Terms Of Pixels Research Articles

Effect of Subconjunctival Bevacizumab (Avastin) on Experimental Corneal Neovascularization in Guinea Pigs

To evaluate the effect of subconjunctival bevacizumab (Avastin) on experimental corneal neovascularization in guinea pigs. Forty eyes of 40 guinea pigs were chemically cauterized with 75% silver nitrate and 25% potassium nitrate sticks. Fifteen eyes (group 1) received 2 subconjunctival injections of bevacizumab (0.1 mL, 1.25 mg) simultaneously with cauterization and 3 days later. Fifteen eyes (group 2) received 2 subconjunctival injections of bevacizumab (0.1 mL, 1.25 mg) 3 and 5 days after cauterization. Ten eyes (group 3, control group) received 2 subconjunctival injections of 0.1 mL of balanced salt solution 3 and 5 days after cauterization. After we determined the burn and neovascularization scores for all groups, the animals were killed on the 10th day. The percentages of neovascularization on the surface of the cornea were measured in terms of pixels on digital photographs. The average number of vessels at maximally vascularized areas was determined for each specimen. Neovascularization score was 1.1 +/- 0.3 in group 1, 2.46 +/- 1.3 in group 2, and 3.5 +/- 0.5 in the control group. The difference was statistically significant (P < 0.001). The area of neovascularization at the cornea surface was 15.6% +/- 10.1% in group 1, 19.74% +/- 11.2% in group 2, and 23.5% +/- 7.4% in the control group (P = 0.194). The average number of neovascular vessels at group 1 was significantly reduced in comparison with group 2 and the control group (P < 0.001). Subconjunctival injection of bevacizumab decreases the extent of chemically induced corneal neovascularization in guinea pigs. The antineovascular effect of bevacizumab is higher if the injection is performed simultaneously with the chemical cauterization.

Spatiochromatic statistics of natural scenes: first- and second-order information and their correlational structure

Spatial filters that mimic receptive fields of visual cortex neurons provide an efficient representation of achromatic image structure, but the extension of this idea to chromatic information is at an early stage. Relatively few studies have looked at the statistical relationships between the modeled responses to natural scenes of the luminance (LUM), red-green (RG), and blue-yellow (BY) postreceptoral channels of the primate visual system. Here we consider the correlations among these channel responses in terms of pixel, first-order, and second-order information. First-order linear filtering was implemented by convolving the cosine-windowed images with oriented Gabor functions, whose gains were scaled to give equal amplitude response across spatial frequency to random fractal images. Second-order filtering was implemented via a filter-rectify-filter cascade, with Gabor functions for both first- and second-stage filters. Both signed and unsigned filter responses were obtained across a range of filter parameters (spatial frequency, 2-64 cycles/image; orientation, 0-135 degrees). The filter responses to the LUM channel images were larger than those for either RG or BY channel images. Cross correlations between the first-order channel responses and between the first- and second-order channel responses were measured. Results showed that the unsigned correlations between first-order channel responses were higher than expected on the basis of previous studies and that first-order channel responses were highly correlated with LUM, but not with RG or BY, second-order responses. These findings imply that course-scale color information correlates well with course-scale changes of fine-scale texture.

Rapid hybrid interpolation methods

We propose rapid hybrid interpolation methods that employ more than one interpolation algorithm, and choose the most appropriate interpolation algorithm that provides high-quality images with a minimum number of operations. Although a complex interpolation algorithm generally outperforms a simple interpolation algorithm, the differences are negligible for most pixels, with major differences occurring around edges. Thus, in the proposed algorithm, we first apply a test to predict which interpolation is most appropriate for a given pixel in terms of complexity and performance. Then, a simple interpolation algorithm is used for pixels for which the simple interpolation algorithm provides acceptable performances, and a complex interpolation algorithm is used for pixels for which the complex interpolation algorithm significantly outperforms the simple interpolation algorithm. Consequently, it is possible to obtain high-quality images without significantly increasing the number of operations.

