficient setting unit 26 refers to the quantization table 54 based on T-act, which is the total value of the activity B-act (i, j) in block units, which is calculated by the total activity calculation unit 24 for the normalization coefficient α. And set.

The normalization coefficient α is weighted by the weighting coefficient T set by the parameter setting unit 52 and output to the normalization unit 16.

The image data normalized by the normalization unit 16 is two-dimensionally Huffman coded by the two-dimensional Huffman coding unit 18 and output to the AC code amount counting unit 50 and the multiplexer 64.

The parameter setting unit 52 selects the image quality mode (compression ratio of image data) according to the application, outputs the weighting coefficient T necessary for setting the normalization coefficient α to the normalization coefficient setting unit 26, and also the image quality and the image. A parameter for specifying the number of recorded sheets is output to the bit factor calculation unit 44.

The quantization table 54 stores the activity of the entire screen, that is, the total value T-act of the activity in block units.
2 is a table showing the relationship between the normalization coefficient α and

On the other hand, the DC quantization unit 28 calculates a difference value between blocks for the low frequency (DC) component of the block-by-block image data output from the blocking unit 12. Huffman encoder 40
Performs Huffman coding on the difference value output from the DC quantizer 28. The DC code amount counting unit 42 counts the code amount output from the Huffman encoding unit 40 and outputs the total number to the bit factor calculation unit 44.

The reproduction processing circuit 70 reproduces the image data read from the blocking unit 12 into a video signal of a predetermined format, and outputs the video signal to the monitor device 72.

The monitor device 72 receives the video signal output from the reproduction processing circuit 70, and displays an image on the display screen, for example, an image represented by the image data captured by the digital electronic still camera and temporarily stored in the blocking unit 12. .

As shown in FIG. 3, of the image 92 displayed on the display screen 90 of the monitor device 72, the area designating unit 74 designates the area 94 on the screen where the bit distribution should be increased during the image data compression processing. Done.

A mouse, for example, is used as the area designating unit 74.

Further, as shown in FIG. 3, the area designating unit 70 designates an area 94 (inside a dotted frame 95) on the display screen 90 of the monitor device 72 where the bit distribution should be increased during the image data compression processing. In this case, the area 94 is specified by specifying the coordinate data indicating the center position O of the frame 95 displayed on the monitor device 72 on the screen 90 with a mouse or the like. For example, as shown in Fig. 4, the horizontal and vertical sides of the frame 95 are 2
If p, 2q, the center position O of the frame 95 is the origin (0,
0), the coordinates of the vertices A, B, C, D of the frame 95 are
A (p, q), B (-p, q), C (-p, -q), D (p, -q).

When the coordinate data O (x, y) of the center position O of the frame 95 is designated by the area designating unit 74, the position information is obtained by the area computing unit
Entered in 6.

In the area calculation unit 76, along with the designation of the center position O (x, y) of the frame 95, the coordinates A (p + x) of the vertices A, B, C, D after the frame 95 is moved on the display screen 90 of the monitor device 72. , q + y), B (-p
+ X, q + y), C (-p + x, -q + y), D (p + x, -q +
y) and the number of blocks A-b1k (n) included in the area 94 defined by these vertices A, B, C and D and the area other than this designated area. The movement of the frame 95, that is, the designation of the area 94 is allowed within the range in which the calculated coordinate data of each vertex is included in the display screen 90.

Note that n is a number given to each area when the screen 90 is divided into a plurality of areas.

The calculation output of the area calculation unit 76 is input to the area storage unit 78 and the area bit allocation calculation unit 82.

The area storage unit 78 stores the position information for specifying the area 94, which is the calculation output of the area calculation unit 76.

The position information read from the area storage unit 78 is input to the image quality weighting count setting unit 80.

The image quality weighting factor setting unit 80 sets the image quality weighting factor W (n) for the region 94 on the screen 90 designated by the area designating unit 74 and each region other than this region. Here, the total value of the image quality weighting factors W (n) is set to be 1, for example.

The image quality weighting coefficient setting unit 80 outputs the image quality weighting coefficient W (n) to the area bit allocation calculation unit 82.

The area bit allocation calculation unit 82 receives the number of blocks A-b1k from the area calculation unit 76 and the image quality weighting coefficient setting unit 80, respectively.
(N) and the image quality weighting coefficient W (n) are taken in and the following equation (1)
The number of bits A-bit (n) distributed to each area is calculated by.

