JPH0365886A - Picture converter for still video camera - Google Patents

Abstract

PURPOSE:To attain data compression with the highest efficiency without losing picture information by providing a highly efficient code conversion means possible selecting the conversion efficiency of a quantization code, selecting the conversion efficiency of the quantization code in the highly efficient code conversion means so as to vary the conversion efficiency in response to an object field depth. CONSTITUTION:Based on an object field depth detected by an object field depth detection means, that is, the requirement of the resolution of the picture, a conversion efficiency selection means selects the conversion efficiency of a quantization code in the high efficiency code conversion means to vary the conversion efficiency in response to the object field depth thereby varying the quantization level of a picture signal stored in a picture storage means. That is, the compression control of the high efficiency code converter 7 is implemented by the software or hardware information from an object field depth calculation processor 11 as a conversion efficiency selection means and the object field depth detection means. Thus, the picture signal is coded with a high efficiency and the memory capacity is saved and a high picture level is obtained altogether.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an image conversion device for a still video camera.
More specifically, the present invention relates to an image conversion device designed to variably control conversion efficiency in encoding image data.

<Prior Art> In recent years, in place of conventional optical cameras, cameras have been developed which convert an optical image signal from a subject into an electrical image signal using an image sensor and store the electrical image signal in a memory equivalent to a conventional film. A still video camera is being developed.

Currently, magnetic disks are generally used as memory for such still video cameras, but magnetic disks require a rotating mechanism, making it difficult to miniaturize the camera. A/
A still video camera has been proposed in which a digital image signal obtained by D conversion is stored in a semiconductor memory (see Japanese Patent Laid-Open No. 72283/1983, etc.).

In such a digital storage type still video camera, the digital image signal is compressed and converted using a high efficiency code conversion method such as discrete cosine transform coding (DCT) before being stored in the memory. We are trying to save capacity.

<Problems to be Solved by the Invention> However, in reality, there are cases in which the subject is photographed at a relatively close distance in dim lighting indoors, as shown in Fig. 10, or in sunny conditions, as shown in Fig. 11. There are various modes, such as when photographing a distant view outdoors on a sunny day.

Here, when the photograph is taken indoors in dark lighting and at a relatively close distance, as shown in Figure 10, the aperture is open because the focal position of the lens is close and the exposure is dark.
The depth of field for photography becomes shallower.

For this reason, the image of a subject that is slightly out of focus will be blurred, and images of background shadows often do not require detailed resolution. is often photographed in a large size over the entire screen, and the overall image has a low spatial frequency and a soft tone, making it difficult to stand out even with high data compression.

On the other hand, when photographing a distant view outdoors on a sunny day, as shown in Figure 11, the focal point of the lens is far away and the aperture value is small, resulting in a deep depth of field and a detailed resolution of the entire screen. More often it is needed. Furthermore, if we take into account the characteristics of an image of a distant view, the main subject will often be the entire screen or a single point in the distance, and the image as a whole will be an emphasized pattern with a relatively high spatial frequency.
If data compression is applied too strongly, the sharpness of each point on the subject will decrease, resulting in poor shooting.

Furthermore, when taking pictures using a macro lens, the subject is usually enlarged, and in addition to the shallow depth of field, the correlation between pixels in the image is high and spatial The screen tends to have a low frequency.

In this way, the compression rate that allows data to be compressed most efficiently without sacrificing image clarity varies depending on the shooting conditions, so if data compression of digital image signals is performed at a different compression rate, the stored image may be unsatisfactory. However, there is a problem that unnecessary redundant data may be stored in the memory.

The present invention has been made in view of the above problems, and provides an image conversion device that can change the compression rate of a digital image signal according to shooting/storage conditions such as depth of field, without damaging image information. The purpose is to compress data with the highest efficiency.

<Means for Solving the Problems> Therefore, in the present invention, as shown in FIG. Depth of field detection means for detecting the depth of field of a subject in a still video camera comprising: Conversion efficiency selection for selecting the conversion efficiency of the quantization code in the high-efficiency code conversion means based on the depth of field detected by the depth of field detection means and changing the conversion efficiency according to the depth of field. The image conversion device is configured to include means.

Further, as shown by the dotted line in FIG. 1, field/frame dependent conversion efficiency variable means is provided which changes the conversion efficiency of the quantization code in the high efficiency code conversion means depending on whether the image signal is a field image or a frame image. It may also be provided.

