High-contrast Markings Research Articles

Ground-nesting birds learn egg appearance to guide background choice for camouflage

Camouflage is vital for the survival of many prey species1,2, including ground-nesting birds3,4,5,6. Egg camouflage via background matching and disruptive coloration (high contrast markings that break up the body outline) is often behaviourally mediated by selecting substrates that enhance egg camouflage1,2,3,4,5,6. However, the mechanisms controlling this behaviour in birds have remained unknown. Several, not mutually exclusive, mechanisms have been suggested to control background choice for egg camouflage7. These include where individual background preferences are genetically linked to egg coloration, enabled through learning egg appearances from previous breeding attempts, or modified by imprinting on visual backgrounds during early life7, Here, using predator vision models, we compared the camouflage of Japanese quail (Coturnix japonica) eggs among females who were allowed to choose one of four coloured substrates on which to lay3. Birds were divided into experienced females who had been given the opportunity to observe the appearance of their eggs, versus naïve females breeding for the first time. Our experiment revealed that breeding experience leads to improved background choices made for egg background matching. However, substrate choice for disruptive coloration appeared genetically determined, as both bird groups chose backgrounds that enhanced egg disruptiveness regardless of experience. These mechanisms underpin behaviours that are likely essential for birds and other animals to optimise camouflage and avoid predation6.

Camouflage patterning modulates neural signatures of attention and decision-making.

Many animals rely on visual camouflage to avoid detection and increase their chances of survival. Edge disruption is commonly seen in the natural world, with animals evolving high-contrast markings that are incongruent with their real body outline in order to avoid recognition. While many studies have investigated how camouflage properties influence viewer performance and eye movement in predation search tasks, researchers in the field have yet to consider how camouflage may directly modulate visual attention and object processing. To examine how disruptive coloration modulates attention, we use a visual object recognition model to quantify object saliency. We determine if object saliency is predictive of human behavioural performance and subjective certainty, as well as neural signatures of attention and decision-making. We show that increasing edge disruption not only reduces detection and identification performance but is also associated with a dampening of neurophysiological signatures of attentional filtering. Increased self-reported certainty regarding decisions corresponds with neurophysiological signatures of evidence accumulation and decision-making. In summary, we have demonstrated a potential mechanism by which edge disruption increases the evolutionary fitness of animals by reducing the brain's ability to distinguish signal from noise, and hence to detect and identify the camouflaged animal.

High-Contrast Marking of Stainless-Steel Using Bursts of Femtosecond Laser Pulses.

The marking and surface structuring of various materials is important in various industrial fields such as biomaterials, luxury goods, anti-counterfeiting, automotive and aerospace, electronics and semiconductor industries, and others. Recent advances in laser technology, such as burst-mode lasers, have opened new ways of affecting the surfaces of various materials, inducing a different appearance and/or properties of the laser-exposed areas. From earlier studies, it is known that when splitting a single pulse into multiple pulses and thus creating a quasi-MHz-GHz repetition rate regime, it is possible to increase not only the ablation efficiency but it also provides the possibility to tune the heat in-flow into the surface. Such new regimes enable the control of the surface roughness as well as the optical properties and corrosion resistance. In this work, we analyze the effect of the different burst-mode regimes for the marking of stainless-steel samples, aiming to produce high-contrast marking having different shades of black/white color (black-gray-white). Moreover, we investigate the angular dependence of the reflected light after laser treatment numerically from the measured surface morphology.

Preparation and Laser Marking Properties of Poly(propylene)/Molybdenum Sulfide Composite Materials

In this study, using molybdenum sulfide (MoS2) as laser-sensitive particles and poly(propylene) (PP) as the matrix resin, laser-markable PP/MoS2 composite materials with different MoS2 contents ranging from 0.005 to 0.2% were prepared by melt-blending. A comprehensive analysis of the laser marking performance of PP/MoS2 composites was carried out by controlling the content of laser additives, laser current intensity, and the scanning speed of laser marking. The color difference test shows that the best laser marking performance of the composite can be obtained at the MoS2 content of 0.02 wt %. The surface morphology of the PP/MoS2 composite material was observed after laser marking using a metallographic microscope, an optical microscope, and a scanning electron microscope (SEM). During the laser marking process, the laser energy was absorbed and converted into heat energy to cause high-temperature melting, pyrolysis, and carbonization of PP on the surface of the PP/MoS2 composite material. The black marking from carbonized materials was formed in contrast to the white matrix. Using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and Raman spectroscopy, the composite materials before and after laser marking were tested and characterized. The PP/MoS2 composite material was pyrolyzed to form amorphous carbonized materials. The effect of the laser-sensitive MoS2 additive on the mechanical properties of composite materials was investigated. The results show that the PP/MoS2 composite has the best laser marking property when the MoS2 loading content is 0.02 wt %, the laser marking current intensity is 11 A, and the laser marking speed is 800 mm/s, leading to a clear and high-contrast marking pattern.

