JP2004040519A - Digital camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital camera capable of shortening a photographing interval. <P>SOLUTION: Raw image data of the same resolution as the effective resolution of a CCD (charge coupled devices) imager 16 are first written in an SDRAM 38. A signal processing circuit 24 and a zoom circuit 28 generate freeze image data for display on the basis of the raw image data, a JPEG codec 34 compresses the generated freeze image data at an initial compression rate, and a CPU 48 calculates an optimum compression rate on the basis of the size of the compressed freeze image data. The signal processing circuit 24 and a zoom circuit 26 generates main image data for recording on the basis of the raw image data stored in the SDRAM 38, and the JPEG codec 34 compresses the main image data according to the optimum compression rate. The compressed main image data are recorded on a recording medium 46. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a digital camera, and more particularly to a digital camera that displays, for example, a captured subject image on a monitor and records the captured image on a recording medium in a compressed state.
[0002]
[Prior art]
In a conventional digital camera, when a photographing operation is performed, a main image signal of a subject is compressed at an initial compression ratio, and an optimal compression is performed based on a size of the compressed main image signal obtained by this compression, a target size, and an initial compression ratio. The compression ratio is calculated, the main image signal is recompressed according to the calculated optimum compression ratio, and the compressed main image signal obtained by the recompression is recorded on the recording medium.
[0003]
[Problems to be solved by the invention]
However, in the related art, since it is necessary to perform the compression process twice on the main image signal, there is a problem that it takes time from the photographing operation to the completion of recording, and the photographing interval becomes long.
[0004]
Therefore, a main object of the present invention is to provide a digital camera capable of shortening a photographing interval.
[0005]
[Means for Solving the Problems]
According to a first aspect of the present invention, in a digital camera for displaying a subject image captured by an image sensor on a monitor and recording the captured image on a recording medium in a compressed state, a writing unit for writing a captured image signal having the same resolution as the effective resolution of the image sensor to a memory A first generation unit that generates a display image signal based on a captured image signal stored in a memory, a specification unit that specifies an optimal compression ratio that can compress a display image signal to a target size, and a desired resolution from a plurality of resolutions. Selecting means for selecting, a second generating means for generating a recorded image signal having a desired resolution based on the captured image signal stored in the memory, and a compressing means for compressing the recorded image signal according to an optimal compression ratio. Digital camera.
[0006]
According to a second aspect, a first image signal of a YUV format having a first resolution and a second image signal of a YUV format having a second resolution higher than the first resolution are generated based on a captured image signal, and In a digital camera that displays an image based on an image signal on a monitor and records the second image signal in a compressed state on a recording medium, a Y signal component, a U signal component, and a V signal component included in the first image signal are individually Writing means for writing to a memory; specifying means for specifying an optimum compression ratio capable of compressing a Y image component, a U signal component, and a V signal component stored in the memory to compress a first image signal to a target size; and a second image signal Is a digital camera characterized in that it comprises a compression means for compressing at an optimum compression ratio.
[0007]
[Action]
In the first invention, when the subject image photographed by the image sensor is displayed on a monitor and recorded in a compressed state on a recording medium, first, a photographed image signal having the same resolution as the effective resolution of the image sensor is written into the memory by the writing means. Written. The first generation unit generates a display image signal based on the captured image signal stored in the memory, and the specification unit specifies an optimal compression ratio that can compress the display image signal to a target size. When a desired resolution is selected from the plurality of resolutions by the selecting means, the second generating means generates a recording image signal having the desired resolution based on the captured image signal stored in the memory. The generated recording image signal is compressed by the compression means in accordance with the optimum compression ratio.
[0008]
As described above, even when any one of the plurality of resolutions is selected, the display image signal is generated based on the captured image signal having the same resolution as the effective resolution of the image sensor, and the optimal compression ratio is determined based on the display image signal. Specified.
[0009]
Preferably, the resolution that can be selected by the selection means is equal to or less than the effective resolution. The monitor displays an image based on the display image signal, and the recording medium records the compressed recording image signal generated by the compression unit.
[0010]
Preferably, the specifying means compresses the display image signal at a predetermined compression ratio, detects the size of the compressed display image signal obtained thereby, and calculates an optimum compression ratio based on the detected size.
