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What is Bilinear Interpolation?

Bilinear interpolation estimates a new pixel by applying linear interpolation across the four nearest source pixels in two dimensions. It offers moderate smoothing with relatively low computational cost.

How Bilinear Interpolation works

Bilinear interpolation locates an output sample within a source grid cell and blends the four corner samples according to horizontal and vertical distance. It performs a linear blend along one axis and then the other, although the combined surface includes an interaction between coordinates. The small neighborhood makes it fast and predictable but often softer during enlargement. Renderers use it for routine scaling, transforms, and texture sampling.

Key facts

  1. The weights of the four source samples sum to one for an interior point, preserving a constant-color region while smoothly changing influence across a grid cell.
  2. Bilinear filtering is separable, so implementations can interpolate horizontally and vertically in stages; this is useful for optimized image and texture pipelines.
  3. Because it cannot reconstruct frequencies lost or absent in the sample grid, large upscales show blur, and downscales still need adequate low-pass filtering to avoid aliasing.

When Bilinear Interpolation matters

Use bilinear interpolation for fast resizing, texture sampling, or geometric transforms where moderate quality is sufficient. Fine edges may blur, so detailed artwork can benefit from a higher-quality filter.

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