JPH0564143A - Electronic still camera - Google Patents

Abstract

PURPOSE:To save compression picture data to be saved while the setting of a compression rate is varied automatically to obtain desired number of the data and to obtain a best picture state within this range. CONSTITUTION:A control section 100 is operated to ensure a memory area able to record two still pictures or over to a memory card 12 in terms of coded compression picture data. A counter circuit 14 measures a contained data quantity when each memory area stores the compressed picture data. An error detection circuit 15 calculates an error between a measured value of the counter circuit and a prescribed value. A comparator circuit 18 discriminates the quantity of an error obtained by the error detection circuit. The control section 100 changes a processing parameter to implement coding processing for an optional number of times and writes the result to an optional memory area till a time reaches a limit time or the magnitude of the error reaches a prescribed value when original picture data picked up precedingly are stored in a memory area till a succeeding image pickup instruction is received after an image pickup instruction is first received.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic still camera which compresses still image data and records it in a storage device such as a memory card.

[0002]

2. Description of the Related Art Recently, an electronic still camera has been commercialized which can digitize photographed still image data and record it on a recording medium such as a floppy disk or a memory card. In order to store many images, a method has been adopted in which captured still image data is compressed and the amount of data is reduced before recording. Especially DCT
The compression method using the (discrete cosine transform) is attracting attention as the most powerful compression method in the future because the compression rate is high although the deterioration of the image quality is small.

If the DCT compression method is used, it is possible to store about 20 still image data in one memory card having a capacity of 2 Mbytes. Of course, since the original image data is compressed to about 1/8, it does not mean that the image quality does not deteriorate at all, but from a practical point of view, it is possible to shoot with one memory card. Securing a certain number of sheets is also an important issue. FIG. 3 shows a configuration example of an electronic still camera using the DCT compression method.

The optical image captured by the optical system lens 1 is CC
It is converted into an electric signal by the solid-state imaging device 2 using D (charge transfer device) and sent to the signal processing circuit 3 as a video signal. In the signal processing circuit 3, color processing is performed, and at the same time, analog-digital (A / D) conversion is performed, and a digital signal is temporarily stored in the frame memory 4. In the frame memory 4, the stored video signal for one image is divided into blocks and sent to the DCT circuit 5. However, the same transfer operation is performed in order to determine the parameters required for a series of compression encoding work. Two
Repeat. In the first transfer, the transform data orthogonally transformed by the DCT circuit 5 is sent to the activity calculation circuit 6. Here, the total activity amount for one image is obtained, and the coefficient (hereinafter referred to as a) necessary for determining the quantization step size is calculated, and the bit allocation circuit 7 performs bit allocation for luminance / color signals. decide. At the time of the second transfer, the conversion data is sent to the quantization circuit 8, but here, the quantization calculated by the operation of the coefficient a previously obtained and the data of the quantization table 9 is performed. Quantization is performed according to the steps.

The conversion data is also sent to the activity calculation circuit 6 in the same manner as the first transfer, but the first time the total activity amount for one image is obtained, while the second time is in block units. The activity amount will be calculated sequentially.

As a result, the final bit allocation for each block is obtained based on the bit allocation determined in the first transfer. In the encoding circuit 10, the encoding bit amount is adjusted according to the bit allocation and encoding is performed. And the output data is recorded in the memory card 11 through the interface 11.

In the electronic still camera, the DCT compression method in which the fixed length coding as shown in FIG. 3 is performed is desirable. This is because when the length is variable, the amount of coded data changes remarkably depending on the pattern to be photographed, and the number of photographable images per memory card cannot be determined. In other words, in order to prevent the inconvenience of being able to record 20 images while shooting a certain pattern, but only 13 when recording another type of pattern, the purpose could not be achieved. Fixed length is required.

[0008]

The greatest point of fixed length is how to determine the coefficient a. Certainly, it can be easily inferred that increasing the coefficient a increases the data compression rate, and decreasing the coefficient a decreases the data compression rate. However, the fact that the data compression rate becomes what the coefficient a is, cannot be expressed by a simple relationship because it depends on the design. Therefore, experimentally picking up various kinds of patterns, the correlation between the total activity amount and the coefficient a under the condition that the data compression rate is constant is obtained in advance, and the actual photographing is performed based on these empirical data. The coefficient a is calculated backward from the total activity amount of one image.
For this reason, it can be said that it is extremely difficult to realize a completely fixed length.

