L_DigitalSubtractBitmap

L_INT EXT_FUNCTION L_DigitalSubtractBitmap (pBitmap, pMaskBitmap, uFlags);

pBITMAPHANDLE pBitmap;	/* pointer to the destination, live, bitmap handle */
pBITMAPHANDLE pMaskBitmap;	/* pointer to the source mask bitmap handle */
L_UINT uFlags;	/* flags that specify how to process the bitmap */

Subtracts the live (destination) bitmap from the mask (source) bitmap to show the differences between the two bitmaps. This function is available in the Medical and above toolkits.

Parameter	Description
pBitmap	Pointer to the bitmap handle referencing the live bitmap. The live bitmap is the destination bitmap that will contain the result of the subtraction.
pMaskBitmap	Pointer to the bitmap handle referencing the mask bitmap. The mask bitmap is the source bitmap. pMaskBitmap will not be affected.
uFlags	Flags that control how the function works. Valid values are 0 (which means no enhancement), one or both of the following values:
	Value	Meaning
	DS_CONTRASTENH	[0x0001] Perform a contrast enhancement after applying the subtraction.
	DS_OPTIMIZERANGE	[0x0002] Optimize and increase the tonal range of the bitmap after applying the subtraction.

Returns

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

Comments

Performs a digital subtraction between two images. The resulting image may be enhanced using the uFlags options. Digital subtraction is mainly used to show the differences or the changes between two images. For the process to be meaningful both images should be related to each other. Digital Subtraction Angiography (DSA) is a practical example of digital subtraction.

Digital Subtraction Angiography (DSA) and Quality Control (QC) are both major fields that use image subtraction. An example of DSA is explained below.

DSA is a technology used for the visualization of blood vessels in the human body. A mask image is obtained using X-ray film of the body part of interest. Then vessels of that part are injected using a contrast medium. A sequence of images is taken after the injection. These are called live images. After applying subtraction between the mask and live images the resulting images are images that show the passage of the contrast medium in the vessels.

Both pBitmap and pMaskBitmap should have the same bits per pixel, number of channels and image dimensions; otherwise the function will return an error code.

If DS_CONTRASTENH flag is set then the contrast of the subtracted image will be enhanced.

If DS_OPTIMIZERANGE flag is set then the tonal range of the subtracted image will be optimized. That is, the image intensity will be distributed among the full image intensity range.

The result of the subtraction is placed in pBitmap.

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

This function supports 12 and 16-bit grayscale and 48 and 64-bit color images. Support for 12 and 16-bit grayscale and 48 and 64-bit color images is available only in the Document/Medical toolkits.

It also can process the whole image or a region of the image. If a bitmap has a region, the effect is applied only to the region.

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.

Functions:	L_ShiftBitmapData, L_SelectBitmapData, L_ColorizeGrayBitmap, L_MultiScaleEnhancementBitmap, L_CombineBitmap
Topics:	Raster Image Functions: Modifying Intensity Values
	Processing an Image