Video post-processing

The term post-processing (or postproc for short) is used in the video/film business for quality-improvement image processing (specifically digital image processing) methods used in video playback devices, (such as stand-alone DVD-Video players), and video players software and transcoding software. It is also commonly used in real-time 3D rendering (such as in video games) to add additional effects.

Uses in video production

Video post-processing is the process of changing the perceived 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 performed 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 artifacts 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.

• Image scaling and multivariate interpolation:
  • Nearest-neighbor interpolation
  • linear interpolation
  • bilinear interpolation
  • cubic interpolation
  • bicubic interpolation
  • Bézier surface
  • Lanczos resampling
  • trilinear interpolation
  • Tricubic interpolation
• SPP (Statistical-Post-Processing)
• Deblocking
• Deringing
• Sharpen / Unsharpen (often referred to as "soften")
• Requantization
• Luminance alterations
• Blurring / Denoising
• Deinterlacing
  • weave deinterlace method
  • bob deinterlace method
  • linear deinterlace method
  • yadif deinterlace method
• Deflicking
• 2:3 pull-down / ivtc (inverse telecine) for conversion from 24 frames/s and 23.976 frames/s to 30 frames/s and 29.97 frames/s
• 3:2 pull-up (telecine conversion) for conversion from 30 frames/s and 29.97 frames/s to 24 frames/s and 23.976 frames/s

Uses in 3D rendering

Additionally, post-processing is commonly used in 3D rendering, especially for video games. Instead of rendering 3D objects directly to the display, the scene is first rendered to a buffer in the memory of the video card. Pixel shaders are then used to apply post-processing filters to the image buffer before displaying it to the screen. Post-processing allows effects to be used that require awareness of the entire image (since normally each 3D object is rendered in isolation). Such effects include:

• High dynamic range rendering
• Bloom
• Motion blur
• Screen Space Ambient Occlusion
• Cel shading
• Crepuscular rays
• Film grain simulation
• Depth of field
• Shadow mapping

See also

• Post-production

External links

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