JPH0348589A - Still video camera and reproducing apparatus for the same - Google Patents

Abstract

PURPOSE:To save memory capacity by providing a gradient compression means which compresses the gradient of a digital image signal and stores it in a memory, and a switching means which switches the operating and non-operating states of the gradient compression means selectively, CONSTITUTION:A selection signal which decides whether or not the gradient from a gradient compression selection switch 10 should be compressed is inputted to a control unit 9, and also, a comprssibility instruction signal from a compressibility selection switch 11 as a compression level varying means is inputted to the unit. A serial signal on which a gradient compression processing is applied is converted to the parallel signals with a serial-parallel converter 12, and is stored in the memory 13 when eight bits are compressed to three bits. Therefore, only information of one picture element is recorded on data 1, 2, and 3 whose addresses are designated ordinarily, and the information of three picture elements can be obtained from the data 1, 2, and 3, however, the information of eight picture elements can be recorded with 24 bits in the data 1, 2, and 3 by performing gradient compression, which saves the memory capacity required for the recording of one image.

Description

Detailed Description of the Invention <Field of Industrial Application> The present invention relates to a still video camera and a playback device for still video cameras. The present invention relates to a still video camera that allows effective use of capacity, and a playback device applied to such a still video camera.

<Conventional technology> In recent years, in place of conventional film cameras, optical image signals from a subject are converted into electrical image signals using an image sensor.
A still video camera has been developed that stores the electrical image signals in a memory equivalent to film, and the electrical image signals stored in the memory can be played back and viewed on a monitor or printed as hard copies using a printer. ing.

A magnetic disk is generally used as memory for such still video cameras, and in this case, for example, an optical image signal obtained by passing through an optical lens is photoelectrically converted by a solid-state image sensor such as a COD, and the converted The electrical image signals obtained by the above are subjected to analog processing such as color separation, gamma correction, line sequentialization, and FM modulation, and then electromagnetically converted using a magnetic head or the like and magnetically recorded on a magnetic disk.

Furthermore, during playback, magnetic signals recorded on a magnetic disk are electromagnetically converted, processed into analog signals, and displayed on a monitor.

However, this method of magnetically recording analog signals on magnetic disks requires analog processing and electromagnetic conversion of the signals, which tends to cause signal deterioration.
Since both the camera and the player require a rotating drive mechanism for the magnetic disk, they inevitably become larger and more expensive, which is a cause of slowing down their widespread use not only for business use but also for home use.

In view of this, the applicant has proposed a system in which a digital signal obtained by A/D converting an electrical image signal obtained by an image sensor is stored in a semiconductor memory (
According to this, it is possible to prevent signal deterioration due to analog processing, and
Since there is no need for a drive mechanism like in the case of magnetic disks, cameras and playback devices can be made smaller and lighter, and cost reductions can be achieved.

<Problems to be Solved by the Invention> By the way, since semiconductor memory is expensive, it is desirable to increase the number of images that can be recorded by minimizing the number of bits used to record one image. It is necessary to increase the number of bits used for each image light, which reduces the number of images that can be recorded.

However, still video cameras are not only used for general purposes that require high image quality, but may also be used, for example, for photographing and recording black and white documents. When recording a black and white document like this, there is only the white background (paper) and the black text, and there are almost no intermediate tones.
It is wasteful to use a digital image signal with a bit number that can accurately represent halftones, and also causes dirt on documents and uneven lighting to be recorded. However, in response to high image quality demands, for example, 8 bits are used to represent 256 gradations, so even if the subject has no intermediate tones, such as a black and white document, many The number of bits required for recording is large, and although it is desirable to save memory capacity as much as possible, there was a problem in that the memory capacity was wasted when photographing documents.

The present invention was made in view of the above-mentioned problems, and it is possible to switch the gradation represented by the digital image signal recorded in the memory between fine gradation and coarse gradation depending on the subject. The purpose is to provide a still video camera that can save capacity.

<Means for Solving the Problems> Therefore, in the present invention, an optical image signal of a subject obtained by an optical lens is converted into an electrical image signal by an image sensor, and further A/D converted by an A/D converter. A still video camera configured to store a digital image signal in a memory includes a gradation compression means for compressing the gradation of the digital image signal and storing it in the memory, and an activation/deactivation control of the gradation compression means. A switching means for selectively switching is provided.

