Added triangle method

tfjs-core/src/ops/image/threshold.ts

@@ -29,10 +29,24 @@ import { add } from '../add';
 import { mul } from '../mul';
 import { div } from '../div';
 import { sub } from '../sub';
+import {atan} from '../atan';
+import {tan} from '../tan';
+import {slice} from '../slice';
+import {argMax} from '../arg_max';
+import {max} from '../max';
+import {argMin} from '../arg_min';
+import {less} from '../less';
 import { round } from '../round';
 import { where } from '../where';
+import {reshape} from '../reshape';
+import {sqrt} from '../sqrt';
+import {pow} from '../pow';
+import {abs} from '../abs';
+import {gatherND} from '../gather_nd';
+import {clone} from '../clone';
+import {reverse} from '../reverse';
+import {zerosLike} from '../zeros_like';
 import { fill } from '../fill';
-import {slice} from '../slice';
 import { range } from '../range';
 import { tensor } from '../tensor';
 import * as util from '../../util';
@@ -44,7 +58,7 @@ import { convertToTensor } from '../../tensor_util_env';
  * @param image 3d tensor of shape [imageHeight,imageWidth, depth],
  * where imageHeight and imageWidth must be positive.The image color
  * range should be [0, 255].
- * @param method Optional string from `'binary' | 'otsu'`
+ * @param method Optional string from `'binary' | 'otsu' | 'triangle' `
  * which specifies the method for thresholding. Defaults to 'binary'.
  * @param inverted Optional boolean whichspecifies
  * if colours should be inverted. Defaults to false.
@@ -109,6 +123,12 @@ function threshold_(
             256);
         $threshold = otsu($histogram, totalPixelsInImage);
     }
+    else if(method === 'triangle'){
+        const $histogram = bincount(cast(round(grayscale), 'int32') as Tensor1D,
+            tensor([]),
+            256);
+        $threshold = triangle($histogram);
+    }
 
     const invCondition = inverted ?
         lessEqual(grayscale, $threshold) : greater(grayscale, $threshold);
@@ -160,4 +180,73 @@ function otsu(histogram: Tensor1D, total: number):Tensor1D {
     return bestThresh;
 }
 
+function triangle (histogram: Tensor1D){
+
+    const histogramTrimmed = trimZeros(histogram);
+
+    const maxIdx = + argMax(histogramTrimmed).toString().replace(/[^0-9]/g, '');
+
+    const increasing = lessEqual(histogramTrimmed.shape[0]/2, maxIdx)
+        .toString().includes('true');
+
+    const sliced = increasing ? slice(histogramTrimmed, 0, maxIdx+1) :
+        slice(histogramTrimmed, maxIdx);
+
+    const cathetusB = max(sliced);
+
+    const cathetusA = sliced.shape;
+
+    const aTan = atan(div(cathetusB, cathetusA));
+
+    let derivativeTriangle = increasing ? range(1, cathetusA[0]+1, 1 ,'float32')
+        :
+        range(cathetusA[0], 0, -1 ,'float32') ;
+
+    derivativeTriangle = mul(derivativeTriangle, tan(aTan));
+
+    let cathetusDerivativeB  = sub(derivativeTriangle, sliced);
+
+    cathetusDerivativeB = where(less(cathetusDerivativeB,0),
+        zerosLike(cathetusDerivativeB), cathetusDerivativeB);
+
+    const cathetusDerivativeA =  div(cathetusDerivativeB, tan(aTan));
+
+    const hiposDerivate = sqrt( add( pow(cathetusDerivativeA,2 ),
+        pow(cathetusDerivativeB,2)    )  );
+
+    const heights = div(mul(cathetusDerivativeB, cathetusDerivativeA)
+        , hiposDerivate);
+
+    const maxheightIdx = argMax(heights);
+
+    const valueInHistoSliced = gatherND(sliced, reshape(maxheightIdx, [1]));
+
+    const bestThresh =  argMin( abs(sub(histogram, valueInHistoSliced)) );
+
+    return bestThresh;
+
+}
+
+function trimZeros(histogram: Tensor1D){
+
+    const histogramCopy = clone(histogram);
+
+    const divideToZero = div(histogramCopy,0);
+
+    const leftPointer = + argMax(divideToZero)
+        .toString().replace(/[^0-9]/g, '');
+
+    const leftSideClean = slice(histogramCopy, leftPointer);
+
+    const divideToMZero = div(reverse(leftSideClean), -0);
+
+    const rightPointer = + argMin(divideToMZero)
+        .toString().replace(/[^0-9]/g, '');
+
+    const clean = slice(leftSideClean,
+        0, leftSideClean.shape[0] - rightPointer );
+
+    return clean;
+}
+
 export const threshold = op({ threshold_ });