Different view on diffraction-limited imaging optics design.

The task of imaging optics design starts with choosing a subset of imaging parameters such as the object distance, the image magnification, the image resolution, and the depth of field. It is clear that the imaging parameters are inter-related and their appropriate trade-off is the key problem of final optical design. We provide a novel analysis of the optical design considering diffractive imaging phenomena and thin lens approximation, and we derive formulas for the solution of individual parameters. We show that combinations of three independent optical design input variables determine all other optical and geometrical parameters under diffraction-limited optical imaging. We also formulate an invariant relation in the object space if the depth of field is one of the design's target parameters.

Optomechanical design of rotary kaleidoscope for bidirectional texture function acquisition.

Optical systems are traditionally used for accurate recording and measurement of the real world's appearance. Present techniques allow us to form a computer-based virtual world, which is used in a variety of technical fields. The crucial issue for future applications of virtual reality is the fidelity of rendered images to real-world objects. This is strongly affected by the appearance of the rendered object's surfaces. Currently, the most applied method of describing a surface's visual appearance of spatially nonuniform surfaces is bidirectional texture function (BTF). We have designed, optimized, built, and tested a unique portable instrument based on a rotary kaleidoscope principle for BTF acquisition in situ. To the best of our knowledge, such an instrument has never been used before to measure BTF of a surface. We enhanced a common static kaleidoscope by adding rotation, which allows us to get a larger number of images of the sample for more combinations of illumination directions and viewing directions. This results in a higher directional and spatial resolution of measured BTF data. In this paper, we focus on the optomechanical design of the rotary BTF measurement instrument and issues related to its alignment to keep the desired mechanical precision.

Lightdrum-Portable Light Stage for Accurate BTF Measurement on Site.

We propose a miniaturised light stage for measuring the bidirectional reflectance distribution function (BRDF) and the bidirectional texture function (BTF) of surfaces on site in real world application scenarios. The main principle of our lightweight BTF acquisition gantry is a compact hemispherical skeleton with cameras along the meridian and with light emitting diode (LED) modules shining light onto a sample surface. The proposed device is portable and achieves a high speed of measurement while maintaining high degree of accuracy. While the positions of the LEDs are fixed on the hemisphere, the cameras allow us to cover the range of the zenith angle from 0 ∘ to 75 ∘ and by rotating the cameras along the axis of the hemisphere we can cover all possible camera directions. This allows us to take measurements with almost the same quality as existing stationary BTF gantries. Two degrees of freedom can be set arbitrarily for measurements and the other two degrees of freedom are fixed, which provides a tradeoff between accuracy of measurements and practical applicability. Assuming that a measured sample is locally flat and spatially accessible, we can set the correct perpendicular direction against the measured sample by means of an auto-collimator prior to measuring. Further, we have designed and used a marker sticker method to allow for the easy rectification and alignment of acquired images during data processing. We show the results of our approach by images rendered for 36 measured material samples.

Optomechanical design of a portable compact bidirectional texture function measurement instrument.

Recent developments in optoelectronics and material processing techniques make it possible to design and produce a portable and compact measurement instrument for bidirectional texture function (BTF). Parallelized optics, on-board data processing, rapid prototyping, and other nonconventional production techniques and materials were the key to building an instrument capable of in situ measurements with fast data acquisition. We designed, built, and tested a prototype of a unique portable and compact multi-camera system for BTF measurement which is capable of in situ measurement of temporally unstable samples. In this paper, we present its optomechanical design.

Parallel On-Demand Hierarchy Construction on Contemporary GPUs.

We present the first parallel on-demand spatial hierarchy construction algorithm targeting ray tracing on many-core processors such as GPUs. The method performs simultaneous ray traversal and spatial hierarchy construction focused on the parts of the data structure being traversed. The method is based on a versatile framework built around a task pool and runs entirely on the GPU. We show that the on-demand construction can improve rendering times compared to full hierarchy construction. We evaluate our method on both object (BVH) and space (kd-tree) subdivision data structures and compare them mutually. The on-demand method is particularly beneficial for rendering large scenes with high occlusion. We also present SAH kd-tree builder that outperforms previous state-of-the-art builders running on the GPU.