JPH11275520A - Digital camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital camera that momentarily displays an image to confirm a photographed image in recording in a finder mode even when the capacity of a mounted memory is comparatively small. SOLUTION: A digital camera is provided with a conversion means S2 that receives a photographing signal of an object picked up by an image pickup means and converts the photographing signal into an image signal consisting of a luminance signal and color difference signals, a compression means S4 that compresses the image signal at a prescribed compression rate, a recording means S9 that records the compressed data by the compression means S4 on a record medium and a display means S6 that displays the object image based on the image signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a digital camera, and more particularly to a digital camera configured to compress a digital image signal and record it in a memory.

[0002]

2. Description of the Related Art In a digital camera, a memory card is detachably connected to a camera body having an image pickup optical system and a solid-state image pickup device, and image information representing a still image picked up by the image pickup device is transmitted to the memory card as a digital signal. Accumulated in the form. The stored image information is reproduced and displayed on a liquid crystal monitor or the like built in the camera body.

In a digital camera, a digital image signal before being recorded in a memory is subjected to data compression using, for example, a discrete cosine transform (DCT) or the like, and then recorded in the memory, thereby saving memory capacity. I have.

When a digital image signal is subjected to data compression by orthogonal transform coding or the like and recorded in a memory, the data compression ratio varies depending on the definition of the image, and a monotone image having a low spatial frequency has a high compression ratio. In an image having a small amount of data and containing many high-frequency components, the compression rate is low and the amount of data is large. Therefore, the number of images that can be recorded in one memory varies depending on the image to be photographed and is undefined, and is inconvenient to use. Therefore, data compression is performed so that the data amount per image is constant. Considering that the number of images that can be recorded in the memory is constant.

Further, a method has been devised in which, at the time of recording, a data compressed data is decompressed and displayed on a liquid crystal monitor so that it is possible to confirm whether or not an appropriate compression ratio is selected (Japanese Patent Laid-Open No. 4-886). .

[0006]

However, in order to confirm the image by expanding the image data which has been subjected to the data compression as described above, the processing time becomes long, and as a result, the power consumption also increases. In addition, when the number of pixels of the image sensor increases, a large-size buffer memory is required to simultaneously store data obtained from the image sensor and data obtained by converting the data into a luminance signal and a color difference signal on a memory. turn into.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to enable a digital camera having a relatively small memory capacity to instantaneously check whether or not a recorded image is captured in a good condition.

[0008]

A digital camera according to the present invention captures an image signal of a subject by an image pickup means, converts the image pickup signal into an image signal of a luminance signal and a color difference signal, and converts the image signal into an image signal of a luminance signal and a color difference signal. Compression means for compressing the compressed data at a predetermined compression rate, recording means for recording the data compressed by the compression means on a recording medium, and display means for displaying the subject based on the image signal. And

In the present invention having such a configuration,
Displaying a captured image on a display unit using an image signal obtained by converting an imaging signal obtained from an imaging unit before calculation of a generated code amount performed by a compression unit when recording a video while operating in the finder mode. Accordingly, even with a digital camera having a small memory capacity, the photographer can instantly confirm whether or not the photographed image is photographed in a good state.

Further, since data before the compression processing is used, there is no need to perform a conversion processing to special display data, and
The waiting time until the image data is displayed can be reduced. Further, if necessary, the exposure, white balance, or the presence or absence of strobe light emission can be changed to evaluate the quality of the image. In this way, by instantly viewing the actually captured image, only image data determined to be good can be recorded on the recording medium, and unnecessary recording of image data can be avoided.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of the configuration of an embodiment of the present invention. In the figure, the same parts are indicated by the same reference numerals. In the figure, 1 is an imaging lens, 2 is an aperture, 3 is an imaging device, Device. 4 is a sample-and-hold, 5 is an amplifier, 6 is an A / D converter, 7 is a signal processing unit that converts an image signal into a luminance signal and a color difference signal, and further performs compression processing of these signals, and 8 is a D / A converter. 9 is a liquid crystal display unit, 10 is a timing generator, 11 is a system controller, 12 is a recording unit, 13 is a work buffer, 14 is a photometric element, 15 is a video amplifier, and 16 is an operator designating whether or not a viewfinder is operated. , And an operation unit indicating a shutter release and the like.

Next, the operation in such a configuration will be described. Photographing, reproduction, transfer of various data, and other processes in the digital camera are controlled by the system controller 11. When the viewfinder mode is selected by the operation unit 16, the amount of the subject image captured by the imaging lens 1 is controlled by the aperture 2 and is formed on the imaging element 3. The image pickup signal photoelectrically converted by the image pickup device 3 is sampled by a sample hold 4 and amplified by an amplifier 5 at an appropriate amplification rate.
Is converted into a digital signal.

The digital signal is input to a signal processing unit 7 and subjected to pre-processing such as clamping, shading correction, white balance processing, and gamma correction.
Data for one screen is stored in the work buffer 13.
The work buffer 13 has a display data area for display data in addition to storing the data for one screen.

Further, the pre-processed data stored in the work buffer 13 is again input to the signal processing unit 7 and converted into a luminance signal and a color difference signal.
3 is stored in a display data area in a format suitable for outputting a video signal. The data stored in the work buffer 13 is sequentially transferred to a digital video encoder built in the signal processing unit 7 by a DMA controller built in the signal processing unit 7, where the data is stored in the NTS.
After being converted into a C video signal, it is converted into an analog signal by a D / A converter 8 and supplied to a monitor built into the main body or an external monitor via a video amplifier 15.

