Systems and methods for optically filtering for color specific enhancement

An optical filtering apparatus fashioned as a pair of glasses; that enhance the contrast and visibility of objects with specified colors. A set of distinct attenuations are combined to produce an optical filter that promotes a specified color.

BACKGROUND

The present disclosure relates to a method of optical filtration and to lenses employing the optical filtration. This optical filtration enhances the visibility of objects that exhibit specified colors.

Sportsmen are often required to track colored objects. Hunters track blood-trails that are predominately red in color; while competitive shooters track flying clay discs that are commonly orange in color.

Regarding blood-trails, hunters spend considerable time recovering game that have been shot. When the game runs away their blood-trails can become increasingly faint to non-existent. During daytime, recovery of the blood-trail is observed in the presence of natural sunlight. During nighttime, recovery of the blood-trail is illuminated with an artificial light source (e.g. flashlight or lantern). Hunters know that the blood-trail can come down to a single drop of blood; which can mean the difference in a lost animal or a found trophy.

Regarding shotgun shooting events like skeet, trap, and sporting clays; shooters must quickly identify flying colored clay discs and shoot them before they hit the ground. Shooter success is tied to their ability to quickly identify the target objects and to maintain track of these objects amid a variety of backgrounds and lighting conditions. Background conditions include sky, trees, and hillsides. Lighting conditions range from bright daylight to late afternoon with overcast clouds.

Often Shooters wear protective glasses and as such have a variety of commercial lenses from which to choose. Some of these commercial lenses provide simple colored tinting while other lenses offer complex manipulations of the visible light spectrum (notches, windows, dips). Since most all shooting events are held outdoors, glasses with partial shading (sunglasses) are often used. Tinted lenses can provide the shading effect but sometimes create an altered reality whereby the visual scenes take on the colored tint. For example, popular yellow tinted lenses used by shooters create visual scenes in which everything takes on the yellow tint while providing no significant increase in visibility of the colored discs.

SUMMARY

To overcome the shortcomings of the current art, an optical filtering apparatus is provided. And as such this apparatus employs a set of distinct and purposeful optical attenuations that are combined to form an optical filter that improves the visibility of objects with specified colors. This set of optical attenuations is described in terms of three categories: global, local, and color-balance. The global attenuations consist of an initial attenuation of all wavelengths of visible light for the purpose of a general shading effect (sunglasses). An additional global attenuation is applied across the visible spectrum to attenuate those wavelengths of light that are not significantly contributing to the color of the target object. A local attenuation is applied to a set of wavelengths near those wavelengths that are significantly contributing to the color of the target object. A color-balance attenuation is application specific and determines the amount of color balance that is applied to the background (visual scene).

DETAILED DESCRIPTION

The present disclosure provides lenses that improve the visibility of colored objects like blood-trails and orange clay discs. For blood-trailing applications, the present disclosure describes lenses that effectively improve the visibility of blood-trails during daytime recovery while in the presence of natural sunlight; and lenses that are equally effective during nighttime recovery in the presence of artificial light (flashlights, lanterns). For competitive shooting applications, the present disclosure describes lenses that improve the visibility of the colored clay discs amid a variety of backgrounds and lighting conditions while preserving color-balance of the backgrounds (visual scenes).

The present disclosure describes an optical filtering apparatus that can be worn by a sportsman as a pair of glasses (eyewear), and these glasses improve the visibility of objects with specified colors. Sportsmen are often required to track colored objects. For example, hunters track blood-trails while competitive shooters track flying colored clay discs. The apparatus combines certain properties of color processing found in human vision with optical properties of the colored objects. A set of distinct and purposeful attenuations are combined to create an optical filter that improves the visibility of certain colored objects like animal blood and orange clay discs.

In one embodiment the apparatus comprises a set of optical attenuations that are categorized as global, local, and color-balance. The global attenuations consist of an initial attenuation of all wavelengths of visible light for the purpose of a general shading effect similar to sunglasses. An additional global attenuation is applied across the visible light spectrum to attenuate those wavelengths of light that are not significantly contributing to the color of the target object. This effectively suppresses other colors and gives preference to the specified color of interest.

