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Control of CRT Contrast by Internal Etching

IP.com Disclosure Number: IPCOM000041413D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Beeteson, JS: AUTHOR [+4]

Abstract

Etching or stippling of the internal surface of a CRT has to been used to reduce the specular reflections from that surface. By choosing the etch to give a particular etch pit density, the diffuse reflectivity can be adjusted to control the contrast of the CRT. U.S. Patent 3,813,568 describes a technique for etching the internal surface of a CRT so that there are 3.5 x 105 to 3.5 x 107 pits/cm with optimum results for minimum specular reflection at 1 x 107 pits/cm and a pit depth of 1.5 microns. We have now found that within this range there is an intermediate range which allows control of the diffuse reflectivity as well as the specular reflectivity. Within the range of 2.8 x 106 to 2 x 107 pits/cm , the diffuse reflectivity and hence the contrast can be finely tuned.

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Control of CRT Contrast by Internal Etching

Etching or stippling of the internal surface of a CRT has to been used to reduce the specular reflections from that surface. By choosing the etch to give a particular etch pit density, the diffuse reflectivity can be adjusted to control the contrast of the CRT. U.S. Patent 3,813,568 describes a technique for etching the internal surface of a CRT so that there are 3.5 x 105 to 3.5 x 107 pits/cm with optimum results for minimum specular reflection at 1 x 107 pits/cm and a pit depth of 1.5 microns. We have now found that within this range there is an intermediate range which allows control of the diffuse reflectivity as well as the specular reflectivity. Within the range of 2.8 x 106 to 2 x 107 pits/cm , the diffuse reflectivity and hence the contrast can be finely tuned. Thus two different manufacturers may use different black-matrix materials on their color CRTs giving different contrast affects to the viewer. It is desirable from a human factors point-of-view for the contrast not to vary between different CRTs. It would be prohibitively expensive to require one or other of the CRT manufacturers to change his black-matrix technology to give a common contrast. However, by specifying different etch pit densities within the above range, the contrasts of the two different CRTs can be adjusted to give identical appearances. Without changing the specular reflectivity, the diffuse reflectivity can be varied over the screen of t...