Furthermore, as shown by the dotted line in Figure 1, there is a light amount reaching distance detecting means for detecting the light amount reaching distance of the flash device, a subject distance detecting means for detecting the distance to the subject, and a distance detecting means for detecting the distance to the subject detected by the subject distance detecting means. The conversion efficiency by the flash device changes the conversion efficiency of the quantization code in the high-efficiency code conversion means to a higher side when the distance is the object distance detection means for detecting the light amount reaching distance detected by the light amount reaching distance detecting means. A variable means may also be provided.

Further, it may be configured such that at least one of automatic exposure control means and automatic focus control means is provided, and the depth of field detection means detects the depth of field using control information in these control means.

<Operation> According to the image conversion device for a still video camera configured as described above, the conversion efficiency selection means selects a high-efficiency code based on the depth of field detected by the depth of field detection means, in other words, the required resolution of the image. The conversion efficiency of the quantization code in the conversion means is selected and the conversion efficiency is changed according to the depth of field, and the quantization level (data compression level) of the image signal stored in the image storage means is changed.

Furthermore, since the resolution of an image differs depending on whether the image is a field image or a frame image, the field/frame dependent conversion efficiency variable means is capable of high efficiency code conversion depending on whether the image is a field image or a frame image. The conversion efficiency of the quantization code in the means is changed.

Furthermore, when the object distance detection means detects the distance to the subject detected by the object distance detection means rather than the light amount reach distance of the flash device detected by the light amount reach distance detection means, the conversion efficiency variable means by the flash device The conversion efficiency of the quantization code in the high-efficiency code conversion means is changed to a higher side, and the conversion efficiency of the image signal is increased when the subject is at a distance where the amount of light from the flash device does not reach.

Furthermore, in devices equipped with at least one of automatic exposure control means and automatic focus control means, the depth of field detection means uses control information (for example, distance to the subject and aperture value) in these control means to detect the subject. If the configuration is configured to detect the depth of field, there is no need to obtain information individually by means of using common information.

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

In FIG. 2 showing a still video camera according to an embodiment of the present invention, an optical image signal of a subject imaged on an image sensor 2 such as a CCD through an optical lens l is converted into an electrical image signal by the image sensor 2. converted.

The electrical image signal output from the image sensor 2 is subjected to basic analog processing such as correlated double sampling (CDS) and γ correction in a preamplification correction circuit 3, and then sent to an A/D converter 4.
is converted into a digital image signal. Then, the image signal is subjected to decoding operations such as YC separation and RGB separation and address and timing control to the image memory 6 by the digital process circuit 5, and is temporarily stored in the image memory 6.

The image data in the image memory 6 is compressed by a high-efficiency code converter 7 as a high-efficiency code conversion means that performs, for example, discrete cosine transform encoding, using an arithmetic memory 8, and the data-compressed image signal is , and is transferred to and stored in an external memory card 10 as an image storage means via an interface 9 including a buffer memory.

The memory card 10 has a built-in semiconductor memory such as an EEFROM or an SRAM with backup, and is configured to be detachable from the camera body.

The above configuration is a general configuration of a digital storage type still video camera, and next, the configuration according to the present invention will be explained.

In this embodiment, a high-efficiency code converter 7 is used in which the compression rate (conversion efficiency) can be variably selected by software control or hardware control, which has recently been used in the industry. The compression rate control of the high-efficiency code converter 7 is performed using software or hardware information ( compression control signal).

The depth of field calculation processor 11 includes an aperture value detection device 12. From the focal position detection device 13 and the lens focal length detection device 14, aperture value information F corresponding to the brightness of the subject, distance U to the subject, and information on the lens focal length f are obtained. In addition, if the optical lens 1 has a fixed aperture and focal length and there is no lens exchange, the aperture value F, distance U to the subject, and focal length f will be constant values, so the shooting timing will be different. There is no need to input the information each time, and in this case, for example, these data may be stored in the depth of field calculation processor 11 in advance.