A local attenuation is applied to a set of wavelengths near those wavelengths that are significantly contributing to the color of the target object. The width of the local attenuation is relatively small while the amount of attenuation across this window is significantly high. In one embodiment the width of the local attenuation is approximately 34 nm but can sometimes be closer to 45 nm. In this embodiment the local attenuation level is approximately 99 percent yielding a corresponding transmittance of 1 percent. The local attenuation creates a color-shift effect that provides a dramatic improvement to the visibility of certain colored objects like animal blood and orange clay discs. Color-shift refers to an effect where a colored object appears to take on a different color once filtered. In one embodiment the local attenuation applied to a dull orange object makes the object appear deep orange and almost red (i.e. color-shifted from orange to red). A color-balance attenuation is applied but is recognized to be application specific. The color-balance attenuation determines the amount of color balance that is applied to the background visual scenes. The color-balance attenuation is applied in concert with the afore-mentioned global and local attenuations to collectively produce a composite spectrum. The color-balance attenuation is applied to preserve the increased contrast of the specified colored object due to the global and local attenuations; while leveling out the other colors in the background scenes so that they appear natural and seemingly unaltered.

The color-balance attenuation is application specific. For shooting applications involving orange clay discs, the color balance is optimized to allow the background scenes to be observed as natural, virtually unmodified, and largely unfiltered. For blood-trailing applications, the color-balance is relaxed to pass more light in order to compensate for use in low-lighting conditions such as nighttime game recovery using limited artificial light like a flashlight or a lantern.

With reference first toFIG.1, an exemplary eyewear apparatus100as illustrated comprises an impact resistant lens(es)101possessing the aforementioned optical filtration properties. Included are side shield(s)102and a top shield103. The side shield(s)102and top shield103help block light coming in from the sides and top; which helps to apply filtering to most all of the light reaching the wearer's eyes. The side shield(s)102and top shield103can also be constructed as solid plastic to block light entering from the top and sides, or the side shield(s)102and the top shield103may be opaque to reduce light entering from the top and sides. In one embodiment, the shield(s)102and the top shield103may be made of the lens101filter material to selectively filter the light from multiple directions.

The eyewear includes arms104with adjustments105, an optional frame106, and a nose bridge107. These are standard components of traditional safety glasses, but the lens(es) are specially designed to enhance specific colors (e.g. red and orange).

FIG.2compares the light spectrums for artificial light sources (cool white LEDs shown by graph202and warm white LEDs shown by graph203) with natural light sources (sunlight shown by graph201). It is understood that natural sunlight is many times brighter than LEDs so, the curves200are scaled for relative comparison of their spectral distributions. White LEDs have a dominant blue contributor in or around 450 nm. White LEDs also have a somewhat gaussian distribution of intensity between 500 nm and 750 nm. Sunlight on the other hand has a smoother, somewhat flat, distribution between 450 nm and 750 nm. The eyewear described herein filters natural sunlight201during daytime applications like blood-trailing and shooting clay discs and filters artificial light, e.g., LED flashlight202and203, during nighttime applications.

The visible light spectrum204is generally considered to span wavelengths between 360 nm and 830 nm for daylight levels of illumination. While the human eye sees wavelengths across this entire range the span is effectively limited to a range of 400 nm to 700 nm under normal viewing conditions.

Sunlight is distributed across the spectrum and can be decomposed into specific colors that result from the particular wavelengths of light. However, objects whether natural or man-made, are not resigned to a single specific wavelength or wavelength-color, but instead relate to combinations of wavelengths. For example, an orange object does not consist of simply a 600 nm wavelength of light but instead consists of a group of wavelengths that may include red, orange, and yellow wavelengths. Again, an object observed by a human does not consist of a single color wavelength but instead consists of groups of color wavelengths that are processed by the eye and brain (also known as color perception).

