edge - Find edges in a single channel image.

Calling Sequence

E = edge(im, method)

E = edge(im, method, thresh)

E = edge(im, method, thresh, direction)

E = edge(im, method, thresh, sigma)

[E, thresh] = edge(im, method, ...)

Parameters

• im: Input image which must be a single channel image.
• method: may be 'sobel'(default), 'prewitt', 'log', 'fftderiv' or 'canny'. Other methods will appear in the future.
• thresh: sets the threshold level, from 0 to 1. Defaults to 0.2. If negative, then the output image, E, will have the un-thresholded gradient image.
• direction: may be 'horizontal', 'vertical' or 'both'(default). This determines the direction to compute the image gradient.
• sigma: Controls the ammount of high-frequency attenuation in some methods (only the 'fftderiv' method uses this parameter). This can be used to obtain different levels of detail and to filter out high-frequency noise.
• E: edge image which is boolean matrix and has the same size as im. If thresh<0, E is a double un-thresholded image.

Description

The function edge performs edge detection on a grayscale intensity image. The user may set the method, the threshold level, the direction of the edge detection, etc.

E=edge(im, 'sobel', thresh, direction)

Detects edges in im, using the sobel gradient estimator.

E=edge(im, 'prewitt', thresh, direction)

Detects edges in im, using the prewitt gradient estimator.

E=edge(im, 'log', thresh, sigma)

Detects edges in im, using the the Laplacian of Gaussian method. sigma is the standard deviation of the LoG filter and the size of the LoG filter is nxn, where n = ceil(sigma*3)*2+1. The default value for sigma is 2.

E=edge(im, 'fftderiv', thresh, direction, sigma)

Detects edges in im, using the FFT gradient method, default sigma 1.0

E=edge(im, 'canny', thresh, sigma)

Detects edges in im, using Canny method. thresh is a two-element vector, in which the fist element is the low threshold and the seond one is the high threshold. If thresh is a scalar, the low threshold is 0.4*thresh and the high one is thresh. Besides, thresh can not be negative scalar. sigma is the Aperture parameter for Sobel operator, which must be 1, 3, 5 or 7. default thresh 0.2; default sigma 3.

Supported classes: INT8, UINT8, INT16, UINT16, INT32, DOUBLE.

Examples

    im = imread('lena.png');
    im = rgb2gray(im);
    E = edge(im, 'sobel');
    imshow(E);

    E = edge(im, 'canny', [0.06, 0.2]);
    imshow(E);

    E = edge(im, 'sobel', -1);
    imshow(mat2gray(E));

Authors

Shiqi Yu <shiqi.yu[at]gmail.com>

Ricardo Fabbri <ricardofabbri[at]users.sf.net>

Bibliography

"Shape Analysis and Classification", L. da F. Costa and R. M. Cesar Jr., CRC Press, section 3.3.

Availability

http://sivp.sourceforge.net

See Also

fspecial,  imfilter,  filter2,