Overcoming the detectability costs of symmetrical coloration

For camouflaged prey, enhanced conspicuousness due to bilaterally symmetrical coloration increases predation risk. The ubiquity of symmetrical body patterns in nature is therefore paradoxical, perhaps explicable through tight developmental constraints. Placing patterns that would be salient when symmetrical (e.g. high contrast markings) away from the axis of symmetry is one possible strategy to reduce the predation cost of symmetrical coloration. Artificial camouflaged prey with symmetrical patterns placed at different distances from the axis were used in both visual search tasks with humans and survival experiments with wild avian predators. Targets were less conspicuous when symmetrical patterning was placed outside a 'critical zone' near the midline. To assess whether real animals have evolved as predicted from these experiments, the saliency of features at different distances from the midline was measured in the cryptically coloured forewings of 36 lepidopteran species. Salience, both in absolute terms and relative to wing area, was greatest away from the axis of symmetry. Our work, therefore, demonstrates that prey morphologies may have evolved to exploit a loophole in the ability of mammalian and avian visual systems to spot symmetrical patterns.

Everlasting Dark Printing on Alumina by Laser

Marks or prints are needed in almost every material, mainly for decorative or identification purposes. Despite alumina is widely employed in many different industries, the need of printing directly on its surface is still a complex problem. In this sense, lasers have largely demonstrated their high capacities to mark almost every material including ceramics, but performing dark permanent marks on alumina is still an open challenge.In this work we present the results of a comprehensive experimental analysis on the process of marking alumina by laser. Four different laser sources were used in this study: a fiber laser (1075 nm) and three diode pumped Nd:YVO4 lasers emitting at near-infrared (1064 nm), visible (532 nm) and ultraviolet (355 nm) wavelengths, respectively. The results obtained with the four lasers were compared and physical processes involved were explained in detail. Colorimetric analyses allowed to identify the optimal parameters and conditions to produce everlasting and high contrast marks on alumina.

High-Contrast Laser Marking of Microelectronic Packaging Modules

Laser marking is an attractive technique allowing high-speed and high spatial resolution identification of materials, mechanical parts, tools or packaging modules for traceability, advertising, security or trademark protection reasons. The laser marking process, however, is very sensitive to the chemical composition, physical properties and texture of processed surfaces. We have investigated the role of surface chemistry and morphology of nickel-plated copper lids in achieving high optical contrast marking with a Q-switch Nd:YAG laser. Profilometry, scanning electron microscopy and xray photoelectron spectroscopy measurements have been carried out to characterize investigated samples. The results indicate that a low-contrast marking results from a poor ability of the laser to nanostructure the thermally unstable Ni(OH)2–rich surface. The primary mechanism of high-quality marking is related to laser-induced smoothing of the surface and not to the modification of the chemical composition of the irradiated material. However, thermal processing of the lids in air or N2 environments in the 300-350 °C range, before laser irradiation, has a pronounced effect on the chemical composition as well as on the color of the nickel-plated lids. Laser marking of such colormodified lids leads to drastically improved both resolution and contrast of the process.

Motion dazzle and camouflage as distinct anti-predator defenses

BackgroundCamouflage patterns that hinder detection and/or recognition by antagonists are widely studied in both human and animal contexts. Patterns of contrasting stripes that purportedly degrade an observer's ability to judge the speed and direction of moving prey ('motion dazzle') are, however, rarely investigated. This is despite motion dazzle having been fundamental to the appearance of warships in both world wars and often postulated as the selective agent leading to repeated patterns on many animals (such as zebra and many fish, snake, and invertebrate species). Such patterns often appear conspicuous, suggesting that protection while moving by motion dazzle might impair camouflage when stationary. However, the relationship between motion dazzle and camouflage is unclear because disruptive camouflage relies on high-contrast markings. In this study, we used a computer game with human subjects detecting and capturing either moving or stationary targets with different patterns, in order to provide the first empirical exploration of the interaction of these two protective coloration mechanisms.ResultsMoving targets with stripes were caught significantly less often and missed more often than targets with camouflage patterns. However, when stationary, targets with camouflage markings were captured less often and caused more false detections than those with striped patterns, which were readily detected.ConclusionsOur study provides the clearest evidence to date that some patterns inhibit the capture of moving targets, but that camouflage and motion dazzle are not complementary strategies. Therefore, the specific coloration that evolves in animals will depend on how the life history and ontogeny of each species influence the trade-off between the costs and benefits of motion dazzle and camouflage.

