Focused Practice

I. Answer the following questions:

1. How many switches does a multilevel converter have?

2. What is the main motivation for such converters?

3. How is the sharing achieved?

4. What does the overall switching frequency become?

5. How does it come that it becomes like that?

6. Where do the switching harmonics appear?

7. Have there been any approaches to multilevel control published?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: Motivations for multilevel converters.

Unit 64 Grammar: The Functions of the Infinitive and Gerund Word List:

1. realistic image synthesis	синтез реалистичных изображений для ТV
2. to render	передавать, воспроизводить
3. physically-based rendering methods	физически обоснованные методы воспроизведения изображения
4. light propagation	распространение света
5. perceptual response	способность восприятия
6. over the range of	на протяжении, в пределах
7. CRT (cathode ray tube)	электроннолучевая трубка
8. simulated environments	имитируемая окружающая среда
9. tone reproduction	воспроизведение тонов в изображении
10. glare	ослепительный блеск, резкий свет, блик
11. a glare filter	фильтр, снимающий блики (антибликовый фильтр)
12. illumination engineering work	обеспечение подсветки, освещенности
13. perseptually-based approach	подход, основанный на физическом восприятии
14. threshold visibility	пороговая видимость
15. visual acuity	четкость, различимость, контрастность
16. visual sensitivity	зрительная чувствительность
17. color appearance	цветность
18. visual appearance	зрительный облик

A Model of Visual Adaptation for Realistic Image Synthesis

The goal of realistic image synthesis is to produce images that capture the visual appearance of modeled scenes. Physically-based rendering methods make it possible to accurately simulate the distribution of light energy in scenes, but physical accuracy in rendering does not guarantee that the displayed images will have a realistic visual appearance. There are at least two reasons for this. First, the range of light energy in the scene may be vastly different from the range that can be produced by the display device. Second, the visual states of the scene observer and the display observer may be very different.

To produce realistic images we need to model not only the physical behavior of light propagation, but also the parameters of perceptual response. This is particularly true of the visual system's adaptation to the range of light we encounter in the natural environment since visual function changes dramatically over the range of environmental illumination.

Very little work has been done in computer graphics on adaptation. Earlier work has focused primarily on overcoming the limits of conventional CRT displays and determining how to best display simulated environments within the limited dynamic range available. Tumblin and Rushmeier introduced the concept of tone reproduction to the computer graphics community and developed a tone reproduction operator that preserves the apparent brightness of scene features. Ward has taken a somewhat different approach and has developed a tone reproduction operator that preserves apparent contrast and visibility. Spencer has developed a psychophysical model of glare and has implemented a glare filter that increases the apparent dynamic range of images.

One of the models of adaptation includes the effects of adaptation on threshold visibility, color appearance, visual acuity, and changes in visual sensitivity over time. The algorithm derived from the model is based on the psychophysics of adaptation measured in experimental studies. Therefore, it can be used predictively for illumination engineering work, and can be used to develop perceptually-based approaches to rendering and display.