A-bit (n) = A-b1k (n) .W (n) .T-bit / T-b1k ...
(1) In the above equation (1), T-bit is the target number of bits assigned to one screen, and T-b1k is the number of blocks included in one screen.

The number of bits A-bit (n) obtained by the area bit allocation calculating unit 82 is input to the bit factor calculating unit 44.

In the bit factor calculation unit 44, the number of bits S (i,
A bit factor f (n) that is a coefficient for calculating j) is calculated.

f (n) = A-bit (n) / T-bit = W (n) · A-b1k (n) / T
-B1k (2) The bit factor f (n) calculated by the bit factor calculation unit 44 is input to the bit allocation calculation unit 46. The bit allocation calculation unit 46 includes a block activity calculation unit 20,
The activity B-act (i, j) of each block, which is the output from the total activity calculating unit 24, and the activity T-act of the entire screen are also input.

The bit allocation calculation unit 46 calculates the number of bits S (i, j) allocated to each block of one screen by the following equation.

S (i, j) = f (n) .T-bit.B-act (i, j) / T-act = A-bit (n) .B-act (i, j) / T-act ... ( 3) On the other hand, the AC code amount counting unit 50 counts the AC code amount output from the two-dimensional Huffman encoding unit 18, and outputs it to the encoding stop determination unit 48.

The encoding stop determination unit 48 compares the AC code amount output from the AC code amount counting unit 50 with the bit number S (i, j) output from the bit allocation calculation unit 46, and the AC code amount is the bit number S.
When it exceeds (i, j), the determination signal for stopping the coding of the block is output to the two-dimensional Huffman coding unit 18.

In the above configuration, it is assumed that the image data once stored in the blocking unit 12 is converted into a video signal of a predetermined format by the reproduction processing circuit 70 and input to the monitor device 72 to display a predetermined image. At this time, in the image 92 displayed on the display screen 90 of the monitor device 72, the coordinate data O (x, x, which indicates the center position O of the frame 95 for designating the region 94 in which the bit allocation should be increased during the image data compression process. y) is designated by the area designating unit 74.

Position information indicating the coordinate data O (x, y) is output from the area designating unit 74 to the area calculating unit 76. In the area calculation unit 76, the frame on the display screen 90 of the input monitor device 72 is input.
Area 94 designated based on position information of center position O of 95
Each vertex A of the frame 95 that specifies the position on the display screen 90 of
The coordinates of B, C, D and the number of blocks A-b1k (n) included in the area 94 defined by these vertices A, BC, D and the area other than this designated area are obtained.

The calculation output of the area calculation unit 76 is input to the area storage unit 78 and the area bit allocation calculation unit 82. Area storage
At 78, position information for specifying the area 94 on the display screen 90 of the monitor device 72 designated by the area designation section 74 is stored.

On the other hand, one frame of image data input from the input terminal 10 is input to the block unit 12 and stored therein. The image data for one frame stored in this block unit 12 is
It is divided into a plurality of blocks, read in block units, and sent to the two-dimensional orthogonal transformation unit 14. The two-dimensional orthogonal transformation unit 14 two-dimensionally orthogonally transforms the image data input from the block unit 12 in block units. The output signal of the two-dimensional orthogonal transformation unit 14 is input to the normalization unit 16.

The image data in block units output from the block unit 12 is sent to the block activity calculation unit 20, and the block activity calculation unit 20 calculates the activity B-act (i, j) in block units, and the total activity calculation unit Output to 24. The total activity calculation unit 24 adds the activity B-act (i, j) in block units sent from the block activity calculation unit 20 to calculate the total value T-act of the activities, and the calculated value T-act. It outputs to the normalization coefficient setting unit 26, the bit factor calculation unit 44, and the bit allocation calculation unit 46.

The normalization coefficient setting unit 26 refers to the quantization table 54 and sets the weighted normalization coefficient α · T in the normalization unit 16 based on the setting output of the parameter setting unit 52.

The image data normalized by the normalizer 16 is two-dimensionally Huffman-encoded by the two-dimensional Huffman encoder 18.

On the other hand, the screen 90 set by the image quality weighting factor setting unit 80
, The image quality weighting coefficient W (n) of each area, and the number of blocks A- included in each area of the screen 90 calculated by the area calculation unit 76.
The area bit allocation calculation unit 82 calculates the number of bits A-bit (n) allocated to each area based on b1k (n), and outputs it to the bit factor calculation unit 44.