The depth of field calculation processor 11, into which the information of the aperture value F, distance U to the subject, and focal length f is input, is based on the determination whether the image is a field image or a frame image. Determine the matching circle of confusion δ. The circle of confusion δ is the size of a decomposed image that can be determined from the entire image in a system that captures and displays an image, which is uniquely determined by the eye or the resolution of the display. Therefore, depending on the display capability, etc., it may not be necessary to change this value for field images and frame images. Incidentally, as described above, the depth of field calculation processor 11 also serves as field/frame dependent conversion efficiency variable means.

Here, the above aperture value F and the distance to the subject @u.

From the information on the focal length f and the circle of confusion δ, the depth of field d can be calculated and determined according to the following equation.

t'-u'σ'' F & The above calculation formula calculates the object distance u 11 that allows the image to be formed within the circle of confusion δ during forelight and afterheating as shown in FIG.
* d, -δFu / (f''+uδF), d, -δ, which is obtained as the difference between u t and the subject distance U at the time of focus.
Fu''/(f'' uδF), and if the subject is within the range d centered around the in-focus position, the image will be formed within the circle of confusion δ and will be clearly photographed as an image. Ru.

When the depth of field d is obtained as described above, the corresponding compression rate η is searched from a map of compression rates (code conversion rates) η that are preset corresponding to this depth of field d. I ask. Here, the compression ratio η map is such that the smaller (shallower) the depth of field d, the higher the compression ratio η, and when the image is a frame image, it is higher than when it is a field image. This is so that a high compression ratio η is selected. When the depth of field d is shallow, the image will be blurred even at a point slightly deviated from the in-focus point, and the image of the background often does not require detailed resolution, so the compression ratio η is set high as described above. Conversely, when the depth of field d is deep, the entire screen often requires detailed resolution, so the compression ratio η should be set low. Furthermore, when the same object is photographed, a lower compression ratio η is selected for a field image with less effective remaining amount of resolution information than a frame image.

Note that whether the image is a field image or a frame image is determined based on a switching signal from a field/frame switching switch 15 provided on the camera body and operated arbitrarily by the photographer.

When the compression rate (code conversion rate) η is determined in this way, the depth of field calculation processor 11 outputs the information on the compression rate η to the high-efficiency code converter 7, and the information on the compression rate η is The input high-efficiency code converter 7 compresses the image data in the image memory 6 based on the compression ratio η.

Next, the setting control of the compression ratio η based on the depth of field d and field/frame images as described above will be explained with reference to the flowchart shown in FIG.

First, step 1 (indicated as Sl in the figure).

(Similarly below), the distance information U to the subject is input manually, the aperture value F is input in the next step 2, and the focal length f is input in step 3.

Then, in step 4, it is determined whether field recording or frame recording is selected, and the optimum circle of confusion δ for each is determined in step 5.14,
In step 6 and step 15, based on the circle of confusion δ, field recording and frame recording are each
The depth of field d is calculated.

In the map of the compression ratio η, as shown in Figure 5, the thresholds that divide 1/depth of field d into four stages are set separately for field recording and frame recording. When 1/depth of field d is calculated for field recording and frame recording, the threshold value A is calculated for frame recording.

By comparing B, C and 1/depth of field d,
Compression rate (code conversion rate) η(-1/2.1) set for each 1/depth of field d divided by thresholds A, B, and C
/4.1/8.1/16) is selected (steps 7 to 13), while in field recording, thresholds A', B', C' and 1/depth of field d By comparing the compression ratio η(=1/2°1/4.1/
8.1/16) is selected (step 16
~Step 22).

Next, a procedure for determining the code conversion rate of image data in a still video camera equipped with a flash device such as a strobe will be explained.

In the system configuration of FIG. 2, a device 16 for detecting the guide number GNO of the strobe is provided.

Guide number GN as this light amount reaching distance detection means
The O detection device 16 receives, for example, voltage information from a strobe,
In the case of a built-in strobe, the guide number GN0 is detected by storing predetermined setting values.

Strobe guide number obtained in this way〇N
Using O or its equivalent information and the aperture value F detected by the aperture detection device 12 or its equivalent information, the maximum distance X that the strobe light can properly reach is determined by the following formula.

X=GNo/F Image information of a subject located at a distance exceeding the maximum distance If the resolution is improved by lowering the compression ratio η for a dark image, redundancy will occur in the image information.

