The present technology relates to an image processing apparatus, an image processing method and electronic equipment. More particularly, the present technology relates to an image processing apparatus capable of preventing the image quality from deteriorating and relates to an image processing method provided for the apparatus as well as electronic equipment employing the apparatus.
In the past, a solid-state imaging device represented by a CMOS (Complementary Metal Oxide Semiconductor) image sensor has always been required to have a smaller pixel size and a larger pixel count representing the number of pixels which can be provided in the same image area.
The configuration of an ordinary solid-state imaging device is explained by referring to FIGS. 1A to 1C as follows.
FIG. 1A shows a typical color filter 11 for a solid-state imaging device whereas FIG. 1B shows a cross section of a front-irradiation CMOS image sensor 21. FIG. 1C shows a cross section of a rear-irradiation CMOS image sensor 31.
The color filter 11 shown in FIG. 1A includes red, blue and green color filters which are laid out to in the so-called Bayer array. In the Bayer array, a number of pixels each having a cell positioned to face one of the color pixels are laid out in the horizontal and vertical directions. In the Bayer array, B (blue) and Gb (green) color filters are laid out alternately in the horizontal direction along a row so that each of the color filters faces the cell of one of pixels on the same row. By the same token, in the Bayer array, R (red) and Gr (green) color filters are laid out alternately in the horizontal direction along another row so that each of the color filters faces the cell of one of pixels on the same other row. That is to say, the pixels whose cells face the B (blue) and Gb (green) color filters are laid out in the horizontal direction in the Bayer array every other row whereas the pixels whose cells face the R (red) and Gr (green) color filters are laid out in the horizontal direction in the Bayer array also every other row. In addition, the pixels whose cells face the B (blue) and R (red) color filters are not laid out on the same column in the vertical direction.
It is to be noted that, in the following description, a pixel whose cell faces an R (red) color filter is referred to as an R pixel whereas a pixel whose cell faces a Gb (green) color filter is referred to as a Gb pixel. By the same token, a pixel whose cell faces a B (blue) color filter is referred to as a B pixel whereas a pixel whose cell faces a Gr (green) color filter is referred to as a Gr pixel.
The front-irradiation CMOS image sensor 21 shown in FIG. 1B is configured to have a silicon substrate 22 including a photodiode. In addition, the front-irradiation CMOS image sensor 21 also includes an FD (Floating Diffusion) 23 and a reflection prevention film 24. The reflection prevention film 24 is created on the silicon substrate 22 and the FD 23. A wiring layer 26 having wires 25 is created on the reflection prevention film 24. A flattening film 27 is created on the wiring layer 26 whereas a color filter 28 is created on the flattening film 27. Then, an on-chip lens 29 is provided on the color filter 28.
The rear-irradiation CMOS image sensor 31 shown in FIG. 1C is configured to have a silicon substrate 32 including a photodiode. In addition, the rear-irradiation CMOS image sensor 31 also includes a reflection prevention film 33 created on the silicon substrate 32. A light shielding film 34 for preventing crosstalk is created on the reflection prevention film 33. A flattening film 35 is created on the light shielding film 34 whereas a color filter 36 is created on the flattening film 35. Then, an on-chip lens 37 is provided on the color filter 36. It is to be noted that, in the case of the rear-irradiation CMOS image sensor 31, the on-chip filter 37 for receiving incident light is provided on the rear side and a wiring layer not shown in FIG. 1C is provided on the front side.
In the rear-irradiation CMOS image sensor 31, the wiring layer is not provided on the light-incidence side. Thus, incident light is not lost due to the wiring layer so that the amount of incident light arriving at the silicon substrate 32 can be increased to a quantity greater than that of the front-irradiation CMOS image sensor 21. As a result, by making use of the rear-irradiation CMOS image sensor 31, it is possible to obtain high-sensitivity, low-noise and high-quality image. Such rear-irradiation CMOS image sensors 31 are mass-produced and employed in electronic equipment such as a cam coder and a digital still camera.
By the way, since the number of pixels employed in a solid-state imaging device is increased, the absolute quantity of the energy of light incident to a pixel undesirably decreases and crosstalk inevitably occurs. In this case, the crosstalk is a phenomenon in which light leaks out to an adjacent pixel existing among pixels while the light is propagating through the device employing the pixels. In addition, the number of electrons obtained as a result of opto-electrical conversion taking place in the neighborhood of a pixel boundary rises, unavoidably increasing crosstalk as well. In this case, the crosstalk is a phenomenon in which electrons leak out to an adjacent pixel. As a result, these kinds of crosstalk increase. The generation of these kinds of crosstalk is a cause deteriorating the spectroscopic characteristic of the rear-irradiation CMOS image sensor 31.
Next, the spectroscopic characteristics of the rear-irradiation CMOS image sensor 31 are explained by referring to FIGS. 2A to 2C.
FIG. 2A shows spectroscopic characteristics found from signals output by a rectangular rear-irradiation CMOS image sensor 31 having a pixel size of 1.12 micrometers. In FIG. 2A, the horizontal axis represents the wavelength expressed in terms of nm whereas the vertical axis represents an output signal (arb. unit) which is the magnitude of a signal output by the rectangular rear-irradiation CMOS image sensor 31.
As shown in FIG. 2A, the pixel size has a value of an order not much different from the wavelength so that the color separation becomes poor.
FIG. 2B shows spectroscopic characteristics for a configuration including an on-chip filter. In FIG. 2B, the vertical axis represents the transmission (arb. unit) whereas the horizontal axis represents the wavelength lambda expressed in terms of micrometers.
The spectroscopic characteristics shown in FIG. 2B to serve as the spectroscopic characteristics for a configuration including an on-chip filter are compared with the spectroscopic characteristics shown in FIG. 2A as spectroscopic characteristics found from signals output by a rectangular rear-irradiation CMOS image sensor 31 in order to clarify the following. The deterioration of the color separation does not depend on the characteristic of the on-chip color filter, but depends on leaks of light or electrons (that is, signal electric charges) inside the rear-irradiation CMOS image sensor 31.
FIG. 2C shows spectroscopic characteristics found from signals output by a rectangular rear-irradiation CMOS image sensor 31 having a pixel size of 1.12 micrometers for a case in which the incidence angle of light incident to the light receiving surface of the rear-irradiation CMOS image sensor 31 is set at ten degrees. On the other hand, FIG. 2A described above shows spectroscopic characteristics found from signals output by a rectangular rear-irradiation CMOS image sensor 31 having a pixel size of 1.12 micrometers for a case in which the incidence angle of light incident to the light receiving surface of the rear-irradiation CMOS image sensor 31 is set at zero degree. By comparing the spectroscopic characteristics shown in FIG. 2A with those shown in FIG. 2C, it becomes obvious that an increase of the incidence angle of light incident to the light receiving surface of the rear-irradiation CMOS image sensor 31 emphasizes crosstalk.
In addition, for example, applicants for a patent of the present technology have also proposed an imaging apparatus capable of reducing effects on the image quality by carrying out pixel color mixing correction processing in accordance with a correction parameter (refer to, for example, Japanese Patent Laid-Open No. 2009-124282).