@@ -45,23 +45,24 @@ ImagePHash.prototype.distance = function(s1, s2) {
4545 counter ++ ;
4646 }
4747 }
48+
4849 return counter / s1 . length ;
4950} ;
5051
5152// Returns a 'binary string' (like. 001010111011100010) which is easy to do a hamming distance on.
5253ImagePHash . prototype . getHash = function ( img ) {
5354 /* 1. Reduce size.
54- * Like Average Hash, pHash starts with a small image.
55- * However, the image is larger than 8x8; 32x32 is a good size.
56- * This is really done to simplify the DCT computation and not
57- * because it is needed to reduce the high frequencies.
58- */
55+ * Like Average Hash, pHash starts with a small image.
56+ * However, the image is larger than 8x8; 32x32 is a good size.
57+ * This is really done to simplify the DCT computation and not
58+ * because it is needed to reduce the high frequencies.
59+ */
5960 img = img . clone ( ) . resize ( this . size , this . size ) ;
6061
6162 /* 2. Reduce color.
62- * The image is reduced to a grayscale just to further simplify
63- * the number of computations.
64- */
63+ * The image is reduced to a grayscale just to further simplify
64+ * the number of computations.
65+ */
6566 img . grayscale ( ) ;
6667
6768 const vals = [ ] ;
@@ -74,23 +75,23 @@ ImagePHash.prototype.getHash = function(img) {
7475 }
7576
7677 /* 3. Compute the DCT.
77- * The DCT separates the image into a collection of frequencies
78- * and scalars. While JPEG uses an 8x8 DCT, this algorithm uses
79- * a 32x32 DCT.
80- */
78+ * The DCT separates the image into a collection of frequencies
79+ * and scalars. While JPEG uses an 8x8 DCT, this algorithm uses
80+ * a 32x32 DCT.
81+ */
8182 const dctVals = applyDCT ( vals , this . size ) ;
8283
8384 /* 4. Reduce the DCT.
84- * This is the magic step. While the DCT is 32x32, just keep the
85- * top-left 8x8. Those represent the lowest frequencies in the
86- * picture.
87- */
85+ * This is the magic step. While the DCT is 32x32, just keep the
86+ * top-left 8x8. Those represent the lowest frequencies in the
87+ * picture.
88+ */
8889 /* 5. Compute the average value.
89- * Like the Average Hash, compute the mean DCT value (using only
90- * the 8x8 DCT low-frequency values and excluding the first term
91- * since the DC coefficient can be significantly different from
92- * the other values and will throw off the average).
93- */
90+ * Like the Average Hash, compute the mean DCT value (using only
91+ * the 8x8 DCT low-frequency values and excluding the first term
92+ * since the DC coefficient can be significantly different from
93+ * the other values and will throw off the average).
94+ */
9495 let total = 0 ;
9596
9697 for ( let x = 0 ; x < this . smallerSize ; x ++ ) {
@@ -102,15 +103,15 @@ ImagePHash.prototype.getHash = function(img) {
102103 const avg = total / ( this . smallerSize * this . smallerSize ) ;
103104
104105 /* 6. Further reduce the DCT.
105- * This is the magic step. Set the 64 hash bits to 0 or 1
106- * depending on whether each of the 64 DCT values is above or
107- * below the average value. The result doesn't tell us the
108- * actual low frequencies; it just tells us the very-rough
109- * relative scale of the frequencies to the mean. The result
110- * will not vary as long as the overall structure of the image
111- * remains the same; this can survive gamma and color histogram
112- * adjustments without a problem.
113- */
106+ * This is the magic step. Set the 64 hash bits to 0 or 1
107+ * depending on whether each of the 64 DCT values is above or
108+ * below the average value. The result doesn't tell us the
109+ * actual low frequencies; it just tells us the very-rough
110+ * relative scale of the frequencies to the mean. The result
111+ * will not vary as long as the overall structure of the image
112+ * remains the same; this can survive gamma and color histogram
113+ * adjustments without a problem.
114+ */
114115 let hash = '' ;
115116
116117 for ( let x = 0 ; x < this . smallerSize ; x ++ ) {
@@ -169,6 +170,7 @@ function applyDCT(f, size) {
169170 f [ i ] [ j ] ;
170171 }
171172 }
173+
172174 sum *= ( c [ u ] * c [ v ] ) / 4 ;
173175 F [ u ] [ v ] = sum ;
174176 }
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