/
sobel.js
61 lines (58 loc) · 1.29 KB
/
sobel.js
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/**
* Sobel edge detection
*/
export default class Sobel {
// http://www.mis.med.akita-u.ac.jp/~kata/image/sobelprew.html
/**
* @param {number} th Threshold
*/
constructor(th) {
this._threshold = th
}
_convolute(x, kernel) {
const a = []
for (let i = 0; i < x.length; i++) {
a[i] = []
for (let j = 0; j < x[i].length; j++) {
let v = 0
for (let s = 0; s < kernel.length; s++) {
let n = i + s - Math.floor(kernel.length / 2)
n = Math.max(0, Math.min(x.length - 1, n))
for (let t = 0; t < kernel[s].length; t++) {
let m = j + t - Math.floor(kernel[s].length / 2)
m = Math.max(0, Math.min(x[n].length - 1, m))
v += x[n][m] * kernel[s][t]
}
}
a[i][j] = v
}
}
return a
}
/**
* Returns predicted edge flags.
*
* @param {Array<Array<number>>} x Training data
* @returns {Array<Array<boolean>>} Predicted values. `true` if a pixel is edge.
*/
predict(x) {
const gx = this._convolute(x, [
[1, 0, -1],
[2, 0, -2],
[1, 0, -1],
])
const gy = this._convolute(x, [
[1, 2, 1],
[0, 0, 0],
[-1, -2, -1],
])
const g = []
for (let i = 0; i < gx.length; i++) {
g[i] = []
for (let j = 0; j < gx[i].length; j++) {
g[i][j] = Math.sqrt(gx[i][j] ** 2 + gy[i][j] ** 2) > this._threshold
}
}
return g
}
}