Implementation of digital HDTV encoder with parallel sub-picture encoding modules and its joint bit-allocation strategy

Parallel processing is a feasible scheme for a digital HDTV encoder, to get round the dilemma in high-speed digital processing circuitry and real-time compression. This paper suggests an implementation procedure and a novel bit-allocation strategy for a digital high definition television (HDTV) encoder system with parallel processing architecture based on six horizontal strips division. Multiple sub-pictures encoding modules (SEMs) perform MPEG-2 coding respectively and simultaneously. Owing to the inherent deficiencies of MPEG-2 Test Model 5 (TM5) rate control scheme, how to allocate bit-rate among sub-pictures would become an inevitable challenge, which might behave with the coding quality to decrease worse and the buffer to underflow at scene changes, moreover give birth to non-consistent sub-pictures visual quality and dynamic quality variation in a composite HDTV frame on subjective and objective evaluation. We adapt a hierarchical joint optimized bit-allocation with sub-pictures' average complexity measure and average bits per pixel in terms of their average quantization distortion, moreover incorporates scene detection to alleviate a possible worse sub-pictures quality inconsistency. In the paper, we describe an elaborate procedure including general framework, sub-pictures division module, sub-picture encoding module and sub-pictures synthesis module, then deduce the joint bit-allocation strategy for sub-pictures encoding and the auxiliary rate adaptive procedure for scene changes. Experimental results demonstrate that our proposed scheme not only alleviates the boundary effect, but also promises the sub-pictures quality consistency. The proposed scheme might be devoted to the multiprogram broadcast application and the multiple access sceneries.

Randomization of transfer functions in control systems via computer vision with pixel noises of order n

Complex-valued fractional Brownian motion of order n can be defined either as rotating Gaussian white noise on the net defined by the n th roots of the unity, or as the limit of a random walk in the complex plane. After a brief background, one shows that this stochastic process is quite relevant in computer vision, as the result of the definition of image in terms of pixels. It follows that in control systems involving numerical vision, one will have to consider disturbances in the form of fractional white noise of order n with independent increments, and the present paper deals with this problem. By using the central limit theorem, it is possible to consider the Laplace transform of such a process as a fractional Gaussian variable of order n of which the n th moment is the integral of the n th moment of the white noise. One can then use this result to carry on a statistical analysis of linear feedback systems subject to disturbing fractional white noises (or pixel noises) in control via computer vision. Stochastic optimal control of order n is outlined.

Complex-valued Wiener measure: An approach via random walk in the complex plane

In the present paper, it is shown that the heat equation of order n and its companion complex-valued Brownian motion of order n can be obtained in a very simple manner as the limit of a random walk defined in the complex plane, by means of the complex roots of the unity. This probabilistic model unifies Hochberg's and Sainty's approaches, and its main advantages is to enlighten the practical physical meaning of signed measures of probability (Hochberg), and to suggest simulation techniques. The complex-valued Brownian motion of order 4 should be of direct application in computer vision, as a result of the definition of image in terms of pixel.

Results obtained using a 61-pixel Hybrid Photodiode scintillation camera

In this paper, the performance characteristics of a small prototype gamma-camera system based on the use of the recently developed Multi-pixel Hybrid Photodiode (M-HPD) are described. A compact read-out system has been developed to record the signals from all 61 pixels in the device. Single photo-electrons can be detected in each pixel. This provides an excellent means for calibrating the signal detected in each pixel in terms of the number of photo-electrons. The position-resolution of the detector has been measured as a function of the number of photo-electrons by using a finely collimated beam of light. The spatial resolution (FWHM) was measured to be 0.5 mm for a signal level of 100 photo-electrons. The M-HPD has also been used in a miniature Anger-camera system to locate the position of interaction of gamma-ray photons in a scintillator. The light-pool generated by each event in a continuous scintillation crystal is spread in the 2mm thick entrance window of the M-HPD so that the photo-electron cloud is detected by a small cluster of anode pixels. The light-spread information has been measured and is compared with optical Monte Carlo simulations.

