Subtracts the live (destination) bitmap from the mask (source) bitmap to show the differences between the two bitmaps.


#include "ltwrappr.h"

virtual L_INT LBitmap::DigitalSubtract (pMaskBitmap, uFlags)

virtual L_INT LBitmap::DigitalSubtract (plMaskBitmap, uFlags)



Pointer to the bitmap handle referencing the mask bitmap. The mask bitmap is the source bitmap. pMaskBitmap will not be affected.

L_UINT 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.

LBitmapBase *plMaskBitmap

Pointer to the bitmap object referencing the mask bitmap. The mask bitmap is the source bitmap. plMaskBitmap will not be affected.


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


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 LBase::EnableStatusCallback.

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 32-bit grayscale images. It returns the error code ERROR_GRAY32_UNSUPPORTED if a 32-bit grayscale image is passed to this function.

The sign flag in the BITMAPHANDLE structure must be the same for all images listed. That is, all images must be either signed or unsigned.

Digital Subtraction Angiography Function - Before

Digital Subtraction Angiography Function - Before

Digital Subtraction Angiography Function - After

Digital Subtraction Angiography Function - After

View additional platform support for this Digital Subtraction Angiography function.

Required DLLs and Libraries


Win32, x64.

See Also




L_INT LBitmap__DigitalSubtractExample(LBitmap *pLeadBitmap, LBitmap *pMaskBmp)  
   /* This example performs digital subtraction. */ 
   return pLeadBitmap->DigitalSubtract (pMaskBmp, DS_CONTRASTENH);  
   // Now we have the resulting image in LiveBmp 
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