Television – Camera – system and detail – With single image scanning device supplying plural color...
Reexamination Certificate
2000-03-03
2004-10-12
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
With single image scanning device supplying plural color...
C348S273000, C348S278000, C382S260000, C358S515000
Reexamination Certificate
active
06803955
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to color imaging device and color imaging apparatus capable of reducing size and cost, and suppressing color moire.
Imaging devices, typically image pick-up tubes and solid-state imaging devices, are extensively used for imaging apparatuses. Particularly, single-tube or single-sensor color imaging devices used for color imaging apparatuses, have a merit that an imaging apparatus can be constructed with a single imaging device. The devices also have many other merits such as no requirement of any color separating prism causing lens size reduction, free from various multiple sensor type adjustments, typically registration, and consume low power. The devices have many contributions to the size and power consumption reduction of imaging apparatuses. Particularly, single-sensor color cameras using color CCD imaging devices which are solid-state devices, have become leading imaging apparatuses.
The above color imaging devices all obtain color information with a single light-receiving surface by color coding therein with color filters called stripes filters or mosaic filters. For example, three, i.e., R, G and B, color filters are applied in a predetermined regular array to each photo-electric converting element, thus providing a peculiar spectral sensitivity to each pixel. Thus, an image signal obtained by imaging a scene contains point-sequential color data corresponding to the predetermined color filter array. It is thus possible to take out color data by separating and taking out the signal corresponding to each color filter in compliance with the predetermined color filter array. To obtain luminance signal (or Y signal), at least three pixels (i.e., one R, one G and one B pixel) are necessary, and this means that the color imaging can be obtained with a single imaging device although the luminance resolution is sacrificed.
RGB Bayer array is one of such well-known arrays as noted above. While several arrays are well known as the Bayer array,
FIG. 6
shows a typical one of such arrays. This array is obtained by sequentially arranging a plurality of two-dimensional unit arrays each of four, i.e., 2×2, pixels to fully fill a plane, that is, it is a two-dimensional periodic array of four-pixel, i.e., (2×2)-pixel, unit arrays.
FIG. 7
shows another example of the RGB stripes array. This array is constituted by three color filter stripes (arranged as sequential columns), that is, it is a two-dimensional periodic array of unit arrays each of three, i.e., 3×1, pixels.
Both the above RGB Bayer and RGB stripes arrays use original (RGB) color filters of good color reproducibility. The Bayer array has a feature that the proportions of the R, G and B pixel numbers are set to 1:2:1, that is, an increased density of G pixels which have great contribution to the luminance signal is provided, thus providing an increased luminance resolution. In addition, since the pixels are arranged likewise in the vertical and horizontal directions, the resolutions obtainable in the two directions are alike.
The stripes array has no color coding in the vertical direction, and its luminance resolution in this direction is extremely high (i.e., as high as comparable to the monochromatic case). In addition, since the R, G and B pixel densities are the same, this array features that the color signal-to-noise ratio is good and that the color reproducibility is better than that of the Bayer array.
Although the above Bayer and stripes arrays are excellent as described above, in the usual imaging device no particular consideration is given to the securing of the dynamic range (i.e., luminance reproduction range) of imaging a scene. Therefore, imaging of a scene having a great luminance distribution range from high to low luminance readily results in white missing or blackening.
More specifically, the imaging range is not simply determined by the sole imaging device, but it also depends on the signal processing in the imaging apparatus using the imaging device. More specifically, on the high luminance side the saturation level of the imaging device is a limit, and on the low luminance side the noise level of the imaging device output assembled in the imaging apparatus is a limit. Therefore, it has been impossible to obtain an imaging range which at least exceeds the above range.
A usual imaging device used for constructing an imaging apparatus has a photoelectric conversion characteristic as shown in the graph of FIG.
8
. In the graph, the ordinate is taken for the logarithm of the signal level, and the abscissa is taken for the logarithm of the incident light intensity. In the graph, UL represents a high luminance side limit level, and LL represents a low luminance side limit level. The level UL substantially corresponds to the saturation level of the imaging device. The level LL, on the other hand, is not the noise level NL itself, but is determined as a signal level having such a predetermined limit signal-to-noise ratio as to withstand appreciation even in coexistence with noise. The range between the levels UL and LL is the effective luminance range, that is, the difference (UL-LL) between these ranges (on the logarithmic axis) is the imaging range.
The imaging range is in many cases about 5 to 6 EV (30 to 36 dB) although it depends on the design and manufacture of the imaging apparatus, and its further improvement has been desired. However, it has been difficult to further improve the range because of limitations imposed on the improvement of the saturation level of the imaging device and the noise level.
Now, among a variety of color coding patterns, which have been proposed and used in practice as the filter array, are 3-original-color filters such as RGB stripes filters and Bayer type RGB mosaic filters (including various varieties) and complementary color filters such as 4-color, e.g., YeMgCy stripes and YeMgCyw and YeMgCyG, mosaic filters.
The present invention points out essential problems, which are inherent in the electronic structures of the color imaging device (such as picture tube, solid-state imaging device, CCD and other types) and the various kinds of color coding (such as original colors and complementary colors or three colors and four colors), and show means for solving the problems. In the following description, unless particularly noted otherwise, only examples are considered.
Among the prior art color coding arrays, an example of Bayer type RGB arrays will now be described with reference to FIGS.
13
(A) and
13
(B). As shown in FIG.
13
(A), the Bayer type RGB array is constituted by a plurality of unit arrays each of four, i.e., (2×2), pixels. As shown in FIG.
13
(B), these unit arrays are sequentially arranged to fill a plane. This array has a feature that the proportions of the R, G and B pixel numbers are set to 1:2:1, that is, an increased density of G pixels which have great contribution to luminance signal is provided for increasing luminance resolution. In addition, since the pixels are arranged likewise in the vertical and horizontal directions, the resolutions obtainable in the two directions are alike, which is different from the stripe filter. The array shown in FIG.
13
(B) is constituted by 64, i.e., (8×8), pixels.
However, since the Bayer type array uses a regular array as described above, it poses a significant problem causing false resolution image or so-called color moire due to space sampling based on its array. An intrinsically colorless, i.e., monochromatic, scene will now be considered, which happens to contain a scene portion having a luminance pattern (i.e., white-and-black pattern) of the same period as the period of the array. Assuming that an RG row as one horizontal line of the scene is such that R represents white color and G represents black color, the scene causes the output of a signal, which is equivalent to a signal obtainable from a red scene free from luminance changes, that is, an output of a color which is not intrinsically present is generated. Due to such stripe
Garber Wendy R.
Olympus Corporation
Pokotylo John C.
Struab & Pokotylo
Ye Lin
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