Further, a compression level variable means for variably setting the compression level by the gradation compression means may be provided.

Furthermore, a threshold variable means may be provided for variably setting a threshold value used in gradation compression by the gradation compression means.

Further, it is preferable to provide a gradation compression data storage means for storing data related to gradation compression in the gradation compression means in a memory together with the digital image signal.

In this way, in the case where the gradation compressed data is stored in the memory together with the image signal, the digital image signal is converted to an initial word length based on the gradation compressed data stored in the gradation compressed data storage means in the playback device. It is preferable to include word length conversion means for converting the word length.

<Function> In a still video camera having such a configuration, an optical image signal of a subject obtained by an optical lens is converted into an electric image signal by an image sensor, and this electric image signal is further converted to an electric image signal by an A/D converter.
Convert to obtain a digital image signal. This digital image signal is then stored in memory.

On the other hand, as a configuration according to the present invention, the gradation compression means is A
The gradation of the digital image signal obtained by /D conversion is compressed and stored in the memory, and the gradation compression by the gradation compression means is selectively activated or deactivated by the switching means. Therefore, when the switching means selects the operation of the gradation compression means, the gradation is compressed and stored in the memory compared to when it is not activated, so it is possible to reduce the memory capacity (number of bits) required for image recording. If this option is enabled, and if you choose to disable it, uncompressed gradations will be recorded to ensure high image quality.

Further, the compression level variable means varies the image quality of the image stored in the memory and the memory capacity required for storage by variably setting the compression level by the gradation compression means.

Further, the threshold variable means variably sets the threshold value used when compressing the gradation by the gradation compression means, and varies the threshold even if the gradation after compression is the same level. By doing so, the contrast etc. of the image stored in the memory can be made variable.

Further, the gradation compression data storage means stores data related to gradation compression in the gradation compression means (activation/inactivation of gradation compression, compression level, threshold value of gradation compression, etc.) together with the digital image signal. and supplies gradation compression data to the playback device.

Furthermore, if the word length of the digital image signal is shortened by gradation compression, the digital/analog converter for the initial word length cannot convert it, so a dedicated D/A converter is required on the playback device. , if the playback device is equipped with word length conversion means for converting to the initial word length (initial number of bits), the initial word length D/
It is converted into an analog signal using an A converter.

<Example> The present invention will be explained in detail below.

In FIG. 1 showing the first embodiment, a still video camera l is provided with an optical lens 2 that forms an optical image of a subject. A light image is formed. Said C0D
3 is driven by a drive circuit 5 to which a synchronization signal from a synchronization signal generator 4 is input, photoelectrically converts the optical image formed on the light receiving surface and outputs it as an analog signal. The image sensor is a MOS, which is a solid-state image sensor like a CCD.
, CPD, and various other imaging tubes may be used.

The A/D converter 6 converts the analog signal from the CCD 3 via the amplifier 7 into a digital signal in accordance with the synchronization signal from the synchronization signal generator 4.

The digital image signal output from the A/D converter 6 is 1
A pixel is output as 8-bit data, for example, and a processing circuit 8 to which this digital signal is input performs various signal processing and compresses this 8-bit data into the number of bits instructed by a control unit 9. Therefore, the processing circuit 8 corresponds to the gradation compression means in this embodiment.

In this embodiment, when shooting in the normal mode, color shooting is performed in which each pixel is represented by 8-bit data.
When the photographer selects gradation compression, the camera switches to black and white shooting and compresses the gradation of the brightness signal Y. In Fig. 1, the gradation compression mode is selected. A hardware configuration in which only the chant signal Y is recorded is shown. However, the still video camera 1 may be a black and white camera, and the black and white gradation may be selectively switched.

The control unit 9 receives a selection signal from the gradation compression selection switch 10 indicating whether or not to compress the gradation, and also receives a compression ratio instruction signal from the compression ratio selection switch 11 as a compression level variable means. is input. When the subject is black and white without fine intermediate tones, such as a document, the photographer specifies recording of a black and white image with compressed tones using the tone compression selection switch IO,
Further, the compression ratio selection switch 11 is used to instruct how much the black and white gradations are to be compressed.

