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Evolution of the Live Preview in Digital Photography

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With the release of the world’s first live preview on a DSLR camera, we reflect upon the roots of the liquid crystal display and the live preview. Not too long ago, photographers had to rely solely upon an optical viewfinder to frame their pictures. Sometimes the viewfinder was inaccurate and other times it was simply just too small a view to be practical.

What is now a standard feature on compact digital cameras took decades to develop. Just two years ago, a 2-inch LCD screen was considered large; this year, the norm has shifted to 2.5 inches. What was once a live television screen planted on the back of a camera has become a standard feature on digital cameras.

Live preview, or the ability to see the changing scene through the lens on a digital camera’s LCD, is something we now take for granted on compact digital cameras. When in capture mode, even the most inexpensive point-and-shoot will display the changing scene in front of the lens on the LCD, which is itself a species of live preview. But it wasn’t always this way. Digital photography is only a few decades old, and taking a peek at the role of the live preview in its short but innovative past better puts Olympus’ new E-330 in context.

**Live Preview Prerequisites **

The history of the live preview in digital photography is inseparable from the history of the electronic viewfinder - the former is not possible without the latter. After all, how can an in-camera real-time image appear if there is no screen on which to display it?

Like their analog counterparts, primitive digital cameras in the late ‘80s and early ‘90s used optical viewfinders for framing the shot. A separate display device had to be used for reviewing the captured images; at the time, display devices mostly relied upon cathode-ray tube technology, and a monitor that used cathode-ray tubes was far too bulky to be built into a portable consumer camera.

Different manufacturers had different approaches to the solution. In the early ‘80s, most digital cameras recorded to floppy disk for delayed display on a computer. A few years later, some cameras came with their own proprietary cathode-ray tube monitors that were hooked up to the camera via a specialized port; these assemblies looked much like CB radios. Other cameras needed to be hooked up to computers before users could download and access images. In the late ‘80s manufacturers began to experiment with memory cards as another method of image transfer to a playback display.

In 1985, Nippon Kogaku K.K. of Nikon filed a U.S. patent (patent no. 4,754,333) for "Electronic still camera provided with an electrical viewing system," a year after doing so in Japan. Nikon’s invention picked up signals from the "solid-state imaging device" (CCD) and flashed them through the optical system 30 times per second so the view looked smooth to the human eye. This would have been the first viewfinder, but a prototype wasn’t built for awhile.

Interest in liquid crystal technology began to grow during this period and in September 1991, Fuji Film Photo Co. Ltd. applied for a U.S. patent for a "Camera having a liquid crystal view finder" (patent no. 5,164,834), a little less than a year after applying for the same thing in Japan.

**For Sale in 1995: Two Cameras with Live Preview **

Fuji may have held the patent for the first digital camera with an LCD, but U.S. patent law allows other manufacturers to patent the same thing with one or more important differences. This is precisely what Casio Computer Co., Ltd. did in 1994 when they filed a patent for a "Portable compact imaging and displaying apparatus with rotatable camera" (patent no. 5,612,732). Though Casio had made vague and contradictory references to electronic still cameras using LCDs in a couple patents filed in 1990, their 1994 patent provided much firmer innovation. Casio stated that their invention was a camera that contained an LCD, but a key difference was that the lens assembly was on a rotatable portion - much like the 2005 Nikon Coolpix S4, for example. The camera could also export NTSC signals, which was not a trait of Fuji’s invention as described in their 1991 patent.

One year later, in March 1995, Casio announced and sold the QV-10, the first consumer digital camera with an LCD, and the first with live preview. Users could now frame their shots with an in-camera display device. In the same year, Ricoh came out with the Ricoh RDC-1, which also had an LCD that offered live view; however, the 2.5-inch LCD monitor was detachable and technically not built-in.

Other manufacturers were similarly behind in the trend. In 1996, Sony rolled out the Cyber-shot DSC-F1, which offered a fixed LCD. At the 1996 Photo Marketing Association Trade Show, Pentax displayed the EI-C90 which had a bulky detachable LCD monitor. The EI-C90 wasn’t available until 1997, the same year Canon made available its PowerShot 350 and Konica Minolta offered its DiMage V in Japan – both with live view LCDs. By 1998, a significant number of compact consumer cameras offered LCDs; by 1999, it was the norm.

