Electronic Design

Electronic Cameras Have Some Serious Catching Up To Do

Millions of years of evolution have given the human visual system a jump on the electronics industry. Sean Adkins, vice president of Advanced Technology at Imax Corp. in Vancouver, believes digital motion-picture cameras have to overcome many obstacles to counter the brain's tendency to detect and perceive patterns, like unwanted artifacts and distortion.

Speaking at last month's IEEE International Conference on Image Processing in Vancouver, Adkins added that digital innovators have a ways to go to catch up with the well-entrenched, photochemical motion-picture camera. Almost a century old, this device successfully combats visual artifacts. If digital designers want to surpass it, Adkins cautioned, they have to convey the highest bandwidth possible to the brain.

Achieving a sense of presence is essential. While 8 bits per color may be adequate for still photos, Adkins noted, it's not enough for motion pictures. It tends to display artifacts such as steps and contouring. The brain operates by detecting patterns, so it easily perceives these irregularities. Consequently, digital motion pictures require at least a linear 15-bit representation.

Photochemical camera systems exhibit a graceful S-shaped transfer function, which contributes to their excellent performance. CCD and other electronic sensors employed in electronic camera systems will have to emulate this function to achieve a corresponding response to images under practical working conditions. A 24-fps shutter speed blurs the image and reduces the sense of realism. That's why a 4000-pixel/line, 60-fps imaging system is necessary. A dynamic range of 10,000:1 to 100,000:1 is desirable both for capture and projection as well. The 12-bit representation often found in electronic systems isn't adequate.

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