Operators |
corner_response — Searching corners in images.
corner_response(Image : ImageCorner : Size, Weight : )
The operator corner_response extracts gray value corners in an image. The formula for the calculation of the response is:
R(x,y) = A(x,y) B(x,y) - C^2(x,y) - Weight (A(x,y) + B(x,y))^2 __ 2 A(x,y) = W(u,v) * (\/x I(x,y)) __ 2 B(x,y) = W(u,v) * (\/y I(x,y)) __ __ C(c,y) = W(u,v) * (\/x I(x,y) \/y I(x,y)) A and B are the smoothed directional derivatives and C is the smoothing of the products of the directional derivatives,
where I is the input image and R the output image of the filter. The operator gauss_image is used for smoothing (W), the operator sobel_amp is used for calculating the derivative.
The corner response function is invariant with regard to rotation. In order to achieve a suitable dependency of the function R(x,y) on the local gradient, the parameter Weight must be set to 0.04. With this, only gray value corners will return positive values for R(x,y), while straight edges will receive negative values. The output image type is identical to the input image type. Therefore, the negative output values are set to 0 if byte images are used as input images. If this is not desired, the input image should be converted into a real or int2 image with convert_image_type.
Input image.
Result of the filtering.
Number of elements: ImageCorner == Image
Desired filtersize of the graymask.
Default value: 3
List of values: 3, 5, 7, 9, 11
Weighting.
Default value: 0.04
Typical range of values: 0.0 ≤ Weight ≤ 0.3
Minimum increment: 0.001
Recommended increment: 0.01
read_image(&Fabrik,"fabrik"); corner_response(Fabrik,&CornerResponse,3,0.04); local_max(CornerResponse,&LocalMax); disp_image(Fabrik,WindowHandle); set_color(WindowHandle,"red"); disp_region(LocalMax,WindowHandle);
gauss_image, sobel_amp, convert_image_type
C.G. Harris, M.J. Stephens,
“A combined corner and edge detector”';
Proc. of the 4th Alvey Vision Conference; August 1988; pp. 147-152.
H. Breit,
“Bestimmung der Kameraeigenbewegung und Gewinnung von
Tiefendaten aus monokularen Bildfolgen”;
Diplomarbeit am Lehrstuhl für Nachrichtentechnik der TU München;
30. September 1990.
Foundation
Operators |