[0011]
According to the second aspect, a first image signal of a YUV format having a first resolution and a second image signal of a YUV format having a second resolution are generated based on the captured image signal. An image based on the first image signal is displayed on the monitor, and the second image signal is recorded on the recording medium in a compressed state. Here, the writing means individually writes the Y signal component, the U signal component and the V signal component included in the first image signal into the memory, and the specifying means writes the Y signal component, the U signal component and the V signal component stored in the memory. An optimum compression ratio at which the signal component is compressed to compress the first image signal to a target size is specified. The second image signal is compressed at an optimum compression ratio by the compression means.
[0012]
Since the Y signal component, the U signal component, and the V signal component included in the first image signal are individually written into the memory, the compression of the first image signal for calculating the optimal compression ratio is quickly performed.
[0013]
Preferably, the specifying means compresses the display image signal at a predetermined compression ratio, detects the size of the compressed display image signal obtained thereby, and calculates an optimum compression ratio based on the detected size.
[0014]
【The invention's effect】
According to the first aspect, since the optimum compression ratio is specified based on the display image signal, the recompression of the recording image signal is not required, and the photographing interval can be shortened. In addition, even when any one of the plurality of resolutions is selected, the display image signal is generated based on the captured image signal having the same resolution as the effective resolution of the image sensor, so that the optimal compression ratio is set regardless of the selected resolution. It can be obtained with high accuracy.
[0015]
According to the second aspect, since the optimum compression ratio is specified based on the low resolution first image signal, recompression of the high resolution second image signal becomes unnecessary, and the photographing interval can be shortened. . Further, by individually writing the Y signal component, the U signal component, and the V signal component included in the first image signal into the memory, the compression of the first image signal for calculating the optimal compression ratio is quickly performed. This also contributes to shortening the photographing interval.
[0016]
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.
[0017]
【Example】
Referring to FIG. 1, a digital camera 10 of this embodiment includes a CCD imager 16. The light receiving surface of the CCD imager 16 is covered by a color filter 14 in which color elements of Cy (cyan), Ye (yellow), Mg (magenta) and G (green) are arranged in a mosaic pattern as shown in FIG. The optical image of the subject is applied to the light receiving surface of the CCD imager 16 via the optical lens 12 and the color filter 14. Note that the number of effective pixels of the CCD imager 16 is about 4 million pixels, there are "2288" effective pixels in the horizontal direction of the light receiving surface, and "1712" effective lines in the vertical direction of the light receiving surface. .
[0018]
When the power is turned on, the CPU 48 commands the TG (Timing Generator) 22 to repeat exposure and thinning-out reading in order to display a real-time moving image (through image) of the subject on the LCD monitor 42. The TG 22 exposes the CCD imager 16 in response to a vertical synchronizing signal generated every 1/30 seconds, and converts a raw image signal (charge) generated by the exposure by a vertical thinning method in response to a 24 MHz clock. read out. From the CCD imager 16, a raw image signal in which vertical lines are thinned out to 1/8 is output. When attention is paid to eight vertically continuous lines, only the first Cy, Ye,... Line and the eighth Mg, G,... Line line are read out, and the other line signals are swept away. . Therefore, the raw image signal of 2288 pixels × 214 lines output from the CCD imager 16 includes all the color information of Cy, Ye, Mg and G.
[0019]
The raw image signal output from the CCD imager 16 is subjected to noise removal and level adjustment by a CDS / AGC circuit 18. The A / D converter 20 converts the raw image signal output from the CDS / AGC circuit 18 into digital data (raw image data) at a clock rate of 24 MHz. When displaying the through image on the monitor 42, the CPU 48 connects the switch SW1 to the terminal S1, and connects the switch SW2 to the terminal S3. Accordingly, the raw image data of 2288 pixels × 214 lines output from the A / D converter 20 is provided to the signal processing circuit 24 via the switch SW1, and is subjected to signal processing such as color separation or YUV conversion to obtain Y: U: It is converted into V = 4: 2: 2 YUV data. When a through image is output, the signal processing circuit 24 operates at a clock rate of 24 MHz, and YUV data is output from the signal processing circuit 24 at a transfer rate of 24 MHz.
