This invention relates to improved methods and apparatus for the production of digitized stereoscopic polarizing images.
Ordinary (unpolarized) light is made of electromagnetic waves vibrating equally in all directions perpendicular to their direction of travel. Absorption-polarizing sheets polarize these light waves by partially or wholly absorbing the vectorial components vibrating in a specified direction transverse to the direction of travel.
A stereoscopic image based on the polarization of light is generally formed of a pair of polarizing images, each of which presents a light-polarizing design or image that selectively transmits light of a predetermined vector of polarization.
Stereoscopic image pairs, having a left-eye light-polarizing image superimposed on a right-eye light-polarizing image, enable the perception of a three-dimensional image when the image pair is viewed through a pair of polarizing filters, or analyzers, oriented to allow the left-eye polarized image to reach the left eye and the right-eye polarized image to reach the right eye. A polarizing image can be made by a sheet that polarizes light to different percentages, depending upon the density of the image at each point. In particular, the percentage of polarization is directly related to the image's density, nearly all light being polarized in high-density areas and only a small amount of light being polarized in low-density areas.
When forming the stereoscopic polarizing image, the most effective arrangement occurs when the polarization axis of the left-eye image is at right angles to the polarization axis of the right-eye image, and when the two layers are superimposed in such position with respect to each other that the images carried thereby are stereoscopically registered. An observer using viewing spectacles comprising orthogonal polarizing left-eye and right-eye lenses, then has each of his or her eyes receiving only the image intended for it, and the pair of images appears as a single three-dimensional image.
Various techniques exist for producing light-polarizing images on the light polarizing sheets. For example, in Land, U.S. Pat. No. 2,204,604, a light-polarizing sheet may initially be formed by a light polarizing material, such as an optically oriented suspension of minute crystals of herapathite or other polarizing material, in a suitable medium, such as cellulose acetate. A picture may then be reproduced on the light polarizing sheet by altering the polarizing characteristics of the sheet over pre-determined areas of the sheet, forming the negative of the desired image. The areas forming the design may be protected with a coating, such as wax, and the sheet subjected to a treatment that destroys or otherwise alters the polarizing characteristics of the exposed areas.
An alternative method for forming the stereoscopic print, as described in Land, U.S. Pat. No. 2,281,101, is to employ a Vectograph.TM. sheet material comprising a linear hydrophilic polymer, such as polyvinyl alcohol (hereinafter "PVA"), which has been treated such that its molecules are substantially oriented to be parallel to a specific axis. Orientation of polyvinyl alcohol generally can be accomplished by softening the PVA sheet, as for example by subjecting it to heat, or to the action of a softening agent, until the sheet may be stretched or extended, and then by stretching or extending until suitable orientation of the molecules has been obtained. In the case of polyvinyl alcohol for example, the sheet would generally be extended from two to four or five times its length. Once stretched, the PVA sheet is ready for lamination to a non-depolarizing base.
Further in accordance with Land, U.S. Pat. No. 2,281,101, polarizing images may be formed in PVA by printing thereon with certain dichroic, water-soluble, direct dyes of the azo type, or by staining the sheet with iodine in the presence of an iodide. The color of the dichroic image reproduced in this sheet may be controlled by selecting suitable dyes, stains or the like. The stain or dye is applied to the sheet from a halftone plate or a gelatin relief.
The term dichroism is used herein as meaning the property of differential absorption of the components of polarization of an incident beam of light, depending upon the vibration directions of the components. Dichroic dye or stain as used herein refers to a dye or stain whose molecules possess the property of becoming linearly disposed within the oriented sheet material. For example, when a molecularly-oriented polymeric sheet is dyed with a dichroic dye, the sheet will appear dichroic, i.e., it will absorb differently the vectorial components of polarization of an incident beam of light.
According to another method for forming polarizing images, disclosed in Land, U.S. Pat. No. 2,289,714, polarizing images in full color may be produced. In this process, the use of three subtractive dichroic dyes--a minus Red, a minus Green, and a minus Blue dye forming respectively the Cyan, Magenta, and Yellow images--allows the production of a full color image. To achieve full-color stereoscopic images, the Land '714 patent teaches that six well-registered gelatin relief images, a cyan pair, a magenta pair, and a yellow pair, must first be prepared; one relief for each color component in each of the two directions of polarization. Each of the six gelatin reliefs is then appropriately dyed, and an image from each relief is subsequently transferred to the appropriately oriented PVA layer.
One of the drawbacks of this method for producing full color stereoscopic images, as it is currently practiced, is the difficulty and time involved in transferring an image to the oriented polymer sheets. For example, to produce a full-color image with known methods requires transferring each color component of the image from a gelatin relief to the polymer sheet. Besides being time-consuming and expensive, this technique requires great precision in aligning each of the printed images to produce a clear and precise stereoscopic image. Another drawback with known techniques is the difficulty in masking the image. To alter the final three-color stereoscopic image even slightly, all six gelatin reliefs must be altered.
Masking is a term used to describe various methods for enhancing separation records, or original transparencies, in order to compensate for the unwanted absorptions of the subtractive dyes used in making a full-color stereoscopic image. Conventional photographic negatives and positives are held in register with the original slide or the separations to provide improved highlights, cleaner colors, controlled contrast, improved shadow detail, and ultimately remove unwanted colors. These methods are described in great detail in "The Reproduction Of Colour" by R. W. G. Hunt and "Neblette's Handbook Of Photography and Reprography" edited by John M. Sturge.
There is a need for a more efficient method of producing a stereoscopic image that combines the traditional advantages of the prior art while eliminating some of its disadvantages. Accordingly, an object of the invention is to provide an easier and more efficient method of producing full-color stereoscopic polarizing images having clearer and crisper images.
It is also an object of this invention to provide methods, systems and materials that facilitate ink-jet printing of digitized stereoscopic polarizing images.
It is a further object of the invention to provide ink compositions and inking methods particularly suited for ink-jet printing of stereoscopic images.
Further objects of the invention include providing a coating to be used in producing digitized stereoscopic polarizing images by inkjet printing, and formulating dichroic inks for ink-jet printing.
These and other objects will be apparent from the description that follows.