Therefore, although the length is fixed, it is inevitable that the encoded data amount varies. For this purpose, it is necessary to focus on the data compression rate such that the encoded data can be sufficiently contained in the memory area on the memory card to be recorded even if the encoded data includes variations. must not. Of course, there should never be an over-run, so the center of the compression rate should be set to a rather high level. This is not only inefficient in using the memory, but also wastefully degrading the image quality, which is inconvenient.

Therefore, according to the present invention, the compressed image data to be stored is stored.
The purpose of the present invention is to provide an electronic still camera in which the compression ratio setting is automatically changed and stored so that the desired number of images can be obtained and the best image condition in this range is obtained. To do.

[0011]

SUMMARY OF THE INVENTION According to the present invention, a still image data is coded and compressed to obtain compressed image data and a memory card is obtained.
In an electronic still camera that records to a storage device such as

Area securing means for securing a memory area capable of recording two or more still images as encoded compressed image data, and the compressed image data in each memory area.
Measuring means for measuring the amount of stored data when storing the data,
An error calculation unit that calculates an error between the measurement value of the measurement unit and a predetermined value, a size determination unit that determines the size of the error obtained by the error calculation unit, and a next shooting after receiving a shooting command. The original image data taken in advance in the memory area is held until the instruction is received, and the processing parameters are changed until the limit time or the magnitude of the error reaches the predetermined value. And means for performing the encoding process of the number of times and writing in an arbitrary memory area.

[0013]

The compressed image data coded by the above means is
A memory area in which two or more still images can be recorded as data is prepared, and the amount of stored data when the compressed image data is stored in each memory area is measured. Then, the error between the measured value and the predetermined value is calculated. Next, as a result of comparing the respective errors, the compressed image data in the memory area with a small error is saved as it is, the compressed image data in the memory area with a large error is invalidated, the compression ratio is changed, and the compressed image data is changed again. The encoded compressed image data to be processed is written, and the compressed image data with less error is left one after another. As a result, the number of compressed image data to be stored can be set as desired, and the setting of the compression ratio can be automatically changed and stored, so that the best image state can be obtained within this range.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The image information captured by the lens 1 is converted into an electric signal by the solid-state image sensor 2 using a CCD (charge coupled device), and is sent to the signal processing circuit 3 as a video signal. Color processing is performed in the signal processing circuit 3, and at the same time analog digital (A / D)
It is converted into a digital signal and is once stored in the frame memory 4
Stored in.

In the frame memory 4, the stored video signal for one image is divided into blocks and sent to the DCT (discrete cosine transform) circuit 5. DCT circuit 5 at the first transfer
The transform data subjected to the orthogonal transform by is sent to the activity calculation circuit 6. Here, the total activity amount for one image is obtained, the bit distribution circuit 7 determines the bit distribution for the luminance / color signals, and the coefficient a is calculated.

In the second transfer, the transform data is sent to the quantizing circuit 8, but the previously obtained coefficient a and the quantizing table 9 are used.
Quantization is performed according to the quantization step calculated by the calculation with the data of. At this time, the coefficient addition / subtraction circuit 13 does not perform the arithmetic processing on the coefficient a. Regarding the data conversion and the quantization processing, the applicant of the present invention filed Japanese Patent Application No. 2-2
No. 53980 is also described.

On the other hand, the conversion data is sent to the activity calculation circuit 6 as in the case of the first transfer, but the first time the total activity amount for one image is obtained, whereas the second and subsequent times are in block units. The amount of activity of is calculated sequentially. In this way, the final bit allocation for each block unit is obtained based on the bit allocation determined in the first transfer. In the encoding circuit 10, the encoding bit amount is adjusted according to the bit allocation and the code is encoded. Will be converted. The obtained coded data is recorded in the memory card 12 through the card interface 11, and the counter circuit 14 measures the simultaneously recorded data amount.
The count value is a desired value by the error detection circuit 15 (maximum encoded data amount for one still image that can be recorded in the memory card).
And the difference (DE 1) from is detected and set in the register 16 once. The decision circuit 17 decides from the detected error amount whether or not to perform the compression coding process again, and requests the frame memory 4 for the third transfer.

