ImageTools/src/main/scala/com/sothr/imagetools/hash/PHash.scala

package com.sothr.imagetools.hash

import edu.emory.mathcs.jtransforms.dct.FloatDCT_2D
import grizzled.slf4j.Logging

/**
  * Created by dev on 1/22/14.
  */
object PHash extends PerceptualHasher with Logging {
   def getHash(imageData: Array[Array[Int]]): Long = {
     //convert the imageData into a FloatArray
     val width = imageData.length
     val height = imageData(0).length
     //debug(s"Starting with image of ${height}x${width} for PHash")

     val imageDataFloat:Array[Array[Float]] = Array.ofDim[Float](height, width)
     for (row <- 0 until height) {
       for (col <- 0 until width) {
         imageDataFloat(row)(col) = imageData(row)(col).toFloat
       }
     }
     //debug("Copied image data to float array for transform")
     //debug(s"\n${imageDataFloat.deep.mkString("\n")}")

     //perform transform on the data
     val dct:FloatDCT_2D = new FloatDCT_2D(height,width)
     dct.forward(imageDataFloat, true)
     //debug("Converted image data into DCT")
     //debug(s"\n${imageDataFloat.deep.mkString("\n")}")

     //extract the DCT data
     val dctDataWidth:Int = width / 4
     val dctDataHeight:Int = height  / 4

     //calculate the mean
     var total = 0.0f
     for (row <- 0 until dctDataHeight) {
       for (col <- 0 until dctDataWidth) {
         total += imageDataFloat(row)(col)
       }
     }
     val mean = total / (dctDataHeight * dctDataWidth)
     //debug(s"Calculated mean as $mean from ${total}/${dctDataHeight * dctDataWidth}")

     //calculate the hash
     var hash = 0L
     for (row <- 0 until dctDataHeight by 2) {
       //process each column
       for (col <- 0 until dctDataWidth by 1) {
         hash <<= 1
         val pixel = imageDataFloat(row)(col)
         //If the current pixel is at or above the mean, store it as a one, else store it as a zero
         if (pixel >= mean) hash |= 1 else hash |= 0
       }

       if ((row +1) < dctDataWidth) {
         val nextRow = row + 1
         //process each column
         for (col <- (dctDataWidth - 1) to 0 by -1) {
           hash <<= 1
           val pixel = imageDataFloat(nextRow)(col)
           if (pixel >= mean) hash |= 1 else hash |= 0
         }
       }
     }
     //debug(s"Computed PHash: $hash from ${dctDataWidth * dctDataHeight} pixels")
     hash
   }
 }