Normally, the information of each pixel is converted into an 8-bit digital signal, and an image with 256 gradations can be obtained.
When tone compression is instructed by the tone compression selection switch 10, processing is performed to compress the tone of the monochrome image from the normal 256 tone according to the compression rate instructed by the compression rate selection switch 11. The compression ratio selection switch 1 instructs to convert 8-bit data to 5 bits or 3 bits, for example, and when gradation compression is instructed, the compression ratio selection switch 11 instructs to convert 8-bit data to 5 bits or 3 bits. When compression to data is instructed, the normal 256 gradations are compressed to 8 gradations.

However, in general operation of the camera, it is preferable that the compression rate specified by the compression rate selection switch 11 expresses the degree of compression abstractly rather than expressing it in terms of a specific number of bits. Furthermore, in the case of a color still video camera, the gradation compression selection switch 10 instructs to shoot in black and white but with reduced gradation, so it is assumed that gradation compression is used exclusively for shooting documents, etc. Therefore, it is preferable to provide a switch for switching between document copy mode and normal color mode.

When the gradations are compressed according to the photographer's instructions as described above, this compressed image data with a small number of bits is recorded in the memory 13, but the address and one pixel are associated with each other and the data is converted into normal 8-bit data. If information is recorded as is in the memory 13, which is designed to record information, for example, only 3 bits of information will be recorded in an 8-bit memory space, resulting in a waste of memory capacity.

Therefore, the serial signal subjected to gradation compression processing is converted into a parallel signal by the serial/parallel converter 12,
When 8 bits are compressed to 3 bits, the data is recorded in the memory 13 as shown in FIG. Therefore, in the case of the recording state shown in FIG. 2, data 1.2.
Normally (with 256 gradations), only one pixel's worth of information is recorded in each of data 1, 2, and 3, and data 1, 2, and 3 provide information for 3 pixels, but due to gradation compression, data 1, 2, .
3's 24 bits means that 8 pixels of information is recorded, making it possible to reduce the memory capacity required to record one image compared to the normal shooting mode, making it possible to take pictures of documents, etc. Sometimes more images can be recorded in the memory 13 with the same storage capacity.

During normal shooting, the serial/parallel converter 12
A digital image signal represented by 8 bits per pixel of normal gradation is serially recorded in a memory for each pixel without going through the gradation.

When performing such gradation compression processing, the playback device must determine whether it is a normal gradation image, a compressed gradation image, how many bits it has been compressed to, and the threshold value for compression. Because we need data that can determine what level, etc.
Data related to such gradation compression is stored at the beginning of each image signal. This function corresponds to a gradation compressed data storage means.

That is, in the still video camera playback machine shown in FIG.
The control unit 23 first reads data related to gradation compression from the memory 13. Then, depending on the gradation compression data, it is selected whether the subsequent image signals should be passed through the parallel/serial converter 21 or directly input to the signal processing circuit 24. If the image signal has been subjected to gradation compression and serial/parallel conversion, a parallel/serial converter (
A P/S converter 21 converts the data into serial data according to the number of bits, and a decoding circuit 22 converts it back into 8-bit data according to the threshold value. For example, threshold values 30H and 60H.

If the data is converted to 2-bit data (2-bit word length) using BOH, 1 byte contains 4 pixel data, so it is converted back to serial data of 2 bits each and decoded as word length conversion means. In circuit 22, depending on the threshold value, 0
Convert to 8-bit data (initial 8-bit word length): OOH (or 18H) if 0, 30H (or 48H) if 01, 60H (or 88H) if 10, BOH (or DBH) if 11. It is output to the signal processing circuit 24. This allows the signal processing circuit 24 and D/A converter 25 for normal gradation images (normal word length) to be used as they are. However, the signal processing circuit 24 is dedicated to 2-bit data.
This does not apply to playback machines equipped with a D/A converter 25.

In addition, the camera is equipped with a monitor function so that more appropriate instructions can be given when switching the gradation compression level.
The temporarily stored digital image signal before gradation compression is gradation-compressed at the specified compression rate, and the gradation-compressed image is displayed on a monitor to achieve the gradation level that the photographer has confirmed is optimal. It is also possible to configure such that only those items are selectively recorded in the memory.

