Method and apparatus for making monochrome facsimiles of color images on color displays

• US 4,308,553 A
• Filed: 03/03/1980
• Issued: 12/29/1981
• Est. Priority Date: 03/03/1980
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Roetling, Paul G.
• Primary Examiner(s): Richardson, Robert L.
• Application Number:
  US06/126,801
• Time in Patent Office: 666 Days
• Field of Search: 358/75, 358/80, 358/81, 358/21, 358/22, 364/521, 340/730
• US Class Current: 358/507
• CPC Class Codes: H04N 1/40012 Conversion of colour to monochrome
• CPC Class Codes: H04N 1/508 using the same reproducing head for two or more colour components
• CPC Class Codes: H04N 1/52 Circuits or arrangements for halftone screening
• CPC Class Codes: H04N 1/58 Edge or detail enhancement; Noise or error suppression, e.g. colour misregistration correction H04N1/62 takes precedence

Abstract

Method and apparatus are disclosed for making 35 mm color slides from a color image created on a color cathode ray tube (CRT) terminal. The color terminal transmits commands to a remote central processing unit (CPU) that in turn operates a 35 mm camera device to expose 35 mm color slide film. Prior to transmitting the commands, a black on white facsimile of the color image is created by a graphic printer located at the color terminal. The black and white facsimile uses different halftone dot patterns in a monochrome graphic image to simulate the different colors created at the color terminal. The halftone dot pattern density is related to the luminance of the color it represents and the scale of the dot pattern is large to enable ready detection by the human eye. Also, different dot patterns are used for different colors and on edge enhancement technique is used to distinguish one simulated color region from another in the monochrome image.

Claims

1. A method of simulating an electronic polychrome raster image represented by color signals with an electronic monochrome raster image represented by marking signals comprising

providing multiple sets of screen signals with each set defining unique halftone dot patterns for different colors represented by the color signals and

generating marking signals from the color signals and screen signals that simulate different colors in the polychrome raster image with the unique halftone dot patterns of the screen signals.

2. The method of claim 1 wherein each set of screen signals defines a halftone dot pattern that has a comparative density related to the comparative luminance of different colors in a polychrome raster image.

3. The method of claim 1 wherein each set of screen signals defines a halftone dot pattern having a spatial frequency readily detectable by the human eye when converted to marks on a graphic medium.

4. The method of claim 1 wherein each set of screen signals defines a halftone dot pattern having a spatial frequency readily detectable by the human eye when converted to marks on a graphic medium and wherein each set of screen signals defines a halftone dot pattern that has a comparative density related to the comparative luminance of different colors in a polychrome image.

5. The method of claim 1 further including the step of enhancing the appearance of edges between halftone patterns represented by the marking signals by changing the portion of the halftone dot pattern adjacent the edges.

6. The method of claim 5 including the step of magnifying the color signals representative of the polychrome image prior to generating the marking signals from the color and screen signals and enhancing the edges to minimize the loss of color information in the monochrome raster image.

7. The method of claim 1 wherein color signals include at least first and second sets of color signals with each set representative of a single color and with the combination of the two representative of a third color and wherein at least first and second sets of screen signals represent the two colors represented by each set of color signals and the combination of the two sets of screen signals represent the third color represented by the combination of the two sets of color signals.

8. The method of claim 7 wherein green, red and blue sets of color signals represent green, red and blue colors in a polychrome raster image and wherein green, red and blue sets of screen signals represent the green, red and blue color signals in a monochrome raster image.

9. The method of claim 8 wherein the step of generating the marking signals from the color signals and the screen signals includes relating the two signals according to the Boolean algebra expression

G(b).GS(k)+R(b).RS(k)+B(b).BS(k)=M

wherein the dot is a logical and operator and the plus is a logical or operator,

G(b), R(b) and B(b) are corresponding color signals from the green, red and blue sets of color signals repsectively with b defining the locations within each set,

GS(k), RS(k) and BS(k) are corresponding screen signals from the green, red and blue sets of screen signals respectively with k defining the locations within each set and

M defines the marking signal or the logical inverse of the marking signal.

10. The method of claim 9 wherein the green, red and blue color signals are the color signals associated with a polychrome raster display image created on color display means and further including the step of coupling the marking signals to graphic printing means to generate a graphic monochrome raster image of the polychrome raster image.

11. The method of claim 10 wherein the color display means includes a color CRT display device and wherein said printing means creates the monochrome image by creating monochrome visible marks on paper.

12. The method of claim 10 wherein the printing means includes an electrostatic printer having at least one row of stylii adapted to mark a graphic medium in response to the marking signals to form a latent electrostatic raster image.

13. The method of claim 1 further including the steps of creating a 35 mm color slide from signals derived from the color signals representative of the polychrome raster image and the step of applying the marking signals to monochrome printing means to create a monochrome facsimile of the 35 mm color slide to verify the composition of the color slide.

14. The method of claim 1 wherein halftone dot patterns have zero screen angles.

15. The method of claim 1 wherein the halftone dot patterns have non-zero screen angles.

16. The method of claim 1 wherein the screen signals define nonzero angle halftone dot patterns generated by cycling and shifting screen signals.

17. Apparatus for generating a monochrome raster scan graphic image of a polychrome raster scan image created on the face of a polychrome CRT comprising

storage means for storing multiple sets of color signals for energizing different color regions in color pixels arranged in a plurality of rows at the face of the CRT for emitting different colors of light when energized by an electron beam to create a polychrome raster scan image on the face of the CRT,

generator means for generating multiple sets on screen signals corresponding to the multiple sets of color signals for creating different pattens in areas in the monochrome raster scan graphic image that correspond to different color areas in the polychrome raster scan image,

microprocessor means for combining the color signals and screen signals to generate a single set of marking signals representative of a raster image having monochrome pixels corresponding to the color pixels at the face of the CRT and

printing means coupled to receive the marking signals to generate visible monochrome marks on a graphic medium to form a monochrome raster scan graphic image wherein different patterns associated with the screen signals represent colors in the polychrome raster scan image at the face of the CRT.

18. The apparatus of claim 17 further including a 35 mm color slide camera means for generating 35 mm color slides of polychrome images of the polychrome raster scan image created on the face of the CRT after a monochrome graphic image has been created on the printing means to verify the composition of the polychrome image.