Real Time 3D Week 1 Tutorial

Q5. A display device has a resolution of 800×600 pixels and uses 24 bit color for each pixel. If we generate a video with 25 frames per second which we want to upload onto the Internet, calculate the Internet speed required to transmit the video.

A5. We would need a bandwith of (at least) 800×600×24×25 bits per second, which equals 288Mbps if we don't consider any additional transmitted data and eventual compression algorithms.

Q1. The pipeline approach to image generation is nonphysical. What are the main advan- tages and disadvantages of such a nonphysical approach?

A1. The main advantage of the pipeline is that each primitive can be processed independently. Not only does this architecture lead to fast performance, it reduces memory requirements because we need not keep all objects available. The main disadvantage is that we cannot handle most global effects such as shadows, reflections, and blending in a physically correct manner.

Q2. The human visual system has all the components of a physical imaging system, such as a camera or a microscope. What are the main cells or light sensors present in the human eye? List them and explain their uses.

A2. The light sensors in the human visual system are the rods and cones (so named because of their appearance when magnified) located on the retina. They are excited by electromagnetic energy in the range of 350 to 780 nm. The rods are low-level-light sensors (high sensitivity) that account for our night vision and are not color sensitive; the cones are responsible for our color vision. Human color-vision capabilities are due to the different sensitivities of the three types of cones. There are three types of cones and a single type of rod. The sizes of the rods and cones, coupled with the optical properties of the lens and cornea, determine the resolution of our visual systems, or our visual acuity. Resolution is a measure of what size objects we can see. More technically, it is a measure of how close we can place two points and still recognize that there are two distinct points. The optic nerves are connected to the rods and cones in an extremely complex arrangement that has many of the characteristics of a sophisticated signal processor. The connection with the cones is dedicated, as opposed to the rods. This involves a higher influence of the former in the visual acuity, explaining why in poor lighting conditions we are only able to identify coarse shapes in monochrome tones (only rods are activated in such case).

Q3. The memory in a frame buffer must be fast enough to allow the display to be refreshed at a rate sufficiently high to avoid flicker. A typical workstation display can have a resolution of 1400×1200 pixels. If it is refreshed 60 times per second, how fast must the memory be? That is, how much time can we take to read one pixel from memory? What is this number for an 800×600 that operates at 50 Hz but is interlaced?

A3. We have to process 1400×1200×60 pixels/sec. If we process each successively, there is only 9.92 nanoseconds to process each. For a 800×600 interlaced display operating at 50 Hz we must process only 800 × 600 × 25 pixels/sec which gives us about 83.33 nanoseconds to process each pixel.

Q4. Movies are generally produced on 35 mm film that has a resolution of approximately 3000×2000 pixels. What implication does this resolution have for producing animated images for television as compared with film? Consider high resolution video of 1920×1080 pixels.

A4. Each frame for a 1920×1080 pixel video display contains only about 2M pixels whereas the 3000×2000 pixel movie frame has 6M pixels, or about 3 times as many as the video display. Thus, it can take 3 times as much time to render each frame if there is a lot of pixel-level calculations. This can affect transmission bandwidth, forcing the use of efficient video compression schemes for broadcasting.