The term post-processing (or postproc for short) is used in the video and film industry for quality-improvement
image processing (specifically
digital image processing) methods used in video playback devices, such as stand-alone
DVD-Video players; video playing 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.
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 and optionally
vertex shaders are then used to apply post-processing filters to the image buffer before displaying it to the screen. Some post-processing effects also require multiple-passes, gamma inputs, vertex manipulation, and
depth buffer access. 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: