1. Field of the Invention
The present invention relates to a color solid-state imaging apparatus for use in an image information apparatus, such as a digital still camera, a digital video camera, a PC (personal computer) camera, and a mobile phone camera (i.e., a mobile phone including a built-in camera), which decimatingly reads image data obtained by its imaging section. The present invention also relates to an image information apparatus using such a color solid-state imaging apparatus.
2. Description of the Related Art
Conventionally, a color solid-state imaging apparatus using an entire-pixel data reading (progressive scanning) method reads entire pixel data in one reading operation and employs a Bayer array color filter as illustrated in FIG. 12 in which a green (G) filter segment is provided on every other pixel in horizontal and vertical directions so as to form a checkered pattern, and red (R) and blue (B) filter segments are provided in pixel positions on alternate rows where the green filter segment is not provided.
FIG. 13 illustrates spatial resolutions of G, R and B signals in the case where information is read from all of the pixels in the Bayer array of FIG. 12. In FIG. 13, the number “1”, indicated in both horizontal (X) and vertical (Y) directions, represents a Nyquist threshold frequency of a signal obtained from a monochrome image obtained without using a color filter. The green (G) signal, which contributes to a luminance signal the most, has high resolutions in both horizontal (X) and vertical (Y) directions. The other two color signal components, the red (R) and blue (B) signals, have equal resolution in both horizontal (X) and vertical (Y) directions, so that a well-balanced color signal resolution can be obtained. Thus, the most efficient spatial resolution can be obtained for both the luminance and color signals.
When a color filter having the Bayer array structure shown in FIG. 12 is used, a suitable timing of a read signal is as shown in FIG. 14. FIG. 14 illustrates two types of lines in which one line type alternately includes G and R signals for each pixel period (=T), and the other line type alternately includes G and B signals for each pixel period (=T). These lines alternate with each other for each horizontal scanning period (=H). In the example illustrated in FIG. 12 where the number of pixels included in a row is m, and the number of pixels included in a column is n, a signal corresponding to m pixels can be obtained in each horizontal scanning period (1H).
Japanese Laid-Open Publication No. 9-312849, “Solid-State Imaging Apparatus”, proposes a data reading method by which pixel data obtained from the above-described Bayer array color filter is read in a ½ decimated manner. In this method, as illustrated in FIG. 15, data corresponding to pixels in two adjacent rows is read, and then data corresponding to pixels in the next two rows is skipped. This procedure is sequentially repeated. It should be noted that the phrase “to read pixel data in a ½ decimated manner” described herein means that data corresponding to a half of the pixels (R, G, and B) included in a pixel array is read.
However, in the conventional data reading method described above, the resolution for one field of pixels is extremely deteriorated. FIGS. 16A, 16B and 16C illustrate sampling points of R, G and B signals, respectively. As illustrated in FIG. 17, the spatial resolutions of the R, G and B signals obtained from the sampling points of FIGS. 16A, 16B and 16C are high in the horizontal direction (X direction), but extremely low in the vertical direction (Y direction), resulting in a poorly-balanced resolution characteristic. As a result, the obtained image appears unnatural since the resolution thereof extremely deteriorates in the vertical direction. In the Bayer array of FIG. 15, if pixel data is read using an interlaced scanning method, the vertical resolution can be slightly improved. However, such a method cannot be used for obtaining a still image from one field of pixels, e.g., when one frame is recorded as a still image during dynamic image recording, the interlaced scanning method cannot be used to read pixel data.