Next, the operation when the shutter release of the operation unit 16 is pressed in the viewfinder mode will be described with reference to FIG. When the shutter release is pressed during the viewfinder mode, the system controller 11 transmits an imaging data capture request command to the signal processing unit 7. Upon receiving the imaging data capture request, the signal processing unit 7 suspends the viewfinder mode currently being processed, sets a recording signal processing coefficient, and stores the imaging signal in the work buffer 13 (S1). At this time, similar to the viewfinder processing,
The amount of light of the subject image captured by the imaging lens 1 is controlled by the aperture 2 and is formed on the imaging element 3. Image sensor 3
The photoelectrically converted image signal is sampled by the sample-and-hold 4, amplified by the amplifier 5 at an appropriate amplification rate, and then converted by the A / D converter 6 into a digital signal.
This digital signal is input to the signal processing unit 7 and subjected to pre-processing such as clamp processing, shading correction processing, white balance processing, and gamma correction. In addition, the signal processing unit 7 does not stop the DMA transfer for outputting the video signal even after receiving the imaging data capture request, and continues the operation. The image immediately before being pressed continues to be displayed.

The image data for one screen stored in the work buffer 13 is read out to the signal processing unit 7 one pixel at a time in units of 8.times.8 pixels. From data with repetition period,
It is converted into a luminance signal and a color difference signal (S2). The converted data for one pixel is sub-sampled and stored in the display data area of the work buffer 13 for display in a finder (S3). This process is continued until one screen is stored as described below.

On the other hand, the converted data is subjected to a compression process in order to determine a compression coefficient at the time of recording (S4). The compression coefficient at this time is a predetermined value (for example,
Coefficient corresponding to the lowest compression ratio). By performing the compression process, the generated code amount of the block in units of 8 × 8 is calculated. The luminance and chrominance signals generated for calculating the generated code amount are temporarily discarded at this time to reduce the memory capacity. By repeating this process for one screen, the generated code amount when the image for one screen is compressed is calculated, and the preview data of the captured image is generated in the work buffer 13 (S5). Compression loop).

When the processing for one screen is completed, the signal processing unit 7 stops the DMA transfer for monitor output, and starts the monitor output DMA transfer from the preview data area generated from the image data. This image data is D /
The A converter 8 converts the signal into an analog video signal. As a result, the captured image is displayed on the monitor built into the main body or on the external monitor immediately after the image capturing (S6).

The photographer can check the state of the photographed image by viewing the image displayed on the built-in monitor or the external monitor. The signal processing unit 7 determines a compression coefficient to be used in the recording compression process (second compression loop) from the relationship shown in FIG. 3 based on the value indicating the generated code amount calculated by the first compression loop for the data of the entire screen. (S7). That is, the compression coefficient at the time of the first compression loop is Q
0, and the generated code amount obtained at this time is C0. Assuming that the target generated code amount at the time of recording is C1, the compression coefficient used in the second compression loop is set by referring to the table for the compression coefficient Q1 corresponding to the generated code amount C1 for the captured image from the relationship shown in FIG. I do.

Thus, when the compression coefficient is set to a predetermined generated code amount, the work buffer 13 is renewed.
Is read out to the signal processing unit 7 in units of 8 × 8 pixels and converted into a luminance signal and a color difference signal (S8), and a two-dimensional discrete cosine transform (DCT) is performed. The obtained DCT coefficient is quantized and compression processing is performed (S9). If image data for one screen is stored, the compressed image data is sent to the recording unit 12 and recorded on a recording medium (not shown) (S
9).

On the other hand, at the time of reproduction, image data is read out from a recording medium (not shown) to the work buffer 13 via the recording unit, and the signal processing unit 7 performs processing reverse to that at the time of recording, and converts the compressed data into a luminance signal. A color difference signal is generated, expanded in the work buffer 13, and converted into a D / A signal as a video signal.
The signal is converted into an analog signal by the converter 8 and supplied to a monitor built in the main body or to an external monitor via the video amplifier 15. In the above embodiment, the number of pixels to be processed in the first compression loop is all pixels. For example, this is achieved by using image data that is sub-sampled in both the horizontal and vertical directions by サ ン プ ル. The processing time may be further reduced.

[0022]

As described above, according to the configuration and method of the present invention, the image data is left in the buffer memory as it is, and the luminance signal and chrominance generated in the first compression loop for determining the compression coefficient are determined. Since the data for monitor output is sub-sampled from the signal and stored in the memory, the memory capacity can be reduced compared to the case where the luminance signal and color difference signal for the entire screen are stored in the memory, and the compression can be performed. It is possible to confirm the state of a captured image more quickly than when decompressing data again and creating display data.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a processing flow of the present invention.

FIG. 3 is a schematic diagram illustrating a relationship between a compression coefficient and a generated code amount according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Imaging lens 2 Aperture 3 Image sensor 4 Sample hold 5 Amplifier 6 A / D converter 7 Signal processing unit 8 D / A converter 9 Liquid crystal display unit 10 Timing generator 11 System controller 12 Recording unit 13 Work buffer 14 Photometric device 15 Video Amplifier 16 Operation unit

Claims (1)

[Claims] A converting means for capturing an image signal of a subject by an image capturing means and converting the image signal into an image signal of a luminance signal and a color difference signal; and a compressing means for compressing the image signal at a predetermined compression rate based on the image signal. A digital camera, comprising: recording means for recording data compressed by the compression means on a recording medium; and display means for displaying the subject based on the image signal.