On the third and last full day of the HPA Tech Retreat in Indian Wells, California, a panel of imaging experts drilled down into some of the more esoteric topics related to 4K and digital acquisition. Among the topics addressed were sensor-lens options for 4K acquisition; solar activity and lit/stuck/dead pixels; design challenges of long-range zoom lenses for 4K S35 digital cameras; video/D-Cinema camera/sensor noise; the role of nonlinear coding of the TV image; and 4K, HDR and imagers.

HPA Tech Retreat organizer and engineer Mark Schubin discussed various options for sensors and lenses for 4K acquisition. Among the options he considered was to shrink pixels, which creates dead pixels and photon noise, diagonal offset and, last, up-conversion from HDTV.

“This [latter option] may not seem to make sense, but the sensor perfectly matches the optics,” said Schubin.

Joel Ordesky of Court Five Productions discussed the issue of lit/stuck/dead pixels and solar activity. “A lot of my producing friends don’t know what lit pixels are,” he explained, defining it as a “hot or defective pixel.”

“As a rental house, you hear this a lot: your cameras are old or poorly maintained,” he added. He described a rental house client that complained about constant lit pixels with all six rented cameras.

What causes lit pixels? “There are a lot more myths than facts about pixels,” Ordesky explained. “Lit pixels are not manufacturer defects, due to over-heated cameras or because the imager is too old. The truth is that cosmic rays — gamma photons in particular — are the cause of lit pixels.”

There is more exposure in Denver than Los Angeles and more exposure close to North and South Poles. “Simply put, the closer your are to the edge of the atmosphere, the less protection you have,” he said.

Lightning is another source of gamma photons. Solutions include black balancing, automatic pixel noise reduction, manual pixel mapping or, the least desirable choice, fixing it in post.

Canon’s Larry Thorpe discussed the design challenges of developing a portable long zoom 4K Super 35mm lens. He briefly went over the history of contemporary long portable zoom lenses. “There has been many requests for Super 35mm telephoto lenses,” he said. “We learned a lot with our experiments with the sporting world as well as wildlife productions.”

Following extensive consultations with documentary producers, Canon averaged out the many requests as the ability to shoot a 4-to-5 foot object height at 330 feet, with the object filling the frame; there was also a plea for a built-in 1.5x range extender. Those parameters would require a focal length of 1,000mm.

The central challenge was that this lens had to be portable; it couldn’t be heavier than 15 pounds or longer than 16 inches. Maintaining 4K performance with these parameters was also a challenge. Achieving this required “a tremendous collaboration” between optical design simulation and optomechanical design simulation. The result just meets the weight and length parameters required.

Color scientist Charles Poynton focused on video/D-Cinema camera and sensor noise. “The topic is enormous and the specific issue today is how can we expect noise behavior to change as the pixels get smaller,” he said.

“At the size of pixels we’re using and the light coming into the scene, you can count the number of photons arriving at each pixel as in the tens of thousands. At that level, because the photons are discrete and convert to electronics, the clumpy nature of that optical signal actually becomes the dominant source of noise.”

Poynton noted that today we measure the noise when there is no light. “The take-away message is that we should try to come up with a characterization that measures the noise when there’s light,” concluded Poynton. “The noise is in the photons and there’s nothing you can do in the sensor but collect as many photons converted to electronics as you can.”

Masayuki Sugawara of NHK Science and Technology Research Laboratories addressed the role of nonlinear coding of the TV image and Grass Valley’s Peter Centen talked about 4K, HDR and imagers.