JPH04887A - Electronic still camera - Google Patents

Abstract

PURPOSE:To maintain the number of pictures recorded on a recording medium always constant by performing temporary quantization using an arbitrary quantization matrix and deciding the quantization matrix by which the most adequate compressing ratio to obtain a prescribed data quantity can be obtained from the temporary compressing ratio. CONSTITUTION:The image of an object photographed by an image pickup section 1 is inputted to an A/D-converting section 2 as video signals and sent to a coding section 4 after the signals are converted into digital picture data. At the coding section 4, the inputted picture data are divided into plural blocks, each of which is composed of (nXn) picture elements, by means of a discrete cosine transforming(DCT) section 4a and the data are coded by performing two-dimensional DCT at every block. Then the coded data are inputted to a data quantity measuring section 5 and measurement is made to confirm whether or not the quantity of all compression-coded data is smaller than a prescribed data quantity. When the all data quantity exceeds the prescribed quantity, a compressing ratio calculating section 6 calculates the compressing ratio at which the quantity of all compressed data becomes smaller than the prescribed quantity and a quantizing section 4b again makes quantization of the DCT coefficient by selecting another quantization matrix having a threshold which different from that of the preceding quantization matrix.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides a method for compressing and recording captured still images on a recording medium so that the total amount of data after compression is less than or equal to a predetermined amount of data. , relates to a digital electronic still camera that records images by controlling the compression ratio for each image.

[Conventional technology]

Electronic still cameras extract the image of a subject that is formed on the imaging surface of an image sensor through a lens as a video signal, process this video signal as appropriate, and then record it on a recording medium such as a floppy disk. can be played on a television monitor or output as a hard copy on a video printer.

When using a solid-state image sensor such as a CCD as an image sensor,
Because solid-state image sensors are suitable for digital signal processing due to their element structure and operation, the circuitry can be configured entirely digitally, making it possible to downsize the camera, as well as converting image information through high-efficiency compression and encoding processing. The amount of data can be greatly compressed and recorded.

[Problem to be solved by the invention]

Incidentally, an electronic still camera is required to have a function of always keeping the number of still images that can be recorded per recording medium constant regardless of the content of the images to be photographed. Especially in consumer cameras, it is extremely important for the photographer to know how many images can be recorded on the recording medium.

However, since the amount of information contained in an image generally varies from image to image, if digitized image data is compressed and encoded using fixed parameters, the number of images that can be recorded on a recording medium will vary depending on the content of the image being shot. This creates the inconvenience of doing so. For this reason, if you try to secure the storage capacity per image according to the image with the largest amount of information and always record only a certain number of images, the storage capacity will be wasted for images with less information. will occur.

To provide an electronic still camera that can always keep the number of still images that can be recorded per recording medium constant regardless of the amount of information of each image without wasting storage capacity. With the goal.

[Means to solve the problem]

The electronic still camera according to the present invention includes an imaging device that converts a subject image formed through a lens onto an imaging surface of an imaging device into a video signal and outputs the same, and an AD conversion device that converts the converted video signal into digital image data. , a memory means for temporarily storing the digital image data for each screen, and a plurality of nxn two-dimensional data obtained by subjecting the image information formed by the digital image data to two-dimensional orthogonal transformation in the frequency domain. Multiple n for orthogonal transform coefficients
a means for compressing and encoding by dividing each threshold of a quantization matrix consisting of data amount measuring means for determining whether or not;
When the total data amount after the compression measured by the data amount measuring means exceeds the predetermined data amount, calculate the compression ratio necessary to compress the data to the predetermined data amount, and based on the calculation result, a compression ratio calculating means for selecting another quantization matrix having a threshold value different from each threshold value of the quantization matrix; At the time, it is composed of a recording medium for recording all the compressed data.

