A digital camera has a signal processor, a high-frequency detector, a sampling processor, and a compression processor. The signal processor generates luminance and color difference data on the basis of image-pixel signals read from an image sensor. The high-frequency detector detects high-frequency components in the color difference data. The sampling processor carries out a sampling process to the luminance and color difference data in accordance with a given ratio of sampling frequencies. Then, the compression processor compresses the sampled luminance and color difference data. When there is a relatively low number of high-frequency components in the color difference data, the sampling processor samples the color difference data with a low sampling frequency.
1. A digital camera comprising:
a signal processor that generates luminance and color difference data on the basis of image-pixel signals read from an image sensor;
a high-frequency detector that detects high-frequency components in the color difference data;
a sampling processor that carries out a sampling process on the luminance and color difference data in accordance with a given ratio of sampling frequencies; and
a compression processor that compresses the sampled luminance and color difference data;
wherein said sampling processor samples the color difference data with a low sampling frequency when the color difference data includes a relatively low number of high-frequency components, the low sampling frequency being less than a given sampling frequency that is used when high-frequency components more than the relatively low number are included in the color difference data.
2. The digital camera of claim 1 , wherein said sampling processor sets the ratio of sampling frequencies to “4:2:0” when there is a relatively low number of high-frequency components in the color difference data.
3. The digital camera of claim 1 , wherein said sampling processor sets the ratio of sampling frequencies to “4:2:2” when the there is more than a relatively low number of high-frequency components in the color difference data.
4. The digital camera of claim 1 , wherein said high-frequency detector detects the high-frequency components by applying a Laplacian operation to the color difference data.
5. The digital camera of claim 1 , wherein said high-frequency detector detects the high-frequency components on the basis of DCT-processed color difference data.
6. The digital camera of claim 1 , wherein said compression processor carries out a DCT process and a Huffman coding on the luminance and color difference data.
7. The digital camera of claim 1 , further comprising a determiner that determines whether a sum of absolute values of detected high-frequency components is less than a given value.
8. An apparatus for sampling image data when compressing image data, comprising:
a high-frequency detector that detects high-frequency components in image data on the basis of luminance and color difference data; and
a sampling processor that carries out a sampling process on the luminance and color difference data in accordance with a given ratio of sampling frequencies,
wherein said sampling processor samples the color difference data with a low sampling frequency when the color difference data includes a relatively low number of high frequency components, the low sampling frequency being less than a given sampling frequency that is used when high-frequency components more than the relatively low number are included in the color difference data.
9. A non-transitory computer-readable medium that stores a program for sampling image data when compressing image data, comprising:
a high-frequency detecting code segment that detects high-frequency components in image data on the basis of luminance and color difference data; and
a sampling process segment code that controls a sampling circuit that carries out a sampling process on the luminance and color difference data in accordance with a given ratio of sampling frequencies,
wherein said sampling process code segment controls the sampling circuit such that said sampling circuit samples the color difference data with a low sampling frequency when the color difference data includes a relatively low number of high-frequency components,
the low sampling frequency being less than a given sampling frequency that is used when high-frequency components more than the relatively low number are included in the color difference data.
10. A method for sampling image data when compressing image data, comprising:
detecting high frequency components in image data on the basis of luminance and color difference data;
carrying out a sampling process on the luminance and color difference data in accordance with a given ratio of sampling frequencies; and
sampling the color difference data with a low sampling frequency when the color difference data includes a relatively low number of high frequency components, the low sampling frequency being less than a given sampling frequency that is used when high frequency components more than the relatively low number are included in the color difference data.