Image processing apparatus, image processing method, and program

Abstract

In order to provide an edge emphasis technique that can eliminate image deterioration of a digital image, an image processing apparatus includes a region setting unit which sets a region including a pixel of interest, a brightness value derivation unit which derives brightness values of the pixels, a first derivative derivation unit which derives first derivatives of the brightness values derived by the brightness value derivation unit, an edge direction determination unit which determines an edge direction of brightness at a position of the pixel of interest based on the results of the first derivatives, a range determination unit which determines a range, and a replacement unit which replaces the pixel value of the pixel of interest.

1 . An image processing apparatus for processing image data to be printed on a print medium by an image printing unit, comprising:
 a setting unit adapted to set a print characteristic on the print medium in the image printing unit;   a region setting unit adapted to set a region configured by a plurality of pixels including a pixel of interest;   a brightness value derivation unit adapted to derive brightness values of the pixels in the region;   a first derivative derivation unit adapted to derive first derivatives of the brightness values derived by said brightness value derivation unit for a plurality of pixel sequences in different directions, which include the pixel of interest;   an edge direction determination unit adapted to determine an edge direction of brightness at a position of the pixel of interest based on the results of the first derivatives at positions of the pixel of interest in the respective pixel sequences derived by said first derivative derivation unit;   an emphasis level determination unit adapted to determine an emphasis level of a pixel value based on the print characteristic and the first derivatives at respective positions of a plurality of pixels which line up in the edge direction determined by said edge direction determination unit; and   a replacement unit adapted to calculate second derivatives of brightness values at respective positions of the plurality of pixels which line up in the edge direction determined by said edge direction determination unit, to replace a pixel value of the pixel of interest by a pixel value obtained by adding the emphasis level to a pixel value of a pixel which has a minimum brightness value in the pixel sequence when the second derivative at the position of the pixel of interest assumes a positive value, and to replace a pixel value of the pixel of interest by a pixel value obtained by adding the emphasis level to a pixel value of a pixel which has a maximum brightness value in the pixel sequence when the second derivative at the position of the pixel of interest assumes a negative value,   wherein said replacement unit adjust the calculated second derivatives of brightness values in accordance with the print characteristic on the print medium set by said setting unit, and   wherein said emphasis level determination unit comprises:
 a fluctuation count derivation unit adapted to derive a fluctuation count of brightness values based on the first derivatives at the respective positions of the plurality of pixels which line up in the edge direction; and 
 a fluctuation amount derivation unit adapted to derive a fluctuation amount of brightness values based on the first derivatives at the respective positions of the plurality of pixels which line up in the edge direction, and 
   wherein said emphasis level determination unit determines the emphasis level of the pixel value based on at least one of the fluctuation count and the fluctuation amount, and   wherein said emphasis level determination unit comprises a second comparison unit adapted to compare the fluctuation count with a third threshold and a fourth threshold larger than the third threshold, sets the emphasis level to be a designated minimum value when the fluctuation count is smaller than the third threshold, sets the emphasis level to a designated maximum value when the fluctuation count is larger than the fourth threshold, and sets the emphasis level by linear interpolation using the maximum value and the minimum value when the fluctuation count is larger than the third threshold and is smaller than the fourth threshold.   
     