Regarding shotgun shooting applications, the apparatus of the present disclosure improves the visibility of colored clay discs. These objects are often referred to as clays or skeet. With reference toFIG.3, there are three major shotgun sporting events—trap, skeet, and sporting clays. Trap has clay targets moving away from the shooter, while skeet has them crossing from side to side. In sporting clays, targets can fly in multiple directions. Protective eyewear is required for these events. Shooters301must quickly acquire and track these flying colored objects304and shoot the clay disc305with a shotgun302before they hit the ground. The clay discs are most commonly bright orange in color. However, other disc colors such as white, black, and yellow (sometimes with an occasional black outer ring) are used. But a popular fluorescent orange color has been overwhelmingly adopted as it provides additional brightness in the presence of ultraviolet (UV) sunlight.

Shooters have to contend with a variety of background environments and lighting conditions. Background environments include clear sky, cloudy sky, trees of various colored foliage, hillsides and ground cover of various colors. Lighting conditions can vary between clear bright daylight and overcast late afternoon.

FIG.4shows the spectral profile of an orange sporting clay disc. A popular fluorescent orange paint is used that provides additional intensity when exposed to ultraviolet light. This fluorescent paint has a normal spectral profile401when exposed to incandescent light. But when ultraviolet light shown by graph402is added, the spectral intensity is increased as shown by graph403. Regardless of the light source the peak in the spectral profile of the fluorescent paint is near 605 nm shown by line404and diminishes significantly below 580 nm shown by line405. The visible light spectrum406is included in this figure for reference.

Regarding blood-trails, the apparatus of the present disclosure improves the visibility of blood-trails.FIG.5Adepicts a hunter501using the apparatus502while tracking a blood-trail503in the presence of natural light (sunlight504).FIG.5Bdepicts a hunter505using the apparatus506while tracking a blood-trail507in a nighttime scenario with limited natural light (moonlight508) but supplemented with artificial light (flashlight509). In either case the optical filtering apparatus (glasses)506are used to increase the visibility of specified colored object (blood-trail).

The actual color of blood depends on several factors to include the oxygenation levels of the blood, the amount of time that the blood has existed outside of its host body, and environmental conditions (e.g. temperature and moisture).

FIG.6shows an exemplary plot of the spectral absorbance of blood. The vertical peaks indicated by lines601,602, and603near 575 nm, 540 nm, and 440 nm, respectively, indicate areas in the visible light spectrum604where light wavelengths are predominately absorbed by the blood. It should be noted that this curve is plotted with a logarithmic scale, which enables one to see additional features that are not nearly as noticeable when plotted on a linear scale.FIG.6details three distinct regions (Region1, Region2, Region3) that are separated by the absorption peaks indicated by lines601,602,603. Wavelengths in Region1receive the least amount of absorption as compared to the amounts of absorption in Region2and Region3. This relates to more of these wavelengths getting sent to the eye. Region2and Region3have noticeable valleys that relate to local minima for absorption. The relative proportions of the absorption in Region1, Region2, and Region3are significant as they define the optical properties of blood.

FIG.7shows an exemplary plot of the spectral transmittance of blood. This figure details three distinct regions (Region1, Region2, Region3) bounded by wavelengths indicated by lines701,702,703, corresponding to wavelengths near 575 nm, 540 nm, and 440 nm respectively, again indicating areas in the visible light spectrum707where light wavelengths are predominately absorbed by the blood. Region1contains wavelengths that are predominately red, and the transmittance for these wavelengths is significantly higher than those of the wavelengths in the other two regions. Region3contains wavelengths that are predominantly blue with some green and the peak amplitude of the hump in this region is significantly less than the peak amplitude of Region1. Region2contains wavelengths that are predominately green and the peak amplitude of the hump in this region is less than the peak amplitude of Region3.

