Method of extracting a characteristic figure from a color picture and an apparatus used therefor

• US 5,524,069 A
• Filed: 11/30/1994
• Issued: 06/04/1996
• Est. Priority Date: 01/13/1992
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Inoue, Akira
• Primary Examiner(s): Mancuso, Joseph
• Assistant Examiner(s): DEL ROSSO, GERARD DOMNICK
• Application Number:
  US08/351,142
• Time in Patent Office: 552 Days
• Field of Search: 382/128, 382/130, 382/254, 382/270, 382/273, 382/282, 358/500, 358/540
• US Class Current: 382/270
• CPC Class Codes: G06V 10/28 Quantising the image, e.g. histogram thresholding for discrimination between background and foreground patterns

Abstract

An original density picture is produced from an input color picture, a pixel in a background area is designated and the density of the designated pixel is used as a reference density. A background density picture is produced by processing the original density picture with the reference density. Or a background density picture is produced by filtering the original density picture through low pass filter means. By subtracting the background density picture from the original density picture, a characteristic figure superimposed on a background scenery is extracted.

Claims

1. A method of extracting a characteristic figure from a color picture, wherein the color picture is composed of the characteristic figure superimposed on a background area, said method comprising:

(a) a step of scanning the color picture and electrically storing the scanned color picture as an array of pixels such that each pixel is represented by three color intensity values ##EQU21## where 0≦

R, G, B≦

1;

(b) a step of converting the three color intensity values ##EQU22## of each pixel to corresponding three color density values ##EQU23## utilizing equations D_r =-logR, D_g =-logG, D_b =-logB, thereby producing an original density picture;

(c) a step of designating a pixel in the background area of the color picture and determining a reference density from the three color density values ##EQU24## ascertained for the designated pixel in said converting step;

(d) a step of determining, for each pixel, a maximum value a_max of a coefficient `a` in an equation ##EQU25## under a restriction where D_r'"'"' ≧

0, D_g'"'"' ≧

0, and D_b'"'"' ≧

0;

(e) a step of selecting a value for a background elimination coefficient k₁ in a range of 0<

k₁ <

1;

(f) a step of multiplying, for each respective pixel, k₁ ·

a_max with the reference density ascertained in said converting step for said respective pixel, thereby composing a background density picture composed of modified three color density values for each pixel;

(g) a step of subtracting the modified three color density values of each pixel in the background density picture from the three color density values of a corresponding pixel in the original density picture, thereby producing a characteristic density picture composed of resultant three color density values ##EQU26## of each pixel;

(h) a step of reverse-converting the resultant three color density values ##EQU27## of each pixel in the characteristic density picture to three color intensity values ##EQU28## utilizing equations R₂ =10 Exp (-D_r2), G₂ =10 Exp (-D_g2), B₂ =10 Exp (-D_b2); and

(i) a step of displaying an image represented by the three color intensity values ##EQU29## of each pixel.

2. The method of extracting a characteristic figure according to claim 1, wherein:

the background area has plural regions of different respective colors,

after said step (g) is performed, said steps (c) to (g) are repeated for each of the plural regions, such that each iteration of said steps (c) to (g) corresponds to one of the plural regions, and

for each of the iterations following an initial iteration, the characteristic density picture of a previous iteration is used as the original density picture.

3. A method of extracting a characteristic figure from a color picture, wherein the color picture is composed of the characteristic figure superimposed on a background area, said method comprising:

(a) a step of scanning the color picture and electrically storing the scanned color picture as an array of pixels such that each pixel is represented by three color intensity values ##EQU30## where 0≦

R, G, B≦

1;

(b) a step of converting the three color intensity values ##EQU31## of each pixel to corresponding three color density values ##EQU32## utilizing equations D_r =-logR, D_g =-logG, D_b =-logB, thereby producing an original density picture;

(c) a step of producing a filtered density picture, composed of filtered three color intensity values ##EQU33## of each pixel, by (i) sequentially designating each pixel as an object pixel in the original density picture, and, for each object pixel, (ii) calculating an average value of corresponding components of three color density values of neighboring pixels situated in a predetermined range extending from the object pixel, and substituting, for each component of the three color density values of tile object pixel in the original density picture, the calculated average value of the corresponding components;

