Built-in Filters

Built-in filters are ordinary MTIFilter implementations backed by render, compute, MPS, or Core Image kernels. They share the lazy image model. Alpha types, output extent, pixel format, and device capabilities still vary by filter. Two built-in filters are not interchangeable just because they share the same protocol.

Color and tone

These filters adjust color matrices, tone curves, transfer functions, lookup tables, and local contrast.

• MTIColorMatrixFilter applies a 4×4 color matrix and bias.
• MTIVibranceFilter adjusts saturation with skin-tone-aware behavior.
• MTIRGBToneCurveFilter evaluates per-channel tone curves.
• MTIRGBColorSpaceConversionFilter converts among supported RGB transfer functions.
• Image conveniences cover saturation, exposure, brightness, contrast, and vibrance adjustments.
• MTIColorLookupFilter applies supported 2D or 3D color lookup representations.
• MTICLAHEFilter performs local contrast-limited adaptive histogram equalization and supports explicit HDR headroom.

Blur, detail, and convolution

These filters cover Metal Performance Shaders blurs and edges, plus Raster's own detail and bokeh approximations.

• MTIMPSGaussianBlurFilter, MTIMPSBoxBlurFilter, and MTIMPSConvolutionFilter use Metal Performance Shaders.
• MTIMPSUnsharpMaskFilter, MTIMPSDefinitionFilter, and MTIMPSSobelFilter provide detail and edge operations.
• MTIHexagonalBokehBlurFilter builds a multi-pass bokeh approximation.
• MTIHighPassSkinSmoothingFilter combines high-pass detail separation with smoothing controls.

MPS-backed filters require context.isMetalPerformanceShadersSupported. Their exact numerical results can vary slightly across GPU families and SDK implementations. Tests that do not treat bit identity as part of the API should use tolerances.

Geometry and shape

These filters change viewport, crop, corners, distortion, and stylized sampling.

• MTITransformFilter applies 2D/3D transforms and controls the output viewport.
• MTICropFilter selects pixel or normalized regions.
• MTIRoundCornerFilter clips to circular or continuous corners.
• MTIBulgeDistortionFilter applies radial distortion.
• MTIPixellateFilter, MTIColorHalftoneFilter, and MTIDotScreenFilter create stylized sampling patterns.

Alpha and composition

These filters convert alpha representation and combine images through blends, masks, chroma keys, and layer stacks.

• MTIPremultiplyAlphaFilter and MTIUnpremultiplyAlphaFilter convert alpha representation.
• MTIBlendFilter combines one source with one background across the registered blend-mode set.
• MTIBlendWithMaskFilter controls a blend through a mask.
• MTIChromaKeyBlendFilter removes a keyed color and composites a background.
• MTIMultilayerCompositingFilter and its Swift MultilayerCompositingFilter surface compose ordered layers with transforms, masks, tint, corners, and blend modes.

Histogram and analysis

These filters produce or consume histogram data.

• MTIMPSHistogramFilter produces histogram data through MPS.
• MTICLAHEFilter builds local histograms internally and applies their lookup tables to the image.

Core Image coverage

MTICoreImageUnaryFilter is a bridge that makes the broader CIFilter catalogue available inside a Raster graph. Each Core Image filter still brings its own alpha, extent, and optimization behavior. Generators and infinite-extent filters need a finite output size. Adjacent Core Image work can stay in Core Image until the result returns to Raster.

Blend modes

The built-in registry contains:

• normal
• darken, multiply, color burn, linear burn, and darker color
• lighten, screen, color dodge, add, and lighter color
• overlay, soft light, hard light, vivid light, linear light, pin light, and hard mix
• difference, exclusion, subtract, and divide
• hue, saturation, color, and luminosity
• the 512×512 color-lookup mode

Custom modes can be registered with MTIBlendFunctionDescriptors. Their blend function is the two-argument float4 blend(float4 backdrop, float4 source).