In one embodiment the relative proportions of the peak amplitudes of Region1, Region2, and Region3ofFIG.7can be carried forward in the creation of the filtration lenses. Narrow-band absorbers located at wavelengths between the three regions and one to the left of Region3can be integrated with the lens(es) to filter light and produce a filtered transmittance that mimics that of blood. That is to say that the resulting transmittance of the filter will resemble the transmittance of blood.

A narrow-band absorber can be added between the red and green regions701near 575 nm that absorbs light and produces a local minima705. Another narrow-band absorber can be added between the green and blue regions702near 540 nm, and absorb light and produce a local minima706. Another narrow-band absorber can be added near 440 nm indicated by line703. The importance of the absorbers being narrow-band is that they are sufficiently narrow that their attenuation does not extend into the red region, because a goal is that the red region receives as little attenuation as possible.FIG.7also shows a threshold wavelength indicated by line704whereby the transmittance for all of the visible wavelengths above which are significantly higher than the transmittance for any of the visible wavelengths below the threshold wavelength indicated by line704.

FIG.8Aillustrates certain physical aspects of the human eye801. Light enters thru a lens802and the amount of light is controlled by the iris803. The light is focused onto the retina804which contains a variety of light-sensing photoreceptors. The eye has two primary types of light-sensing cells referred to as rods and cones. Their names refer to their actual geometric shapes. The retina has a small area referred to as the fovea805where the cone density807peaks and concentration of photoreceptors is exclusively cones. The distribution of rods808exists outside of the fovea and does however include a very small number of cones. The photoreceptors convert the light to impulses that are sent thru the optic nerve806to the brain for additional processing.FIG.5Billustrates the concept of overlapping photoreceptor fields809withing the eye810. Actual receptive field size is much smaller than shown.

FIG.9illustrates the response of the human eye in dark, near-dark, and daylight environments. Cones process visual information with a photopic response901in bright light (daytime). Rods process visual information with a scotopic response902in dark lighting conditions (nighttime). Between photopic and scotopic light levels is a range called mesopic. Mesopic response903exists in moderately low (but not dark) lighting conditions where the effectiveness of the cones is diminished; and rods strongly affect color perception by mixing with or tinting the color of the still active cones. As intimated byFIG.9, human vision is vastly different in dark, near-dark, and daylight environments. The application of the apparatus described herein will relate primarily to the photopic and mesopic responses.

FIG.10illustrates the responses of the four types of photoreceptors. Red-sensitive cones have a response curve1001showing particularly sensitive to longer wavelengths (“L”) with a peak sensitivity at or near 560 nm. Green-sensitive cones have a response curve1002showing a sensitivity to medium wavelengths (“M”) with a peak sensitivity at or near 530 nm. Blue-sensitive cones have a response curve1004showing a sensitivity to short wavelengths (“S”) with a peak sensitivity at or near 420 nm. The rods have a response curve1003with a peak sensitivity near 500 nm. The visible light spectrum1005is included in this figure for reference.

There are two major theories for the color processing in human vision: Young-Helmholtz trichromatic theory and Hering color opponent process theory. These theories are complementary and together explain how humans process color. Trichromatic theory explains how color vision works at the receptor level, while color-opponent theory explains how it works at the neural level.

FIG.11illustrates color processing that is associated with color opponent theory. A first stage of color processing1101occurs in the retina. The red1106, green1105, and blue1104sensitive cones are wired to produce color opponent pairs. The receptive fields809(FIG.8) are configured into center and surround areas like bullseyes. The color opponent pairs include Red center/Green surround1110, Green center/Red surround1109, Blue center/Yellow surround1107, and Yellow center/Blue surround1108. There are also black versus white opponent pairs1111and1112; but they do not affect our color sense. The color opponent channels1102from the retinal processing1101continue thru to a second stage of color processing1103occurring in the cortex. The B-Y (Blue-Yellow) opponent response curve1114shows that the blue side dominate for wavelengths below 500 nm while the yellow dominates at wavelengths above 500 nm. The R-G (Red-Green) opponent response curve1113shows the red dominating at each end while the green dominates in the middle. Every color is seen as a balance between these two channels. For example, looking at the two response curves1113and1114at 450 nm, the blue plus red sums to a specific blue.

