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Scaling Down CMOS

Jun 1, 2005 12:00 PM, By D. W. Leitner

Compact CMOS camcorder features high-speed image processing.

What were the odds of an entirely new, pro-quality, 1080i HDV Handycam coming from Sony, right on the heels of the company's groundbreaking HVR-Z1U? Who would have imagined a single-chip CMOS design?

Sony's HVR-A1U exceeds expectations in its breakthroughs. “This is a radical departure from what we have grown accustomed to,” says Juan Martinez, product manager at Sony Broadcast and Professional.

At 1.5lbs. (roughly a third of the size of the Z1 — think helmet-cam), the A1 boasts virtually every feature of the Z1, including DVCAM and DV formats, internal downconversion to SD, aspect-ratio conversion, 4X focus assist, even the clever Shot Transition. Its SMPTE timecode capabilities and SMPTE color bars are identical to the Z1.

The only elements missing are the prism optics used on the Z1's three CCDs. To create color, the A1's single 1/3in. CMOS chip introduces a Bayer pattern filter. Developed by Kodak in the 1970s, this filter covers each pixel with a red, green, or blue micro-filter in an RGBGRGBG pattern that results in twice as much green (luminance) detail as red or blue.

The A1's CMOS reads six signal channels at a time out of this pattern: one from each of the four green samples, plus one channel containing two red samples and another channel containing two blue samples. (By comparison, each of the Z1's CCDs reads out one complete row of samples at a time and outputs it on a single channel.)

This high-speed image processing is required for 60i HDV because the A1's 1920×1440 CMOS sensor captures a true 1920×1080 matrix of square pixels in HDV mode.

The Z1, with a horizontal count of 960 non-square pixels, falls well short of this resolution and requires a pixel-shift technique to achieve the 1440 horizontal samples needed for HDV. The A1 captures 1920 horizontal pixels and downsamples to meet the 1440 horizontal sample requirement.

To manage the A1's high-speed image processing, Sony has developed a new downstream digital signal-processing engine, the Enhanced Imaging Processor (EIP). EIP shares elements of DSP with the Z1, including 14-bit A/D conversion, and supports unique capabilities of the A1's CMOS architecture.

Maximizing Photosensitivity

CMOS pixels, unlike CCD pixels, can be addressed individually. As a result, each CMOS pixel can, in theory, have its own built-in noise reduction or A/D circuitry (that's why CMOS is sometimes called “system-on-a-chip”). However, in order to gain light sensitivity, Sony has opted instead to maximize each pixel's photosensitive area by: 1) restricting on-chip signal processing to correlated double sampling, a technique for canceling spurious read-out noise, and 2) using the latest 90nm semiconductor technology, commercialized by Intel and others, to shrink transistors on the A1's CMOS to less than 90nm.

Fourteen-bit A/D conversion occurs downstream in EIP, as do DSP, image scaling, downconversion, and manipulation of filters like black stretch. EIP's black stretch, for example, can open up shadow detail on the fly using algorithms that isolate and analyze texture patterns and tonal scale components, with no effect on midtone or highlight detail. Highlight detail can also be “repositioned” using this technique.

Characterizing black stretch as a “filter” is unconventional, but introducing Photoshop-like image manipulation in a camcorder is a big step up from the conventions and limitations of video signals. The A1's flip-out LCD can even display a dynamically shifting histogram superimposed over a live HDV image. A histogram is a distribution chart of pixel brightness levels, popular in both digital still cameras and photo-editing programs like Photoshop.

Individually addressable pixels give the A1's CMOS sensor intrinsic shape-shifting ability. Its native 4:3 aspect ratio does not dictate the as-pect ratio of the captured image. As a result, the A1 can be either a 2.8-megapixel still camera, with all its 1920×1440 square pixels dedicated to the creation of a progressive-scan 4:3 photo, or a video camera, with 1920×1080 square pixels organized into a 16:9, interlaced HDV raster — or anything in between. EIP manages these different formats.

All this should be no surprise coming from Sony, the source of the massive 12.4-megapixel CMOS sensor in Nikon's new top-of-the-line D2X digital SLR. In addition to its CCD design and manufacture, Sony has been shipping large quantities of CMOS sensors for mobile phone cameras since 2003 and is aiming for industry leadership of broadcast CMOS products.

The A1 is its first shot over the professional bow, joining the consumer version of the A1, the $2,000 HDR-HC1, and the standard-definition consumer DCR-PC1000, a tiny $1,300 “matchbook” MiniDV camcorder with three 1/6in. CMOS chips.

Designing a Lens

Because an image can be no better than the lens forming it, Sony has enlisted Zeiss to create a compact 5.1mm to 55mm (10X optical) Vario-Sonnar f1.8 zoom with a switchable focus/zoom ring. A novel Tele Macro function enables the user to capture macro images at the telephoto end, opening up new possibilities in close-up and depth-of-field. Notable also are its small 37mm threaded diameter and Zeiss' famed T* antireflection coatings.

However, ND filters and an optical stabilization system are missing, along with the prism optics. Sony's Juan Martinez says, “With the very high dynamic range of CMOS and EIP, the A1 does not need the ND filter.” (A conventional ND filter can easily be screwed on the front of the lens anyway, as photographers and filmmakers have always done.) Shutter speeds range from 1/4 sec. to 1/10,000 sec.

Like the consumer HDR-HC1, the A1 offers electronic Super SteadyShot image stabilization, which requires 5 percent of the available CMOS real estate around the edges for image movement, leaving fewer than 1920×1080 pixels to form the HDV image. Enter EIP scaling.

Touchscreen Functionality

The A1's 250,000-pixel color viewfinder is identical to the Z1's. Unlike the Z1, however, the A1 has no handle-mounted 250,000-pixel hybrid (indoors/outdoors) LCD screen — the compact A1 has no handle. Instead, Instead, it features a smaller, 2.7in., 16:9, 123,000-pixel hybrid touchscreen on the operator side that can be flipped into mirror mode if desired.

This touchscreen function is critical because the A1's body has far fewer external controls than the Z1. Along the left edge of the touchscreen itself, for instance, are membrane buttons for wide and tele control of zoom, along with a record button. Manual controls for gain and two channels of audio are available elsewhere, but most controls are accessed partly or entirely by touchscreen.

Also retained from the consumer HDR-HC1: spot focus and spot metering, which allow the operator to move a focus or “spot metering” zone around the A1's touchscreen by finger; Infrared Super NightShot and Super NightShot Plus for colors; and a memory stick slot for still photos. The camcorder takes InfoLithium M-type batteries smaller than the Z1's.

For professional audio, an optional dual XLR input module attaches to a shoe above the lens. With its external mic holder on top and row of power switches on the side, it looks like it has been severed from the handle of a PD170.

The unit will be available in early fall at a projected list price of $3,500. Its street price is anyone's guess.

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D.W. Leitner is a filmmaker in New York.

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© 2009 Penton Media, Inc.