**Tweaks and Refinements **

While Casio was the first to sell live preview to the masses, other manufacturers refined the technology. In February 2001, Minolta Co., Ltd. filed a patent that detailed design that reduced post-capture "black-out" of live preview on the LCD, normally caused by a processor preoccupied with recording the freshly captured image (patent no. 6,963,374). Minolta solved this problem by giving image processing priority to the live view, and only fully process the captured image data immediately prior to playback, when the camera was not in capture mode and not expected to be ready to snag a shot. In September 2004, Hewlett-Packard Development Company, L.P. filed two slightly different patents for a digital camera that offered gain adjustment on the LCD during live preview, either through automatic or manual adjustment (patent no. 6,900,840 and 6,970,198).

Still, the essential mechanism of live preview remains unchanged. Image data is buffered to the LCD at a predetermined refresh rate; the stream only breaks when users trigger the shutter to close and thus snap a picture.

**The Digital SLR Exception **

Previously, when compact digital camera owners handled a DSLR they often questioned how to turn on the live view on the LCD. This prompted many conversations about mirrors, image sensors, and design – with the conclusion that it just wasn’t possible to have a live view on a DSLR.

DSLRs and compacts take pictures in fundamentally different ways. In a compact digital camera, light enters through the lens and falls on the sensor continuously. The sensor reads the changes in the light and buffers them to the LCD, where users can watch the scene unfold in real-time. When users take a picture, the constant stream of light hitting the sensor is saved to memory until the shutter closes off the stream. (This is why leaving the shutter open longer makes for a blurry image; the scene has time to change before the recording stops, and these changing light paths are recorded to the image as blur. Conversely, a fast shutter freezes action because the light hitting the sensor has little time to change.)

In a typical DSLR, mirrors reflect incoming light upward to an optical viewfinder. When users of a conventional DSLR take a picture, the reflective shutter inside moves aside, breaking the stream of light it reflects to the viewfinder. The open shutter now lets the incoming light move forward and hit the exposed sensor. When the shutter falls shut, the image recording is complete. This design makes it impossible to have both a live view and a through-the-lens optical viewfinder.

**Live Preview in DSLRs **

A few manufacturers have tried to solve the DSLR live preview problem. Olympus actually made their initial attempt in 2000 and 2001 with the E-10 and E-20; while these cameras did not have interchangeable lenses, they split the beam of light that entered the lens, sending part to the viewfinder and part to the sensor. However, this resulted in poor sensitivity and a dim view through the viewfinder.

More recently, in 2005 Fuji released the FinePix S3 Pro and Canon released the EOS-20Da for astrophotography. Both of these cameras offer mirror lockup, which held open the shutter, permitting light to fall on the sensor and stream a live view. However, this method also prevented light from reaching both the viewfinder and the phase detection AF/auto exposure mechanisms, which also need some light to function.

**Olympus E-330: A New Solution **

The Olympus E-330 meets the definition of an SLR - it uses a system of mirrors and a viewfinder to provide a though-the-lens view - but yet it also offers live preview. Olympus has gotten around the problem this time by building a camera with two sensors: one for conventional still image capture and the other dedicated to live preview.

The interior of the E-330 works like this: light coming into the camera gets reflected off a shutter and away from the still image sensor, as in a typical DSLR. Towards the top of the camera, the light path breaks into two: 80 percent of the light is reflected to the optical viewfinder and 20 percent is reflected onto a CCD, which creates the live view.

Twenty percent of the light doesn’t sound like much, and it seems like the E-10 or E-20 all over again. However, the E-330 incorporates a bit of new technology that these two earlier cameras didn’t have; namely, the dedicated live view CCD with Bright Capture Technology. The E-330 uses the same CCD that is used in the Stylus 800, but uses it only to capture information for the live view. Olympus’ Bright Capture Technology boosts the brightness of the image recorded as well as the image seen onscreen, so the 20 percent of light the CCD received is enough for a decent view - or so we anticipate.

**Looking Ahead **

When innovative technology hits the market, it’s likely that other manufacturers will come out with their own versions to compete. Within the next few years, DSLRs may all very well have live views. In the end, Olympus may not get much out of its breakthrough technology. Casio was the first to sell the live view to consumers, but it’s not in the top five camera manufacturers. Olympus may only reap the benefit of its technology if it follows the E-330 with more solid technology. Either way, Olympus offers a unique solution to the DSLR live preview problem which the market will have to respond to and compete with. In the end, consumers are sure to benefit.