|Sony KDL-46Z4100 LCD HDTV|
|Home Theater Flat Panel HDTVs LCD HDTVs|
|Written by Tom Volotta|
|Thursday, 30 April 2009|
Page 6 of 9Motion Processing
There are parts of this that have to be some of the more complicated, least understood and most hyped aspects of modern television technology. It’s one of those areas that seem to make sense when first explained, but it can quickly get confusing. Notions like film and video running at 24 and 30 frames per second, 60 field per second video, 2:3 pulldown, 3:2 pulldown, inverse telecine, judder, interlaced, progressive, high speed electronically enhanced frame rates of 60, 72, 120 and 240 Hz, frame interpolation and more. Add the manufacturer’s various trade names for these processes (we’ll be talking about Sony’s Motionflow™ and CineMotion®) and it just about gives you a headache trying to keep it all straight.
The purpose of all this is to overcome the technical obstacles of integrating various formats with seemingly conflicting characteristics, in order to make the moving pictures on your TV screen look as accurate and smooth as possible. A simple concept, but the implementation is not, and is the subject of controversy and disagreement among amateurs and professionals alike. Count me as one who gets the basics, but has to pull out the manuals and draw little pictures on the back of an envelop to understand the many intricacies that compose this black art.
Many of the problems, typically seen as a stuttering motion or judder, blurring or smearing is due to objects moving quickly within the frame or the movement of the camera by tracking or panning are a reflection of the inherent constraints in creating media through electro-mechanical devices. The natural world does not have a frame rate.
Motion picture film has been exposed and projected at 24 frames per second for decades. This frame rate was arrived at largely through a trial & error process which took both the minimum number of frames per second necessary to convey relatively smooth motion to the human brain, and the economics of purchasing and processing the amount of film stock required for production and distribution. The previous, silent movie era standard of 18 fps left frame-to-frame motion gaps that was unacceptable, and became more so when soundtracks were added. Much higher film frame rates have been experimented with constantly, and nearly unimaginable speeds in the millions of frames per seconds can be achieved in certain scientific settings - but that a whole other universe. Several years ago, Douglas Trumbull (One of the special effects supervisors on Stanley Kubrick’s 2001: A Space Odyssey. Trumbull was responsible for the slit-scan camera technique for the famous “Star Gate” sequence flying through the psychedelic colors and shapes of the universe.) developed the Showscan process. Showscan shot 65mm film at 60 frame per second, then projected 70mm prints at 60 fps to create a greatly heightened sense of realism by capturing and playing high resolution images as such a fast frame rate. Although not a commercial success in the theatrical market because of the prohibitively high cost, Showscan is still used for motion simulation rides and specialty applications such as theme parks, science centers, etc.
Because of the 60Hz electrical system in the United States, video was designed to run at 30 frames per second - actually, each video frame is composed of two interlaced partial frames called fields, each 1/60 of a second in duration. The first field is labeled and ‘odd’ the second as ‘even.’ How does film’s 24 fps fit into video’s 30 fps? The six-frame difference between 24 and 30 is accommodated through the process of playing back the film through a telecine device to record onto video. This results in a repetitive sequence where every other frame of film being recorded onto the video as three fields instead of the normal film frame filling two fields of video. This pattern of 1 frame of film onto 2 fields of video, then the next frame of film onto 3 video fields is repeated for the duration of the program, and is referred to a 2:3 pulldown (aka 3:2 pulldown). To complicate things, the telecine process also introduces a mixing of different film frames within the same video frame. Since the images are constantly moving, the very slight offset and overlapping mixing of different film frames into the same video frame, along with almost imperceptible variations in speed, typically isn’t a problem for normal viewing. However, with the superior image quality of modern displays, a wide range of standard and high definition resolutions, combining progressive scan and interlaced media, along with specialized compression & decompression techniques to store and playback content, flaws are amplified to the point where countermeasures need to be employed.
There are two main categories of motion processing: High frame rate scanning to help reduce blur and generally increase clarity, and special detection and processing of film-based material. Sony calls these Motionflow™ and CineMotion® respectively.
The 120Hz frame rates so popular now with LCD displays is what Motionflow is about. By repeating the number of images displayed per second, content will appear somewhat smoother with less blurring. Of course, motion blur is part of what makes film and video seem natural, so the notion of completely eliminating blur is not completely sought after.
120Hz Motionflow is always functioning in the 46Z4100, but through the Motion Enhancer control, you can increase its effect in Standard and High modes. When set to High, the interpolation circuit is activated which analyzes the differences in motion between two sequential frames, then reconstruct a new, intermediate frame, inserts it and play it back between the two originals, smoothing out the action. This is similar to computer animation techniques that use “key framing” to automate the animation and rendering process. Basically, only significant action points on a path of movement will be created as original images. Once the behavior of the object and the surrounding elements are plotted and the various shading, gravity and other dynamics accounted for in the computer, the intermediate frames between the key frames will be generated automatically from the calculations. The Sony 46Z4100 does something similar, actually analyzing the difference between sequential frames, then making new, intermediate frames on the fly. Pretty amazing! However some people may not like what is termed a smoother, more ‘video’ like result. Compression artifacts in backgrounds can also be generated on High, depending greatly on the nature of the content material and the quality being feed into the TV.