HD graphics
Aug 1, 2006 12:00 PM, BY NIR GOSHEN
For the stations that have made the transition to digital facilities, generating HD graphics often remains a challenge. Stations usually have a large library of graphics designed specifically for SD material used repeatedly on news and sports broadcasts, as well as in interstitials.
Unfortunately, there is no straightforward way of generating video by an SD graphics system to HD. Scaling up an SD signal with 4:3 aspect ratio to an HD signal with 16:9 aspect ratio will both blur the graphic and stretch it horizontally. For example, a sharp SD circle will look like a blurred oval on an HDTV set. While there is still a large audience for analog or SD signals, you don't want to alienate the HD audience. Fortunately, there are ways to make both sets of viewers happy.
Resolution-independent
The graphic system should be resolution-independent, meaning that the images are implemented as vectors rather than raster-based. This allows the shapes and colors to be mathematical formulas residing in the brains of the software, and they are rendered (or created) as pixels at the desired frame rate.
For example, a circle that fills half the screen renders as 320 × 320 pixels, and a twice-larger circle renders at 640 × 640. Both circles are based on the same mathematical formula, but are handed over to the video board as a different area of pixels, so the edges maintain sharpness.
This is the case with material (color) when applied to geometrical objects. Following the same concept, materials are also represented by formulas and rendered in real time. This process maintains the desired resolution and image smoothness and sharpness while preventing color banding. The material will calculate its color values per frame and interpolate the values it allocates to pixels based on the size the shape takes on the screen.
Editing and playout
Once you have an engine that can create the high-resolution graphics, the next step is to provide both editing and playout control over them. Stations sometimes employ two types of control systems. One focuses on content creation tasks, and the other focuses on graphics playout.
Broadcasters may consider deploying either or both platforms, depending on the needs of their organization. It's typically recommended that the CG system reside on top of the same render engine so the control room operator sees precisely how the next graphics fit on-screen and can see immediately if safe limits are exceeded.
An important characteristic in a graphics design environment is the wysiwyg (i.e., what you see is what you get) aspect. Without this feature, the designer has to guess how the graphics will look in the final output. For example, take a designer who is trying to compensate for the anemographic distortion between 4:3 and 16:9 images without the benefit of both types of viewers to see the images. Without the wysiwyg capability, the designer may end up with either great-looking SD or HD graphics, but seldom both. In a multiformat environment, maintaining the wysiwyg capability during the design process can save many working hours and result in more compatible images over different types of TV screens.
Once a new graphics hardware and software platform has been installed, the art of graphic design can be tackled. When broadcasting graphics in multiple video formats, there are three main challenges (in increasing order of difficulty): frame rate, resolution and aspect ratio.
Frame rate
When graphics systems handle animation speed independently from frame rate, no special considerations are needed for graphics without animation. Broadcasters adopting an HD standard with the same frame rate as their existing SD standard will incur no frame rate issues.
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