(d) a step of determining, for each pixel, a maximum value a_max of a coefficient `a` in an equation ##EQU34## under a restriction where D_r2'"'"' ≧

0, D_g2'"'"' ≧

0, and D_b2'"'"' ≧

0, and where ##EQU35## are the filtered three color density values of a corresponding pixel in the filtered density picture;

(e) a step of selecting a value for a background elimination coefficient k₁ in a range of 0<

k₁ ≦

1;

(f) a step of multiplying, for each respective pixel, k₁ ·

a_max with the three color density values of each said respective pixel in the filtered density picture, thereby composing a processed density picture composed of processed three color density values for each pixel; and

(g) a step of subtracting the processed three color density values of each pixel in the processed density picture from the three color density values of a corresponding pixel in the original density picture, thereby producing a characteristic density picture composed of resultant three color density values ##EQU36## of each pixel;

(h) a step of reverse-converting the resultant three color density values ##EQU37## of each pixel in the characteristic density picture to three color intensity values ##EQU38## utilizing equations R₂ =10 Exp (-D_r2), G₂ =10 Exp (-D_g2), B₂ =10 Exp (-D_b2); and

(i) a step of displaying an image represented by the three color intensity values ##EQU39## of each pixel.

4. An apparatus for extracting a characteristic figure from a color picture, wherein the color picture is composed of the characteristic figure superimposed on a background area, said apparatus comprising:

an image input device that stores the color picture electrically as an array of pixels such that each pixel is represented by three color intensity values ##EQU40## where 0≦

R, G, B≦

1;

conversion means for converting the three color intensity values ##EQU41## of each pixel to corresponding three color density values ##EQU42## utilizing equations D_r =-logR D_g =-logG, D_b =-logB, thereby producing an original density picture;

designation means for designating a pixel in the background area of the color picture and determining a reference density from the three color density values ##EQU43## ascertained for the designated pixel in said converting step;

calculation means for producing a background density picture from said original density picture, comprising;

(a) means for determining, for each pixel, a maximum value a_max of a coefficient `a` in an equation ##EQU44## under a restriction where D_r'"'"' ≧

0, D_g'"'"' ≧

0, and D_b'"'"' ≧

0, and

(b) means for multiplying, for each respective pixel, k₁ ·

a_max with the reference density ascertained by said conversion means for said respective pixel, thereby composing the background density picture of modified three color density values for each pixel, where k₁ is a background elimination coefficient determined by design in a range 0<

k₁ ≦

1;

subtraction means for producing a characteristic density picture composed of resultant three color density values ##EQU45## of each pixel by subtracting the modified three color density values of each pixel in the background density picture from the three color density values of a corresponding pixel in the original density picture;

reverse-converting means for converting the resultant three color density values ##EQU46## of each pixel in the characteristic density picture to three color intensity values ##EQU47## utilizing equations R₂ =10 Exp (-D_r2), G₂ =10 Exp (-D_g2), B₂ =10 Exp (-D_b2); and

an image output device for displaying an image represented by the three color intensity values ##EQU48## of each pixel.

5. An apparatus used for extracting a characteristic figure according to claim 4, further comprising:

a contrast intensifier means for converting the three color intensity values of each pixel output by said reverse conversion means into contrast-enhanced three color intensity values.

6. An apparatus used for extracting a characteristic figure according to claim 4, wherein said image output device comprises a CRT display.

7. An apparatus used for extracting a characteristic figure according to claim 4, wherein said image output device comprises a three color printer.

