×

Method of and apparatus for establishing a reference point on a gradation correction curve

  • US 4,984,071 A
  • Filed: 12/05/1989
  • Issued: 01/08/1991
  • Est. Priority Date: 12/09/1988
  • Status: Expired due to Term
First Claim
Patent Images

1. A method of establishing a reference point on a gradation correction curve employed in gradation correction of image data, said method comprising the steps of:

  • (a) preparing image data representing density values of a plurality of basic colors with respect to each pixel in an original;

    (b) averaging said density values of respective basic colors with respect to each pixel to obtain an average density DM of each pixel;

    (c) generating a histogram representing average density distribution in the form of a relation between said average density DM and a number of pixels Np ;

    (d) generating a cumulative histogram representing said average density distribution in the form of a relation between said average density DM and a cumulative number of pixels RN;

    (e) finding a reference average density DMrf corresponding to a prescribed value of a reference cumulative number of pixels RNrf on said cumulative histogram;

    (f) selecting one of two terminal density values DMn at which said cumulative histogram saturates and which is closer to said reference average density;

    (g) finding a set of pixels having said average density in a range essentially between said reference average density DMrf and a selected terminal density value DMm ;

    (h) averaging said density values of said plurality of basic colors for said set of pixels with respect to each of said plurality of basic colors, to thereby obtain reference color density values Drf for respective basic colors; and

    (i) establishing said reference point on the basis of said reference color density values Drf.

View all claims
  • 1 Assignment
Timeline View
Assignment View
    ×
    ×