What's in a name? Nomenclature for colour aberrations in birds reviewed

The Sub‐Angstroem‐Low‐Voltage‐Electron‐Microscope (SALVE) corrector was designed and built by the CEOS GmbH for the SALVE III project [1], a joined project of the group of Prof. Dr. Ute Kaiser at the University of Ulm (Germany), FEI company in Eindhoven (Netherlands) and CEOS GmbH (Germany). This C c ‐C s ‐corrector is a dedicated low‐voltage corrector based on the so‐called Rose‐Kuhn‐Design [2], operated in a cubed FEI Titan Themis TEM for acceleration voltages from 20kV to 80kV. For all these high tensions it can be aligned such that it provides uniform phase contrast transfer for all image features up to an aperture angle of θ max = 50mrad and at the same time for a considerable field of view. To achieve such an excellent performance the corrector allows correcting all axial aberrations of fourth order and for certain unround axial aberrations of fifth order. Furthermore, C 5 can be adjusted to its optimum positive value for bright atom contrast. All axial aberrations up to third order and all off‐axial aberrations up to third order depending linearly on the distance from the axis can be adjusted. For all residual axial aberrations of fourth and fifth order, the lower order aberrations of same respective multiplicity can be adjusted for optimal compensation. This means that the integrated squared deviation from the ideal phase shift (±π/2 in case of C 1 , C 3 , C 5 and zero for all other multiplicities) over the entire aperture is minimized for each azimuthal multiplicity separately [3]. The predicted performance of the corrector has already been demonstrated for the five acceleration voltages 20kV, 30kV, 40kV, 60kV and 80kV [4]. Figure 1 (a) shows that even within the largest field of view reasonable with the mounted Ceta 4k camera the wave aberration hardly changes up to a scattering angle of 50mrad. Since the corrector will also be used together with a post column energy filter, we currently investigate both, theoretically and experimentally, how the optical performance of an EFTEM image is affected by the corrector. After correction of the linear chromatic aberration C c , an energy window of at least 20eV can be transferred by the corrector with a negligible focus change even at a beam energy of 20keV, see figure 1 (b). However, there are many more potentially harmful types of chromatic aberrations to consider for an EFTEM image of a given finite width of the energy window: Axial chromatic aberrations (depending on scattering angle and energy loss) can deteriorate the quality of the axial PCTF. For large EFTEM windows also the chromatic spherical aberration has to be taken into account. Off‐axial chromatic aberrations (depending on scattering angle, distance from the axis and energy loss) can effectively decrease the field of view, because they affect the quality of the transfer function in the outer image parts. Chromatic distortions (depending on distance from the axis and energy loss) can deteriorate the information limit in the outer regions of an EFTEM image. Residual dispersions of higher order in energy change could affect the information limit of all regions of the EFTEM image. In this work we will analyze in detail how the residual higher order chromatic aberrations, the remaining chromatic distortions and the residual dispersions of the SALVE corrector affect the EFTEM performance. [5]

In texts on geometrical optics and lens design usually two types of chromatic aberrations are discussed: longitudinal and transverse. From basic considerations on first order geometrical optics follows that, for an axially symmetric system there are three paraxial constants. Therefore three, instead of two types of chromatic aberrations can be discerned. The third, new, chromatic aberration can be called chromatic pupil aberration. We describe the consequences of this aberration for the color correction of optical systems, and show that stable chromatic correction requires the elimination of all three chromatic errors. We give expressions that can be used in the lay-out of optical systems. In teaching geometrical optics it is necessary to determine the generic aberrations of a system of given symmetry from first principles: our treatment of chromatic aberrations is an example of this necessity.

The correction of chromatic aberrations is typically performed using aberration formulas or by using real ray tracing. While the use of aberration formulas might be effective for some simple optical systems, it has limitations for complex and fast systems. For this reason chromatic aberration correction is usually accomplished with real ray tracing. However, existing optimization tools in lens design software typically mix the correction of monochromatic and chromatic aberrations by construction of an error function that minimizes both aberrations at the same time. This mixing makes the correction of one aberration type dependent on the correction of the other aberration type. We show two methods to separate the chromatic aberrations correction of a lens system. In the first method we use forward and reverse ray tracing and fictitious nondispersive glasses, to cancel the monochromatic aberration content and allow the ray tracing optimization to focus mainly on the color correction. On the second method we provide the algorithm for an error function that separates aberrations. Furthermore, we also demonstrate how these ray tracing methods can be applied to athermalize an optical system. We are unaware that these simple but effective methods have been already discussed in detail by other authors.