Performance comparison between multiple-quantum-well modulator-based and vertical-cavity-surface-emitting laser-based smart pixels

We compared multiple-quantum-well modulator-based smart pixels and vertical-cavity-surface-emitting laser (VCSEL) based smart pixels in terms of optical switching power, switching speed, and electric-power consumption. Optoelectronic circuits integrating GaAs field-effect transistors are designed for smart pixels of both types under the condition that each pixel has an optical threshold and gain. It is shown that both types perform maximum throughput of ~3 Tbps/cm(2). In regard to design flexibility, the modulator type is advantageous because switching time can be reduced by supplying large electric power, whereas switching time and electric-power consumption are limited to larger than certain values in the VCSEL type. In contrast, in regard to optical implementation, the VCSEL type is advantageous because it does not need an external bias-light source, whereas the modulator type needs bias-light arrays that must be precisely located because the small modulator diameter, <10 µm, is essential to high-speed operation. A bias-light source that increases the total power consumption of the system may offset the advantages of the modulator type.

Size distribution standards measured by digital SEM imaging

The National Institute of Standards and Technology (NIST) certifies several size and size distribution Standard Reference Materials (SRMs) using spherical particles ranging in diameter from submicron to several millimeters. Glass beads are used as SRMs for a variety of laboratory applications. Their broad size distribution and spherical shape make them a model material for calibration of instruments for powder measurements.The glass bead standard (SRM1017b) covering the diameter range from 50μm to 350μm is currently being certified using SEM backscatter electron imaging. The digital images are acquired using an AMRAY SEM connected to a Apple Power Macintosh via a 4pi digital interface. The public domain computer program, NIH Image, is used in the image acquisition and size analysis. Figure 1 shows the spherical nature of the glass beads. Measurement of the circular area of each particle permits the calculation of the particle volume and diameter. The system magnification in terms of pixels per micrometer using an optical stage micrometer calibrated at NIST by laser interferometry.

Optical filling algorithm

The technique of optical symbolic substitution is applied to development of a new filling algorithm that reconstructs an image from its boundary in constant time, whereas known filling algorithms have at least O(n log N) time complexity, where n is the number of boundary pixels of a polygon and N is the diameter of the image expressed in terms of pixels.

Nonuniform image motion estimation using Kalman filtering

This correspondence presents a new pixel-recursive algorithm for estimating the nonuniform image motion from noisy measurements. The proposed method is performed in two steps. First, the pixels are examined to identify the (detectable) moving pixels, using a binary hypothesis testing. Then, characterizing the motion of the identified moving pixels in terms of a unitary transformation, the motion coefficients are estimated using a Kalman filter. Because the motion vector is typically (spatially) slowly varying, the size of the motion coefficient vector is significantly reduced. Consequently, the proposed Kalman filter need only search for the truncated coefficients of the motion field. The proposed method is simulated on a computer, and results are compared with the algorithm reported by Netravali and Robbins (see Bell Syst. Tech. J. vol.58, no.3, p.631-70, Mar. 1979).

Noninvasive Quantification of Platelet Accumulation and Release on Indwelling Venous Catheters

