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Added Edge Detection module (#168)
* step 1 grayscale Signed-off-by: tech4GT <varun.gupta1798@gmail.com> * add basic edge detection resolves #166 * updated the description Signed-off-by: tech4GT <varun.gupta1798@gmail.com> * fixed typo Signed-off-by: tech4GT <varun.gupta1798@gmail.com> * updated the description for edge detection module Signed-off-by: tech4GT <varun.gupta1798@gmail.com> * add NonMaxSuppression and DoubleThreshold Signed-off-by: tech4GT <varun.gupta1798@gmail.com> * comlpeted edge detection Signed-off-by: tech4GT <varun.gupta1798@gmail.com> * cleared remaining weak edges Signed-off-by: tech4GT <varun.gupta1798@gmail.com>
This commit is contained in:
Varun Gupta
committed by
Jeffrey Warren
Jeffrey Warren
parent
32c5a29906
commit
bbef4bca57
179
src/modules/EdgeDetect/EdgeUtils.js
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179
src/modules/EdgeDetect/EdgeUtils.js
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const _ = require('lodash')
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//define kernels for the sobel filter
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const kernelx = [[-1,0,1],[-2,0,2],[-1,0,1]],
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kernely = [[-1,-2,-1],[0,0,0],[1,2,1]]
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let angles = []
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let mags = []
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let strongEdgePixels = []
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let weakEdgePixels = []
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module.exports = exports = function(pixels,highThresholdRatio,lowThresholdRatio){
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for(var x = 0; x < pixels.shape[0]; x++) {
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angles.push([])
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mags.push([])
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for(var y = 0; y < pixels.shape[1]; y++) {
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var result = changePixel(
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pixels,
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pixels.get(x,y,0),
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pixels.get(x, y, 3),
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x,
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y
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)
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let pixel = result.pixel
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pixels.set(x, y, 0, pixel[0]);
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pixels.set(x, y, 1, pixel[1]);
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pixels.set(x, y, 2, pixel[2]);
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pixels.set(x, y, 3, pixel[3]);
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mags.slice(-1)[0].push(pixel[3])
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angles.slice(-1)[0].push(result.angle)
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}
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}
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return hysteresis(doubleThreshold(nonMaxSupress(pixels),highThresholdRatio,lowThresholdRatio))
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}
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//changepixel function that convolutes every pixel (sobel filter)
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function changePixel(pixels,val,a,x,y){
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let magX = 0.0
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for(let a = 0; a < 3; a++){
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for(let b = 0; b < 3; b++){
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let xn = x + a - 1;
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let yn = y + b - 1;
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magX += pixels.get(xn,yn,0) * kernelx[a][b];
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}
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}
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let magY = 0.0
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for(let a = 0; a < 3; a++){
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for(let b = 0; b < 3; b++){
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let xn = x + a - 1;
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let yn = y + b - 1;
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magY += pixels.get(xn,yn,0) * kernely[a][b];
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}
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}
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let mag = Math.sqrt(Math.pow(magX,2) + Math.pow(magY,2))
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let angle = Math.atan2(magY,magX)
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return {
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pixel:
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[val,val,val,mag],
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angle: angle
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}
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}
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//Non Maximum Supression without interpolation
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function nonMaxSupress(pixels) {
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angles = angles.map((arr)=>arr.map(convertToDegrees))
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for(let i = 1;i<pixels.shape[0]-1;i++){
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for(let j=1;j<pixels.shape[1]-1;j++){
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let angle = angles[i][j]
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let pixel = pixels.get(i,j)
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if ((angle>=-22.5 && angle<=22.5) ||
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(angle<-157.5 && angle>=-180))
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if ((mags[i][j]>= mags[i][j+1]) &&
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(mags[i][j] >= mags[i][j-1]))
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pixels.set(i,j,3,mags[i][j])
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else
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pixels.set(i,j,3,0)
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else if ((angle>=22.5 && angle<=67.5) ||
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(angle<-112.5 && angle>=-157.5))
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if ((mags[i][j] >= mags[i+1][j+1]) &&
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(mags[i][j] >= mags[i-1][j-1]))
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pixels.set(i,j,3,mags[i][j])
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else
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pixels.set(i,j,3,0)
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else if ((angle>=67.5 && angle<=112.5) ||
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(angle<-67.5 && angle>=-112.5))
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if ((mags[i][i] >= mags[i+1][j]) &&
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(mags[i][j] >= mags[i][j]))
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pixels.set(i,j,3,mags[i][j])
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else
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pixels.set(i,j,3,0)
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else if ((angle>=112.5 && angle<=157.5) ||
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(angle<-22.5 && angle>=-67.5))
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if ((mags[i][j] >= mags[i+1][j-1]) &&
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(mags[i][j] >= mags[i-1][j+1]))
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pixels.set(i,j,3,mags[i][j])
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else
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pixels.set(i,j,3,0)
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}
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}
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return pixels
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}
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//Converts rasians to degrees
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var convertToDegrees = radians => (radians * 180)/Math.PI
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//Finds the max value in a 2d array like mags
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var findMaxInMatrix = arr => Math.max(...arr.map(el=>el.map(val=>!!val?val:0)).map(el=>Math.max(...el)))
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//Applies the double threshold to the image
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function doubleThreshold(pixels,highThresholdRatio,lowThresholdRatio){
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const highThreshold = findMaxInMatrix(mags) * 0.2
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const lowThreshold = highThreshold * lowThresholdRatio
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for(let i =0;i<pixels.shape[0];i++){
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for(let j=0;j<pixels.shape[1];j++){
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let pixelPos = [i,j]
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mags[i][j]>lowThreshold
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?mags[i][j]>highThreshold
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?strongEdgePixels.push(pixelPos)
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:weakEdgePixels.push(pixelPos)
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:pixels.set(i,j,3,0)
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}
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}
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strongEdgePixels.forEach(pix=>pixels.set(pix[0],pix[1],3,255))
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return pixels
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}
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// hysteresis edge tracking algorithm
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function hysteresis(pixels){
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function getNeighbouringPixelPositions(pixelPosition){
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let x = pixelPosition[0],y=pixelPosition[1]
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return [[x+1,y+1],
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[x+1,y],
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[x+1,y-1],
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[x,y+1],
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[x,y-1],
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[x-1,y+1],
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[x-1,y],
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[x-1,y-1]]
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}
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//This can potentially be improved see https://en.wikipedia.org/wiki/Connected-component_labeling
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for(weakPixel in weakEdgePixels){
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let neighbourPixels = getNeighbouringPixelPositions(weakEdgePixels[weakPixel])
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for(pixel in neighbourPixels){
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if(strongEdgePixels.find(el=> _.isEqual(el,neighbourPixels[pixel]))) {
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pixels.set(weakPixel[0],weakPixel[1],3,255)
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weakEdgePixels.splice(weakPixel,weakPixel)
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break
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}
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}
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}
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weakEdgePixels.forEach(pix=>pixels.set(pix[0],pix[1],3,0))
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return pixels
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}
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