JP3344720B2 - Image data recording apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is designed such that, when still image data is compression-encoded and recorded on a recording medium, the code amount after compression-encoding is equal to or less than a predetermined target code amount. By recording after compression to
An image data recording apparatus and method for guaranteeing the number of images that can be recorded on a recording medium having a fixed storage capacity,
In particular, it is suitable for application to an electronic still camera.

[Conventional technology]

As a high-efficiency compression coding technology for natural images (still images), a method combining variable-length coding with orthogonal transform is considered to be effective, and this method will be adopted as an international standard for color natural image coding. (Journal of the Institute of Image Electronics Engineers of Japan: Vol.
18, No. 6, P398-P407).

In this type of coding method, the image quality of the decoded image and the output code amount after coding can be controlled by controlling certain parameters. The relationship between the code amount and the image quality is such that the larger the code amount, that is, the smaller the degree of compression, the smaller the deterioration of the image quality from the original image, and conversely, the smaller the code amount, that is, the larger the degree of compression, the more the original image The image quality is greatly degraded. However, in this type of coding method, since adaptive processing is performed using local correlation of images at the time of coding, highly efficient compression coding according to the image quality of the target image becomes possible. I have.

[Problems to be solved by the invention]

By the way, in general, images with fine patterns have a large code amount,
A flat image with many solids has a small code amount. For this reason, even if compression encoding is performed with the same code amount control parameter, the obtained code amount differs for each target image. Therefore, it is difficult to predict in advance the amount of code generated by compression coding in this type of coding method, so that the coding is performed so that a certain amount of code can be obtained for an arbitrary target image. It is not always easy to do. In particular, the application of natural image coding to date has been considered mainly for image transmission of still picture videophones and facsimile machines, storage in image databases, etc., so encoding is performed so that a fixed code amount can be obtained. It was not always required.

However, if this type of encoding method is applied to, for example, an electronic still camera, it is necessary to guarantee the number of images that can be recorded on a recording medium, and when recording image data after compression encoding on a recording medium, A technology for compressing and encoding a target image with a fixed code amount is required.

The present invention changes the code amount control parameter for each target image in order to guarantee the number of images that can be recorded when compressing and recording a plurality of still image data on a recording medium having a fixed storage capacity. It is another object of the present invention to provide an image data recording apparatus and method for compressing image data of each target image so as to be equal to or less than a predetermined target code amount and recording the compressed image data on a recording medium.

[Means for solving the problem]

According to the first aspect of the present invention, a means for extracting image data for one screen from continuously input image data and compressing and encoding the code data, and the code amount after the compression coding exceeds the target code amount for the first time. Until or below, by changing the code amount control parameter of the means for compression encoding,
Means for sequentially trial compression encoding a plurality of image data;
When the code amount of the trial compression encoding exceeds the target code amount for the first time, the code amount of the trial compression encoding is used for the first time by using the code amount control parameter in the code amount equal to or less than the target code amount immediately before. Means for compressing and encoding the image data next to the image data subjected to the trial compression encoding by using the code amount control parameter at the time when the number of the image data falls, and recording the encoded image data on a recording medium.

Further, in the invention according to claim 3, until the code amount after extracting and compressing and encoding one screen of image data from the continuously input image data, exceeds or falls below the target code amount for the first time. By changing the code amount control parameter for compression encoding, a plurality of image data are sequentially trial compression encoded, and when the trial compression encoded code amount exceeds the target code amount for the first time, Using a code amount control parameter at a code amount equal to or less than the target code amount,
When the amount of test compression-encoded code falls below the target code amount for the first time, the next image data of the test compression-encoded image data is compression-encoded using the code amount control parameter at that time, and the recording medium To record.

[Action]

According to the present invention, when the target image is compression-encoded and recorded on the recording medium, trial encoding is performed on the image immediately before the target image, and the resulting code amount and a predetermined amount per screen are obtained. A comparison is made between the target code amount and a code amount control parameter that allows the code amount of the target image after compression coding to be equal to or less than the target code amount from the comparison result. The actual compression encoding is performed, and the data after compression is recorded on a recording medium. In this way, the number of still images that can be recorded on the recording medium can be reliably guaranteed.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of an image data recording apparatus according to the present invention, and shows an example in which the present invention is applied to an electronic still camera.