FIG.12provides additional explanation of the Red-Green1201and Blue-Yellow1202color opponent response curves. Humans perceive pure green1203around 500 nm where the B-Y (blue-yellow) cancel and green is unopposed. Pure blue1204is perceived near 477 nm where R-G (red-green) cancel and blue is unopposed. Pure yellow1205is perceived near 580 nm where R-G (red-green) cancel and yellow is unopposed. Unique red is non-trivial as it falls outside of the spectrum. A peak in the R-G response curve occurs near 614 nm indicated by line1206; the importance of which will be discussed later. The R-G response curve1201has a peak near 614 nm. The visible light spectrum1207is included for reference.

Combining an understanding of the color processing that occurs in human vision with the knowledge of the spectral profiles of the colored objects (blood-trails and orange clay discs), allows an optical filter to be tailored to increase the contrast and visibility of an object with a specified color. A set of distinct attenuations are combined into an optical filter that manipulates the visible light spectrum for this purpose. This set of optical attenuations is now described in terms of three categories: global, local, and color-balance.

FIG.13illustrates global attenuations to be applied to the visible light spectrum1304. The global attenuations consist of an initial attenuation shown by line1301of all wavelengths of visible light for the purpose of a general shading effect, like sunglasses. An additional global attenuation1302is applied across the visible spectrum to attenuate those wavelengths of light that are not significantly contributing to the color of the target object. A threshold wavelength identified by line1303delineates these two global attenuations. The wavelength is near 590 nm for blood-trailing applications and near 580 nm for shooting applications involving orange clay discs. Wavelengths above the threshold wavelength indicated by line1303receive minimal attenuation as shown by line1301for general purpose shading effect (sunglasses), while wavelengths below the threshold wavelengths shown by line1303receive substantially more attenuation as shown by line1302. In one embodiment the attenuation of wavelengths above the threshold wavelength1303is 20 percent yielding an average 80 percent transmittance shown by line1301, and the attenuation of wavelengths below the threshold wavelength indicated by line1303is 75 percent yielding an average 25 percent transmittance shown by line1302.

FIG.14illustrates the addition of a second attenuation representing a local attenuation of wavelengths that are close to and below those wavelengths comprising the colored object. Wavelengths of light between line1405and line1404receive a significant “local” attenuation shown by line1402which is substantially stronger than the “global” attenuations shown by line1401and line1403. Selecting a critical wavelength indicated by line1405that is above the threshold wavelength1303(FIG.13) for the colored object, produces a color-shift effect that adds unmistakable improvements to contrast and visibility. The critical wavelength indicated by line1405provides significant color-shift when located near 614 nm, which corresponds to the peak indicated by line1206(FIG.12) of the R-G color-opponent response curve1201(FIG.12). The color-shift results from the suppression of wavelengths between line1404and line1405. This attenuation is applied to an area of the visible light spectrum1406to exploit the relative differences between the R-G color-opponent response curve1201(FIG.12) and the B-Y response curve1202(FIG.12).

In one embodiment of the apparatus the local attenuation is applied to wavelengths between 580 nm at line1404and 614 nm at line1405, where the local attenuation indicated by line1402is nearly 99 percent, yielding a 1 percent transmittance. And in this embodiment the global attenuation of wavelengths above the critical wavelength indicated by line1405yields a transmittance of approximately 81 percent, and the global attenuation of wavelengths below1404yields an average transmittance of approximately 25 percent.