     
         2 . An image processing apparatus for processing image data to be printed on a print medium by an image printing unit, comprising:
 a setting unit adapted to set a print characteristic on the print medium in the image printing unit;   a region setting unit adapted to set a region configured by a plurality of pixels including a pixel of interest;   a brightness value derivation unit adapted to derive brightness values of the pixels in the region;   a first derivative derivation unit adapted to derive first derivatives of the brightness values derived by said brightness value derivation unit for a plurality of pixel sequences in different directions, which include the pixel of interest;   an edge direction determination unit adapted to determine an edge direction of brightness at a position of the pixel of interest based on the results of the first derivatives at positions of the pixel of interest in the respective pixel sequences derived by said first derivative derivation unit;   an emphasis level determination unit adapted to determine an emphasis level of a pixel value based on the print characteristic and the first derivatives at respective positions of a plurality of pixels which line up in the edge direction determined by said edge direction determination unit; and   a replacement unit adapted to calculate second derivatives of brightness values at respective positions of the plurality of pixels which line up in the edge direction determined by said edge direction determination unit, to replace a pixel value of the pixel of interest by a pixel value obtained by adding the emphasis level to a pixel value of a pixel which has a minimum brightness value in the pixel sequence when the second derivative at the position of the pixel of interest assumes a positive value, and to replace a pixel value of the pixel of interest by a pixel value obtained by adding the emphasis level to a pixel value of a pixel which has a maximum brightness value in the pixel sequence when the second derivative at the position of the pixel of interest assumes a negative value,   wherein said replacement unit adjust the calculated second derivatives of brightness values in accordance with the print characteristic on the print medium set by said setting unit, and   wherein the image data includes a character image, and the print characteristic is a designation of a line width of a character to be printed on the print medium.   
     
     
         3 . An image processing apparatus for processing image data, comprising:
 a region setting unit adapted to set a region configured by a plurality of pixels including a pixel of interest;   a determination unit adapted to determine a change characteristic of an image associated with the pixel of interest using the plurality of pixels in the set region;   a print characteristic setting unit adapted to set a print characteristic on a print medium by a printing unit; and   a modification unit adapted to modify the pixel of interest using the pixels in the region set by said region setting unit, and to correct a value of the modified pixel of interest based on the set print characteristic.   
     
     
         4 . The apparatus according to  claim 3 , wherein the change characteristic includes a fluctuation amount and a fluctuation count of brightness values of the plurality of pixels in the region, and
 said modification unit replaces a color of the pixel of interest by a color calculated using a pixel having a maximum brightness value or a minimum brightness value in the region in accordance with a fluctuation acceleration, and corrects the fluctuation acceleration as the correction.   
     
     
         5 . An image processing method for processing image data, comprising:
 a region setting step of setting a region configured by a plurality of pixels including a pixel of interest;   a determination step of determining a change characteristic of an image associated with the pixel of interest using the plurality of pixels in the set region;   a print characteristic setting step of setting a print characteristic on a print medium by a printing unit; and   a modification step of modifying the pixel of interest using the pixels in the region set by said region setting unit, and correcting a value of the modified pixel of interest based on the set print characteristic.   
     
     
         6 . The method according to  claim 5 , wherein the change characteristic includes a fluctuation amount and a fluctuation count of brightness values of the plurality of pixels in the region, and
 in the modification step, a color of the pixel of interest is replaced by a color calculated using a pixel having a maximum brightness value or a minimum brightness value in the region in accordance with a fluctuation acceleration, and the fluctuation acceleration is corrected as the correction.   
     
     
         7 . A non-transitory computer-readable storage medium, storing, in executable form, a program for making a computer execute processing of image data, said program comprising:
 a program code for implementing a region setting step of setting a region configured by a plurality of pixels including a pixel of interest;   a program code for implementing a determination step of determining a change characteristic of an image associated with the pixel of interest using the plurality of pixels in the set region;   a program code for implementing a print characteristic setting step of setting a print characteristic on a print medium by a printing unit; and   a program code for implementing a modification step of modifying the pixel of interest using the pixels in the region set by said region setting unit, and correcting a value of the modified pixel of interest based on the set print characteristic.   
     
     
         8 . The non-transitory computer-readable medium according to  claim 7 , wherein the change characteristic includes a fluctuation amount and a fluctuation count of brightness values of the plurality of pixels in the region, and
 the program code for implementing the modification step replaces a color of the pixel of interest by a color calculated using a pixel having a maximum brightness value or a minimum brightness value in the region in accordance with a fluctuation acceleration, and corrects the fluctuation acceleration as the correction.