Chromatic aberration is an optical defect that causes light rays of different wavelengths to focus at different points along the optical axis of the lens. It is manifested as band of one color at frame transitions around contrasting edges in the photo. There are two types of chromatic aberration: longitudinal and lateral. Lateral chromatic aberration is the color fringing that occurs because the magnification of the image differs with wavelength. It tends to be far more visible than longitudinal. The aim of this research is to examine the influence of depth of field on the appearance of lateral chromatic aberration. For the purposes of the experiment, we used one mirrorless camera (Sony a1), while the lenses were variable. We used Sigma 85mm f/1.4 DG DN and Sigma 40mm f/1.4 to check which type of lens shows the most chromatic aberration and how much the change in f-number affects its appearance.

Leucism is a colour anomaly defined by a lack of pigmentation, which may be partial or full in any individual. Although genetic and environmental factors contribute to a high incidence of plumage colour aberrations in wild birds, the true incidence of these aberrations in wild populations has been studied very less. The present report describes an instance of partial leucism in a Greater Coucal (Centropus sinensis) from Chhattisgarh, India. This colour aberration in this species was first documented in 1990. More research is needed to determine the exact reasons for the high incidence of partial leucism in wild birds, which might include nutrition, lifespan, behaviour, parasitism, or other environmental factors.

In optical reconstruction of time-multiplexed color holography, three types of chromatic aberrations exist: magnification chromatic aberration (MCA), lateral chromatic aberration (LCA), and axial chromatic aberration (ACA). MCA is due to wavelength change of light source for reconstruction of different color components. In order to compensate for MCA, a different number of pixels for each color component is suggested and demonstrated. LCA causes mismatch of image centers for the three-color components. The use of digital blazed gratings superposed on the computer-generated hologram (CGH) is demonstrated as an effective way to correct for LCA. The error due to non-integer period is analyzed, and the maximum red wavelength is deduced in use based on the critical value of resolving power of human eyes. For ACA, where the images of the three reconstructing wavelengths focus at different planes, adding specific phase values for digital achromatization is proposed. The image quality is numerically evaluated by the mean square error. The techniques summarized in this paper are used during generation of the CGH and thus avoids mechanical complexity.

Chromatic aberrations are defects in an imaging system caused by the fact that different wavelengths or colors of light are refracted by different amounts. There are two types of chromatic aberration: longitudinal and lateral. Longitudinal Chromatic Aberration arises when a lens fails to focus various colors sharply in the same plane. If white light is used, the resulting image will be unsharp due to the different focal points of its component colors. Some colors will be in focus (and therefore sharp) and other colors will be out of focus. Lateral Chromatic Aberration results in a lateral shift of the different color components of an image as a single lens with a fixed refractive index will disperse each color by different amounts. This results in color stripes at slightly different magnifications, much like a rainbow, around hard edges and a general softening or decrease in resolution in all areas.

Este artículo analiza 61 casos de aberraciones cromáticas del plumaje (ausencia total o parcial de pigmentos en algunas o en todas las plumas) en 43 especies de aves silvestres ecuatorianas, agrupadas en 21 familias, incluyendo 51 nuevos registros y siendo este el primer reporte de aberraciones en Ecuador para 14 familias. Esta compilación incluye datos colectados por los autores, comunicaciones personales de expertos observadores de aves y visitas a colecciones ornitológicas de museos en Quito, Ecuador. La alteración más común fue el leucismo y las especies con mayor número de reportes fueron el Mirlo Grande Turdus fuscater y el Gorrió Ruficollarejo Zonotrichia capensis. La mayoría de registros proviene de áreas rurales en la zona altoandina, siendo Pichincha la provincia con más registros. La documentación de la distribución y frecuencia de estas aberraciones de coloración de plumaje tiene importantes implicaciones de conservación y monitoreo, permitiendo evidenciar las posibles causas que inducen estas alteraciones en las poblaciones de aves; por ello también presentamos definiciones de los principales tipos de aberraciones cromáticas con el fin de familiarizar a los observadores de aves y estimular la difusión de sus registros.

The wide deployment of colour imaging devices owes much to the use of colour filter array (CFA). A CFA produces a mosaic image, and normally a subsequent CFA demosaicking algorithm interpolates the mosaic image and estimates the full-resolution colour image. Among various types of optical aberrations from which a mosaic image may suffer, chromatic aberration (CA) influences the spatial and spectral correlation through the artefacts such as blur and mis-registration, which demosaicking also relies on. In this paper we propose a simulation framework aimed at an investigation of the influence of CA on demosaicking. Results show that CA benefits demosaicking to some extent, however CA lowers the quality of resulting images by any means.