However, in the third transfer, the coefficient addition / subtraction circuit 1
The value of the coefficient a is changed by 3 to perform the compression encoding process. The determination circuit 17 determines and controls the magnitude of change and addition / subtraction switching according to the magnitude polarity of the miscalculation amount. In this way, the coded data (CMD2) having a different coefficient a is newly recorded in the memory card 12, but the coded data (CMD1) obtained by the first compression coding process is stored. Other area (MA1) different from the stored memory area (MA1).
Place in 2). At the same time, the counting circuit 14 and the error detection circuit 1
5, the error (DE2) with respect to the data amount of the encoded data (CMD1) is detected and set in the register 16. Then, the comparison circuit 18 compares which of the errors of DE1 and DE2 is smaller. In the comparison result, a value having a positive polarity and a smaller value is selected (if the polarity is negative, it means that the memory size is over), and the determination circuit 17 performs the compression encoding process again. Determine whether or not.

In the fourth transfer, that is, in the third compression coding process, not only the value of the coefficient a is changed, but also the coding data (CMD3) obtained by the compression coding process is to be accommodated in the memory area. , And the set area of the register 16 for setting the error (DE3) detected by the counting circuit 14 and the error detection circuit 15 must be designated. This is determined by the comparison between DE1 and DE2 described above. The memory area corresponding to the set area in which the polarity is positive and the smaller value is left and the other error value is set is the comparison circuit. Specified by 18. As a result, the data of the area of the method with a small error remains. Based on the comparison result, it is determined whether the data of the memory interface 11 is sent to the memory card 12.

In this way, while leaving the encoded data whose amount of data is closer to the desired value (maximum encoded data for one still image recordable in the memory card), 6, 7
..Repeat the compression encoding process once. This can be performed as long as the time permits (until the next shutter is pressed), but the error value may reach a predetermined value, or may be finished at a specific time in consideration of saving power consumption. .. The operation procedure of the entire system is controlled by timing pulses from the system controller 100 and area designation address data of the memory card. FIG. 2 (A) shows an example of the transition of the contents corresponding to the areas in the card memory 12 when the data has been fetched and corrected up to the fourth time.

The image area for one image (area 1) has a sufficient margin with respect to the amount of captured data for the first time, and area 2 for the captured data for the second time. On the other hand, there is a small margin (area 1 and area 2 have the same capacity). Furthermore, the third time shows a state where the predetermined area is exceeded. Therefore, in this case, the second data is left and the fourth data is the previous 3
The data is written in the area (area 1) corresponding to the data of the first time. In this case, there is only a slight margin for area 1. The encoding condition for each data acquisition process is
As described above, the data is corrected so that it becomes optimal one after another, so that it is stored as the most efficient data amount for the specified area. When the next shooting is performed, the area 2 and the next area 3 are secured, and the same processing as above is performed. When new image data is input to the frame memory 4 by the next shooting command, the compression coding process returns to the stage of obtaining the total activity and restarts.
It becomes

The memory area in which the encoded data obtained by the compression encoding processing should be accommodated is one of MA1 and MA2 which accommodated the encoded data of the preceding image (the desired data amount is desired). The area corresponding to two images, in which a memory area called MA3 is newly added to the area apart from the value) is targeted.

Since the compression coding processing is performed using the memory area for two images, the data amount may not be sufficiently close to the desired value even if the next photographing command is issued during the processing. Although it is not known, since some coding data has already been obtained, the compression coding process at that point can be stopped and the compression coding process for a new image can be immediately started.

At the time of the last photographing, however, a memory area for two images cannot be secured in the memory card. However, since it is the last, the next shooting command does not suddenly occur, and if it occurs, it is necessary to specify which of the already-written memory areas should be erased, which can be predicted. It does not matter if the processing time is considered sufficient. Securing a memory area for two images is a measure against continuous shooting, and if the time for compression encoding processing is secured, the same memory area is rewritten many times while leaving data with little error. But there is no problem.