FIG.15Aillustrates a composite spectral profile created from a of a set of attenuations that are applied to the visible light spectrum1511; as configured for shooting applications involving orange clay discs. This set consists of global, local, and color-balance attenuations that are described as follows. First the global attenuations are indicated by line1501, line1503, and line1505. Line1501applies to wavelengths above the critical wavelength that is indicated by line1506. Line1503is a global attenuation that applies to wavelengths between line1508and line1507. Line1505is a global attenuation that applies to wavelengths between line1510and line1509. Second is the local attenuation indicated by line1502that is applied to wavelengths between line1507and line1506. And third is a color-balance attenuation indicated by line1504that is applied to wavelengths between line1509and line1508. The purpose of the color-balance attenuation is to provide a natural and seemingly unaltered background scene. In one embodiment, the composite spectral profile for shooting applications that involve orange clay discs can be described as follows. First the global attenuation indicated by line1501has a corresponding average transmittance of approximately 81 percent for wavelengths above a critical wavelength near 614 nm as indicated by line1506. This embodiment includes a global attenuation indicated by line1505with a corresponding average transmittance of approximately 25 percent for wavelengths between approximately 400 nm as indicated by line1510and 465 nm indicated by line1509. This embodiment includes a global attenuation indicated by line1503with a corresponding average transmittance of approximately 25 percent for wavelengths between approximately 540 nm indicated by line1508and 580 nm indicated by line1507. Second is a local attenuation indicated by line1502located between approximately 580 nm indicated by1507and a critical wavelength near 614 nm indicated by line1506. And third is a color-balance attenuation indicated by line1504with a corresponding average transmittance of approximately 45 percent that is applied to wavelengths between approximately 465 nm indicated by line1509and 540 nm indicated by line1508.

FIG.15Billustrates a composite spectral profile1500created from a set of attenuations that are applied to the visible light spectrum as configured for shooting applications involving orange clay discs. Specifically, global attenuation is applied to wavelengths of the visible light spectrum above the critical wavelength λc. Further, global attenuation is applied to the visible light spectrum between wavelengths λ1and λ2. As shown by lines1501and1503, the transmittance above the critical wavelength λcis greater than the transmittance between wavelengths λ1and λ2. Also, global attenuation is applied to the visible light spectrum between wavelengths λ3and λ4. As shown by lines1505,1501and1503, the transmittance between wavelengths λ3and λ4is substantially equal to the transmittance between wavelengths λ1and λ2, but the transmittance between λ3and λ4is less than the transmittance for wavelengths above the critical wavelength λc. Additionally, local attenuation is applied to wavelengths of the visible light spectrum between wavelengths λ2and λc, which are above the wavelengths λ1and λ2but below the critical wavelength λc. As shown by line1502, the transmittance between λ2and λcis less than the transmittance between wavelengths λ1and λ2and the transmittance above the critical wavelength λc.

In addition, color-balance attenuation is applied to wavelengths of the visible light spectrum between λ4and λ1, which is below wavelength λ1and above wavelength λ4. As shown by lines1504,1501and1505, the transmittance between wavelengths λ4and λ1is above the transmittance between wavelengths λ3and λ4, wavelengths λ1and λ2, wavelengths λ2and λcbut below the transmittance above the critical wavelength λc.

