Camera re-calibration after zooming based on sets of conics

We describe a method to compute the internal parameters (focal and principal points) of a camera with known position and orientation, based on the observation of two or more conics on a known plane. The conics can even be degenerate (e.g. pairs of lines). The proposed method can be used to re-estimate the internal parameters of a fully calibrated camera after zooming to a new, unknown, focal length. It also allows estimating the internal parameters when a second, fully calibrated camera observes the same conics. The parameters estimated through the proposed method are coherent with the output of more traditional procedures that require a higher number of calibration images. A deep analysis of the geometrical configurations that influence the proposed method is also reported

Linear pose estimate from corresponding conics

We propose here a new method to recover the orientation and position of a plane by matching at least three projections of a conic lying on the plane itself. The procedure is based on rearranging the conic projection equations such that the non linear terms are eliminated. It works with any kind of conic and does not require that the shape of the conic is known a-priori. The method was extensively tested using ellipses, but it can also be used for hyperbolas and parabolas. It was further applied to pairs of lines, which can be viewed as a degenerate case of hyperbola, without requiring the correspondence problem to be solved first. Critical configurations and numerical stability have been analyzed through simulations. The accuracy of the proposed algorithm was compared to that of traditional algorithms and of a trinocular vision system using a set of landmarks

The Khepera IV Mobile Robot: Performance Evaluation, Sensory Data and Software Toolbox

Taking distributed robotic system research from simulation to the real world often requires the use of small robots that can be deployed and managed in large numbers. This has led to the development of a multitude of these devices, deployed in the thousands by researchers worldwide. This paper looks at the Khepera IV mobile robot, the latest iteration of the Khepera series. This full-featured differential wheeled robot provides a broad set of sensors in a small, extensible body, making it easy to test new algorithms in compact indoor arenas. We describe the robot and conduct an independent performance evaluation, providing results for all sensors. We also introduce the Khepera IV Toolbox, an open source framework meant to ease application development. In doing so, we hope to help potential users assess the suitability of the Khepera IV for their envisioned applications and reduce the overhead in getting started using the robot

Real-time accurate circle fitting with occlusions

Accurate location of circles inside images is a common problem in many scientific fields. Traditional algorithms, based on fitting a parameterized model, cannot accurately determine the circle in presence of partial occlusions. A novel problem formulation, based on maximum likelihood, allows estimating circles in real-time with sub-pixel accuracy also when occlusions are present

Compression and smart coding of offset ad gain maps for intraoral digital x-ray sensors

The response of indirect x-ray digital imaging sensors is often not homogenous on the entire surface area. In this case, calibration is needed to build offset and gain maps, which are used to correct the sensor output. The sensors of new generation are equipped with an on-board memory, which serves to store these maps. However, because of its limited dimension, the maps have to be compressed before saving them. This step is critical because of the extremely high compression rate required. The authors propose here a novel method to achieve such a high compression rate, without degrading the quality of the sensor output. It is based on quad tree decomposition, which performs an adaptive sampling of the offset and gain maps, matched with a RBF-based interpolation strategy. The method was tested on a typical intraoral radiographic sensor and compared with traditional compression techniques. Qualitative and quantitative results show that the method achieves a higher compression rate and produces images of superior quality. The method can be adopted also in different fields where a high compression rate is required

A new switching median filter for digital radiography

Localized hardware failures on sensor and communication channel often introduce in digital radiographies a characteristic impulsive noise, known as "salt & pepper". Eliminating these failures, which generate the corrupted pixels, is a very costly or even impossible task; therefore, image processing techniques have been developed to correct the gray level values of these pixels. We propose here a new switching median filter for digital radiography, which has been inspired by the properties of the human visual system: a pulse is detected on nie radiography by measuring its visibility in terms of local contrast and signal to noise ratio. The local background value is estimated applying a 3 73 median filter to the image, and noise distribution is evaluated by means of a simple and reliable model, which describes the properties of the digital sensor and incorporates the statistical characteristic of the noise. Since the filter requires no iteration, it can work in real time also on large images (less than 0.7s for 12 bit, 4.8MPixel images). The presence of edges does not affect the pulse detection and correction, thus resulting in a more efficient approach with regards to more traditional methods. Some residual pulse may remain visible only in the darkest zones of the radiography, which are usually poor of diagnostic information

