Image processing apparatus

Abstract

An image processing apparatus for processing RGB image data output from an image capturing element including a primary-color filter, includes: a middle-high range luminance component compensation section for compensating for a middle-high range luminance component of a low-frequency luminance signal generated based on the RGB image data such that the low-frequency luminance signal has substantially an ideal frequency luminance characteristic which is lower than or equal to a predetermined frequency.

1 . An image processing apparatus for processing RGB image data output from an image capturing element including a primary-color filter, comprising: 
 a middle-high range luminance component extraction section for extracting a middle-high range luminance component which has a zero amplitude at an angular frequency ω=π and a maximum amplitude at an angular frequency ω between π/2 and π from a first luminance signal generated based on RGB image data; and    a first synthesis section for adding the middle-high range luminance component to a low-frequency luminance signal generated based on the RGB image data so as to generate a second luminance signal.    
   
   
       2 . An image processing apparatus according to  claim 1 , wherein the middle-high range luminance component extraction section uses at least one filter having a size of an even-number of pixels to arithmetically process the first luminance signal.  
   
   
       3 . An image processing apparatus according to  claim 2 , wherein the filter having a size of an even-number of pixels is a two-dimensional filter and has coefficients symmetrically arranged with respect to a x-direction and a y-direction.  
   
   
       4 . An image processing apparatus according to  claim 3 , wherein: 
 the filter having a size of an even-number of pixels includes a first low-pass filter having a differentiation capability and a second low-pass filter; and    a difference between an output obtained by arithmetically processing the first luminance signal using the first low-pass filter and an output obtained by arithmetically processing the first luminance signal using the second low-pass filter is output as the middle-high range luminance component.    
   
   
       5 . An image processing apparatus according to  claim 4 , further comprising: 
 a first interpolation section for interpolating missing components among R-, G-, and B-components for each pixel before the generation of the first luminance signal,    wherein the first interpolation section interpolates missing components by arithmetically processing the RGB image data using a filter having a size of 3 pixels×3 pixels.    
   
   
       6 . An image processing apparatus according to  claim 2 , wherein: 
 the filter having a size of an even-number of pixels includes a first low-pass filter having a differentiation capability and a second low-pass filter; and    a difference between an output obtained by arithmetically processing the first luminance signal using the first low-pass filter and an output obtained by arithmetically processing the first luminance signal using the second low-pass filter is output as the middle-high range luminance component.    
   
   
       7 . An image processing apparatus according to  claim 6 , further comprising: 
 a first interpolation section for interpolating missing components among R-, G-, and B-components for each pixel before the generation of the first luminance signal,    wherein the first interpolation section interpolates missing components by arithmetically processing the RGB image data using a filter having a size of 3 pixels×3 pixels.    
   
   
       8 . An image processing apparatus according to  claim 7 , further comprising: 
 a second interpolation section for interpolating missing components among R-, G-, and B-components for each pixel before the generation of the low-frequency luminance signal,    wherein the second interpolation section interpolates missing components by arithmetically processing the RGB image data using a filter having a size of an even-number of pixels.    
   
   
       9 . An image processing apparatus according to  claim 8 , wherein at least one of the first and second interpolation sections interpolates the RGB image data by using a median method for a G-component and a bilinear method for R- and B-components.  
   
   
       10 . An image processing apparatus according to  claim 8 , further comprising: 
 a median filtering section for removing, with a median filter, noise inherent to the image capturing element which is contained in a color-difference signal generated based on a RGB image signal from the second interpolation section;    wherein the median filtering section changes the size of the median filter according to an amount of the noise.    
   
   
       11 . An image processing apparatus according to  claim 2 , further comprising: 
 a first interpolation section for interpolating missing components among R-, G-, and B-components for each pixel before the generation of the first luminance signal,    wherein the first interpolation section interpolates missing components by arithmetically processing the RGB image data using a filter having a size of 3 pixels×3 pixels.    
   
   
       12 . An image processing apparatus according to  claim 1 , further comprising: 
 a first interpolation section for interpolating missing components among R-, G-, and B-components for each pixel before the generation of the first luminance signal,    wherein the first interpolation section interpolates missing components by arithmetically processing the RGB image data using a filter having a size of 3 pixels×3 pixels.    
   
   
       13 . An image processing apparatus according to  claim 12 , further comprising: 
 a second interpolation section for interpolating missing components among R-, G-, and B-components for each pixel before the generation of the low-frequency luminance signal,    wherein the second interpolation section interpolates missing components by arithmetically processing the RGB image data using a filter having a size of an even-number of pixels.    
   
   
       14 . An image processing apparatus according to  claim 13 , wherein at least one of the first and second interpolation sections interpolates the RGB image data by using a median method for a G-component and a bilinear method for R- and B-components.  
   
   
       15 . An image processing apparatus according to  claim 13 , further comprising: 
 a median filtering section for removing, with a median filter, noise inherent to the image capturing element which is contained in a color-difference signal generated based on a RGB image signal from the second interpolation section;    wherein the median filtering section changes the size of the median filter according to an amount of the noise.    
   
   
       16 . An image processing apparatus according to  claim 1 , further comprising: 
 a second interpolation section for interpolating missing components among R-, G-, and B-components for each pixel before the generation of the low-frequency luminance signal,    wherein the second interpolation section interpolates missing components by arithmetically processing the RGB image data using a filter having a size of an even-number of pixels.    
   
   
       17 . An image processing apparatus according to  claim 16 , further comprising: 
 a median filtering section for removing, with a median filter, noise inherent to the image capturing element which is contained in a color-difference signal generated based on a RGB image signal from the second interpolation section;    wherein the median filtering section changes the size of the median filter according to an amount of the noise.    
   
   
       18 . An image processing apparatus according to  claim 1 , further comprising: 
 a middle/high-range luminance component extraction section for extracting at least one of a middle-range luminance component and a high-range luminance component based on the second luminance signal; and    a second synthesis section for adding at least one of the middle-range luminance component and the high-range luminance component to the second luminance signal so as to generate a third luminance signal.    
   
   
       19 . An image processing apparatus according to  claim 18 , wherein the middle/high-range luminance component extraction section arithmetically processes the second luminance signal by using one filter which has an adjustable coefficient.