Demo implementation of client-side image blurriness detection on Android using renderscript.

BlurrinessDetection.kt

/*
 * Copyright (c) 2018. Uber Technologies
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.uber.blurdetectiondemo

import android.content.Context
import android.graphics.Bitmap
import android.graphics.Color
import android.renderscript.Allocation
import android.renderscript.Element
import android.renderscript.RenderScript
import android.renderscript.ScriptIntrinsicBlur
import android.renderscript.ScriptIntrinsicColorMatrix
import android.renderscript.ScriptIntrinsicConvolve3x3
import android.widget.Toast
import androidx.annotation.ColorInt

object BlurrinessDetection {

  private val CLASSIC_MATRIX = floatArrayOf(
      -1.0f, -1.0f, -1.0f,
      -1.0f, 8.0f, -1.0f,
      -1.0f, -1.0f, -1.0f
  )

  /**
   * This attempts to determine if a given [sourceBitmap] is blurry using a combination of
   * renderscript utilities.
   *
   * Operations go like this:
   * - Soft blur
   * - Greyscale
   * - 3x3 convolution
   *
   * @return if the source bitmap is "blurry"
   */
  fun runDetection(context: Context, sourceBitmap: Bitmap): Boolean {
    val rs = RenderScript.create(context)

    // First apply a soft blur to smoothen out visual artifacts
    val smootherBitmap = Bitmap.createBitmap(sourceBitmap.width,
        sourceBitmap.height,
        sourceBitmap.config
    )
    val blurIntrinsic = ScriptIntrinsicBlur.create(rs, Element.RGBA_8888(rs))
    val source = Allocation.createFromBitmap(rs,
        sourceBitmap,
        Allocation.MipmapControl.MIPMAP_NONE,
        Allocation.USAGE_SHARED
    )
    val blurTargetAllocation = Allocation.createFromBitmap(rs,
        smootherBitmap,
        Allocation.MipmapControl.MIPMAP_NONE,
        Allocation.USAGE_SHARED
    )
    blurIntrinsic.apply {
      setRadius(1f)
      setInput(source)
      forEach(blurTargetAllocation)
    }
    blurTargetAllocation.copyTo(smootherBitmap)

    // Greyscale so we're only dealing with white <--> black pixels, this is so we only need to
    // detect pixel
    // luminosity
    val greyscaleBitmap = Bitmap.createBitmap(sourceBitmap.width,
        sourceBitmap.height,
        sourceBitmap.config
    )
    val smootherInput = Allocation.createFromBitmap(rs,
        smootherBitmap,
        Allocation.MipmapControl.MIPMAP_NONE,
        Allocation.USAGE_SHARED
    )
    val greyscaleTargetAllocation = Allocation.createFromBitmap(rs,
        greyscaleBitmap,
        Allocation.MipmapControl.MIPMAP_NONE,
        Allocation.USAGE_SHARED
    )

    // Inverts and greyscales the image
    val colorIntrinsic = ScriptIntrinsicColorMatrix.create(rs)
    colorIntrinsic.setGreyscale()
    colorIntrinsic.forEach(smootherInput, greyscaleTargetAllocation)
    greyscaleTargetAllocation.copyTo(greyscaleBitmap)

    // Run edge detection algorithm using a laplacian matrix convolution
    // Apply 3x3 convolution to detect edges
    val edgesBitmap = Bitmap.createBitmap(sourceBitmap.width,
        sourceBitmap.height,
        sourceBitmap.config
    )
    val greyscaleInput = Allocation.createFromBitmap(rs,
        greyscaleBitmap,
        Allocation.MipmapControl.MIPMAP_NONE,
        Allocation.USAGE_SHARED
    )
    val edgesTargetAllocation = Allocation.createFromBitmap(rs,
        edgesBitmap,
        Allocation.MipmapControl.MIPMAP_NONE,
        Allocation.USAGE_SHARED
    )

    val convolve = ScriptIntrinsicConvolve3x3.create(rs, Element.U8_4(rs))
    convolve.setInput(greyscaleInput)
    convolve.setCoefficients(CLASSIC_MATRIX) // Or use others
    convolve.forEach(edgesTargetAllocation)
    edgesTargetAllocation.copyTo(edgesBitmap)

    @ColorInt val mostLuminousColor = mostLuminousColorFromBitmap(edgesBitmap)
    val colorHex = "#" + Integer.toHexString(mostLuminousColor)
    val isBlurry = mostLuminousColor > Color.parseColor("#CECECE") // Demo threshold
    // Note - in Android, Color.BLACK is -16777216 and Color.WHITE is -1, so range is somewhere in between. Higher is more luminous
    Toast.makeText(context,
        "Most luminous color is $colorHex. Blurry = $isBlurry",
        Toast.LENGTH_SHORT
    ).show()
    return isBlurry
  }

  /**
   * Resolves the most luminous color pixel in a given bitmap.
   *
   * @param bitmap Source bitmap.
   * @return The most luminous color pixel in the `bitmap`
   */
  @ColorInt
  fun mostLuminousColorFromBitmap(bitmap: Bitmap): Int {
    bitmap.setHasAlpha(false)
    val pixels = IntArray(bitmap.height * bitmap.width)
    bitmap.getPixels(pixels, 0, bitmap.width, 0, 0, bitmap.width, bitmap.height)

    @ColorInt var mostLuminousColor = Color.BLACK

    for (pixel in pixels) {
      if (pixel > mostLuminousColor) {
        mostLuminousColor = pixel
      }
    }
    return mostLuminousColor
  }

}