8. An apparatus for extracting a characteristic figure from a color picture, wherein the color picture is composed of the characteristic figure superimposed on a background area, said apparatus comprising:

an image input device that stores the color picture electrically as an array of pixels such that each pixel is represented by three color intensity values ##EQU49## where 0≦

R, G, B≦

1;

conversion means for converting the three color intensity values ##EQU50## of each pixel to corresponding three color density values ##EQU51## utilizing equations D_r =-logR, D_g =-logG, D_b =-logB, thereby producing an original density picture;

low pass filter means for producing a filtered density picture composed of filtered three color density values ##EQU52## of each pixel, by (i) sequentially designating each pixel as an object pixel in the original density picture, and, for each object pixel, (ii) calculating an average value of corresponding components of three color density values of neighboring pixels situated in a predetermined range extending from the object pixel, and substituting, for each component of the three color density values of the object pixel in the original density picture, the calculated average value corresponding components;

calculation means for producing a processed density picture from said filtered density picture, comprising;

(a) means for determining, for each pixel, a maximum value a_max of a coefficient `a` in an equation ##EQU53## under a restriction where D_r2'"'"' ≧

0, D_g2'"'"' ≧

0, and D_b2 ≧

0, and where ##EQU54## are the filtered three color density values of a corresponding pixel in the filtered density picture, and

(b) means for multiplying, for each respective pixel, k₁ ·

a_max with the three color density values of each said respective pixel in the filtered density picture, thereby composing the processed density picture of processed three color density values for each pixel, where k₁ is a background elimination coefficient determined by design in a range 0<

k₁ ≦

1;

subtraction means for producing a characteristic density picture composed of resultant three color density values ##EQU55## of each pixel by subtracting the processed three color density values of each pixel in the processed density picture from the three color density values of a corresponding pixel in the original density picture;

reverse-converting means for converting the resultant three color density values ##EQU56## of each pixel in the characteristic density picture to three color intensity values ##EQU57## utilizing equations R₂ =10 Exp (-D_r2), G₂ =10 Exp (-D_g2), B₂ =10 Exp (-D_b2); and

an image output device for displaying an image represented by the three color intensity values ##EQU58## of each pixel.

9. An apparatus used for extracting a characteristic figure according to claim 8, further comprising:

a contrast intensifier means for converting the three color intensity values of each pixel output by said reverse conversion means into contrast-enhanced three color intensity values.

10. An apparatus for extracting a characteristic figure from a color picture, wherein the color picture is composed of the characteristic figure superimposed on a background area, said apparatus comprising:

an image input device that stores the color picture electrically as an array of pixels such that each pixel is represented by three color intensity values ##EQU59## where 0≦

R, G, B≦

1;

first conversion means for converting the three color intensity values ##EQU60## of each pixel to corresponding three color density values ##EQU61## utilizing equations D_r =-logR, D_g =-logG, D_b =-logB, thereby producing an original density picture;

low pass filter means for producing a filtered color picture composed of filtered three color intensity values ##EQU62## of each pixel, by (i) sequentially designating each pixel as an object pixel in the original color picture, and, for each object pixel, (ii) calculating an average value of corresponding components of three color intensity values of neighboring pixels situated in a predetermined range extending from the object pixel, and substituting, for each component of the three color intensity values of the object pixel in the original color picture, the calculated average value of the corresponding components;

second conversion means for converting the calculated average value of the corresponding components of each pixel to corresponding filtered three color density values ##EQU63## utilizing equations D_R2 =-logR₀, D_G2 =-logG₀, D_B2 =-logB₀, thereby producing a filtered density picture from said filtered color picture;

calculation means for producing a processed density picture from said filtered density picture, comprising;

(a) means for determining, for each pixel, a maximum value a_max of a variable `a` in an equation ##EQU64## where ##EQU65## are the filtered three color density values of a corresponding pixel in the filtered density picture, under a restriction where D_r2'"'"' ≧

0, D_g2'"'"' ≧

0, and D_b2'"'"' ≧

0, and

(b) means for multiplying, for each respective pixel, k₁ ·

a_max with the three color density values of each said respective pixel in the filtered density picture, thereby composing the processed density picture of processed three color density values for each pixel, where k₁ is a background elimination coefficient determined by design in a range 0<

k₁ ≦

1;

subtraction means for producing a characteristic density picture composed of resultant three color density values ##EQU66## of each pixel by subtracting the processed three color density values of each pixel in the processed density picture from the three color density values of a corresponding pixel in the original density picture;

reverse-converting means for converting the resultant three color density values ##EQU67## of each pixel in the characteristic density picture to three color intensity values ##EQU68## utilizing equations R₂ =10 Exp (-D_r2), G₂ =10 Exp (-D_g2), B₂ =10 Exp (-D_b2); and

an image output device for displaying an image represented by the three color intensity values ##EQU69## of each pixel.

