Gradation conversion device, gradation conversion method, and program

Abstract

A gradation conversion device that converts a gradation of an image, includes: dither means for dithering the image by adding random noise to pixel values forming the image; and one-dimensional ΔΣ modulation means for performing one-dimensional ΔΣ modulation on the dithered image.

1 . A gradation conversion device that converts a gradation of an image, comprising:
 dither means for dithering the image by adding random noise to pixel values forming the image; and   one-dimensional ΔΣ modulation means for performing one-dimensional ΔΣ modulation on the dithered image.   
   
   
       2 . The gradation conversion device according to  claim 1 , wherein the dither means has an HPF (High Pass Filter) that filters signals, filters the random noise with the HPF, and adds a high-frequency component of the random noise resulting from the filtering to the pixel values. 
   
   
       3 . The gradation conversion device according to  claim 2 , wherein a filter coefficient of the HPF is determined so that a characteristic at high frequencies of an amplitude characteristic of the HPF is a characteristic opposite to a spatial frequency characteristic of the visual sense of human. 
   
   
       4 . The gradation conversion device according to  claim 3 , wherein the filter coefficient of the HPF is determined so that the characteristic at high frequencies of the amplitude characteristic of the HPF may be the characteristic opposite to the spatial frequency characteristic of the visual sense of human based on a characteristic equal to or less than a spatial frequency corresponding to resolution of display means for displaying image on which the ΔΣ modulation has been performed among the spatial frequency characteristics of the visual sense of human. 
   
   
       5 . The gradation conversion device according to  claim 4 , wherein the filter coefficient of the HPF is determined so that amplitude characteristic of the HPF may increase more rapidly than an amplitude characteristic of noise shaping by ΔΣ modulation using a Floyd filter or a Jarvis filter. 
   
   
       6 . The gradation conversion device according to  claim 4 , further comprising setting means for setting the filter coefficient of the HPF based on the spatial frequency characteristic of the visual sense of human and the resolution of the display means. 
   
   
       7 . The gradation conversion device according to  claim 6 , wherein the setting means further adjusts the filter coefficient of the HPF in response to an operation by a user. 
   
   
       8 . The gradation conversion device according to  claim 1 , wherein the one-dimensional ΔΣ modulation means has:
 a one-dimensional filter that filters quantization errors;   calculation means for adding the pixel values of the dithered image and output of the one-dimensional filter; and   quantization means for quantizing output of the calculation means and outputs quantization values containing the quantization errors as a result of one-dimensional ΔΣ modulation,   wherein a filter coefficient of the one-dimensional filter is determined so that a characteristic at high frequencies of an amplitude characteristic of noise shaping performed by the one-dimensional ΔΣ modulation means may be a characteristic opposite to the spatial frequency characteristic of the visual sense of human.   
   
   
       9 . The gradation conversion device according to  claim 8 , wherein the filter coefficient of the one-dimensional filter is determined so that the characteristic at high frequencies of the amplitude characteristic of noise shaping may be the characteristic opposite to the spatial frequency characteristic of the visual sense of human based on a characteristic equal to or less than the spatial frequency corresponding to the resolution of the display means for displaying the image on which the ΔΣ modulation has been performed among the spatial frequency characteristics of the visual sense of human. 
   
   
       10 . The gradation conversion device according to  claim 9 , wherein the filter coefficient of the one-dimensional filter is determined so that the characteristic at high frequencies of the amplitude characteristic of noise shaping performed by the one-dimensional ΔΣ modulation means may increase more rapidly than the amplitude characteristic of noise shaping by ΔΣ modulation using the Floyd filter or the Jarvis filter. 
   
   
       11 . The gradation conversion device according to  claim 8 , further comprising setting means for setting the filter coefficient of the one-dimensional filter based on the spatial frequency characteristic of the visual sense of human and the resolution of the display means. 
   
   
       12 . The gradation conversion device according to  claim 11 , wherein the setting means further adjusts the filter coefficient of the one-dimensional filter in response to an operation by the user. 
   
   
       13 . The gradation conversion device according to  claim 8 , wherein the one-dimensional filter has:
 plural delay means for storing input and delaying;   multiplication means for multiplying output of the plural delay means by the filter coefficient,   wherein the stored values of the delay means are not initialized but stored without change in the delay means in a horizontal flyback period of the dithered image.   
   
   
       14 . The gradation conversion device according to  claim 8 , wherein the one-dimensional filter has:
 plural delay means for storing and delaying input;   multiplication means for multiplying output of the plural delay means by the filter coefficient,   wherein the stored values of the delay means are initialized by random numbers in a horizontal flyback period of the dithered image.   
   
   
       15 . A gradation conversion method of a gradation conversion device that converts a gradation of an image, comprising the steps of:
 allowing the gradation conversion device to dither the image by adding random noise to pixel values forming the image; and   allowing the gradation conversion device to perform one-dimensional ΔΣ modulation on the dithered image.   
   
   
       16 . A program allowing a computer to function as a gradation conversion device that converts a gradation of an image, the program allowing the computer to function as:
 dither means for dithering the image by adding random noise to pixel values forming the image; and   one-dimensional ΔΣ modulation means for performing one-dimensional ΔΣ modulation on the dithered image.   
   
   
       17 . A gradation conversion device that converts a gradation of an image, comprising:
 a dither unit configured to dither the image by adding random noise to pixel values forming the image; and   a one-dimensional ΔΣ modulation unit configured to perform one-dimensional ΔΣ modulation on the dithered image.