Streaming Media - December 2008/January 2009 - (Page 22)

tutorial Improving Video Color Quality Over the past 10-plus years, many customers and colleagues have asked me how to improve the quality of their web videos. The first thing I tell them is to get out of the it’s-only-for-the-web mentality. Web viewership is growing faster than anyone thought possible, and its acceptance has surpassed TV’s adoption over the same time span. So think quality first, and remember that a shoot for the web is the same as a shoot for HDTV. Once you’re in that mind-set, there are three more ways to improve quality. First, know your equipment and how to adjust for optimal output. Second, adjust your white-and-black balances during acquisition. Finally, raise your contrast and complexity during encoding. By doing these things, you can make your video look great and differentiate yourself from everyone else. A major element of great-looking webcasts or streaming media is content acquisition. Without a decent camera and knowledge of its characteristics, the video will look unimpressive. The first step is getting to know your camera. There isn’t one brand that is best—that’s totally subjective and up to personal preference—but simply knowing your camera’s brand will tell you quite a bit about its characteristics. It doesn’t matter if you are doing a single-camera or a multicamera shoot. Just knowing the brand and how each one differs allows you to set up the camera properly. These differences affect the white balance and color saturation. You might notice how one camera’s reds look brighter and appear to “pop,” while another brand’s reds are dull but the blues appear to pop. This can be true whether the camera is professional or prosumer. One brand’s camera might use complementary metal oxide semiconductors (CMOS) while another brand uses chargecoupled devices (CCD) sensors. By S. Scott Grizzle Making the CMOS/CCD Decision The difference between CMOS and CCD isn’t something most people need to know. However, understanding how each one works and the differences between them can tell you which filters you should be using and how light is affected. One good question to ask is, “What is CMOS, and why is it good for a camera and my production?” CMOS sensors use multiple transistors to amplify and move the charge provided by incoming photons of light, enabling the pixels to be read individually. One of the advantages of CMOS is its low power consumption. CMOS sensors consume up to 100 times less power than CCDs. Because CCDs are essentially capacitive devices, they need external control signals and large clock swings to achieve acceptable charge transfer efficiencies. 22 STREAMING MEDIA December 2008/January 2009 Another advantage of CMOS is that it is adaptable for high frame rates and resolutions. Most CMOS sensors are set at HD resolutions, but since their resolutions are so high and their sensors can access just the pixels of a region, they allow high frame rate. Basically, reducing the resolution allows the higher frame rates. This is a real advantage of CMOS. Now, you can set your camera up right and use it in high frame rate applications. One last thing that is good about CMOS is that the sensors don’t have artifacts, smear, or blooming. They have a clean, high-quality image. However, like everything else in life, CMOS sensors have their drawbacks. First, they aren’t as sensitive to light as your typical CCD sensors. So if you’re in a low-light setting, you might run into problems. Another issue is that these sensors usually don’t have infrared (IR) filters installed on them. In industrial applications, this is more common. But without an IR filter, your colors will be skewed. Basically, your spectrum will be adjusted so that your greens will be brown. But this is an easy fix—simply add a filter. Many CMOS sensors use a Bayer filter that passes red, green, or blue light to selected pixels. Lastly, CMOS is considered to be noisier than CCDs, but, in most cases, this is only noticeable on test equipment. The alternative to CMOS is the older standard, CCD, and three-CCD solutions. Many people know the term CCD, but what is it? Well, again, it’s not a know-or-fail thing, but it helps to understand the complete workflow. The CCD is a solid-state chip that turns light into electric signals. In a full-frame device, all of the image area is active, and there is no electronic shutter. A mechanical shutter must be added to this type of sensor or the image will smear as the device is clocked or read out. The sensors respond to 70% of the incident light, making them far more efficient than photographic film, which captures only about 2% of the incident light. Most common types of CCDs are sensitive to infrared light, which allows zero lux (or near-zero lux) video recording. Many CCDs, like CMOS sensors, use a Bayer mask over the CCD. Each square of four pixels has one filtered red, one blue, and two green. The result of this is that luminance information is collected at every pixel, but the color resolution is lower than the luminance resolution. Better color separation can be reached by three-CCD devices (3CCD). Each of the three CCDs in these devices is arranged to respond to a particular color. Another advantage of 3CCD over a Bayer-mask device is higher efficiency (and, therefore, higher light sensitivity for a given aperture size). This is because, in a 3CCD

Table of Contents Feed for the Digital Edition of Streaming Media - December 2008/January 2009

Streaming Media - December 2008/January 2009 Table of Contents User-Generated Politics Netflix Needs a Business Model Technology and Business Trends by the Numbers Improving Video Color Quality What Makes for Compelling Video? Game On: Bringing the NHL to IPTV Give! The New Era of Corporate Communications New Video Frontiers: Taking It Beyond the PC The HD Showdown: Codec Vendors Battle It Out for Supreme Quality The Ultimate Guide to Creating Online Video Content That Works, Part 2 Planning for Webcasting Success: Considerations for Deploying an Enterprise Video Communications Platform All Mobile Devices Are Not the Same Datmedia Datpresenter LSI Tarari Encoder Accelerator LCPX-6140 Gomez Active Streaming XF Transcoding for Global Reach Executive Visions 2009 The Revolution Is Being Televised

Streaming Media - December 2008/January 2009

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