Patrick Mannion
TechOnline

So, what's inside?
On removing the covers, I was at once disappointed and amazed. The disappointment derives from the gadget-freak in me that loves to see a maze of springs, motors and actuators supported by a rats nest of wires and myriad, complex-looking ICs. That was definitely not the case. In fact, I was amazed that the camera simply comprises the 2.8-cm-high lens, two mini connectors (for the USB and button-control interfaces) and a single processing board with the sensor, video processor and two memory ICs.

However, it's the choice of components, and the software that went into them, that gives the Flip Ultra its uniqueness and edge. At the heart of the system is the marriage of a Micron 1/4-inch VGA CMOS sensor with a Zoran Coach 8M (ZR36460BGCF) image processor. According to John Furlan, vice president of engineering at Pure Digital, the Micron sensor (MT9V011D00STC) was chosen not just because he believes Micron makes high-quality sensors, but also because it had the right pixel size of 5.6-micron square that would give maximum performance across all light ranges, from bright to poor. It also has the necessary frame rate of 30 to 90 fps, programmable gain via a two-wire interface, on-board 10-bit analog-to-digital converter and a 10-bit parallel output.

This output feeds directly into the Zoran processor. It is here where much of Pure Digital's intellectual property resides. According to Furlan, the team chose to go with Zoran as they already had a history of working with the company for its one-time-use cameras. However, they chose the Coach 8 specifically because, "it's very integrated, with a high-quality image-processing pipeline, as well as high-quality image compression — in hardware, versus DSP — plus USB," said Furlan. In addition, Zoran made the full image-processing pipleline available to Pure Digital so they could perform the configurability they wanted, while still achieving the full 30 fps, even in low light.

Fast digital image processing

The frame rate brings up an interesting point and speaks well of the Coach 8's processing power. Typical still cameras take a second or more to process an image, so how does the Flip manage 30 in a second? According to Furlan, as discussed previously, the video resolution is 640x480, which translates to approximately 0.25 Mpixels. "So, a camera that can process and store a 4-Mpixel image in 1 second can process a 0.25-Mpixel image in 1/16 of a second." Also, typical digital still cameras can process multiple frames per second. "In the end, it's the speed of the underlying hardware that permits us to process a video frame 30 times per second," he said.

Secret sauce? Exposure control algorithms

The configurability of the processor also allowed Furlan's team to implement proprietary algorithms and core intellectual property to overcome one of the main obstacles to smooth digital video: auto exposure control. Careful control of both sensor gain and exposure across the range of scenes with appropriate smoothing is mandatory to ensure the user doesn't see significant changes in exposure on a frame-by-frame basis. This control of exposure, gain and image processing over a range of lighting conditions is a detail that's often overlooked, said Furlan.

Digital still cameras don't have this issue, as it's one exposure, one shot, while more expensive digital camcorders have external sensors and electromechanical light control. But the Pure Digital team had to do this digitally.

The "Eureka" moment came with the development of proprietary damping algorithms to implement a non-linear response curve off stasis to give a smooth 'landing' quickly, without instability in the system. "For slow or little change, we keep the auto exposure stable or make very small changes which cannot easily be discerned by viewers," said Furlan. While the auto exposure has no impact on the underlying video frame rate, it does improve the perception that as the camera moves from one scene to the next, there were no significant jumps in brightness.

The end result is a digital camcorder experience for $150 that rivals that of camcorders in the $500- to $600-range.

The Zoran 8 is supported by two memory chips from Samsung: the K4D551638H moviNAND in 1- or 2-Gbyte versions with MMC controller for main storage, and the KMAFN0000M-S998 (728) on the back for buffering.

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