[For production]

According to the configuration of the present invention, the encoding means performs two-dimensional orthogonal transformation and quantization on the image data digitized by the AD conversion means, and performs compression encoding processing of the image data. In this case, since the amount of image data varies depending on the target image, it is impossible to predict which quantization matrix should be used for quantization to obtain the necessary compression rate. Therefore, first perform temporary quantization using an arbitrary quantization matrix, calculate the compression rate at that time as a temporary compression rate, and obtain the most appropriate compression rate to obtain a predetermined amount of data from this temporary compression rate. A quantization matrix that can achieve this is determined by a compression ratio calculation means.

Compression encoding is performed again using the new quantization matrix determined in this way, and when the amount of data after compression becomes less than a predetermined amount of data, all the data at that time is recorded on the recording medium.

In this way, the amount of data after compression is reliably equal to or less than the predetermined amount of data, and the number of images recorded on the recording medium is always kept constant regardless of the content of the target image to be recorded.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of an electronic still camera according to the present invention.

This embodiment includes an imaging section 1 consisting of a solid-state imaging device such as a CCD for converting a subject image formed through a lens into a video signal, and an imaging section 1 that converts the video signal output from the imaging section 1 into digital image data. An AD converter 2, a frame memory 3 that temporarily stores converted digital image data, and a two-dimensional orthogonal transform in the frequency domain for this digital image data, and each threshold of a quantization matrix for the resulting transform coefficients. An encoding unit 4 that performs quantization by dividing , a data amount that measures the total data amount after compression of the image data compressed by the encoding unit 4 and determines whether the data amount is less than a predetermined data amount. When the measurement unit 5 determines that the total amount of data after compression exceeds a predetermined data amount, it calculates the compression ratio necessary to compress the data to the predetermined amount, and uses the calculation result to calculate the previous quantization matrix. is another quantization mask having a different threshold value) A compression ratio calculating section 6 that selects the IJ box, and a recording device such as a floppy disk that stores all the compressed data when the amount of data after compression is less than a predetermined amount of data. It consists of medium 7.

The encoding unit 4 divides the image data of one frame into a plurality of blocks consisting of 1 block rl×n pixels, for example, 8×8 pixels, in the horizontal and vertical directions, and
Dimensional discrete cosine transform (DCT)
e Co51ne Transforma+) DC
It consists of a T section 4a and a quantization section 4b which quantizes nxn DCT coefficients obtained by the conversion by dividing each threshold value of a quantization matrix consisting of nxn threshold values.

In this configuration, a subject image captured by the imaging section 1 is input to the AD conversion section 2 as a video signal, converted to digital image data, and sent to the encoding section 4. In the encoding unit 4, a DCT unit 4a divides the input image data into a plurality of blocks each consisting of n×n pixels, and performs two-dimensional DCT on each block to encode the data. DCT is a type of orthogonal transform in the frequency domain, and transform coefficients are
, (i, j=o, l,..., n-1), If one block of image data is fij, then C,1= 1/-' 2 (w=0)=
1 (w≠0), and each obtained transformation coefficient FiJ indicates a component obtained by decomposing one block of image data into spatial frequencies. Of this conversion coefficient F, the coefficient F0° is a value (
DC component) and variable 1? As J increases, a higher frequency component (alternating current component) is shown. The n×n DCT coefficients obtained in this way are quantized by being divided by each threshold of a quantization matrix consisting of n×n thresholds for each block in the quantization unit 4b. FIG. 2 shows an example of a quantization matrix consisting of 8×8 threshold values. The increase or decrease in the amount of data after compression can be adjusted by adjusting the size of each threshold value of this quantization matrix.

The image data compressed and encoded by the encoding unit 4 in this way is
The data is then input to the data amount measuring section 5, and it is measured whether the total data amount after compression encoding is less than or equal to a predetermined data amount. If the amount of data is less than the predetermined amount, it is recorded on the recording medium 7 as is.