[0020]
The YUV data of 2288 pixels × 214 lines output from the signal processing circuit 24 is provided to the zoom circuit 28 via the switch SW2. When outputting a through image, the CPU 48 sets the horizontal zoom magnification “768/2288” and the vertical zoom magnification “240/214” in the zoom circuit 28. The zoom circuit 28 performs a zoom process according to the set zoom magnification, and thereby the YUV data of 768 pixels × 240 lines is output from the zoom circuit 28. The output YUV data of 768 pixels × 240 lines is supplied to the buffer control circuit 30.
[0021]
Referring to FIG. 4, buffer control circuit 30 includes controllers 302a to 302e. Buffers 301a to 301e for temporarily storing data and counters 303a to 303e incremented at a clock rate of 96 MHz are individually assigned to the controllers 302a to 302e. A reference address value is loaded by the CPU 48 into the controllers 302a to 302e.
[0022]
Data writing to the SDRAM 38 is performed by the controllers 302a to 302c. Each of these controllers provides a write request signal to SDRAM control circuit 36. On the other hand, when the acknowledge signal is returned from the SDRAM control circuit 36, the controller reads out the data stored in its own buffer at a clock rate of 96 MHz, and reads the loaded reference address value and the count value of its own counter. , And outputs the read data and the determined address value to the SDRAM control circuit 36. As a result, data is written to a desired address of the SDRAM 38 by the SDRAM control circuit 36.
[0023]
Data reading from the SDRAM 38 is performed by the controllers 302d to 302e. Each of these controllers supplies a read request signal to the SDRAM control circuit 36. When the approval signal is returned from the SDRAM control circuit 36, the controller outputs the SDRAM address value determined based on the loaded reference address value and the count value of its own counter to the SDRAM control circuit 36. As a result, the data written at the desired address of the SDRAM 38 is read by the SDRAM control circuit 36. The read data is written to its own buffer at a clock rate of 96 MHz.
[0024]
Since the SDRAM 38 employs the burst transfer method, the output of the address value from each of the controllers 302a to 302e to the SDRAM control circuit 36 is performed intermittently.
[0025]
The YUV data of 768 pixels × 240 lines output from the zoom circuit 26 shown in FIG. 1 at the time of the through image output is input to the controller 302a and subjected to frequency conversion (24 MHz → 96 MHz) by the buffer 301a. The SDRAM 38 is mapped in the manner shown in FIG. 3, and the controller 302a is loaded with the start address value of the display image area 38a as a reference address value. Therefore, the YUV data of 768 pixels × 240 lines read from the buffer 301a is written into the display image area 38a by the controller 302a and the SDRAM control circuit 36.
[0026]
The top address value of the display image area 38a is loaded as a reference address value into the controller 302e shown in FIG. Therefore, the YUV data of 768 pixels × 240 lines stored in the display image area 38a is read out by the controller 302e and the SDRAM control circuit 36, and given to the video encoder 40 through frequency conversion (96 MHz → 24 MHz) by the buffer 301e. Can be The video encoder 40 converts the YUV data into a composite image signal, and provides the converted composite image signal to the LCD monitor 42. As a result, a through image having a resolution of 768 pixels × 240 lines is displayed on the monitor screen.
[0027]
Referring to FIG. 5, two banks A1 and B1 each capable of storing YUV data of 768 pixels × 240 lines are formed in display image area 38a. When the YUV data is written to the bank A1, the YUV data is read from the bank B1, and when the YUV data is written to the bank B1, the YUV data is read from the bank A1.
[0028]
When the shutter button 50 is operated, the CPU 48 commands the TG 22 to perform one exposure and one all-pixel reading in order to record the subject image on the recording medium 46. The TG 22 exposes and reads out all pixels to the CCD imager 16, whereby a raw image signal of 2288 pixels × 1712 lines is output from the CCD imager 16 at a speed of 24 MHz. The CCD imager 16 is an interlaced scan type image sensor, and outputs a raw image signal of 2288 pixels × 856 lines generated by odd lines in an odd field, and 2288 pixels × 856 lines generated by even lines in an even field. Is output.