FIG.16Aillustrates a composite spectral profile created from a of a set of attenuations that are applied to the visible light spectrum1614; as configured for blood-trailing applications. This set consists of global, local, and color-balance attenuations that are described as follows. First the global attenuations are indicated by line1601and line1603. Line1601applies to wavelengths above the critical wavelength that is indicated by line1608. Line1603is a global attenuation that applies to wavelengths between line1610and line1609. Second is the local attenuation indicated by line1602that is applied to wavelengths between line1609and line1608. And third this embodiment includes a color-balance attenuation that is indicated by line1605and line1604. Line1605applies to wavelengths between line1613and line1611. Line1604applies to wavelengths between line1611and line1610. The purpose of the color-balance attenuation is to provide a natural and seemingly unaltered background scene. However, the color-balance for blood-trailing applications has a twist because it should accommodate use in low-light conditions such as nighttime game recovery with limited light from an artificial source (flashlight, lantern). Low-light scenarios require the filter to transmit additional light to keep the color photoreceptors (cones) properly engaged. This is accomplished by relaxing the attenuation of wavelengths between line1613and line1611to allow more light to come thru the optical filter. The shaded area1606represents the color-balance attenuation applied for orange clay discs; while the shaded area1607represents the relaxation required to transmit more light in order to optimize the effectiveness of the color photoreceptors (cones). In one embodiment the composite spectral profile for shooting applications involving orange clay discs can be described as follows. First the global attenuation indicated by line1601has a corresponding average transmittance of approximately 81 percent for wavelengths above a critical wavelength near 614 nm as indicated by line1608. This embodiment includes a global attenuation indicated by line1603with a corresponding average transmittance of approximately 25 percent for wavelengths between approximately 540 nm indicated by line1610and 580 nm indicated by line1609. Second is a local attenuation1602with a corresponding average transmittance of 1 percent as applied to wavelengths between approximately 580 nm indicated by1609and a critical wavelength near 614 nm indicated by line1608. And third this embodiment includes a color-balance attenuation indicated by line1605and line1604. The color-balance attenuation indicated by line1605has a corresponding average transmittance of approximately 99 percent that is applied to wavelengths between approximately 400 nm indicated by line1613and 505 nm indicated by line1611. The color-balance attenuation indicated by line1604has a corresponding average transmittance of approximately 45 percent that is applied to wavelengths between approximately 505 nm as indicated by line1611and 540 nm indicated by line1610.

FIG.16Billustrates a composite spectral profile created from a set of attenuations that are applied to the visible light spectrum; as configured for blood-trailing applications.

Specifically, global attenuation is applied to wavelengths of the visible light spectrum above the critical wavelength λc. Further, global attenuation is applied to the visible light spectrum between wavelengths λ1and λ2, which are below the critical wavelength λc. As shown by lines1601and1603, the transmittance above the critical wavelength λcis greater than the transmittance between wavelengths λ1and λ2.

Additionally, local attenuation is applied to wavelengths of the visible light spectrum between wavelengths λ2and λc, which are above the wavelengths λ1and λ2but below the critical wavelength λc. As shown by line1602, the transmittance between wavelengths λ2and λcis less than the transmittance between wavelengths λ1and λ2and the transmittance of wavelengths above the critical wavelength λc.

In addition, color-balance attenuation is applied to wavelengths of the visible light spectrum. In this regard, color-balance attenuation is applied between wavelengths λ3and A and between wavelengths λ2and λc, both of which are below wavelength λ1. As shown by lines1605, the transmittance between wavelengths λ3and λ4is above the transmittance between wavelengths λ4and λ1, wavelengths λ2and λc, and wavelengths λ1and λ2. Note that in one embodiment, transmittance between wavelengths λ3and λ4may be slightly above, equal to, or less than the transmittance above the critical wavelength λc. As shown by line1604, the transmittance between wavelengths λ4and λ1is below the transmittance between wavelengths λ3and λ4and below the transmittance above the critical wavelength λc. However, the transmittance between wavelengths λ4and λ1is above the transmittance between wavelengths λ1and λ2and between wavelengths λ2and λc.

FIG.17combines the color opponent response curves (R-G curve1701and B-Y curve1702) with the composite spectral profile indicated by line1703of the apparatus100as tailored for shooting applications with orange clay discs. The transitions of line1704, line1705, line1706, line1707, and line1708of the composite spectral profile1703correspond to peaks and zero-crossings of the color opponent response curves. For example, the upper critical wavelength indicated by line1704for the local attenuation indicated by line1709aligns with the peak of the R-G color opponent response curve1701, where the R-G color opponent response dominates the B-Y response curve1702. A color-shift effect results from the local attenuation of wavelengths between line1705and line1704. The visible light spectrum1710is included for reference.

FIG.18combines the color opponent response curves (R-G curve1801and B-Y curve1802) with the composite spectral profile indicated by line1803of the apparatus100as tailored for blood-trailing applications. The transitions indicated by line1804, line1805, line1806, line1807, and line1808of the composite spectral profile1803correspond to peaks and zero-crossings of the color opponent response curves. For example, the upper critical wavelength indicated by line1804for the local attenuation indicated by line1809aligns with the peak of the R-G color opponent response curve1801where the R-G curve1801color opponent response dominates the B-Y response curve1802. A color-shift effect results from the local attenuation of wavelengths between line1805and line1804. The visible light spectrum1810is included for reference.