Therefore, the headlight field position Y = u - dx (d, = δFu”
/ (f" + uδF)), and if there is not enough depth of field from the in-focus point at the position where the strobe light can reach the maximum with the current aperture value F, the image information will be strongly compressed. That is, even in a distance region within the maximum distance X where the amount of light is appropriate, if a sufficiently small circle of confusion δ is not obtained, the image will have a soft tone and high compression can be applied.

Therefore, according to the values of the maximum distance The compression ratio η is switched when using a strobe depending on whether the Z value of ) is positive or negative, and when Z is positive, the strobe light intensity and depth of field are appropriate. The compression ratio η is set based on the depth of field d and field/frame recording described above, and when 2 is negative, compression can be applied strongly, so the maximum value is selected as the compression ratio η. Note that the focus position detection means for detecting the distance U to the subject used for calculating the foreground field position Y corresponds to the subject distance detection means.

The flowchart in FIG. 6 shows the compression ratio η determination control (conversion efficiency variable means using a flash device) when using a strobe.

First, in step 31, the strobe kite number G
If NO is input, the distance U to the subject is input in step 32, and the aperture value F is further input in step 33.

Then, in step 34, the maximum distance x (←G, , /F) that the strobe light can properly reach is calculated.

In step 35, the focal length f of the lens is input, and in the next step 36, the circle of confusion δ is determined. Then, in step 37, the headlight depth of field d2 is calculated from the aperture value F, the distance U to the subject, the focal length f, and information about the circle of confusion δ.

In step 3, the headlight field position Y (=u-d,
> is calculated, and in the next step 39, by comparing X and Y+α (α is a correction term), it is determined whether the image exceeds the reachable distance of the strobe light, and the strobe light reaches If the distance is exceeded and it is impossible to form an image with an appropriate amount of light (X<Y+α), the process proceeds to step 4o, and the maximum compression ratio η in this embodiment is selected as 1/16. - On the other hand, when the subject is at a distance that the strobe light can reach with an appropriate amount of light (X≧Y+α), the compression ratio η is determined based on the depth of field d and field/frame recording shown in the flowchart of Fig. 4. Let it happen.

In this way, in this embodiment, information on the aperture value F, distance U to the subject, focal length f, circle of confusion δ, and information on the strobe guide number 〇NO are stored in the depth of field calculation processor 1.
1 to determine the compression ratio η, but this information used to determine the compression ratio η is input to the automatic focus control device (automatic focus control means) and the automatic exposure control device (automatic exposure control The compression ratio η determination control shown in this embodiment can be combined with the automatic focus control function and the automatic exposure control function.

That is, the distance U to the subject can be obtained by conventionally known active or passive automatic focus control devices (AF), and from the automatic exposure control device (AE), the apex value Av of the F number, that is, can be obtained from the following relationship. The aperture value F can be obtained.

Av1 Tv-Ev=Lv-3v+Bv Bv-F, +-Pv However, Av: Apex value of F number Tv: Apex value of shutter exposure time (seconds) Ev: Apex value of exposure value Lv: Previous apex value Sv : Apex value of the sensitivity of the image sensor Bv: Apex value of the brightness of the subject In the case of TTL photometry, F, 4: Apex value of the aperture value of the lens optical system Pv: Apex value of the photometric value Therefore, automatic focus control function and automatic exposure If the camera is equipped with a control function, information on the distance U to the subject and the aperture value F can be obtained as information for automatic focus control and automatic exposure control without the need to provide separate sensors.

FIG. 7 shows the system configuration when the automatic focus control function, automatic exposure control function, and compression ratio η determination control are provided together as described above, and the aperture value detection device in FIG. 12 and the focus position detection device 13 are omitted, and instead an aperture diaphragm/shutter control device 17. is used for automatic focus control and automatic exposure control. Focus position control device 18. Lens opening F, value detection device 19. Photometric device 20.
A distance measuring device 21 is provided.

Here, the lens open FM value detection device 19. Photometric device 20. The detection result from the distance measuring bag 221 is input to the AE/AFF depth of field calculation processor 11, and the AE-AP depth of field calculation processor 11 is also inputted in the same way as in the case of FIG. Strobe guide number detection device 16. Information from the lens focal position detection device 14 is also input. And A.E.
- The AFF depth of field calculation processor 11 outputs control signals to the aperture diaphragm/shutter control device 17 and the focus position control device 18 based on various information to perform automatic focus control and automatic exposure control. The compression ratio η is optimally set as described above using the aperture value F and the distance U to the subject obtained from the exposure control.

