> ## Documentation Index
> Fetch the complete documentation index at: https://docs.abbyy.com/llms.txt
> Use this file to discover all available pages before exploring further.

# ApplySigmaFilter Method of the ImageDocument Object

This method applies a noise reducing filter to the image. It is mostly useful for photographs.

We recommend experimenting on typical input images to find the parameter values which would work best for you, starting with Radius equal to 15 and Threshold equal to 3.0.

## Syntax

### C++

```cpp theme={null}
HRESULT ApplySigmaFilter(
  int    Radius,
  double Threshold
);
```

### C\#

```csharp theme={null}
void ApplySigmaFilter(
  int    Radius,
  double Threshold
);
```

### Visual Basic .NET

```vb theme={null}
Sub ApplySigmaFilter( _
  Radius As Integer, _
  Threshold As Double _
)
```

## Parameters

**Radius**

\[in] The smoothing radius. Should be in the range from 15 to 30.

**Threshold**

\[in] The noise intensity threshold. Should be in the range from 3 to 5.

## Return values

This method has no specific return values. It returns the [standard return values of ABBYY FineReader Engine functions](/fine-reader/engine/api-reference/return-codes).

## See also

[ImageDocument](/fine-reader/engine/api-reference/image-related-objects/imagedocument)