The phenomena of colour aberration (albinism, leucism, piebaldism, melanism, hypomelanism, and blue-eyed colour morph) is reported in various mammalian species throughout the world including India. A total of 239 such instances in Indian mammals was tabulated in this study along with maps showing locations of the records. The records from 1886 to 2017 (till July) were gathered from published scientific literature, magazines, and images uploaded on various websites. The records were reviewed along with their order-wise and family-wise representation and were analyzed. Appropriate identification of colour aberration was attempted on the basis of any presented evidence. Altogether, 56 (out of 421) mammalian species belonging to eight orders and 19 families were reported to exhibit various types of colour aberrations, amounting to 13.3% of the total mammalian species found in India. Of these, albinos constituted 21.8%, leucistic 14.2%, piebald 5.4%, melanistic 25.5%, hypomelanistic 18.4%, and blue-eyed white morph 1.3%; the remaining 13.4% was undetermined. The study highlights 1) the absence of records of colour aberrations in the largest mammal family Vespertilionidae, which contrasts with studies elsewhere, 2) the persistent occurrence of albinos in Spotted Deer and Blackbucks in Gujarat, 3) the high number of melanistic leopards in India over the years and recent instances of melanistic Asian Golden Cats in Sikkim, 4) regular records of hypomelanism in Gaurs of the southern Western Ghats except in the last few years. Overall, a need for further studies in colour aberration in mammals is urged.

The influence of spatial and chromatic aberrations on the parameters of the 730 MeV beam extracted from a SALO recirculator is studied using numerical simulation. The influence of fringing fields and the heterogeneity of the guide field of dipole magnets on the beam parameters at the extraction point is studied for different orders and types of aberrations. Estimates of the contributions of the different types of aberrations to the extracted beam emittance are presented.

Although there are 935 species of birds in Costa Rica, scientific reports of pigmentation abnormalities in this group are limited. Nevertheless, several cases have been recently documented, including Leucism, Ino mutation, Progressive Graying, Dilution, and two unusual color aberrations in a toucan and a motmot. Here we describe seven cases of color aberrations observed over a period of five years in native birds of Costa Rica. An Eastern Wood-Pewee Contopus virens and a White-collared Manakin manacus candei were Brown. A Scintillant Hummingbird Selasphorus scintilla and a Talamanca Hummingbird, Eugenes spectabilis, also showed a Brown mutation, however, these two cases may be Ino. In addition, two cases of Progressive Graying were recorded in a Gray-necked Wood-rail Aramides cajaneus and a Great-tailed Grackle Quiscalus mexicanus. An indeterminate case was also observed in the Turkey Vulture Cathartes aura. Identifying plumage abnormalities in wild birds is challenging and can lead to misidentifications. However, documentation of color variation and behavior in birds can help inform future research. We encourage the reporting of observations of abnormally colored birds to further our understanding of this phenomenon.

Colour aberrations of plumage or bare parts of the body have been described in many avian taxa but their frequency in populations is low. In recent years, due to the development of cameras and the ability to share observations via social media, reports on observations of aberrantly coloured birds have become more common even in groups of birds breeding in less accessible sites, such as seabirds. In this study we review colour aberrations of integumentary structures (plumage and bare parts: beak, eye iris, legs) in a group of pelagic seabirds, alcids. To illustrate particular aberrations, we used our own photographs and conducted searches for similar images online and in published papers. In total, we collected 82 cases of unusually coloured individuals of nine alcid species. We revised the types of aberrations described in collected material in accordance with the recently proposed classification and terminology, and found that only 25.6% of cases were properly classified. The most commonly misused term for observed aberrations in collected images was “leucism” (34.1% of cases), which usually would have been more accurately described as Brown, Ino, Progressive Greying, rather than true Leucism. We also found that Progressive Greying (37.8%) and Brown (19.5%) were the most frequently recorded colour aberrations in the studied group. Our synthesis offers an updated summary of the colour plumage aberrations in alcids and a practical tool for identification of various colour aberrations in the group. It can help to classify the aberrations in future studies. Given that the frequency of colour aberrations may be indicative of an increased mutation rate or a high rate of inbreeding in a population, we encourage researchers to correctly identify and note those cases.

Color aberrations in birds are well documented, but frequently their terminology is misinterpreted. We report a record of color aberration in an adult ruddy ground dove Columbina talpacoti in Rio de Janeiro State, observed foraging with other conspecifics with normal pattern coloration. The color aberration was similar to a previous record of this species from the Rio de Janeiro municipality, but differed substantially from a third anomalous-colored specimen recorded in Venezuela. We suggest that the two Brazilian reports are cases of a non-phaeomelanin schizochroism based on the absence of the reddish-brown colors despite the presence of black and grey colors in feathers. We highlight the importance of using the right terminology for a better understanding of the frequencies of each color aberration type.

We report a case of chromatic aberration (progressive greying) of a Eurasian Coot (Fulica atra) from a drainage canal neighbouring a recently restored wetland from Latium, central Italy (third case for this rail at the regional level). Moreover, we reviewed the cases of chromatic aberrations (leucism, progressive greying, albinism, etc.) in this species for Italy (1990-2024), obtaining records for 13 sites. However, the complete albinos mentioned in the literature are very questionable since many different conditions should be met for a correct diagnosis of this aberration. We suggest that, when genetic data are lacking, repeated behavioural observations should be conducted on focal animals recorded at different times, therefore carrying out a correct diagnosis about the type of chromatic aberration characterizing these birds.