[0029]
Raw image signals of a total of 2288 pixels × 1712 lines output from the CCD imager 16 pass through the CDS / AGC circuit 18 and are converted into raw image data at the A / D converter 20 at a clock rate of 24 MHz. The converted raw image data is directly provided to a controller 302b (see FIG. 4) provided in the buffer control circuit 30. When the shutter button 50 is operated, the CPU 48 loads the starting address value of the raw image / compressed main image area 38b shown in FIG. 3 into the controller 302b as a reference address value. For this reason, the raw image data of 2288 pixels × 1712 lines subjected to the frequency conversion (24 MHz → 96 MHz) by the buffer 301b is written into the raw image / compressed main image area 38b by the controller 302b and the SDRAM control circuit 36.
[0030]
Since the raw image data of 2288 pixels × 1712 lines is interlaced scan data, odd field data is stored in the first half of the raw image / compressed main image area 38b, and even field data is stored in the raw image / compressed main image area 38b. Stored in the second half. That is, the odd field area and the even field area are formed in the raw image / compressed main image area 38b as shown in FIG.
[0031]
The head address value of the raw image / compressed main image area 38b is loaded as a reference address value into the controller 302f shown in FIG. The raw image data stored in the raw image / compressed main image area 38b is read by the controller 302f and the SDRAM control circuit 36. However, the raw image data is alternately read line by line from the odd field area and the even field area, whereby the interlaced scan data is converted into progressive scan data.
[0032]
When the shutter button 50 is operated, the switch SW1 is connected to the terminal S2, and the horizontal zoom magnification “768/2288” and the vertical zoom magnification “240/1712” are set in the zoom circuit 28. The raw image data read from the raw image / compressed main image area 38b undergoes frequency conversion (96 MHz → 48 MHz) in the buffer 301f, and is then supplied to the signal processing circuit 24 via the switch SW1. The signal processing circuit 24 performs signal processing such as color separation, RGB conversion, white balance adjustment, and YUV conversion on the given raw image data, and outputs YUV data of 2288 pixels × 1712 lines.
[0033]
The operation speed of the signal processing circuit 24 is changed from 24 MHz to 48 MHz in response to the operation of the shutter button 50. Therefore, even if the transfer rate of the raw image data output from the controller 302f is 48 MHz, the processing does not fail.
[0034]
The YUV data output from the signal processing circuit 24 is subjected to zoom processing according to the above-described zoom magnification by the zoom circuit 28. The resolution of the YUV data output from the zoom circuit 28 is reduced to 768 pixels × 240 lines. The YUV data output from the zoom circuit 28 is provided to the controller 302a shown in FIG. Since the start address value of the display image area 38a shown in FIG. 3 is loaded as a reference address value in the controller 302a, the YUV data is displayed by the SDRAM control circuit 36 after the frequency conversion (48 MHz → 96 MHz) by the buffer 301a. It is written to the image area 38a.
[0035]
Since the head address value of the display image area 38a is also loaded in the controller 302e, the YUV data stored in the display image area 38a is read by the controller 302e and the SDRAM control circuit 36, and is subjected to frequency conversion (96 MHz) by the buffer 301e. → 24 MHz) to the video encoder 40. The video encoder 40 converts the YUV data into a composite image signal, and provides the converted composite image signal to the LCD monitor 42. As a result, a freeze image having a resolution of 768 pixels × 240 lines is displayed on the monitor screen.
[0036]
When the shutter button 50 is operated, the controller 302a fixes the YUV data write destination to the bank A1, and the controller 302e also fixes the YUV data read destination to the bank A1. Thus, the subject image captured in response to the operation of the shutter button 50 is displayed on the monitor screen as a frozen image. The YUV data stored in the bank A1 in response to the operation of the shutter button 50 is defined as freeze image data.
[0037]
After writing 768 pixels × 240 lines of YUV data corresponding to the freeze image into the display image area 38a, the CPU 48 loads the head address value of the display image area 38a into the controller 302f as a reference address value, and switches the switch SW2 to the terminal Connect to S4. Further, the CPU 48 sets both the horizontal zoom magnification and the vertical zoom magnification of the zoom circuit 28 to "1.0", and loads the top address value of the JPEG work area 38c into the controllers 302a and 302d as a reference address value.
