The term post-processing (or postproc for short) is used in the video/film business for quality-improvement image processing

Image processing

In electrical engineering and computer science, image processing is any form of signal processing for which the input is an image, such as a photograph or video frame; the output of image processing may be either an image or, a set of characteristics or parameters related to the image...

 (specifically digital image processing

Digital image processing

Digital image processing is the use of computer algorithms to perform image processing on digital images. As a subcategory or field of digital signal processing, digital image processing has many advantages over analog image processing...

) methods used in video playback devices, (such as stand-alone DVD-Video

DVD-Video

DVD-Video is a consumer video format used to store digital video on DVD discs, and is currently the dominant consumer video format in Asia, North America, Europe, and Australia. Discs using the DVD-Video specification require a DVD drive and a MPEG-2 decoder...

 players), and video players software and transcoding software. It is also commonly used in real-time 3D rendering

3D rendering

3D rendering is the 3D computer graphics process of automatically converting 3D wire frame models into 2D images with 3D photorealistic effects on a computer.-Rendering methods:...

 (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

Image scaling

In computer graphics, image scaling is the process of resizing a digital image. Scaling is a non-trivial process that involves a trade-off between efficiency, smoothness and sharpness. As the size of an image is increased, so the pixels which comprise the image become increasingly visible, making...

 routines such as linear interpolation

Linear interpolation

Linear interpolation is a method of curve fitting using linear polynomials. Lerp is an abbreviation for linear interpolation, which can also be used as a verb .-Linear interpolation between two known points:...

, bilinear interpolation

Bilinear interpolation

In mathematics, bilinear interpolation is an extension of linear interpolation for interpolating functions of two variables on a regular grid. The interpolated function should not use the term of x^2 or y^2, but x y, which is the bilinear form of x and y.The key idea is to perform linear...

, or cubic interpolation can for example be performed when increasing the size of images, this involves either subsampling

Downsampling

In signal processing, downsampling is the process of reducing the sampling rate of a signal. This is usually done to reduce the data rate or the size of the data....

 (reducing or shrinking an image) or zooming

Digital zoom

Digital zoom is a method of decreasing the apparent angle of view of a digital photographic or video image. Digital zoom is accomplished by cropping an image down to a centered area with the same aspect ratio as the original, and usually also interpolating the result back up to the pixel...

 (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
  Image scaling
  In computer graphics, image scaling is the process of resizing a digital image. Scaling is a non-trivial process that involves a trade-off between efficiency, smoothness and sharpness. As the size of an image is increased, so the pixels which comprise the image become increasingly visible, making...
  
   and multivariate interpolation
  Multivariate interpolation
  In numerical analysis, multivariate interpolation or spatial interpolation is interpolation on functions of more than one variable.The function to be interpolated is known at given points and the interpolation problem consist of yielding values at arbitrary points .-Regular grid:For function...
  
  :
  • Nearest-neighbor interpolation
  • linear interpolation
    Linear interpolation
    Linear interpolation is a method of curve fitting using linear polynomials. Lerp is an abbreviation for linear interpolation, which can also be used as a verb .-Linear interpolation between two known points:...
    
    
  • bilinear interpolation
    Bilinear interpolation
    In mathematics, bilinear interpolation is an extension of linear interpolation for interpolating functions of two variables on a regular grid. The interpolated function should not use the term of x^2 or y^2, but x y, which is the bilinear form of x and y.The key idea is to perform linear...
    
    
  • cubic interpolation
  • bicubic interpolation
    Bicubic interpolation
    In mathematics, bicubic interpolation is an extension of cubic interpolation for interpolating data points on a two dimensional regular grid. The interpolated surface is smoother than corresponding surfaces obtained by bilinear interpolation or nearest-neighbor interpolation...
    
    
  • Bézier surface
    Bézier surface
    Bézier surfaces are a species of mathematical spline used in computer graphics, computer-aided design, and finite element modeling.As with the Bézier curve, a Bézier surface is defined by a set of control points...
    
    
  • Lanczos resampling
    Lanczos resampling
    Lanczos resampling is an interpolation method used to compute new values for sampled data. It is often used in multivariate interpolation, for example for image scaling , but can be used for any other digital signal...
    
