The present disclosure relates to imaging apparatuses including image compression circuits, and methods for controlling the image compression ratios of imaging apparatuses.
Mobile terminals equipped with built-in cameras as well as apparatuses dedicated to capturing images, such as digital still cameras, digital camcorders, etc., have come into widespread use. These imaging apparatuses employ image data compression techniques, such as the joint photographic experts group (JPEG), the moving picture experts group (MPEG), etc. Note that when an input image is compressed to a predetermined data size in a stepwise manner, it takes a longer time to complete the compression process, and it is necessary to provide a memory having a large capacity to hold all data of the original image.
Therefore, there is a conventional technique of estimating the number of bytes of data which will be obtained by compressing an input image, based on high and low frequency components in the horizontal direction of the input image and high and low frequency components in the vertical direction of the input image, and based on the estimated number of bytes, calculates a compression ratio which allows the input image to be compressed at a time (see Japanese Patent Publication No. 2006-13570.
In the above conventional technique, there is a problem that, for example, when the lens of an imaging apparatus is moved from a scene where high frequency components are dominant to a scene where low frequency components are dominant, the image compression ratio is no longer appropriate, resulting in a degradation in image quality.
An example imaging apparatus includes an imaging element, a section configured to detect frequency information of an input image obtained from the imaging element, a section configured to detect shake information from the imaging element, a section configured to set a compression ratio of the input image based on the frequency information of the input image and the shake information, and a section configured to compress the input image based on the compression ratio.
With this configuration, even when the lens of an imaging apparatus is moved from a scene where high frequency components are dominant to a scene where low frequency components are dominant, an appropriate image compression ratio is set, whereby a degradation in image quality can be reduced or prevented.
According to the present invention, the compression ratio of an input image is set using frequency information of the input image and shake information, whereby a degradation in an image is advantageously reduced or prevented even in a scene in which the image is degraded in the conventional art.
Embodiments of the present invention will be described with reference to the accompanying drawings.
The CPU 108 sends an operation request to the image processing circuit 106, and receives a completion notification, frequency information of an input image, and shake information from the image processing circuit 106. The CPU 108 also sends an operation request and a compression ratio to the compression/decompression circuit 107, and receives a completion notification from the compression/decompression circuit 107.
In S505, the average value A1 of the frequency information calculated in S503 is compared with the threshold 1 set in S501. If the average value A1 of the frequency information is greater than the threshold 1, it is determined that high frequency components are dominant in the input image, and control proceeds to S506, in which the image compression ratio is increased. If the average value A1 of the frequency information is smaller than the threshold 1, it is determined that low frequency components are dominant in the input image, and control proceeds to S509, in which the image compression ratio is decreased. In other words, by utilizing a feature of human visual perception that the human visual system is less sensitive to high frequency components and more sensitive to low frequency components, the compression ratio is increased when high frequency components are dominant and decreased when low frequency components are dominant, thereby reducing or preventing perception of a degradation in image quality while improving encoding efficiency.
Moreover, in S507, the average value A2 of the shake information calculated in S504 is compared with the threshold 2 set in S502. If the average value A2 of the shake information is greater than the threshold 2, it is determined that the input image is moving, and control proceeds to S508, in which the image compression ratio is increased. When the average value A2 of the shake information is smaller than the threshold 2, it is determined that the input image is not moving, and control proceeds to S510, in which the image compression ratio is decreased. In other words, if the input image is moving, the image is smoothed by increasing the compression ratio.
Finally, in S511, the compression ratio which is to be sent from the CPU 108 to the compression/decompression circuit 107 is set. The compression/decompression circuit 107 compresses the input image based on the compression ratio specified by the CPU 108, and stores the result into the memory 105.
In S605, the difference value D1 between the greatest and smallest values of the frequency information calculated in S603 is compared with the threshold 1 set in S601. When the difference value D1 between the greatest and smallest values of the frequency information is greater than the threshold 1, it is determined that high frequency components are dominant in the input image, and control proceeds to S606, in which the image compression ratio is increased. When the difference value D1 between the greatest and smallest values of the frequency information is smaller than the threshold 1, it is determined that low frequency components are dominant in the input image, and control proceeds to S609, in which the image compression ratio is decreased.
Moreover, in S607, the difference value D2 between the greatest and smallest values of the shake information calculated in S604 is compared with the threshold 2 set in S602. When the difference value D2 between the greatest and smallest values of the shake information is greater than the threshold 2, it is determined that the input image is moving, and control proceeds to S608, in which the image compression ratio is increased. When the difference value D2 between the greatest and smallest values of the shake information is smaller than the threshold 2, it is determined that the input image is not moving, and control proceeds to S610, in which the image compression ratio is decreased.
Finally, in S611, the compression ratio which is to be sent from the CPU 108 to the compression/decompression circuit 107 is set. The compression/decompression circuit 107 compresses the input image based on the compression ratio specified by the CPU 108, and stores the result into the memory 105.
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As described above, the imaging apparatus of the present invention has the advantage of compressing an image with high accuracy without increasing cost, and is useful for digital cameras etc.
Number | Date | Country | Kind |
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2008-294459 | Nov 2008 | JP | national |
This is a continuation of PCT International Application PCT/JP2009/004736 filed on Sep. 18, 2009, which claims priority to Japanese Patent Application No. 2008-294459 filed on Nov. 18, 2008. The disclosures of these applications including the specifications, the drawings, and the claims are hereby incorporated by reference in their entirety.
Number | Date | Country | |
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Parent | PCT/JP2009/004736 | Sep 2009 | US |
Child | 13080411 | US |