[0038]
The YUV data of 768 pixels × 240 lines stored in the bank A1 of the display image area 38a is read by the controller 302f and the SDRAM control circuit 36. The read YUV data of 768 pixels × 240 lines is subjected to frequency conversion (96 MHz → 48 MHz) by the buffer 301f, and is then supplied to the controller 302a via the switch SW2 and the zoom circuit 28. The YUV data is written into the JPEG work area 38c by the SDRAM control circuit 36 through frequency conversion (48 MHz → 96 MHz) by the buffer 301a.
[0039]
The JPEG work area 38c has two banks A2 and B2, each of which can store 2288 pixels × 8 lines of YUV data, and the YUV data is alternately written to the banks A2 and B2 every 768 pixels × 8 lines. . At this time, the controller 301a controls addresses so that the Y data, U data, and V data are separated from each other in the bank A2 or B2. As a result, the YUV data of 768 pixels × 8 lines is written in the JPEG work area 38c as shown in FIG.
[0040]
Since the start address value of the JPEG work area 38c is also loaded into the controller 302d, the YUV data of 768 pixels × 8 lines stored in the banks A2 and B2 are alternately read by the SDRAM control circuit 36 and the controller 302d. Also at this time, the bank to which writing has not been performed is selected as the bank to be read.
[0041]
Reading from the bank A2 or B2 is performed in the order of Y data → U data → V data. First, Y data of 768 pixels × 8 lines is read, then U data of 384 pixels × 8 lines is read, and then V data of 384 pixels × 8 lines is read. Each read data is output to the JPEG codec 34 via the buffer 301d.
[0042]
The JPEG codec 34 performs JPEG compression on the given Y data, U data, and V data according to the initial compression ratio (initial Q factor), integrates the size of the compressed YUV data, and sets the integrated value in the register rgst. When JPEG compression for 768 pixels × 240 lines is completed, the setting value of the register rgst indicates the size of the compressed YUV data of 768 pixels × 240 lines. The compressed YUV data corresponding to the freeze image is defined as compressed freeze image data.
[0043]
The CPU 48 fetches the setting value of the register rgst, that is, the compressed freeze image size from the JPEG codec 34, and calculates an optimum compression rate (optimum Q factor) based on the fetched compressed freeze image size and the target compression size. The calculated optimal compression ratio is a compression ratio at which the frozen image data can be compressed to the target compression size.
[0044]
The resolutions that can be selected by the resolution selection button 52 include a high resolution (= 2288 pixels × 1712 lines), a medium resolution (= 1600 pixels × 1200 lines), and a low resolution (= 1024 pixels × 768 lines). The compression ratio selectable by the compression ratio selection button 54 includes a low compression ratio (= 1/3) and a high compression ratio (= 1/8). The target compression size described above depends on the resolution selected by the resolution selection button 52 and the compression ratio selected by the compression ratio selection button 54.
[0045]
When the optimum compression ratio is calculated, the CPU 48 loads the starting address value of the raw image / compressed main image area 38b into the controller 302f as a reference address value, connects the switch SW1 to the terminal S2, and connects the switch SW2 to the terminal S3. Connecting. The CPU 48 further sets the horizontal zoom magnification and the vertical zoom magnification corresponding to the resolution selected by the resolution selection button 52 in the zoom circuit 26.
[0046]
When the high resolution is selected, the horizontal zoom magnification and the vertical zoom magnification are both set to “1.0”. When the medium resolution is selected, the horizontal zoom magnification and the vertical zoom magnification are set to "1600/2288" and "1200/1712", respectively. When the low resolution is selected, the horizontal zoom magnification and the vertical zoom magnification are set to “1024/2288” and “768/1712”, respectively.
[0047]
By loading the start address value of the raw image / compressed main image area 38b into the controller 302f, the raw image data stored in the raw image / compressed main image area 38b is read by the controller 302f and the SDRAM control circuit 36. The reading destination is switched line by line between the odd field area and the even field area, and the line of Cy, Ye,... And the line of Mg, G,. included.