Cuttlefish camouflage: context-dependent body pattern use during motion

It is virtually impossible to camouflage a moving target against a non-uniform background, but strategies have been proposed to reduce detection and targeting of movement. Best known is the idea that high contrast markings produce 'motion dazzle', which impairs judgement of speed and trajectory. The ability of the cuttlefish Sepia officinalis to change its visual appearance allows us to compare the animal's choice of patterns during movement to the predictions of models of motion camouflage. We compare cuttlefish body patterns used during movement with those expressed when static on two background types; one of which promotes low-contrast mottle patterns and the other promotes high-contrast disruptive patterns. We find that the body pattern used during motion is context-specific and that high-contrast body pattern components are significantly reduced during movement. Thus, in our experimental conditions, cuttlefish do not use high contrast motion dazzle. It may be that, in addition to being inherently conspicuous during movement, moving high-contrast patterns will attract attention because moving particles in coastal waters tend to be of small size and of low relative contrast.

The optical mouse sensor as an incremental rotary encoder

In this paper, a new application and capabilities of the sensor of the optical mouse are presented. An inexpensive incremental rotary encoder is built based on a mechanical assembly where the sensor is at a fixed distance from a rotary white surface onto which a reference black line is drawn. The optical mouse sensor measures changes in position by optically acquiring sequential surface images and mathematically determining the direction and magnitude of movement. The optical sensor uses the information of the images acquired and an attached light source in a closed control loop to keep an average illumination level in the images. In this paper, the registers involved in this control loop are used to detect high contrast marks without any dedicated image-processing procedure. The detection of this reference mark in a rotary white surface allows the correction of long term cumulative errors originated in displacement measurements performed by the optical sensor and enables the use of the rotary encoder in precision measurements close to 1900 counts per revolution.

Concealed by conspicuousness: distractive prey markings and backgrounds.

High-contrast markings, called distractive or dazzle markings, have been suggested to draw and hold the attention of a viewer, thus hindering detection or recognition of revealing prey characteristics, such as the body outline. We tested this hypothesis in a predation experiment with blue tits (Cyanistes caeruleus) and artificial prey. We also tested whether this idea can be extrapolated to the background appearance and whether high-contrast markings in the background would improve prey concealment. We compared search times for a high-contrast range prey (HC-P) and a low-contrast range prey (LC-P) in a high-contrast range background (HC-B) and a low-contrast range background (LC-B). The HC-P was more difficult to detect in both backgrounds, although it did not match the LC-B. Also, both prey types were more difficult to find in the HC-B than in the LC-B, in spite of the mismatch of the LC-P. In addition, the HC-P was more difficult to detect, in both backgrounds, when compared with a generalist prey, not mismatching either background. Thus, we conclude that distractive prey pattern markings and selection of microhabitats with distractive features may provide an effective way to improve camouflage. Importantly, high-contrast markings, both as part of the prey coloration and in the background, can indeed increase prey concealment.

Outline and surface disruption in animal camouflage

Camouflage is an important strategy in animals to prevent predation. This includes disruptive coloration, where high-contrast markings placed at an animal's edge break up the true body shape. Successful disruption may also involve non-marginal markings found away from the body outline that create 'false edges' more salient than the true body form ('surface disruption'). However, previous work has focused on breaking up the true body outline, not on surface disruption. Furthermore, while high contrast may enhance disruption, it is untested where on the body different contrasts should be placed for maximum effect. We used artificial prey presented to wild avian predators in the field, to determine the effectiveness of surface disruption, and of different luminance contrast placed in different prey locations. Disruptive coloration was no more effective when comprising high luminance contrast per se, but its effectiveness was dramatically increased with high-contrast markings placed away from the body outline, creating effective surface disruption. A model of avian visual edge processing showed that surface disruption does not make object detection more difficult simply by creating false edges away from the true body outline, but its effect may also be based on a different visual mechanism. Our study has implications for whether animals can combine disruptive coloration with other 'conspicuous' signalling strategies.

The effect of high-contrast marking of treads on the descent of stairways by low-vision people

Increasing the visibility of the treads of stairs may reduce the risk for falls of low-vision people during the descent of stairs. In the first experiment, eight healthy participants (aged 18.8±1.8 years) descended a stairway under two visual conditions (low-contrast or high-contrast marking at the edge of the treads) and two vision conditions (normal vision and low vision). Low vision was simulated by wearing goggles, decreasing the visual acuity to 20/200. Kinematic parameters related to the risk for falls from stairs were used as dependent variables. In the low-vision condition, participants made smaller steps while approaching the low-contrast stairs and descended this stairway more slowly (p>0.05) than in the other conditions, suggesting that high-contrast treads can compensate for the effects of low visual acuity. In the second experiment, nine participants with age-related macular degeneration (aged 68.3±13.5 years) approached and descended a stairway that was either not marked, marked on the edges of the steps, and marked 5 cm off the edges. The provisional results show that the stride length during the last steps before the descent was shorter, and more misplacements of the foot were observed in the condition (marking at 5 cm from the edge of the treads). It is concluded from the two experiments that marking of treads is beneficial for safely descending stairways and that the marking should be placed on the edge of all treads.

