L_FrqFilterMaskBitmap

#include "l_bitmap.h"

L_INT EXT_FUNCTION L_FrqFilterMaskBitmap(pMaskBitmap, pFTArray, bOnOff)

pBITMAPHANDLE pMaskBitmap;	/* pointer to the Mask bitmap handle */
pFTARRAY pFTArray;	/* pointer to structure */
L_BOOL bOnOff;	/* flag */

Creates a mask filter to remove specific frequency components from a bitmap. This function is available in the Raster Pro and above toolkits.

Parameter	Description
pMaskBitmap	Pointer to the bitmap handle of the mask bitmap.
pFTArray	Pointer to an FTARRAY structure. The acxData field is a two-dimensional array holding the frequency components.
bOnOff	Value that indicates whether the frequency components are removed if the corresponding pixel value is zero. Possible values are:
	Value	Meaning
	TRUE	If the pixel value equals zero the frequency components in its location in acxData will be removed, otherwise no change. A component is "removed" when both members of the corresponding L_COMPLEX structure are set to 0.
	FALSE	The frequency component in the pixel location in acxData will be multiplied by the value of the pixel divided by 255.

Returns

SUCCESS	The function was successful.
< 1	An error occurred. Refer to Return Codes.

Comments

This function is used only when you are dealing with Fourier Transform functions.

The Mask bitmap will be treated as grayscale bitmap. The (0,0) frequency located in mask bitmap center; positive X harmonics located in the right half of the mask bitmap and positive Y harmonics located in the lower half of the mask bitmap. Mask bitmap’s dimensions must be equal to acxData’s dimensions.

To update a status bar or detect a user interrupt during execution of this function, refer to L_SetStatusCallback.

This function does not support 12 and 16-bit grayscale and 48 and 64-bit color images. If the image is 12 and 16-bit grayscale and 48 and 64-bit color, the function will not return an error.

This function does not support signed data images. It returns the error code ERROR_SIGNED_DATA_NOT_SUPPORTED if a signed data image is passed to this function.

Required DLLs and Libraries

LTIMG

For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application.

Platforms

Windows 95 / 98 / Me, Windows 2000 / XP.

See Also

Functions:	L_FFTBitmap, L_DFTBitmap, L_FTDisplayBitmap, L_FrqFilterBitmap, L_AverageFilterBitmap, L_MedianFilterBitmap, L_AddBitmapNoise, L_IntensityDetectBitmap, L_SpatialFilterBitmap, L_BinaryFilterBitmap, L_MaxFilterBitmap, L_MinFilterBitmap, L_AddBitmapNoise, L_IntensityDetectBitmap, L_SpatialFilterBitmap, L_BinaryFilterBitmap, L_MaxFilterBitmap, L_MinFilterBitmap, L_AddShadowBitmap, L_ChangeHueSatIntBitmap, L_ColorThresholdBitmap, L_DFTBitmap, L_AllocFTArray, L_DirectionEdgeStatisticalBitmap, L_FFTBitmap, L_FreeFTArray, L_FrqFilterBitmap, L_FrqFilterMaskBitmap, L_FTDisplayBitmap, L_GetBitmapStatisticsInfo, L_GetFeretsDiameter, L_GetObjectInfo, L_GetRgnContourPoints, L_GetRgnPerimeterLength, L_MathFunctionBitmap, L_RevEffectBitmap, L_SegmentBitmap, L_SubtractBackgroundBitmap, L_UserFilterBitmap, L_FragmentBitmap, L_HighPassFilterBitmap, L_UnsharpMaskBitmap
Topics:	Raster Image Functions: Fourier Transform
	Removing Noise

Example

/* This example cleans noise from an input data. It assumes the two bitmaps being loaded. It also assumes the acxData field of pFTArray structure is large enough to hold the frequency components. See the example for L_FFTBitmap to see how to allocate the acxData field*/
BITMAPHANDLE MaskBitmap, NoisyBitmap;
pFTARRAY pFTArray;

/* Load the noisy bitmap, keeping the bits per pixel of the file */
L_LoadBitmap(TEXT("NoisyXRay.CMP"), &NoisyBitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGR, NULL, NULL);

/* Load the mask bitmap, keeping the bits per pixel of the file */
L_LoadBitmap (TEXT("NoisyMask.CMP"), &MaskBitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGR, NULL, NULL);

/*Allocate FT buffer*/
L_AllocFTArray(&NoisyBitmap, &pFTArray, sizeof(FTARRAY));

/* Assume acxData field of pFTArray is the correct size*/
/* apply DFT*/
L_DFTBitmap(&NoisyBitmap, pFTArray, NULL, DFT_DFT | DFT_GRAY);

/* filter frequencies */
L_FrqFilterMaskBitmap(&MaskBitmap, pFTArray, TRUE);

/* apply inverse DFT */
/* After this call, the image should be clean */
L_DFTBitmap(&NoisyBitmap, pFTArray, NULL, DFT_IDFT | DFT_ALL| DFT_IDFT_SCL);