Post-processing

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See also: Post-production

Post-processing is used in Differential GPS to obtain precise positions of unknown points by relating them to known points such as survey markers. The term post-processing in the video/film buisness for quality-improvement methods used in video playback devices, (such as stand-alone DVD-Video players).

[edit] Differential GPS post-processing

The GPS measurements are usually stored in computer memory in the GPS receivers, and are subsequently transferred to a computer running the GPS post-processing software. The software computes baselines using simultaneous measurement data from two or more GPS receivers.

The baselines represent a three-dimensional line drawn between the two points occupied by each pair of GPS antennas. The post-processed measurements allow more precise positioning, because most GPS errors affect each receiver nearly equally, and therefore can be cancelled out in the calculations.

Differential GPS measurements can also be computed in real-time by some GPS receivers if they receive a correction signal using a separate radio receiver, for example in Real Time Kinematic (RTK) surveying or navigation.

[edit] Video post-processing

Video post-processing is the process of changing the precieved quality of a video on playback (done after the decoding process). Image scaling routines such as linear interpolation, bilinear interpolation, or cubic interpolation) can for example be prefored when increasing the size of images, this involves either subsampling (reducing or shrinking an image) or zooming (enlarging an image). This helps reduce or hide image artifact and flaws in the original film material. It is important to understand that post-processing always involves a trade-off between speed, smoothness and sharpness.

[edit] Post-processing routines

• [Image scaling]]:
  • linear interpolation
  • bilinear interpolation
  • cubic interpolation)
  • bicubic interpolation
  • trilinear interpolation
• SSP (Statistical-Post-Processing)
• Deblocking
• Deringing
• Sharpen / Unsharpen (often refered to as "soften")
• Requantization
• Luminance alterations
• Blurring / Denoising
• Deinterlace
  • weave deinterlace method
  • bob deinterlace method
• 2:3 pull-down / ivtc (inverse telecine) for conversion from 24 frames-per-seconds to 30 frames-per-seconds
• 3:2 pull-up (telecine conversion) for conversion from 30 frames-per-seconds to 24 frames-per-seconds

[edit] External links

• Videotranscoding Wiki -(documentation on server-side usage of MPlayer for transcoding)

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