An important element in the evaluation of biomaterials is quantification of the relationships and the sequence of events between blood elements, blood flow, and the foreign surface. We adapted a qualitative two-dimensional 111In-la-beled platelet imaging method to a quantitative noninvasive analysis of platelet uptake/release kinetics for infusion catheters in a canine model. Bilateral femoral vein 6 Fr. Groshong catheters (one treated with a hydroxylated siloxane to improve albumin affinity) were monitored at femoral vein sites with a GE 400T gamma camera, interfaced with a Technicare 560 image acquisition computer. The field of view was sufficiently large that all events below the diaphragm were recorded without having to move the camera. Image acquisition time was 2.5 min; images were obtained every 5–15 min for 3 hrs. Continuous recordings were obtained from bilateral ultrasonic velocity probes, attached distal to the catheter implant sites. A 5 ml blood sample was placed in the field to permit calibration of gamma emissions per pixel in terms of labeled platelet density. Signal compensation for near field capillary perfusion was performed. The two-dimensional platelet distribution was computed and displayed. Local, time dependent platelet accumulation on the catheters and adjacent vessel walls was observed. Platelet accumulation proceeded in irregular steps during the implant period. Loss of local platelet deposits was observed. Downstream reattachment of platelet emboli was inferred from simultaneous reductions and increases in local platelet densities at two catheter positions. Platelet attachment was inversely related to vein blood velocity. Differences were observed between platelet uptake and release on the treated and control catheters. These preliminary results suggest that the method is feasible for both in vivo and ex vivo evaluation of the interactions of labeled blood elements and medical devices.

A high-resolution, wide-field, optically coupled, digital CCD camera for the JEOL 4000-EX intermediate-voltage electron microscope

We have designed and constructed a camera system for acquisition of digital images directly from a JEOL 4000-EX 400 kV transmission electron microscope. Our major goal was the ablity to sample and test images for suitability for various forms of image processing and analysis during a session on the microscope, rather than after processing and digitizing films, so that adjustments could be made while the specimens were still in place. Our design parameters were 1) good resolution, in terms of pixels in the image, 2) wide field, so low magnification images could be obtained, 3) no interference with normal operation of the microscope, including the film camera, and 4) minimal modification of the microscope.Cameras positioned below the film camera have narrow fields of view because of increase in image size below the film camera and the small size of CCD targets relative to film. We chose a position above the microscope's fluorescent viewing screen, where there is a convenient port on the 4000-EX, and achieved a field width approximately equal to that on film.

Identification of cloud‐free pixels in inhomogenous surfaces from AVHRR radiances

A new method of distinguishing clear and cloud‐contaminated pixels from AVHRR data is described. Whereas most previous methods have difficulty in identifying cloud‐contaminated pixels when the background is inhomogenous, such as is the case for coastal regions or continental regions containing vegetated land and bare soil or land and water, the present method is particularly suited to these situations. Examination of the measured reflectivities in channels 1 and 2 of the AVHRR for these backgrounds and for clear skies suggests that the reflectivities are related linearly. The linear relationship is understandable in terms of pixels being comprised of linear combinations of two different surface types. Advantage is taken of this relationship as well as the radiance in channel 4 to identify cloud‐free pixels for complex surface conditions. The technique is readily automated and combined with other techniques that may be more suitable for homogenous backgrounds.

Stacked frame buffer algorithm for fast recovery of solid synthesis process

Fast recovery in solid modelling design is an important aid for users of CAD systems. A stacked frame buffer algorithm for solid modelling is proposed. This buffer is constructed as a multiframe array whose cells are maintained in an order according to priority of procedure linked to each pixel in terms of x and y elements on the image plane, so that the cells' contents may describe the visibility of current objects as well as the history of visible ones through the modelling process. The algorithm directly processes image data in the display buffer as it runs and recovers step-by-step. Using this method, problems of rapidly recovering from inadvertent operating errors and immediately modifying objects in the CAD process are solved.

A thinning algorithm for discrete binary images

The paper discusses thinning algorithms and introduces a characterization of skeletal pixels in terms of how many arcs of the boundary pass through a pixel. A new algorithm is proposed which proceeds by peeling off successive contours of the set to be thinned while identifying pixels where disjoint parts of the boundary have been mapped. The union of these pixels (plus a few others with similar properties) forms the skeleton. The algorithm can be implemented in such a way as to have time complexity which is a linear function of the area.