Declaration

procedure SelectiveGaussianBlur32(ASource, ADest: TBitmap32; Radius: TFloat; Delta: Integer);

Parameters

Parameter	Type	Description
ASource	TBitmap32	Source 32-bit bitmap to read pixels from.
ADest	TBitmap32	Destination 32-bit bitmap to receive the edge-preserved blurred output.
Radius	TFloat	Spatial blur radius in pixels.
Delta	Integer	Maximum color channel difference threshold (0..255).

Description

SelectiveGaussianBlur32 performs edge-preserving Gaussian blurring on 32-bit ARGB bitmaps.

Neighbor pixels within the spatial window (Radius) are accumulated into the weighted Gaussian sum only if their color channel difference from the center pixel is within the specified Delta threshold:

$$|C_{\text{sample}}-C_{\text{ref}}|\le \text{Delta}$$

Behavior Summary

• Preserving Details: Setting a modest Delta (e.g. $10\dots 30$) smooths noise, JPEG compression artifacts, and flat region variations while leaving sharp contrast edges completely intact.
• Alpha Channel: The Alpha channel is preserved without being blurred.

Example

var
  Src, Dst: TBitmap32;
begin
  Src := TBitmap32.Create;
  Dst := TBitmap32.Create;
  try
    Src.LoadFromFile('photo_noisy.png');

    // Smooth surface noise (Radius=4.0) while preserving sharp edges (Delta=15)
    SelectiveGaussianBlur32(Src, Dst, 4.0, 15);

    Dst.SaveToFile('photo_denoised.png');
  finally
    Src.Free;
    Dst.Free;
  end;
end;

See also

• GammaSelectiveGaussianBlur32
• Blur32