Texture filtering

From Emulation General
Jump to: navigation, search
A comparison between nearest neighbor scaling and HQ2x scaling

In computer graphics, texture filtering or texture smoothing is the method used to smooth textures used in 3D models. Some consoles use texture filtering.

In emulation, texture filtering can be applied even if the original console did not use it. Many emulators support such features.

Consoles[edit]

Console Texture Filtering Types of filtering
Super Nintendo
3DO ?
Atari Jaguar
Sega Saturn
PlayStation
Nintendo 64 Three-sample
Sega Dreamcast Bilinear, trilinear, anisotropic
PlayStation 2 Bilinear, trilinear, Anisotropic
GameCube Bilinear, trilinear, anisotropic
Xbox Bilinear, trilinear, anisotropic
Nintendo DS ?
PlayStation Portable Bilinear, trilinear
Wii Bilinear, trilinear, anisotropic

Types of Texture Filtering[edit]

Filtering type What it does Pros Cons
Nearest neighbor This method sorts pixels into the nearest place relevant to it's placement in the original resolution, in order to display the image at whatever resolution you specify.
  • Very fast.
  • At integer values (eg, exactly double or quadruple resolution) it's practically "unfiltered".
  • Unfiltered pixels tend to look odd, with some being thicker than others. This can result in pixel art losing clarity, and text may become hard to read.
Bilinear This linear filtering method uses color data from the pixels in a nearest-neighbor texture, and combines multiple bits of color data in order to replace some of the pixels with an averaged-out version of the colors, so that the colors gradually switch rather than jump to a new color.
  • Looks better than nearest neighbor for 3D games.
  • It's the least system-intensive form of texture filtering/scaling.
  • At low resolutions, 2D games tend to become very blurry. This is especially noticeable in 2D games, and low res 3D games.
  • If you have the hardware to do so, look into more complex filtering methods to preserve clarity.
Trilinear This linear filtering method does the same thing as bilinear filtering, except it passes through twice, giving a smoother gradient.
  • Looks better than bilinear filtering for 3D games.
  • As with bilinear, low resolution games will more than likely appear overly blurry using this method.
HQx A texture scaling algorithm. Scales up a nearest-neighbor version of the texture and fills in the gaps with copies of the pixels next to said gaps.
  • While it is inherently destructive, some games (eg. Yoshi's Island) may benefit from this filter, as it preserves the cartoony look.
  • Artifacts are common.
  • Curves and slopes that aren't 45­° look jagged compared to everything else.
  • The finer details of the textures/sprites might be obscured by bad edge detection.
  • Posterization is very common. There are deposterization filters in some emulators (e.g. PPSSPP) that can aid this, however.
  • Worse at some things that xBR excels at.
2xSaI A texture scaling algorithm. Scales the texture and fills edges in with a mixture of pixels taken from the source and randomly-guessed colors.
  • Less system-intensive than HQx and xBR.
  • Adequate if it's the best option available (e.g. in Pete's OpenGL2 plugin for PSX emulators).
  • Edge detection is horrible.
  • Artifacts are common.
  • Posterization is very common.
  • Archaic. The alternatives are much better.
xBR A modified version of HQx. It detects edges better, which works better for curved lines, or for slopes that are greater than/less than 45 degrees.
  • Looks great for many 2D games.
  • Edge detection is improved over HQx. This gives textures smoother curves and slopes, as well as fewer artifacts.
  • 3D games look great with it as well.
  • Posterization is common. There are deposterization filters in some emulators (e.g. PPSSPP) that can aid this, however.
  • The finer details of the textures/sprites might be obscured by bad edge detection.
  • Worse at some things that HQx excels at.
xBRZ A modified version of xBR, which is very similar except it's better at scaling up smaller features consisting of <10 pixels.
  • Looks great for many 2D games.
  • Detects small features that get messed up by HQx and xBR.
  • 3D games look great with it as well.
  • Posterization is common. There are deposterization filters in some emulators (e.g. PPSSPP) that can aid this, however.
  • Worse at some things the other scalers excel at.

Durante's Hybrid and Deposterization Filters for PPSSPP[edit]

PPSSPP has a scaling option known as "Hybrid." There's also an option called "Deposterize." Posterization, meaning a sharp contrast in hue from one pixel to another (very common in low-quality gifs) has been a problem plaguing texture scaling algorithms for quite some time. Durante's filter switches between xBR and bilinear/bicubic filtering depending on the texture information. On top of this, the "Deposterize" option tackles posterization edges in compressed textures, allowing for a smooth gradient rather than a sharp transition. Although it's not perfect (a perfect scaler sadly isn't possible with today's computing power) it's still great and it's recommended to use for PPSSPP if you have the specs.

Images[edit]


Further reading[edit]

Wikipedia's entry on Texture Filtering

Forum post from the creator of xBR, explaining how the algorithm works (Warning: is slightly hard to read due to the amount of jargon and big words)

A blog entry by Durante on creating a hybrid texture filter for PPSSPP.