If the total data amount after compression exceeds the specified data amount,
The compression ratio calculation unit 6 calculates the compression ratio at which the total amount of data after compression is less than or equal to a predetermined data amount, and based on the calculation result, calculates the compression ratio of the previous quantization mask (IJ) having a threshold different from the threshold of the IJ. Select the quantization matrix and use D again in the quantization section 4b.
Quantize the CT coefficients. In this case, it is assumed that the quantization unit 4b stores a plurality of quantization matrices each having a different threshold value.

Incidentally, the relationship between the compression rate and the amount of image data is inversely proportional, as shown in the compression rate/data amount curve in FIG. In the figure, the amount of data A when the compression ratio is 1 indicates the amount of original image data when it is not compressed. Now, if the amount of compressed data secured per - screen, that is, the predetermined amount of data, is B, then the compression ratio X1 at point Q on the curve is the required compression ratio. Therefore, an appropriate compression ratio can be obtained by quantizing using a quantization matrix whose compression ratio is closest to Xl.

However, since the amount of data per screen differs from image to image, it is impossible to predict which quantization matrix should be used to obtain an appropriate compression rate. Therefore, first we perform temporary quantization using an arbitrary quantization matrix, and then the compression ratio x
2 is obtained as the temporary compression ratio. Next, the obtained temporary compression ratio
2 to determine the characteristics of the target image, that is, the compression rate that can be obtained by using which quantization matrix. That is, the compression ratio 1 s X2 ,X
Assuming that points P, Q, and R on the curve corresponding to l are substantially on a straight line, the ratio between the compression ratios Xi and X2 is determined from the ratio between the triangle ΔPP'Q and the triangle ΔRR'Q.

Since this ratio is the ratio of each threshold value of the quantization matrix, the quantization matrix to be used can be determined from this ratio.

Next, the DCT coefficients are quantized using each threshold value of the new quantization matrix obtained in this way, and when the amount of data after compression becomes less than the predetermined data amount B, all data at that time is recorded on the recording medium 7. do.

〔Effect of the invention〕

According to this invention, the number of still images recorded on a recording medium can always be kept constant regardless of the content of the target image to be recorded, and the number of still images recorded on the recording medium can be kept constant. It becomes possible to notify the person.

Furthermore, since the compression ratio is adjusted and recorded for each image, the amount of data for each image recorded on the recording medium is a substantially constant amount of data, and the storage capacity of the recording medium can be used without wasting it.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an electronic still camera according to the present invention, FIG. 2 is a table showing an example of a quantization matrix, and FIG. 3 is a compression ratio/data amount characteristic diagram. DESCRIPTION OF SYMBOLS 1... Imaging unit, 2... AD conversion unit, 3... Frame memory, 4... Encoding unit, 5... Data amount measuring unit, 6... Compression rate calculating unit, 7... ··recoding media.

Claims (1)

[Scope of Claims] Imaging means for converting a subject image formed through a lens onto an imaging surface of an image sensor into a video signal and outputting the same; AD conversion means for converting the converted video signal into digital image data; a memory means for temporarily storing the digital image data for each screen; and a plurality of n×n two-dimensional data obtained by subjecting the image information formed by the digital image data to two-dimensional orthogonal transformation in the frequency domain. means for compressing and encoding the orthogonal transform coefficients by dividing each threshold of a quantization matrix consisting of a plurality of n×n thresholds; and measuring the total amount of data after compression of the compression-encoded image data; a data amount measuring means for determining whether the data amount is less than or equal to a predetermined data amount; and when the total data amount after the compression measured by the data amount measuring means exceeds the predetermined data amount, up to the predetermined data amount; Compression ratio calculation means for calculating a compression ratio necessary for compression and selecting another quantization matrix having a different threshold value from each threshold value of the quantization matrix based on the calculation result; and the data amount measurement means. An electronic still camera comprising: a recording medium for recording the entire compressed data when the measured total data amount after the compression is less than the predetermined data amount.