Further, the memory 13 may be any memory card that has a semiconductor memory in the form of a card and is removably attached to the still video camera 1, a magnetic disk, a DAT, or a magneto-optical disk that can record digital signals.

The second embodiment shown in FIG. 3 performs the gradation compression in the first embodiment shown in FIG. 1 not only on the luminance signal Y but also on the color difference signal R.
-Y and B-Y are also applied, and the configuration is such that gradation compression can be performed arbitrarily in recording a color image. In FIG. 3, the same elements as those in FIG. 1 are designated by the same reference numerals and their explanations will be omitted.

Here, the processing circuit 8 separates the digital image signal from the A/D converter 6 into a luminance signal Y and a color difference signal R-Y.
However, when instructed by the control unit 9, each of these gradations is compressed and output.

"The gradation compression of the color difference signal Y and the color difference signals R-Y, B-Y is
This is done in the same way as when compressing the gradation of only the luminance signal Y, and while one normal pixel is 8-bit data, the luminance signal Y and color difference signals R-Y, B-Y each have 8 bits of data.
be represented by fewer bits than bits.

tone-compressed digimole image signal color difference signal RY,
B-Y are serial/parallel converters 12a to 12a, respectively.
The signal inputted to 12c and converted into a parallel signal is then converted back into a serial signal by a parallel-to-serial converter 14 and recorded in the memory 13. By doing this, for example, when an 8-bit gradation is compressed to a 3-bit gradation, each Y is 3 bits.

For example, by dividing R-Y and B-Y in this order into 8 bits and outputting each 8 bits serially, one pixel worth of image information represented by normal 8 bits is stored in the memory space. Y, R-Y.

B-Y information is recorded in a mixed manner.

Therefore, according to this embodiment, instead of obtaining 256 tones represented by 8 bits for each of Y, R-Y, and B-Y, by compressing the tones according to the subject, fewer colors can be obtained. Since the image information can be packed and recorded in the memory, the memory capacity can be used effectively as in the first embodiment.

Note that gradation compression can be achieved in the same manner as in the above configuration even with a configuration in which digital signals of the three primary colors R, G, and B are obtained instead of Y, R-Y, and B-Y.

In the third embodiment shown in FIG. 4, for example, if the photographer wishes to record a monochrome image in only two colors, white or black, for example, 256 gradations using 8-bit data will be recorded. When the photographer selects 2-level gradation compression using 1-bit data for normal shooting, the threshold determines whether the intermediate tones that actually exist in the subject are recorded as white or black. This shows a structure in which the value (threshold level) can be arbitrarily varied.

That is, when two-gradation photography of black and white is selected by the photographer's instruction using the gradation compression selection switch 1o, the digital image signal converted by the A/D converter 6 is sent to the comparator as gradation compression means. 15, it is compared with a predetermined threshold value, and outputs a binary value of l (white) or O (black) depending on the magnitude of the threshold value (see Fig. 5).
The bit signal is recorded in the memory, and the output of the externally operated volume 16 is converted into a digital signal by the A/D converter 17, and the threshold value is set by this digital signal. The threshold value is variably set by externally operating a volume 16 serving as a threshold value variable means.

Therefore, for example, when shooting a document and selecting two-tone recording of white and black using the gradation compression selection switch lO in order to save memory capacity, there will be a gray area on the document that is an intermediate tone. If this gray color does not need to be recorded, the threshold value can be set variably so that it is recorded as the same white as the white of the paper, and if the gray color is to be recorded as distinct from blank paper, this value can be set. If the threshold value is variably set so that gray is identified as black, it is possible to arbitrarily select from what level a gray recording with shading becomes black or white.

In addition, in the fourth embodiment shown in FIG. 6, when a monochrome image <m degree signal Y) is compressed and recorded into four gradations, the threshold value is variable in the same manner as in the third embodiment. It is configured so that it can be done.

In this example, black and white images are divided into white, dark gray, light gray,
The gradation is compressed and recorded as four colors, including black, and three thresholds are required to distinguish them (see Figure 7), but these thresholds can be variably set by external operation. As in the third embodiment, volumes 16a to 16c are provided as threshold variable means for independently varying the respective thresholds.
The outputs of these volumes 16a to 16c are A
A/D converter 17 performs A/D conversion and inputs the signal to control unit 9, and each threshold value is input to latch circuit 18a.
〜18c, and the corresponding comparator 15a
~15c is input.