Method and device for monitoring the risks for sudden infant death syndrom and for positional plagiocephaly

A portable monitoring device (101) performs the monitoring of the short term, mid term and long term risks of Sudden Infant Death Syndrome (SIDS). It is also used to estimate the risk of onset of positional plagiocephaly. The monitoring device (101) is capable to acquire one or more signals associated to the typical breath and positioning patterns of an infant through a tri-axial accelerometer, and to register the data in electronic format. Statistical analysis of the signal and pattern recognition are performed in real time by a processing unit of the monitoring device. The monitoring device (101) can be used for monitoring the breath activity of an infant in various conditions, alerting a caregiver when a potentially dangerous situation is detected, with respect to a SIDS event or to the onset of plagiocephaly.; Thanks to its simplicity of use, small encumbrance and low power consumption, it can be turned on and attached to the clothes of the infant for as long as one day (or more), without the need of further supervision. Registered data can be transferred on a computer through a standard USB port, which can also be used for recharging a battery of the monitoring device (101). Statistical analysis of the registered data can be performed by a computer for quantifying the long term SIDS risk, the risk of plagiocephaly and for optimizing the functional parameters of the monitoring device (101). To get a more accurate estimation of the risk of plagiocephaly, the monitoring device (101) can be attached to the head of an infant

Soft Tissue Filtering

A method is disclosed for enhancing the visibility of at least some features of a radiographic image, the features belonging to at least a first and a second category of features, the method including the steps of determining a histogram of the image, analyzing the histogram in order to determine a distinction between values of image elements that more likely show a feature of the first category and values of image elements that more likely show a feature of the second category, and applying a correction to at least some of the image elements, wherein an image element that, according to the determined distinction, more likely shows a feature of the first category is corrected differently than an image element that, according to the determined distinction, more likely shows a feature of the second category. An apparatus and a computer-readable data carrier are adapted for performing the above steps or for causing a processor to perform the above steps

A New Real Time Filter for Local Exposure Correction in Panoramic Radiography

A new real time filter for local exposure correction in panoramic radiographs is presented here. The filter, called PaRSEC, allows eliminating the exposure artifacts, mainly introduced by Automatic Exposure Control (AEC) systems. These artifacts reduce the image readability and its diagnostic utility. The PaRSEC filter operates a local exposure equalization, based on a reliable estimate of the column mean gray level. Qualitative and quantitative results are reported for typical panoramic radiographs. They show a complete removal of the artifacts. The method compares favorably with other classical methods targeted to exposure correctio

Method And Device For Monitoring The Risks For Sudden Infant Death Syndrom And For Positional Plagiocephaly

A portable monitoring device (101) performs the monitoring of the short term, mid term and long term risks of Sudden Infant Death Syndrome (SIDS). It is also used to estimate the risk of onset of positional plagiocephaly. The monitoring device (101) is capable to acquire one or more signals associated to the typical breath and positioning patterns of an infant through a tri-axial accelerometer, and to register the data in electronic format. Statistical analysis of the signal and pattern recognition are performed in real time by a processing unit of the monitoring device. The monitoring device (101) can be used for monitoring the breath activity of an infant in various conditions, alerting a caregiver when a potentially dangerous situation is detected, with respect to a SIDS event or to the onset of plagiocephaly.; Thanks to its simplicity of use, small encumbrance and low power consumption, it can be turned on and attached to the clothes of the infant for as long as one day (or more), without the need of further supervision. Registered data can be transferred on a computer through a standard USB port, which can also be used for recharging a battery of the monitoring device (101). Statistical analysis of the registered data can be performed by a computer for quantifying the long term SIDS risk, the risk of plagiocephaly and for optimizing the functional parameters of the monitoring device (101). To get a more accurate estimation of the risk of plagiocephaly, the monitoring device (101) can be attached to the head of an infant