Method for color detection in video images

• US 6,574,363 B1
• Filed: 11/12/1999
• Issued: 06/03/2003
• Est. Priority Date: 11/13/1998
• Status: Expired due to Term

• Current Assignee: CNH Industrial Canada, Ltd (CNH Industrial N.V.)
• Original Assignee: Flexi-Coil Ltd. (CNH Industrial N.V.)
• Inventors: Classen, Brian J., Christoff, Jordan C.
• Primary Examiner(s): Wu, Jingge
• Application Number:
  US09/438,405
• Time in Patent Office: 1,299 Days
• Field of Search: 382/162-167, 382/110, 358/504-537
• US Class Current: 382/165
• CPC Class Codes: H04N 9/643 Hue control means, e.g. flesh tone control

Abstract

A method of identifying pixels of a given color in a field of YUV video manipulates color difference signals (R-Y, B-Y) corresponding to defining axes (U,V) of a color space to maximize the video signal in a region of interest of the space, and minimize the signal in all other regions. Additionally, the color difference signal corresponding to one axis may be rotated toward the other axis, or the entire color space may be rotated to bring the region of interest onto or near one of the axes. The signal gains and rotations may be carried out in the signal processing circuits (52) of a conventional color camera (50) so that only one comparator (90) is needed to detect the target color. After rotation and application of gain, the color difference signal defining the region of interest is compared with a threshold value to determine if a pixel is of the target color. A video camera may be mounted on an agricultural sprayer to detect green weeds on the brown soil, by identifying the green pixels in the image captured while the sprayer travels in the field. A spray material may be released upon the weed, once the weed is detected.

Claims

1. A method of processing a video signal to determine when a pixel belongs to a region of interest of a color space, the method comprising the steps of, for each pixel:

a) transforming the video signal into color difference signals corresponding to a set of defining axes of the color space;

b) minimizing signal gain for all color difference signals except for a color difference signal defining the region of interest;

c) establishing a threshold value representing the minimum magnitude that the color difference signal defining the region of interest must have when the pixel belongs to the region of interest of the color space; and

,

d) comparing the color difference signal defining the region of interest with the threshold value to determine if the pixel is in the region of interest of the color space, wherein said region of interest is green, said defining axes are a V axis and a U axis, wherein the V axis is defined as the red axis and the U axis is defined as the blue axis, and the color difference signal defining the region of interest is a negative V axis signal, and wherein the step of minimizing signal gain comprises minimizing the U axis signal and positive V axis signal.

2. A method as claimed in claim 1, further comprising the step of modifying said color difference signals to rotate said color space.

3. A method as claimed in claim 1, further comprising the step of rotating the color difference signal corresponding to one of said axes toward the other of said axes.

4. An apparatus for processing a video signal to determine when a pixel belongs to a region of interest of a color space, the apparatus comprising:

a) a transformation circuit connected to receive a video signal, wherein the transformation circuit transforms the video signal into color difference signals corresponding to a set of defining axes of the color space;

b) gain circuits connected to receive color difference signals from the transformation circuit, wherein the gain circuits minimize the signal gain of all color difference signals except for a color difference signal defining the region of interest; and

,

c) a comparator connected to be responsive to one of the gain circuits, wherein the comparator compares the color difference signal defining the region of interest with a threshold value, the threshold value representing the minimum magnitude that the color difference signal defining the region of interest must have when the pixel belongs to the region of interest of the color space, wherein the comparator produces an output signal indicating that the pixel is in the region of interest of the color space when the color difference signal defining the region of interest exceeds the threshold value.

5. An apparatus as claimed in claim 4, wherein said axes comprise a V axis and a U axis, said color difference signals comprise a V axis signal and a U axis signal, and said apparatus further comprises a matrix for rotating the U axis toward said V axis.

6. An apparatus as claimed in claim 5, wherein said gain circuits comprise means for minimizing the U axis signal and positive V axis signals, said comparator being responsive to negative V axis signals for indicating that a pixel is green when a negative V axis signal exceeds said threshold value.

7. An apparatus as claimed in claim 6, wherein said transformation circuit, said gain circuits and said matrix form a color video camera.

8. An apparatus as claimed in claim 7, wherein said camera is mounted on a spray boom of an agricultural sprayer.

9. An apparatus as claimed in claim 7, in combination with at least one spray nozzle and means responsive to said comparator output signal for energizing said at least one spray nozzle.

10. An apparatus as claimed in claim 6, in combination with means responsive to said comparator for determining when a weed of a least a predetermined size has been detected, and at lease one nozzle actuates by said means responsive to said comparator.