In addition, in FIG. 7, the automatic focus control means is the distance measuring device 21.
．． The automatic exposure control means is composed of a focus position control device and an AE-AFF depth of field calculation processor 11, and includes a lens opening F8 value detection device 19.degree. photometer 20. Lens focal length detection device 14. Aperture diaphragm/shutter control device 17 and AE-AF depth of field calculation processor 11
Consisted of.

By the way, when changing the compression rate η of image data depending on the depth of field d or whether it is field recording or frame recording as in this embodiment, the reproduction side changes the compression rate η based on the compression rate η of each image. Since it is necessary to perform compression processing (expansion processing), the data of the compression ratio η used for the compression processing of the image signal is stored in the memory for each image, as shown in FIGS. 8 and 9, for example. .

In the example shown in FIG. 8, first, the start address of each screen and the compression code (encoded with the compression ratio η) of each screen are stored as a table of contents of the screen that has been photographed and stored. The image data of each screen is stored after the section.

Furthermore, in the example shown in FIG. 9, the memory area is divided into the smallest read areas, and the number (cluster number) indicating each area is stored at the beginning of the memory as a table of contents indicating the storage area of the screen. , Next to the cluster number indicating the area where the image data of each screen is stored, the date code of that screen is stored, and then the compression code of that screen is stored next.

<Effects of the Invention> As described above, according to the present invention, the conversion efficiency of a quantization code in high-efficiency code conversion for quantum encoding an image signal is variably controlled based on the depth of field, and Since the conversion efficiency is variably controlled based on the field/frame image and the amount of light reached by the flash device, the image signal can be encoded with the highest efficiency without sacrificing image clarity, and the memory capacity can be reduced. This has the effect of achieving a high level of both savings in image quality and image quality.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of the present invention, Fig. 2 is a block diagram showing a system outline of an embodiment of the present invention, Fig. 3 is a diagram showing the calculation characteristics of depth of field, and Fig. 4 5 is a flowchart showing the control contents in the above embodiment, FIG. 5 is a diagram showing the variable selection characteristics of the compression ratio (conversion efficiency) in the above embodiment, and FIG. 6 is a flow chart showing the control contents when using the flash device in the above embodiment. The flowchart shown in Figure 7 is
A block diagram showing an embodiment in which a part of the illustrated system outline is changed, FIGS. 8 and 9 are diagrams showing the storage state in the memory in the same embodiment, and FIGS. 10 and 11 respectively.
Each figure is an image sample diagram for explaining the appropriate compression ratio depending on the shooting conditions. 1... Optical lens 2... Image sensor 4...
A/D converter 7... High efficiency code converter 10.
...Memory card 11...Depth of field calculation processor 12...Aperture value detection device 13...Focus position detection means 14...Lens focal length detection device 16.
... Strobe guide number detection device 17... Aperture diaphragm/shutter control device 18... Focal position control device 20... Photometering device 21... Distance measuring device

Claims (4)

[Claims] (1) A high-efficiency code conversion means that can variably select the conversion efficiency of a quantization code, and storing an image signal obtained by an image sensor in the form of a quantization code converted by the high-efficiency code conversion means. A still video camera comprising: an image signal storage means; a depth of field detection means for detecting the depth of field of a subject; and a depth of field detected by the depth of field detection means. An image in a still video camera characterized by comprising: conversion efficiency selection means for selecting the conversion efficiency of the quantization code in the high-efficiency code conversion means and changing the conversion efficiency according to the depth of field. conversion device. (2) A field/frame dependent conversion efficiency variable means is provided for changing the conversion efficiency of the quantization code in the high-efficiency code conversion means depending on whether the image signal is a field image or a frame image. An image conversion device for a still video camera according to claim 1. (3) a light amount range detection means for detecting the light amount range of the flash device; a subject distance detection means for detecting the distance to the subject; and when the detected distance to the subject exceeds the light amount range, 3. The still video camera according to claim 1, further comprising: conversion efficiency variable means using a flash device for changing the conversion efficiency of the quantization code in the efficiency code conversion means to a higher side. Image conversion device. (4) At least one of automatic exposure control means and automatic focus control means is provided, and the depth of field detection means is configured to detect the depth of field using control information in the control means. An image conversion device for a still video camera according to claim 1, 2 or 3.