[0048]
The read raw image data is subjected to frequency conversion (96 MHz → 48 NHz) by the buffer 301f, and is then provided to the signal processing circuit 24 via the switch SW1. The signal processing circuit 24 performs signal processing such as color separation, RGB conversion, white balance adjustment, and YUV conversion on the given raw image data, and supplies YUV data of 2288 pixels × 1712 lines to the zoom circuit 26. In the zoom circuit 26, a zoom process according to the set zoom magnification is performed, whereby YUV data having a desired resolution is output from the zoom circuit 26.
[0049]
That is, when high resolution is selected, YUV data of 2288 pixels × 1712 lines is output from the zoom circuit 26, and when medium resolution is selected, YUV data of 1600 pixels × 1200 lines is output from the zoom circuit 26. When the low resolution is selected, YUV data of 1024 pixels × 768 lines is output from the zoom circuit 26. Note that YUV data of a desired resolution output from the zoom circuit 26 is defined as main image data.
[0050]
Since the head address value of the JPEG work area 38c has already been loaded into the controller 302a, the YUV data output from the zoom circuit 26 undergoes frequency conversion (48 MHz → 96 MHz) by the buffer 301a, and is then JPEG by the SDRAM control circuit 36. The data is written to the work area 38c. Also at this time, the write destination is switched between the banks A2 and B2 every eight lines. The Y data, U data and V data are separated from each other in the bank A2 or B2.
[0051]
As a result, YUV data having a high resolution is written to the JPEG work area 38c as shown in FIG. 8, YUV data having a medium resolution is written to the JPEG work area 38c as shown in FIG. The YUV data is written in the JPEG work area 38c as shown in FIG.
[0052]
The head address value of the JPEG work area 38c has already been loaded into the controller 302d, and the YUV data stored in the banks A2 and B2 are alternately read by the SDRAM control circuit 36 and the controller 302d. Also at this time, the bank to which writing has not been performed is selected as the bank to be read, and reading from the bank A2 or B2 is performed in the order of Y data → U data → V data. Each read data is output to the JPEG codec 34 via the buffer 301d.
[0053]
The JPEG codec 34 performs JPEG compression on the given Y data, U data, and V data according to the above-described optimal compression ratio, and generates compressed YUV data. The generated compressed YUV data is provided to the controller 302c shown in FIG.
[0054]
After the optimum compression ratio is calculated, the CPU 48 loads the starting address value of the raw image / compressed main image area 38b into the controller 302c as a reference address value. Therefore, the compressed YUV data is supplied to the SDRAM controller 36 via the buffer 301c, and is written into the raw image / compressed main image area 38b by the SDRAM controller 36. At this time, the compressed YUV data is written sequentially from the head address of the raw image / compressed main image area 38b. Since the size of the compressed YUV data is smaller than the size of the raw image data, the raw image data for which the YUV conversion and the JPEG compression have not yet been performed will not be overwritten by the compressed YUV data. The compressed YUV data stored in the raw image / compressed main image area 38b is defined as compressed main image data.
[0055]
After one frame of compressed YUV data having the resolution selected by the resolution selection button 52 is secured in the raw image / compressed main image area 38b, the CPU 48 sets the controller 302f using the head address value of the display image area 38a as a reference address value. And the switch SW2 is connected to the terminal S4. The CPU 48 further sets the horizontal zoom magnification “160/768” and the vertical zoom magnification “120/240” in the zoom circuit 28, and loads the head address value of the thumbnail image area 38d into the controller 301a as a reference address value.
[0056]
The YUV data, that is, the freeze image data, stored in the bank A1 of the display image area 38a is read out by the SDRAM control circuit 36 and the controller 302f, and after the frequency conversion (96 MHz → 48 MHz) by the buffer 301f, the zoom circuit via the switch SW2. 28. In the zoom circuit 28, zoom processing according to the set zoom magnification is executed, and YUV data of 160 pixels × 120 lines is output from the zoom circuit 28.
[0057]
The YUV data of 160 pixels × 120 lines is supplied to the controller 302a, and after the frequency conversion (48 MHz → 96 MHz) by the buffer 301a, is written to the thumbnail image area 38d by the SDRAM control circuit 36. The YUV data of 160 pixels × 120 lines is stored in the thumbnail image area 38d as shown in FIG. The YUV data stored in the thumbnail image area 38d is defined as thumbnail image data.
