Description This function will find edges on the input image by the Shen-Castan edge detection method. This function works for 8 and 24 bit per pixel images. Shen-Castan edge detector uses an optima filter function called Infinite Symmetric Exponential Filter (ISEF). This produces better signal to noise ratios and better localisation than Canny. First step is convolving the input image with the ISEF, then localization edges by zero crossing of the Laplacian (similar to the Marr-Hildreth algorithm). The approximation of Laplacian is computed by subtracting the original image from the smoothed one. The result is a band-limited Laplacian image. Next, a binary Laplacian image is generated by setting all the positive valued pixels to 1 and all others to 0. The candidate pixels are on the boundaries of the regions in th binary image. After improving the quality of edge pixels by false zero-crossing suppression, adaptive gradient thresholding and a hysteresis thresholding is applied finally.
Examples
The original 500 x 400 pixel image and the Shen-Castan edge detected image with fSF = 0.8, iLow = 20, iHigh = 22, fRatio = 0.99, iThinFactor = 0, iWndSize = 7 and bDoHysteresis = TRUE parameter values.
Syntax RetVal = [BiFilter.]FilterEdgeSC hDib dSF iLow iHigh dRatio iThinFactor iWndSize bDoHysteresis bShowDialog
Returns RetVal LONGLONG The handle of new filtered DIB, 0 if an error occurred, or -1 if the BIFilter.dll does not installed.
Remarks hDib LONGLONG Handle of the image to filter.
dSF Double Smoothing factor used by the IESF filtering. See the description and examples above for further information and a possible value.
iLow Long Low threshold value of hysteresis thresholding. See the description and examples above for further information and a possible value.
iHigh Long High threshold value of hysteresis thresholding. See the description and examples above for further information and a possible value.
dRatio double This parameter specifies the percents of pixels above the hysteresis thresholding. See the description and examples above for further information and a possible value.
iThinFactor Long Thinning factor (number of pixels). See the description and examples above for further information and a possible value.
iWndSize Long Size of window used by gradient thresholding. See the description and examples above for further information and a possible value.
bDoHysteresis BOOL Do hysteresis thresholding with iLow and iHigh thresholding values.
bShowDialog BOOL This parameter specifies the displaying of the preview dialog. IMPORTANT: The preview dialog will only display, if there is BiDlgs.dll installed
See Also