Light absorbing materials are used in the construction of the lens(es). Lenses can be constructed using a variety of materials such as glass and plastics. The lenses can incorporate light absorbing materials, and these materials can be incorporated externally such as coatings and films. The materials can be incorporated internally such as dyes, pigments, and rare earth minerals. These light absorbing materials generally provide either wide-band or narrow-band filtration.

In one embodiment, the spectral filtering of the eyewear is accomplished via the meticulous combination of light absorbing dyes (or pigments) with polycarbonate materials (plastics). This is referred to as color-compounding, and the resulting compound is used to form the lenses of the glasses. Combinations of narrow-band and wide-band absorbers allow the creation of custom spectrums for the filtered light. The various wavelengths of the filtered light can receive predictable attenuations across the spectrum. These attenuations can vary from slight to significant based on the dye selections and relative concentrations. In one embodiment, combinations of these dyes allow the creation of a filtered spectrum that mimics the spectrum of blood. This filtered spectrum has similar shape, proportions, and wavelength transitions as that of blood.

In another embodiment, rare earth elements may also be mixed in with polycarbonate (or glass) as the lens(es) of the eyewear are being manufactured. Additional coatings or features can be applied to the glasses and include anti-scratch, anti-fog, anti-reflection, anti-glare, and polarization.

Custom interference filters may also be applied to the lens(es) externally via vapor deposition and active ion-sputtering. However, interference filters do not provide the same performance as color-compounding. The interference filters instead block bands of wavelengths producing a binary effect where the wavelengths are either fully passed or blocked, with no variations in the amplitude of the filtered light.

Wide-band absorbers are typically inexpensive but do not offer the necessary performance by themselves. Companies like Rosco provide wide-band filters like their Roscolux™ that use special dyes to provide color filtration. Narrow-band absorbers are by comparison more expensive. Companies like Epolin use special dyes to provide narrow-band color filtration. These narrow-band absorbers can provide extremely sharp notch filtration where wide-band absorbers cannot. These narrow-band absorbers also provide filtration that do not in many cases extend into the red wavelength areas.

FIG.19provides a graph1900that shows the transmittance of a wide-band absorber (Cinelux #16 Light Amber). This type absorber is not able to provide sharp notches and is not able to provide significant optical densities as compared to narrow-band absorbers.

FIG.20provides a graph2000that shows the transmittance of a narrow-band absorber (Epolight 5822) with peak absorbance near 576 nm. This absorber is able to provide a sharp notch and keep the transmittance up around 80% in the red wavelength area.

FIG.21provides a graph2100that shows the transmittance of a narrow-band absorber (Epolight 5838) with peak absorbance near 534 nm.

FIG.22provides a graph2200that shows the transmittance of a narrow-band absorber (Epolight 5843) with peak absorbance near 444 nm.

FIG.23shows the transmission percentage of light of the exemplary eyewear100as applied to shooting applications with orange clay discs (targets). This figure overlays the transmittance of the proposed attenuations2301and the actual transmittance2302of a color-compounded lens produced using narrow-band absorbers in polycarbonate. The visible light spectrum2303is included for reference.

FIG.24shows the transmission percentage of light of the exemplary eyewear100as applied to blood trailing applications. This figure overlays the transmittance of the proposed attenuations2401and the actual transmittance2402of a color-compounded lens produced using narrow-band absorbers in polycarbonate. The visible light spectrum2403is included for reference.

As described above and shown in the associated drawings, the present invention comprises an optical filtering eyewear apparatus. While particular embodiments have been described, it will be understood, however, that any invention appertaining to the apparatus described is not limited thereto, since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. It is, therefore, contemplated by the appended claims to cover any such modifications that incorporate those features or those improvements that embody the spirit and scope of the invention.