The comparators 15a to 15c identify the digital image signals output from the A/D converter 6 based on their respective thresholds, and compare the magnitudes with the respective thresholds.
By outputting bit data and recording this output result in the memo January 3, a monochrome image is recorded in four gradations: white, dark gray, light gray, and black. Therefore, in this example,
Even when photographing a document or the like that has halftones, the halftones can be arbitrarily recorded in either dark gray or light gray.

In addition, the above 3. In the fourth embodiment, the configuration is described in which the threshold value used when compressing the gradation of a black and white image is variably set, but the threshold value can also be set in the same way when compressing the gradation of a color image. For example, when compressing the gradation of the color difference signal RY into three gradations of red, white, and green, as shown in FIG. By shifting the threshold value over the entire screen, the color tone of the entire screen can be made into a red-based tone or a green-based tone.

In addition, even when setting the threshold value variably in gradation compression as described above, the imager can set the optimal threshold value by checking the threshold value on the monitor and setting the threshold value in DI steps. It is possible to do so.

<Effects of the Invention> As explained above, according to the present invention, it is possible to selectively operate to compress the gradation of a digital image signal and store it in the memory. In the case of objects that do not have complex gradations, it is sufficient for practical use to record fewer gradations than those obtained during normal shooting, so the gradation is compressed and recorded in memory. It becomes possible to record a large amount of image data while saving the recording capacity. In addition, by making it possible to change the compression ratio, it is possible to record the necessary and sufficient gradations while saving memory capacity, and it is also possible to change the threshold value used to compress gradations. By doing so, it is possible to both save memory capacity and ensure necessary and sufficient gradations.

In addition, by storing data related to gradation compression together with the image signal, the player can know the details of the gradation compression process, and based on the gradation compression data, the player can store it in memory. Since the word length of the digital image signal is converted to the initial value, there is an effect that a D/A converter, etc. compatible with the normal word length can be used on the playback side even during compression. .

[Brief explanation of drawings]

FIG. 1 is a system block diagram showing a first embodiment of the present invention, FIG. 2 is a diagram showing a recording state of pixel data in the first embodiment, and FIG. 3 is a system block diagram showing a second embodiment of the present invention. 4 is a system block diagram showing the third embodiment of the present invention, FIG. 5 is a diagram showing the relationship between the threshold value and gradation in the third embodiment, and FIG. 6 is a system block diagram showing the third embodiment of the present invention. A system block diagram showing the fourth embodiment, FIG. 7 is a diagram showing the relationship between the threshold value and gradation in the fourth embodiment, and FIG. 8 shows the threshold value when the gradation of the color difference signal is compressed. FIG. 9 is a block diagram showing an embodiment of a still video camera playback device according to the present invention. l...Still video camera 2...Optical lens 3
...CCD 6...A/D converter 8...
Processing circuit 9...Control unit lO・
...Compression selection switch 11...Compression ratio selection switch 13...Memory 15...Comparator 1
6...Volume 22...Decoding circuit

Claims (5)

[Claims] (1) The optical image signal of the subject obtained by the optical lens is converted into an electrical image signal by the image sensor, and then the A/D
A still video camera configured to store in a memory a digital image signal obtained by A/D conversion by a converter, comprising a gradation compression means for compressing the gradation of the digital image signal and storing it in the memory; A still video camera comprising: switching means for selectively switching between activation and non-operation of a gradation compression means. (2) The still video camera according to claim 1, further comprising compression level variable means for variably setting the compression level by the gradation compression means. (3) The still video camera according to claim 1 or 2, further comprising a threshold variable means for variably setting a threshold value used in gradation compression by the gradation compression means. (4) A gradation compressed data storage means is provided for storing data related to gradation compression in the gradation compression means in a memory together with the digital image signal.
The still video camera according to any one of 2 or 3. (5) A playback device for a still video camera that plays back an image signal captured and recorded in a memory by the still video camera according to claim 4, based on the gradation compressed data stored in the gradation compressed data storage means. 1. A playback device for a still video camera, comprising word length conversion means for converting a digital image signal into an initial word length.