Laser-effected darkening in TPEs with TiO 2 additives

Investigations were carried out for laser-effected darkening and damage-free laser marking on thermoplastic elastomers (TPEs). Titanium dioxide (TiO 2) was studied as the laser-sensitive additive to the TPEs for its role in enhancing laser marking contrast and its effect on the TPE properties. Laser beam characteristics, processing variables and percentage loading of TiO 2 in the TPEs were found to have significant effect on the marking contrast. Surface damage-free and high contrast marking have been achieved with short pulse UV lasers. The laser-effected darkening was found to penetrate into the material in the order of a few tens of microns. XPS analysis was carried out to understand the laser-effected darkening mechanism. Potential applications of the technique are highlighted.

Curable Inks for Laser Thermal Transfer Printing

The semiconductor industry has two major printing technologies: pad printing and direct laser marking. Pad printing offers highly legible marks; however, this technology is not digital and solvent-based inks are required. Direct laser etching offers digital capability with poor contrast. Our laser thermal transfer printing technology offers high contrast marks with digital capability on a variety of semiconductor materials including epoxy molding compounds, ceramic, gold, nickel and silicon.Our laser thermal transfer printing process employs a proprietary foil ink which is transferred to an electronic component. The mark is subsequently cured with ultraviolet light or thermal energy to obtain highly durable marks. The prints on these semiconductor parts must be resistant to solvent, acid (solder flux) and abrasion.I will present the requirements for the electronics industry and the chemical approaches that have been taken with various laser printing heads.

Requirements for Hud Raster Image Modulation in Daylight

Head-up displays (HUDs) represent the leading candidate display technology for inclusion in an enhanced or synthetic vision system (EVS or SVS) for commercial transport aircraft. One common EVS concept assumes the raster display of raw or processed sensor (radar or IR) data. However, experience with the use of raster rather than stroke display modes has been largely limited to the presentation of images captured by IR sensitive and image-intensified cameras during night flying conditions when the luminance of the forward scene over which the image will be superimposed is much lower than in daytime. The objective of this work is to generate a specification for minimum HUD raster image modulation assuming real-world luminance values typically found in low-visibility, daylight flight. Six Honeywell pilots rated the image quality and utility of flight video as presented through a military-style HUD in a transport cockpit mockup. Flight video came from daylight FLIR and daylight CCD cameras. The luminance of the forward scene against which the HUD image was superimposed was varied among nine levels ranging from 5 fL to 10,000 fL. The results indicate that HUD raster luminance must be approximately 50% external scene luminance to promote good pilot awareness of general terrain. To maintain good utility and visibility of standard, high-contrast runway markings, runway center line, and runway edges, HUD raster luminance must be approximately 15% of the forward scene luminance.

High contrast marks for e-beam direct write made by reactive ion etching

Square wells, etched in silicon (111) substrates by reactive ion etching, are characterized as alignment marks for direct write electron beam lithography. In addition to compatibility with subsequent silicon bipolar processing steps, the contrast of the marks is comparable to etched V-shaped holes in silicon (100). The mark properties are investigated systematically by varying the size, the depth and the slope of the edges. Marks with a size smaller than 10 μm and a depth larger than about 1 μm have a sufficient contrast (>0.1) for automatic detection by a Philips EBPG-3 after deposition of 0.4 μm SiO 2 and 0.25 μm Ti/ 0.2 μm Pt/0.6 μm Au. Although the slope of the mark edges degrades after deposition of the layers, the marks allow an overlay accuracy between 50 to 100 nm. The application of the marks is not restricted to silicon (111) since the fabrication of the marks only depends on the anisotropic nature of reactive ion etching and this technique is applicable to many other substrates.

Electrically amplified optical recording in polymer films

The laser power required to record high contrast marks in a polymer film can be reduced two orders of magnitude by depositing the film on a transparent conductor-photoconductor-conductor sandwich. The sensitivity of this medium is controlled by adjusting the voltage applied to the conductors. In the power limited regime, as little as 0.1 mW of laser power can increase the ohmic heating at the focus enough to produce symmetric micrometer size bubbles in the adjacent polymer film without damaging the photoconductor. However, due to the high dark resistivity of the photoconductor, the power dissipation in the unilluminated region is only ≊0.01 W/cm2.