The bit factor calculation unit 44 calculates the bit factor f (n) based on the number of bits A-bit (n) input from the area bit distribution calculation unit 82, and the bit distribution calculation unit
Output to 46.

The bit allocation calculation unit 46 receives the block-by-block activity B-act from the block activity calculation unit 20, the total activity calculation unit 24, and the bit factor calculation unit 44.
(I, j) The activity T-act of the entire screen and the bit factor f (n) are taken in, the number of bits S (i, j) distributed to each block of the single screen is calculated, and the coding stop determination unit Output to 48.

On the other hand, the difference value of the DC component between the blocks of the image data in block units output from the blocking unit 12 is the DC quantization unit.
The Huffman coding unit 40 Huffman-encodes the difference value obtained by the step 28. The image data output by the Huffman encoder 40 and the two-dimensional Huffman encoder 18
The image data output by the multiplexer 64 is selectively output by the multiplexer 64.

The encoding stop determination unit 48 compares the AC code amount output from the AC code amount counting unit 50 with the number of bits S (i, j) output from the bit allocation calculation unit 46, and determines that the AC code amount is the number of bits S.
When it exceeds (i, j), the determination signal for stopping the coding of the block is output to the two-dimensional Huffman coding unit 18.

One screen is, for example, as shown in FIG.
On the display screen 90 of the designated area 94 (area number n =
1) and its periphery are divided into four areas (area numbers n = 2 to 5) excluding the designated area 94, and bits are individually allocated to blocks belonging to these areas.

Effect As described above, according to the present invention, an area in which the bit distribution is increased in the captured image displayed on the display screen of the monitor device when the image data for one screen is once stored in the memory and then the image data is compressed. So that you can specify in advance,
In addition, the bit distribution is set to be high for the image data belonging to the designated area during the compression process.

Therefore, according to the present invention, when the main subject in the center of the screen is dark and there is an image of high activity in its periphery, and the main subject is compressed when the image data is compressed with the same normalization coefficient. Even if the image quality is relatively deteriorated, the image quality can be improved by changing the bit allocation.

[Brief description of drawings]

FIG. 1A and FIG. 1B are block diagrams showing a configuration of an embodiment of an image signal compression coding apparatus according to the present invention, and FIG. 2 is an explanatory diagram showing a configuration example of image data forming a block of a screen. FIG. 3 is an explanatory view showing a state where an image is displayed on the display screen of the monitor device, and FIG. 4 is for positioning the frame displayed when an area is designated on the display screen of the monitor device. FIG. 5 is an explanatory diagram of coordinate data necessary for the display, and FIG. 5 is an explanatory diagram showing a state in which the display screen is divided into a plurality of areas. Description of main part code 20 …… Block activity calculation unit 24 …… Total activity calculation unit 44 …… Bit factor calculation unit 46 …… Bit allocation calculation unit 70 …… Reproduction processing circuit 72 …… Monitor device 74 …… Area designation Area 76 …… Area calculation unit 78 …… Area storage unit 80 …… Image quality weighting coefficient setting unit 82 …… Area bit distribution calculation unit

Claims (1)

(57) [Claims] 1. Digital image data constituting one screen is divided into a plurality of blocks on the screen, two-dimensional orthogonal transformation is performed for each block, and the orthogonally transformed image data is given a normalized coefficient. In the image signal compression encoding apparatus for normalizing the image data according to the above, and encoding the normalized image data, the apparatus includes a first storage unit for storing the digital image data, and the first storage unit. An image reproducing means for displaying the digital image data read from the means on the display screen, and an area on the screen where the bit allocation should be increased during the image data compression processing among the images displayed on the display screen. Area designating means, block activity calculating means for calculating the activity for each block, and output from the block activity calculating means Total activity calculation means for calculating the total value of block activity for one screen, and first bit allocation calculation means for calculating the number of bits allocated to each area including the area designated by the area designating means, The number of bits calculated by the first bit allocation calculation means and distributed to each area, the activity for each block belonging to each area calculated by the block activity calculation means, and the activity in block units calculated by the total activity calculation means A second bit allocation calculating means for calculating the number of bits allocated to each block belonging to each area based on the total value of the first bit allocation calculating means specified by the area specifying means. Areas are weighted so that the bit allocation is higher than other areas. An image signal compression encoding device characterized by calculating.