[0058]
After obtaining the YUV data of 160 pixels × 120 lines, the CPU 48 loads the head address value of the thumbnail image area 38d into the controller 302d as the reference address value, and uses the head address value of the compressed thumbnail image area 38e as the reference address value. Load to controller 302c.
[0059]
The Y data, U data, and V data stored in the thumbnail image area 38d are individually read out by the SDRAM control circuit 36 and the controller 302d, and output to the JPEG codec 34 via the buffer 301d. The JPEG codec 34 performs JPEG compression on the given Y data, U data, and V data, and supplies the compressed YUV data obtained thereby to the controller 302c. The compressed YUV data is provided to the SDRAM control circuit 36 via the buffer 301c, and is written to the compressed thumbnail image area 38e by the SDRAM control circuit 36. The compressed YUV data stored in the compressed thumbnail image area 38e is defined as compressed thumbnail image data.
[0060]
After the compressed main image data and the compressed thumbnail image data are secured in the raw image / compressed main image area 38b and the compressed thumbnail image area 38e, the CPU 48 accesses the SDRAM 38 through the SDRAM control circuit 36, and the compressed thumbnail image data and the compressed thumbnail image data are compressed. The main image data is read from the compressed thumbnail image area 38e and the raw image / compressed main image area 38b. The CPU 48 further creates an image file including the read compressed thumbnail image data and the compressed main image data, and records the created image file on the recording medium 46 through the I / F circuit 44.
[0061]
When calculating the optimal compression ratio, the CPU 48 processes the flowchart shown in FIG. The control program corresponding to this flowchart is stored in the ROM 56.
[0062]
First, the resolution selected by the resolution selection button 52 is detected in step S1, and the compression ratio selected by the compression ratio selection button 54 is detected in step S3. In step S5, the target compression size of the main image data is determined based on the detected resolution and compression ratio, and in the following step S7, the target compression size of the freeze image data is calculated according to Equation 1.
[0063]
(Equation 1)
TSf = Rf / Rp * TSp
TSf: Target compression size of freeze image data
TSp: Target compressed size of main image data
Rf: Freeze image resolution
Rp: resolution of main image
In step S9, a freeze image compression process is performed. As a result, the freeze image data read from the display image area 38a is supplied to the JPEG codec 34, and subjected to JPEG compression according to the initial compression ratio. The set value of the register rgst indicates the size of the compressed freeze image. In step S11, the compressed freeze image size is fetched from the JPEG codec 34, and in the following step S13, the optimal compression ratio that can compress the freeze image data to the target compression size is calculated according to equation (2).
[0064]
(Equation 2)
Qs = TSf / CSf * Qi
Qs: optimal compression ratio
Qi: Initial compression ratio
CSf: Compressed freeze image size
As can be understood from the above description, when the subject image captured by the CCD imager 16 is displayed on the LCD monitor 42 and recorded on the recording medium 46 in a compressed state, the raw image data having the same resolution as the effective resolution of the CCD imager 16 is first obtained. Is written to the raw image / compressed main image area 38b of the SDRAM 38. The signal processing circuit 24 and the zoom circuit 28 generate freeze image data based on the raw image data stored in the raw image / compressed main image area 38b.
[0065]
The Y signal component, the U signal component, and the V signal component included in the freeze image data are individually written in the JPEG work area 38c, and then compressed by the JPEG codec 34 at an initial compression rate. The CPU 48 detects the size of the compressed freeze image data, and specifies an optimal compression ratio at which the freeze image data can be compressed to the target compression size.
[0066]
The signal processing circuit 24 and the zoom circuit 26 also generate main image data based on the raw image data stored in the raw image / compressed main image area 38b. The generated main image data has the resolution selected by the resolution selection button 52. The JPEG codec 34 compresses the main image data according to the above-described optimal compression ratio.
[0067]
As described above, regardless of which of the high resolution, the medium resolution, and the low resolution is selected by the resolution selection button 52, the freeze image data is generated based on the raw image data having the same resolution as the effective resolution of the CCD imager 16, The optimum compression ratio is specified based on the raw image data. Therefore, it is possible not only to shorten the photographing interval but also to calculate the optimum compression ratio with high accuracy, as compared with the case where the main image data is compressed a plurality of times as in the related art. In addition, since the Y signal component, the U signal component, and the V signal component included in the freeze image data are individually written in the JPEG work area 38c, the compression of the freeze image data for calculating the optimal compression ratio is promptly executed. Can be.