    
  • trilinear interpolation
    Trilinear interpolation
    Trilinear interpolation is a method of multivariate interpolation on a 3-dimensional regular grid. It approximates the value of an intermediate point within the local axial rectangular prism linearly, using data on the lattice points...
    
    
  • Tricubic interpolation
    Tricubic interpolation
    In the mathematical subfield numerical analysis, tricubic interpolation is a method for obtaining values at arbitrary points in 3D space of a function defined on a regular grid...
    
    
• SPP (Statistical-Post-Processing)
• Deblocking
  Deblocking filter (video)
  A deblocking filter is a video filter applied to blocks in decoded video to improve visual quality and prediction performance by smoothing the sharp edges which can form between macroblocks when block coding techniques are used...
  
  
• Deringing
• Sharpen / Unsharpen (often referred to as "soften")
• Requantization
• Luminance alterations
• Blurring / Denoising
• Deinterlacing
  Deinterlacing
  Deinterlacing is the process of converting interlaced video, such as common analog television signals or 1080i format HDTV signals, into a non-interlaced form....
  
  
  • weave deinterlace method
  • bob deinterlace method
  • linear deinterlace method
  • yadif deinterlace method
• Deflicking
  Deflicking
  In video processing, deflicking is a filtering operation applied to brightness flicker in video to improve visual quality. The flicker effect can be seen when camera framerate and lighting frequency are not adjusted or in video digitized old film...
  
  
• 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
  Telecine
  Telecine is transferring motion picture film into video and is performed in a color suite. The term is also used to refer to the equipment used in the post-production process....
  
   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

3D rendering

3D rendering is the 3D computer graphics process of automatically converting 3D wire frame models into 2D images with 3D photorealistic effects on a computer.-Rendering methods:...

, 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

Video card

A video card, Graphics Card, or Graphics adapter is an expansion card which generates output images to a display. Most video cards offer various functions such as accelerated rendering of 3D scenes and 2D graphics, MPEG-2/MPEG-4 decoding, TV output, or the ability to connect multiple monitors...

. 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
  High dynamic range rendering
  In 3D computer graphics, high dynamic range rendering , also known as high dynamic range lighting, is the rendering of computer graphics scenes by using lighting calculations done in a larger dynamic range. This allows preservation of details that may be lost due to limiting contrast ratios...
  
  
• Bloom
  Bloom (shader effect)
  Bloom is a computer graphics effect used in computer games, demos and high dynamic range rendering to reproduce an imaging artifact of real-world cameras. The effect produces fringes of light around very bright objects in an image, obscuring fine details...
  
  
• Motion blur
  Motion blur
  Motion blur is the apparent streaking of rapidly moving objects in a still image or a sequence of images such as a movie or animation. It results when the image being recorded changes during the recording of a single frame, either due to rapid movement or long exposure.- Photography :When a camera...
  
  
• Screen Space Ambient Occlusion
  Screen Space Ambient Occlusion
  Screen Space Ambient Occlusion is a rendering technique for efficiently approximating the well-known computer graphics ambient occlusion effect in real time...
  
  
• Cel shading
• Crepuscular rays
  Crepuscular rays
  Crepuscular rays , in atmospheric optics, are rays of sunlight that appear to radiate from a single point in the sky. These rays, which stream through gaps in clouds or between other objects, are columns of sunlit air separated by darker cloud-shadowed regions...
  
  
• Film grain
  Film grain
  Film grain or granularity is the random optical texture of processed photographic film due to the presence of small particles of a metallic silver, or dye clouds, developed from silver halide that have received enough photons. While film grain is a function of such particles it is not the same...
  
   simulation
• Depth of field
  Depth of field
  In optics, particularly as it relates to film and photography, depth of field is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image...
  
  
• Shadow mapping
  Shadow mapping
  Shadow mapping or projective shadowing is a process by which shadows are added to 3D computer graphics. This concept was introduced by Lance Williams in 1978, in a paper entitled "Casting curved shadows on curved surfaces"...
  
  

External links

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