In FIG. 1, input image data taken in from an image pickup unit (not shown) is stored in a line memory 1 for every eight lines, and is divided into a plurality of blocks of 8 × 8 pixels in a discrete cosine transform circuit 2. Supplied to Conversion circuit 2
Then, two-dimensional DCT (Discrete Cosine Transform)
form) and supplies it to the quantization circuit 3. The 8 × 8 DCT coefficients F _ij (i, j = 0, 1,..., 7) obtained by the conversion circuit 2 are 1
It represents a component obtained by decomposing the input image data for the block into spatial frequencies. Among the coefficients F _ij , the coefficient F ₀₀ represents a value (DC component) proportional to the average value of the input image data, and the variables i, j
Represents a component having a higher frequency (AC component).

The DCT coefficients F _ij thus obtained are linearly quantized by the quantization circuit 3 with a different quantization step width for each coefficient. The quantization step width corresponds to each threshold value of the quantization matrix composed of 8 × 8 threshold values supplied from the quantization matrix circuit 4,
It is defined by a value obtained by multiplying a coefficient 2 ⁿ (n = 0, ± 1, ± 2,...) By the multiplication circuit 5. In this case, the width n of the coefficient 2 ⁿ is called a scaling factor, and is supplied from the scaling factor control circuit 6. FIG. 2 shows an example of the quantization matrix.

Each coefficient of the DCT coefficient F _ij quantized by the quantization circuit 3 is
The zigzag scanning circuit 7 scans from a low-order coefficient to a high-order coefficient and converts it into one-dimensional data. The run length value of “0” and a valid value (a value other than “0”) are converted into two-dimensional data. Is converted. Next, the data is Huffman-coded by the Huffman coding circuit 8 and is recorded as variable-length coded data on a recording medium 9 such as an IC card. FIG. 3 shows an example of a zigzag scan table.

By the way, the code amount finally obtained from the Huffman coding circuit 8 as variable length coded data can be controlled by changing the scaling factor n. That is, by increasing the scaling factor n, the quantization step width can be increased, and the obtained code amount can be reduced. Conversely, by decreasing the scaling factor n, the quantization step width can be reduced, and the obtained code amount can be reduced. The code amount can be increased. This qualitative relationship is generally established irrespective of the target image, but the quantitative relationship between the scaling factor n and the amount of data after compression is not uniquely determined and differs for each target image. . Therefore, even if the target image is encoded with the same scaling factor n, the obtained code amount differs depending on the content of the image.

Therefore, in this embodiment, a code amount measuring circuit 10 is provided on the output side of the Huffman encoding circuit 8 to compress and encode the target image before recording it on the recording medium 9 with respect to another image immediately before the target image. The trial coding is performed, the resulting code amount is measured by the code amount measurement circuit 10, and the measurement result is supplied to the scaling factor control circuit 6. Control circuit 6
Then, the code amount measured by the code amount measurement circuit 10 is compared with a predetermined target code amount assigned to one screen, and the result of the comparison is such that the code amount after compression encoding becomes equal to or smaller than the target code amount. Find the factor n. Then, actual compression encoding of the target image is performed using the obtained scaling factor n, and the compressed data is stored in the recording medium 9.
To record.

In this case, the encoding of the trial for the other images is 100 msec from the start of the capture of the target image to the start of the actual capture.
Assuming that a degree of delay can be tolerated, if the compression encoding of the target image can be performed in about 30 msec, it should be performed on the three images immediately before the target image as shown in FIGS. 4 (a) and 4 (b). Can be. With such a time delay, the contents of the captured target image and the image immediately before it can be regarded as substantially the same.

That is, in FIG. 4A, the capture of the target image is started at time T ₀ , and the first trial encoding is performed with the scaling factor n ₀ (initial value). As a result, if the code amount after compression encoding is larger than the target code amount,
Increasing the scaling factor n ₀ in scaling factor control circuit 6, a new scaling factor at time T ₁
The second trial encoding is performed at n ₁ (= n ₀ + Δ) (Δ> 0). In this manner, the quantization step width is increased by repeatedly adding Δ to the scaling factor n ₀ until the code amount after compression becomes equal to or less than the target code amount, and the test encoding is repeated. Then, when the code amount after compression becomes equal to or less than the target code amount for the first time, the actual compression coding of the target image is performed by the scaling factor at that time, and the result is recorded on the recording medium 9. In the example 4 (a), since the code amount at the time T ₂ for the first time becomes equal to or less than the target code amount, scaling factor n ₂ at this time (= n ₀ + 2 ×
To start the actual coding storage at T ₃ by delta).

Further, as shown in FIG. 4 (b), the scaling factor n at time T ₀ the capture operation of the target image is started
_When the first trial encoding is performed with ₀ (initial value) and the output code amount is smaller than the target code amount, the scaling factor n ₀ is reduced and a new scaling factor n ₁ (= n ₀ − performing a second round of trial coding at T ₁ by delta). As described above, until the output code amount exceeds the target code amount, Δ is repeatedly reduced from the scaling factor n, and the quantization step width is reduced to repeat the test encoding. Then, the actual compression encoding of the target image is performed by the scaling factor immediately before the output code amount becomes equal to or larger than the target code amount for the first time, and the result is recorded on the recording medium 9. In the example of FIG. 4 (b), the scaling factor at the time T ₁ of the immediately preceding time point T ₂ exceeding the first target code amount n
₁ (= n _{0 -Δ)} perform the actual coding at T ₃ with the starting accumulation of the recording medium 9.

In this way, before starting the encoding and storing of the target image,
Trial encoding is performed on a plurality of images immediately before that, the resultant output code amount is measured and compared with the target code amount, and the output code amount exceeds the target code amount for the first time by increasing or decreasing the scale factor n. Actual encoding and accumulation are performed according to the scaling factor n at or below the time.
By doing so, it is possible to reliably perform the compression encoding of the target image with a code amount equal to or less than the predetermined target code amount.

In the above-described embodiment, the coding method using DCT has been described.However, other coding methods, for example, a vector quantization method, a predictive coding method such as DPCM, or a block coding method are also used. It is applicable and can be applied to all image coding methods using variable length codes.

Further, as the code amount control parameter for controlling the output code amount, the quantization matrix itself may be directly changed in addition to the above-described scale factor.In this case, each coefficient in the DCT coefficient matrix is individually Since it can be changed, more accurate code amount control can be performed.

〔The invention's effect〕

According to the present invention, when a plurality of still images are encoded in real time by a method combining orthogonal transform and variable length encoding and recorded on a recording medium, a plurality of still images immediately before the target image are encoded. To determine the code amount control parameter that is equal to or smaller than the target code amount, and compresses and encodes the target image using the control parameter, so that a still image that can be recorded on a recording medium with a fixed storage capacity is obtained. Can be reliably guaranteed by simple means.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an image data compression recording apparatus according to the present invention, FIG. 2 is a diagram showing a numerical example of a quantization matrix, FIG. 3 is a diagram showing a zigzag scan order, FIG. FIG. 3 is a diagram for explaining a time relationship of the present invention.

Claims (3)

(57) [Claims] 1. A means for extracting image data for one screen from continuously input image data and compressing and encoding the image data, wherein the code amount after the compression encoding exceeds or falls below a target code amount for the first time. Means for changing the code amount control parameter of the means for compressing and encoding to sequentially test-encode a plurality of image data until the first time when the code amount of the trial compression-encoding exceeds the target code amount. The code amount control parameter at the code amount equal to or less than the immediately preceding target code amount, and when the code amount subjected to the trial compression encoding falls below the target code amount for the first time, the code amount control parameter at that time is used. Means for compression-encoding the image data next to the image data subjected to the trial compression-encoding and recording it on a recording medium. 2. An image data recording apparatus according to claim 1, wherein said compression encoding means is a combination of orthogonal transform and variable length encoding, and said code amount control parameter is a scaling factor. apparatus. 3. An image data for one screen is taken out from image data continuously inputted and compression-encoded until the code amount after compression-encoding exceeds or falls below a target code amount for the first time. When a plurality of image data are sequentially trial-compressed and encoded, and the amount of trial-compression-encoded code exceeds the target code amount for the first time, it is equal to or less than the immediately preceding target code amount. When the code amount subjected to the trial compression encoding falls below the target code amount for the first time using the code amount control parameter at the code amount of, the image data of the trial compression encoded using the code amount control parameter at that time is used. An image data recording method, wherein the following image data is compression-encoded and recorded on a recording medium.