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      1 /*
      2  * Copyright (C) 2011 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 #define LOG_NDEBUG 0
     17 
     18 #define LOG_TAG "WhiteBalanceTest"
     19 #include <utils/Log.h>
     20 #include <utils/Timers.h>
     21 #include <cmath>
     22 #include <string>
     23 
     24 #include "vec2.h"
     25 #include "vec3.h"
     26 #include "whitebalancetest.h"
     27 
     28 // White point in XYZ color space under 5200k illumination.
     29 const Vec3f kDaylightWhitePoint(0.9781f, 1.f, 0.9021f);
     30 
     31 // Process the data of checker colors collected under different white balance.
     32 // Assuming the Daylight CCT is set to 5200k, compute the CCT of other white
     33 // balance modes.
     34 void WhiteBalanceTest::processData() {
     35     ALOGV("Start Processing White Balance Test Data!");
     36 
     37     int numPatches = mCheckerColors.size();
     38     ALOGV("Processing %d tests with %d patches", 2, numPatches);
     39 
     40     std::vector<Vec3f> xyzColors(numPatches);
     41     for (int j = 0; j < numPatches; ++j) {
     42         Vec3f xyzCheckerColor = initializeFromRGB(mCheckerColors[j]);
     43         xyzColors[j] = xyzCheckerColor;
     44         ALOGV("XYZ coordinate is %f, %f, %f", xyzCheckerColor.r(),
     45               xyzCheckerColor.g(), xyzCheckerColor.b());
     46     }
     47 
     48     Vec3f meanScale(0.f, 0.f, 0.f);
     49 
     50     if (mMode == "daylight") {
     51         mXyzColorsDaylight = xyzColors;
     52         // For testing the auto white balance mode. Compute a CCT that would
     53         // map the gray checkers to a white point.
     54         for (int j = 1; j < numPatches; ++j) {
     55             meanScale = meanScale +
     56                     (mXyzColorsDaylight[j] / kDaylightWhitePoint);
     57         }
     58     } else {
     59         for (int j = 1; j < numPatches; ++j) {
     60             meanScale = meanScale + (mXyzColorsDaylight[j] / xyzColors[j]);
     61         }
     62     }
     63 
     64     meanScale = meanScale / (numPatches - 1);
     65     ALOGV("Scale: %f, %f, %f", meanScale.r(), meanScale.g(), meanScale.b());
     66 
     67     Vec3f whitePoint;
     68     whitePoint = meanScale * kDaylightWhitePoint;
     69 
     70     ALOGV("White point is %f, %f, %f", whitePoint.r(),
     71          whitePoint.g(), whitePoint.b());
     72 
     73     mCorrelatedColorTemp = findCorrelatedColorTemp(whitePoint);
     74     ALOGV("CCT is %d", mCorrelatedColorTemp);
     75 }
     76 
     77 // Given a white point, find the correlated color temperature.
     78 // Formula taken from the paper "Calculating Correlated Color Temperatures
     79 // Across the Entire Gamut of Daylight and Skylight Chromaticities" by Hernandez
     80 // Andres et al. in 1999. The numbers are fitting parameters.
     81 int WhiteBalanceTest::findCorrelatedColorTemp(const Vec3f &whitePoint) {
     82     Vec2f chromaOfWhitePoint(
     83         whitePoint.r() / (whitePoint.r() + whitePoint.g() + whitePoint.b()),
     84         whitePoint.g() / (whitePoint.r() + whitePoint.g() + whitePoint.b()));
     85 
     86     float n = (chromaOfWhitePoint.x() - 0.3366f)
     87                 / (chromaOfWhitePoint.y() - 0.1735f);
     88     float y = -949.86315f + 6253.80338f * exp(-n / 0.92159f)
     89                + 28.70599f * exp(-n / 0.20039f) + 0.00004f * exp(-n / 0.07125f);
     90 
     91     return static_cast<int>(y);
     92 }
     93 
     94 // Converts a RGB pixel value to XYZ color space.
     95 Vec3f WhiteBalanceTest::initializeFromRGB(const Vec3f &rgb) {
     96     float linearRed = convertToLinear(rgb.r());
     97     float linearGreen = convertToLinear(rgb.g());
     98     float linearBlue = convertToLinear(rgb.b());
     99 
    100     float x = 0.4124f * linearRed + 0.3576f * linearGreen +
    101             0.1805f * linearBlue;
    102     float y = 0.2126f * linearRed + 0.7152f * linearGreen +
    103             0.0722f * linearBlue;
    104     float z = 0.0193f * linearRed + 0.1192f * linearGreen +
    105             0.9505f * linearBlue;
    106 
    107     return Vec3f(x, y, z);
    108 }
    109 
    110 float WhiteBalanceTest::convertToLinear(float color) {
    111     float norm = color/ 255.0f;
    112     float linearColor;
    113 
    114     // Convert from sRGB space to linear RGB value
    115     if (norm > 0.04045f) {
    116         linearColor = pow(((norm + 0.055f) / 1.055f), 2.4f);
    117     } else {
    118         linearColor = norm / 12.92f;
    119     }
    120 
    121     return linearColor;
    122 }
    123