Spectrally balanced scanner

• US 6,219,159 B1
• Filed: 03/09/1998
• Issued: 04/17/2001
• Est. Priority Date: 03/09/1998
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Firl, Gerold G.
• Primary Examiner(s): Grant, II, Jerome
• Application Number:
  US09/037,719
• Time in Patent Office: 1,135 Days
• Field of Search: 358/513, 358/514, 358/509, 358/520, 358/515, 358/516, 358/461, 358/483, 358/482, 358/475, 382/274
• US Class Current: 358/513
• CPC Class Codes: H04N 1/484 with sequential colour illumination of the original

Abstract

A color imaging system in which the lamp spectrum is tuned so that, in the charge coupled device, the signal to noise ratio is maximized for all three RGB channels equally. This result is obtained by a process wherein the fluorescent lamp output is adjusted by alteration of the relative amounts of red, green and blue phosphors which coat the inside surface of the lamp. In this manner, when the lamp spectrum is tuned so that the RGB channels of the CCD have equal levels when scanning a white background, the signal to noise ratio can be maximized for all three channels equally. Thus, it is possible to scan a white paper without saturating and all three colors can be scanned simultaneously, since the lamp brightness can be set at a level which maximizes signal strength for all three color signals. That is, the lamp output spectrum and the RGB response of the CCD are tuned to provide balanced system response.

Claims

1. In a color imaging system wherein the spectral emission phosphors of a lamp are processed by a charge coupled device, a method of matching the lamp phosphor spectral emission with charge coupled device sensitivity, comprising the steps of:

a. determining optimum lamp output chromaticity coordinates for maximizing charge coupled device signal to noise ratios;

b. applying a blend of phosphors to the lamp interior surface;

c. measuring lamp emission chromaticity produced by said phosphor blend; and

d. adjusting said phosphor blend until said optimum chromaticity coordinates are achieved.

2. The method according to claim 1 wherein adjustment of the lamp spectral emission includes controlling the relative intensity of lamp emission to produce light having predetermined chromaticity diagram coordinates.

3. The method according to claim 1 wherein said adjusting step further includes balancing lamp phosphor spectral emission with charge coupled device sensitivity wherein the RGB channel of said charge coupled device function within a range of 10% of each other.

4. The method according to claim 1 wherein the adjusting step includes controlling said phosphor blend to produce chromaticity coordinates of x=0.34±

0.01 and y=0.315±

0.01, on the ICI chromaticity diagram.

5. An imaging system comprising:

a charge coupled device for converting a plurality of different wavelengths of light into at least three different output signals indicative of the wavelengths in the color spectrums of red, green, and blue respectively; and

a light arrangement for producing said pluralities of different wavelength of light;

said light arrangement including a lamp having different phosphor coatings selected in desired ratios to match the spectral response of said charge coupled device so that the different output signals of the charge couple device are maximized and substantially equal in response to substantially white light;

means for determining optimum lamp output chromaticity coordinates for maximizing charge coupled device signal to noise ratios; and

means for measuring lamp emission chromaticity produced by said phosphor ratios.

6. A scanner comprising:

a housing having a transparent supporting surface for supporting from below a medium to be scanned for its informational content;

a charge coupled device mounted in said housing for converting a plurality of different wavelengths of light into at least three different output signals indicative of the wavelengths in the color spectrums of red, green, and blue respectively; and

a light arrangement mounted in said housing for producing said plurality of different wavelengths of light;

said light arrangement including a lamp having different phosphor coatings selected in desired ratios to match the spectral response of said charge coupled device so that the different output signals of the charge couple device are maximized and substantially equal in response to substantially white light;

means for determining optimum lamp output chromaticity coordinates for maximizing charge coupled device signal to noise ratios; and

means for measuring lamp emission chromaticity produced by said phosphor ratios.

7. A method of spectral balancing, comprising:

providing a charge coupled device for converting a plurality of different wavelengths of light into at least three different output signals indicative of the wavelengths in the color wavelength spectrums of red, green, and blue respectively;

providing a lamp for producing said plurality of different wavelengths of light, said lamp having different phosphor coating ratios matched to the spectral response of said charge coupled device so that the different output signals of the charge couple device are maximized and substantially equal in response to light reflecting from a substantially white background;

determining optimum lamp output chromaticity coordinates for maximizing charge coupled device signal to noise ratios; and

measuring lamp emission chromaticity produced by said phosphor ratios.