Lost in Translation: Going from TV to PC
Pixel-squareness artifacts can be mitigated during the scaling process. But they are one more variable that may contribute to imaging problems. People should not look a little chubby or a little thin because of pixel-shape distortion; after a while the distorted images will become annoying.
Viewing Distance
Viewing environments have an impact on image quality. Viewing distances for TV are measured in feet and range from 5'' to 6'–10' or greater. PC is in a "lean forward" activity; distances are measured in inches, with 18" to 24" being the norm.
Television systems have been designed with strict attention to the characteristics of the human visual system. Optimal viewing distance is based on the ability of the eye to resolve detail. The accepted figure is 1 minute of arc. The calculations produce an optimal viewing distance for HD images at three times the picture height. At this distance, pixels are at the threshold where their distinction just disappears. If you are any closer, you can see each pixel; any farther away and image detail is lost.
Now consider viewing a full-screen HD image on a PC. Place the viewer 18" from a 19" diagonal display. Three times the picture height is about 30". At this distance, individual pixels are visible, and artifacts that would be masked, based on perceptual characteristics leveraged in DTV system design, degrade the image.
Scanning Method
An additional step in the image conversion process is sometimes necessary to convert interlaced video from 1080i and 480i broadcast sources to progressive scanning for a PC. Temporal resolution is lost because of the 1/60 interval between field 1 and field 2. Unless a PC decoder has implemented sophisticated motion estimation and compensation processing, image quality will suffer some form of loss of resolution.
Motion Blur
Sharpness controls in pixel grid-based displays actually reduce image quality. If the native resolution of a display is 1280x720 and the source video is also 1280x720, sharpness enhancement attempts to add detail where there is none.
This can lead to motion blur, where a static image detail is noticeably lost when there is movement in the image. Turn the sharpness off for the best picture. Usually a PC display will be set to some degree of sharpness enhancement, adding to image-quality loss.
Display-Image Quality
With the demise of CRT displays, image quality has taken a severe hit. Regardless of the aesthetics and form-factor convenience of flat-panel displays, even consumer DTV receivers do not provide the image quality that’s possible with a CRT. As much of a problem as this is in consumer environments, in professional media production and broadcast operations, it has proven to be a nearly insurmountable impediment to having confidence that content is being released at the highest quality possible. Content is rigorously quality controlled both during production and as it is broadcast. Only recently have "reference-grade" LCD monitors appeared in the professional broadcast equipment marketplace. They also carry a hefty price tag.
Still, many "golden-eyed" industry veterans can see the difference between CRT images and images produced by any flat-panel technology. In some instances, this has led to the installation of broadcast-quality CRT monitors at key points, such as production control rooms. This has facilitated confidence in image quality that is taken to air.
Processing Chain Sequence
Image processing is not transitive. It is not sufficient to simply perform image decoding, reconstruction, and presentation processes; the order in which the processes occur influences image quality. Algorithms and processing sequences that are optimized for one display may produce artifacts on another.
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