4,284 research outputs found
Camera distortion self-calibration using the plumb-line constraint and minimal Hough entropy
In this paper we present a simple and robust method for self-correction of
camera distortion using single images of scenes which contain straight lines.
Since the most common distortion can be modelled as radial distortion, we
illustrate the method using the Harris radial distortion model, but the method
is applicable to any distortion model. The method is based on transforming the
edgels of the distorted image to a 1-D angular Hough space, and optimizing the
distortion correction parameters which minimize the entropy of the
corresponding normalized histogram. Properly corrected imagery will have fewer
curved lines, and therefore less spread in Hough space. Since the method does
not rely on any image structure beyond the existence of edgels sharing some
common orientations and does not use edge fitting, it is applicable to a wide
variety of image types. For instance, it can be applied equally well to images
of texture with weak but dominant orientations, or images with strong vanishing
points. Finally, the method is performed on both synthetic and real data
revealing that it is particularly robust to noise.Comment: 9 pages, 5 figures Corrected errors in equation 1
Correction of image radial distortion based on division model
This paper presents an approach for estimating and then removing image radial distortion. It works on
a single image and does not require a special calibration. The approach is extremely useful in many applications,
particularly those where human-made environments contain abundant lines. A division model is applied, in which
a straight line in the distorted image is treated as a circular arc. Levenberg–Marquardt (LM) iterative nonlinear
least squares method is adopted to calculate the arc’s parameters. Then “Taubin fit” is applied to obtain the initial
guess of the arc’s parameters which works as the initial input to the LM iteration. This dramatically improves the
convergence rate in the LM process to obtain the required parameters for correcting image radial distortion.
Hough entropy, as a measure, has achieved the quantitative evaluation of the estimated distortion based on
the probability distribution in one-dimensional θ Hough space. The experimental results on both synthetic
and real images have demonstrated that the proposed method can robustly estimate and then remove
image radial distortion with high accurac
Recommended from our members
Astigmatism and Pseudoaccommodation in Pseudophakic Eyes
noAdvanced IOLs with circumferential zones of different power provide pseudoaccommodation. We investigated the potential for power variation with meridian, namely astigmatism, to provide pseudo-accommodation. With appropriate power and axis orientations, acceptable pseudo-accommodation can be achieved
Application for photogrammetry of organisms
Single-camera photogrammetry is a well-established procedure to retrieve quantitative
information from objects using photography. In biological sciences, photogrammetry is
often applied to aid in morphometry studies, focusing on the comparative study of shapes
and organisms. Two types of photogrammetry are used in morphometric studies: 2D
photogrammetry, where distance and angle measurements are used to quantitatively
describe attributes of an object, and 3D photogrammetry, where data on landmark
coordinates are used to reconstruct an object true shape. Although there are excellent
software tools for 3D photogrammetry available, software specifically designed to aid in
the somewhat simpler 2D photogrammetry are lacking. Therefore, most studies applying
2D photogrammetry, still rely on manual acquisition of measurements from pictures, that
must then be scaled to an appropriate measuring system. This is often a laborious multistep process, on most cases utilizing diverse software to complete different tasks. In
addition to being time-consuming, it is also error-prone since measurement recording is
often made manually. The present work aimed at tackling those issues by implementing
a new cross-platform software able to integrate and streamline the photogrammetry
workflow usually applied in 2D photogrammetry studies. Results from a preliminary
study show a decrease of 45% in processing time when using the software developed in
the scope of this work in comparison with a competing methodology. Existing limitations
and future work towards improved versions of the software are discussed.Fotogrametria em câmera única é um procedimento bem estabelecido para recolher
dados quantitativos de objectos através de fotografias. Em biologia, fotogrametria é
frequentemente aplicada no contexto de estudos morfométricos, focando-se no estudo
comparativo de formas e organismos. Nos estudos morfométricos são utilizados dois tipos
de aplicação fotogramétrica: fotogrametria 2D, onde são utilizadas medidas de distância
e ângulo para quantitativamente descrever atributos de um objecto, e fotogrametria 3D,
onde são utilizadas coordenadas de referência de forma a reconstruir a verdadeira forma
de um objeto. Apesar da existência de uma elevada variedade de software no contexto de
fotogrametria 3D, a variedade de software concebida especificamente para a a aplicação
de fotogrametria 2D é ainda muito reduzida. Consequentemente, é comum observar
estudos onde fotogrametria 2D é utilizada através da aquisição manual de medidas a partir
de imagens, que posteriormente necessitam de ser escaladas para um sistema apropriado
de medida. Este processo de várias etapas é frequentemente moroso e requer a aplicação
de diferentes programas de software. Além de ser moroso, é também susceptível a erros,
dada a natureza manual na aquisição de dados. O presente trabalho visou abordar os
problemas descritos através da implementação de um novo software multiplataforma
capaz de integrar e agilizar o processo de fotogrametria presentes em estudos que
requerem fotogrametria 2D. Resultados preliminares demonstram um decréscimo de 45%
em tempo de processamento na utilização do software desenvolvido no âmbito deste
trabalho quando comparado a uma metodologia concorrente. Limitações existentes e
trabalho futuro são discutidos
- …