Postprocessing

Or basically, "Photoshop filters but in games"

Postprocessing

• Edits to render of frame in 2D space
• Effectively: render 3D world to create one or more 2D textures
  • Color
  • Depth
  • Velocity
  • other information

Recombined again and again, using these textures to draw just a single screen-space quad

Basically,

• Just extending the 'vanilla' pipeline a little
• After drawing to clip space, don't immediately output to screen
  • Draw to a texture, bind this texture to a quad
  • Render quad (no need for clip space anymore, already there)
    • Lets us use fragment shader in creative ways
  • Repeat as necessary
  • Render final output to screen

HDR Tonemapping and Adaptive Luminance

• Render actual floats, not bytes
  • That is, render ranges outside of 0.0 to 1.0
    • Then scale back down afterwards
  • Change your render target format for this, API-dependent
• Find brightest pixel (Continual subsampling /2), scale that as 1.0
• LERP it over several frames

Scaling brightness:

• Brightness of a pixel =
  • 0.2126 * R + 0.7152 * G + 0.0722 * B
  • Or roughly around that, depending on spec
• Find brightest (faster to subsample from screen resolution to half of that resolution to half of THAT etc. instead of a linear search)
• Scale result
  • New pixel = old pixel RGBA * (old pixel luminance / max pixel luminance)

Why do this?

• Give artists/designers more freedom
  • Not 'capped' at 1.0 brightness
    • Image will scale dynamically, on its own
• If you linearly interpolate the 'target' max brightness, you can fake an effect our eyes do naturally: adjusting to brightly or darkly lit areas

Edge Operators

• Sobel probably most known
• Operate on several possible parameters:
  • Color (see: those embossing filters)
  • Depth (that 'Borderlands' look)

In Games

• Usually use Depth instead of Color as thing to measure for edges

Ambient Occlusion

Usually screen-space for real-time instead of 'true' AO

Shadowing around depth discontinuities

Random sampling of kernel around target pixel of depth texture

Output occlusion factor based on how many pass/fail

Multiply color texture by occlusion factor

Previous sobel operator similar, except just multiply by 0 instead of factor!

Cel-shading

AKA "Toon" shading

Clamp color to levels of saturation

Sometimes conflated with edge detection

Probably the simplest

Have bands of saturation

Clamp pixels to whichever band they fit in