[0068]
In this embodiment, an interlaced scan type CCD imager is used. However, a progressive scan type image sensor may be used instead, or a CMOS type image sensor may be used.
[Brief description of the drawings]
FIG. 1 is a block diagram showing one embodiment of the present invention.
FIG. 2 is an illustrative view showing one example of a color filter applied to the embodiment in FIG. 1;
FIG. 3 is an illustrative view showing one example of a mapping state of an SDRAM applied to the embodiment in FIG. 1;
FIG. 4 is a block diagram illustrating an example of a buffer control circuit applied to the embodiment in FIG. 1;
FIG. 5 is an illustrative view showing one example of a mapping state of a display image area formed on an SDRAM;
FIG. 6 is an illustrative view showing one example of a mapping state of a raw image / compressed main image area formed on an SDRAM;
FIG. 7 is an illustrative view showing one example of a data storage state of a JPEG work area formed in an SDRAM;
FIG. 8 is an illustrative view showing another example of the data storage state of the JPEG work area formed in the SDRAM;
FIG. 9 is an illustrative view showing another example of a data storage state of a JPEG work area formed in the SDRAM;
FIG. 10 is an illustrative view showing still another example of a data storage state of a JPEG work area formed in the SDRAM;
FIG. 11 is an illustrative view showing one example of a data storage state of a thumbnail image area formed in an SDRAM;
FIG. 12 is a flowchart showing a part of the operation of the CPU applied to the embodiment in FIG. 1;
[Explanation of symbols]
10. Digital camera
14 ... CCD imager
24 ... Signal processing circuit
26, 28 ... zoom circuit
30 ... buffer control circuit
34 ... JPEG codec
36 ... SDRAM control circuit
38 SDRAM
42 ... Monitor
48 ... CPU
52 ... resolution selection button
54… Compression ratio selection button

Claims (6)

A digital camera that displays a subject image taken by an image sensor on a monitor and records the compressed image on a recording medium,
Writing means for writing a captured image signal having the same resolution as the effective resolution of the image sensor to a memory,
First generating means for generating a display image signal based on the captured image signal stored in the memory,
Specifying means for specifying an optimal compression ratio capable of compressing the display image signal to a target size,
Selecting means for selecting a desired resolution from a plurality of resolutions,
A second generation unit configured to generate a recording image signal having the desired resolution based on the captured image signal stored in the memory; and a compression unit configured to compress the recording image signal in accordance with the optimal compression ratio. A digital camera. 2. The digital camera according to claim 1, wherein a resolution selectable by said selection means is equal to or less than said effective resolution. The monitor displays an image based on the display image signal,
The digital camera according to claim 1, wherein the recording medium records a compressed recording image signal generated by the compression unit. The specifying unit includes an image compression unit that compresses the display image signal at a predetermined compression rate, a detection unit that detects a size of the compressed display image signal generated by the image compression unit, and a size that is detected by the detection unit. The digital camera according to claim 1, further comprising a calculating unit that calculates the optimum compression ratio based on the digital camera. A first image signal in a YUV format having a first resolution and a second image signal in a YUV format having a second resolution higher than the first resolution are generated based on the captured image signal, and are generated based on the first image signal. A digital camera that displays an image on a monitor and records the second image signal in a compressed state on a recording medium;
Writing means for individually writing a Y signal component, a U signal component, and a V signal component included in the first image signal into a memory;
Specifying means for compressing the Y signal component, the U signal component and the V signal component stored in the memory to specify an optimal compression ratio capable of compressing the first image signal to a target size; A digital camera comprising compression means for compressing at a compression ratio. An image compression unit that compresses the first image signal at a predetermined compression ratio, a detection unit that detects a size of a compressed display image signal generated by the image compression unit, and a size that is detected by the detection unit. 6. The digital camera according to claim 5, further comprising a calculating unit that calculates the optimal compression ratio based on the following.

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