11. An apparatus used for extracting a characteristic figure according to claim 10, further comprising:

a contrast intensifier means for converting the three color intensity values of each pixel output by said reverse conversion means into contrast-enhanced three color intensity values.

12. A method of extracting a characteristic figure from a color picture, wherein the color picture is composed of the characteristic figure superimposed on a background area, said method comprising:

(a) a step of scanning the color picture and electrically storing the scanned color picture as an array of pixels such that each pixel is represented by three color intensity values ##EQU70## where 0≦

R, G, B≦

1;

(b) a step of converting the three color intensity values ##EQU71## of each pixel to corresponding three color density values ##EQU72## utilizing equations D_r =-logR, D_g =-logG, D_b =-logB, thereby producing an original density picture;

(c) a step of designating a pixel in the background area of the color picture and determining a reference density from the three color density values ##EQU73## ascertained for the designated pixel in said converting step;

(d) a step of determining, for each pixel, a maximum value a_max of a coefficient `a` in an equation ##EQU74## under a restriction where D_r'"'"' ≧

0, D_g'"'"' ≧

0, and D_b'"'"' ≧

0;

(e) a step of multiplying, for each respective pixel, a_max with the reference density ascertained in said converting step for said respective pixel, thereby composing a background density picture composed of modified three color density values for each pixel;

(f) a step of subtracting the modified three color density values of each pixel in the background density picture from the three color density values of a corresponding pixel in the original density picture, thereby producing a characteristic density picture composed of resultant three color density values ##EQU75## of each pixel;

(g) a step of reverse-converting the resultant three color density values ##EQU76## of each pixel in the characteristic density picture to three color intensity values ##EQU77## utilizing equations R₂ =10 Exp (-D_r2), G₂ =10 Exp (-D_g2), B₂ =10 Exp (-D_b2); and

(h) a step of displaying an image represented by the three color intensity values ##EQU78## of each pixel.

13. An apparatus for extracting a characteristic figure from a color picture, wherein the color picture is composed of the characteristic figure superimposed on a background area, said apparatus comprising:

an image input device that stores the color picture electrically as an array of pixels such that each pixel is represented by three color intensity values ##EQU79## where 0≦

R, G, B≦

1;

conversion means for converting the three color intensity values ##EQU80## of each pixel to corresponding three color density values ##EQU81## utilizing equations D_r =-logR, D_g =-logG, D_b =-logB, thereby producing an original density picture;

designation means for designating a pixel in the background area of the color picture and determining a reference density from the three color density values ##EQU82## ascertained for the designated pixel in said converting step;

calculation means for producing a background density picture from said original density picture, comprising;

(a) means for determining, for each pixel, a maximum value a_max of a coefficient `a` in an equation ##EQU83## under a restriction where D_r'"'"' ≧

0, D_g'"'"' ≧

0, and D_b'"'"' ≧

0, and

(b) means for multiplying, for each respective pixel, a_max with the reference density ascertained by said conversion means for said respective pixel, thereby composing the background density picture of modified three color density values for each pixel;

subtraction means for producing a characteristic density picture composed of resultant three color density values ##EQU84## of each pixel by subtracting the modified three color density values of each pixel in the background density picture from the three color density values of a corresponding pixel in the original density picture;

reverse-converting means for converting the resultant three color density values ##EQU85## of each pixel in the characteristic density picture to three color intensity values ##EQU86## utilizing equations R₂ =10 Exp (-D_r2), G₂ =10 Exp (-D_g2), B₂ =10 Exp (-D_b2); and

an image output device for displaying an image represented by the three color intensity values ##EQU87## of each pixel.