Patent Application
20080024626
The objects and advantages of the present invention will be better understood from the following description, with reference to the accompanying drawings in which:
The present invention is described below with reference to the embodiments shown in the drawings.
The constitution of a digital camera having a image capturing apparatus is described with reference to
A photographing object image is provided on a CCD 120 through a lens 110, an aperture 112, and a shutter 113. The lens 110, the aperture 112, and the shutter 113 are operated by a motor driving circuit 114 according to a control signal from a DSP 124. When the shutter 113 is closed by operating a release switch 133, the CCD 120 converts the photographing object image into electrical signals. An AFE 122 amplifies electrical signals and converts them into image data. The DSP 124 receives the image data, stores it temporarily in a memory 126, and creates an image file by processing and compressing the image data. The created image file is recorded into a memory medium 130 through a memory medium controller 129. An EEPROM 150 stores various data and programs which are required to operate the DSP 124. An operating switch is provided for operating the digital camera, e.g. displaying an image recorded in the memory medium 130. A user configures the ISO speed and pixel size using the operating switch 132.
A backlight driving circuit 134 turns on a backlight provided in an LCD 138 according to a control signal from the DSP 124. The LCD 138 displays a monitor-through image which is created by periodically updating the image data received from the DSP 120 before an object is photographed, and displays image files recorded into the memory medium 130 after an object is photographed. Additionally, the LCD 138 can display the residual recordable number of images in the memory medium 130. Further, a recordable number display 139 also displays the residual recordable number of images in the memory medium 130.
The amplification factor of the AFE 122, i.e. the gain, is decided using the ISO speed which is configured by a user with the operating switch 132. When the ISO speed is raised, the gain is increased, and consequently noise in an image is also increased. This decreases the S/N ratio, and increases the occurrence of areas in which brightness or color tone precipitously changes, i.e. higher frequency components in an image are increased.
The estimated file size of a compressed image file is found from the average size of various image files which were created by capturing various photographing objects. A similar graph can be drawn for each resolution at which a digital camera is able to photograph.
Compression is executed using the JPEG compression method. The JPEG compression method comprises a discrete cosine transform process, a quantization process, and a Huffman encoding process. The discrete cosine transform process is a kind of orthogonal transform coding. In a discrete cosine transform process and a quantization process, pixel information is unevenly distributed to the lower frequency components, and higher frequency components are rounded off because they occur less in a natural image, i.e. the brightness or color tone in a natural image doom not precipitously change. A Huffman encoding process compresses data using event probability of the data. Therefore, in the case that the gain is increased by raising the ISO speed, higher frequency components in image data output from the AFE 122 is increased. In the case that higher frequency components are increased, the file size of the compressed image data is also increased because the Image data is compressed inefficiently.
Referring to
The EEPROM 150 stores table data which represents the relationship between ISO speed and file size for each pixel size of an image. The table data is created according to the graph shown in
The estimated file size, which is approximately the file size of a photographed image file, is obtained by using the graph shown in
The residual recordable number display process is described reference to
When the digital camera is powered on, a residual recordable number display process is executed. The DSP 124 calculates the remaining recordable capacity in a memory medium with the memory medium controller 129 in step S30, and retrieves the ISO speed as configured by a user in step s32.
In step S34, a residual recordable number calculating process is executed. The DSP 124 retrieves the estimated file size, which is decided using table data created according to the ISO speed and pixel size of an image. The table data is stored in the EEPROM 150. The residual recordable number of images equals the remaining recordable amount of a memory medium divided by the estimated file size. According to this process, a residual recordable number of images is calculated with a high degree of accuracy.
In step S36, the LCD 138 and/or the recordable number display 139 displays the residual recordable number of images, and a user is able to see an accurate residual recordable number of images.
According to this embodiment, the residual recordable number of images is accurately calculated. The time needed for calculation is shortened by using table data stored in the EEPROM 150.
Note that the estimated file size may be calculated using other factors which change the file size of a compressed image file, in addition to pixel size and ISO speed.
The estimated file size may be calculated using a function of pixel size and ISO speed.
The residual recordable number calculating process may be executed after compressed image data is recorded in the memory medium 130. A user can see an accurate residual recordable number of images when the remaining recordable amount in the memory medium is changed.
The residual recordable number calculating process may be executed after a configuration of ISO speed and pixel size is changed. When the configuration of ISO speed and pixel count is changed, the estimated file size is changed. A user can see an accurate residual recordable number of images when the configuration of ISO speed and pixel size is changed.
Moreover, the memory medium 130 may be a detachable memory card, e.g. SD card™, or any storage medium provided in a digital camera.
Although the embodiment of the present invention has been described herein with reference to the accompanying drawings, obviously many modifications and changes may be made by those skilled in the art without departing from the scope of the invention.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2006-203076 (filed on Jul. 26, 2006), which is expressly incorporated herein, by reference, in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-203076 | Jul 2006 | JP | national |