FIG. 2B shows another embodiment according to the present invention, which is a microprocessor for error detection, count addition / subtraction, etc.
It is processed by 19. Since it is normal for the microprocessor to perform shooting control and data writing to the memory card, the microprocessor 19 is responsible for processing such as error detection and coefficient addition / subtraction.

Further, although the coefficient a is targeted as a parameter for increasing / decreasing the amount of encoded data, it may be performed at any stage such as bit allocation / encoding, and further, a recording medium for encoded data. Is not limited to a memory card, and the present invention can be put into practice in various forms.

As described above, in this system, after receiving the photographing command, until the next photographing command is received, that is, until the shutter is pressed once and then the next shutter is pressed, the frame memory is initially stored. The image data of is retained.
Therefore, as long as time permits (until the next shutter is pressed), the compression parameter, for example, the coefficient a can be changed to perform the encoding process as many times as necessary. The encoded data can be recorded in any one of the prepared memory areas for two still images at any time, and which one is to be used is determined based on the size of the error. By repeating this, the error decreases,
The amount of encoded data approaches the planned memory size. That is, it is possible to minimize the image quality deterioration due to compression.

[0029]

EFFECTS OF THE INVENTION Even if the next shooting command is issued during the processing, some coding data has already been obtained, so the compression coding processing at that point is stopped and a new image is immediately created. It is possible to move to the compression encoding processing of. In other words, the continuous shooting operation is not affected at all, and the image quality is improved as long as the time permits, so that the deterioration of the image quality due to the compression can be suppressed to the minimum. Further, it is not necessary to add a new memory, and if error detection, coefficient addition / subtraction, etc. are processed by a microprocessor or the like, there will be no increase in hardware, and an excellent effect can be obtained without increasing the price.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of the present invention.

FIG. 2 is an explanatory view for explaining the operation of the device of the present invention and a structural explanatory view showing another embodiment.

FIG. 3 is an explanatory diagram of a configuration of a conventional electronic still camera.

[Explanation of symbols]

1 ... Lens, 2 ... Image sensor, 3 ... Signal processing circuit, 4 ... Frame memory, 5 ... DCT circuit, 6 ... Activity calculation circuit, 7 ... Bit allocation circuit, 8 ... Quantization circuit, 9 ... Table, 10 ... Code Circuit, 11 ... Memory interface, 12 ... Memory card, 13 ... Addition / subtraction circuit, 14 ...
Counting circuit, 15 ... Error detecting circuit, 16 ... Register, 17
... determination circuit, 18 ... comparison circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location H04N 5/91 J 8324-5C 7/133 Z 4228-5C

Claims (3)

[Claims] 1. An electronic still camera for encoding and compressing still image data to obtain compressed image data and recording the compressed image data in a storage device such as a memory card. Area securing means for securing a memory area capable of recording two or more still images; measuring means for measuring the amount of stored data when the compressed image data is stored in each memory area; Error calculation means for calculating an error between the measured value of the means and a predetermined value, a magnitude determination means for determining the magnitude of the error obtained by the error calculation means, and a next photography command after receiving the photography command. Before receiving the original image data taken in the memory area
Data is held and data is written to an arbitrary memory area by changing the processing parameters and performing an arbitrary number of encoding processes until it is determined that the limit time or the magnitude of the error has reached a predetermined value. An electronic still camera comprising a writing means. 2. The data writing means, when selecting a memory area in which the encoded data obtained by the encoding process again is to be written, has a smaller error based on the magnitude judgment of the error. The compressed image data in the memory area is stored as it is, the compressed image data in the second memory area having a large error is treated as invalid, and the encoded compressed image data to be processed again is stored in the second memory. The electronic still camera according to claim 1, further comprising means for writing in the area. 3. The limit time is after receiving a photographing command,
The electronic still camera according to claim 1, wherein the electronic still camera is a time until the next photographing command is received or an arbitrary time set in advance.