tests/Camera2Tests/SmartCamera/SimpleCamera/jni/contrast.cpp

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * 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.
 */

// Native function to extract contrast ratio from image (handed down as ByteBuffer).

#include "contrast.h"

#include <math.h>
#include <string.h>
#include <jni.h>
#include <unistd.h>
#include <android/log.h>

jfloat
Java_androidx_media_filterfw_samples_simplecamera_ContrastRatioFilter_contrastOperator(
    JNIEnv* env, jclass clazz, jint width, jint height, jobject imageBuffer) {

    if (imageBuffer == 0) {
      return 0.0f;
    }
    float total = 0;
    const int numPixels = width * height;
    unsigned char* srcPtr = static_cast<unsigned char*>(env->GetDirectBufferAddress(imageBuffer));
    float* lumArray = new float[numPixels];
    for (int i = 0; i < numPixels; i++) {
        lumArray[i] = (0.2126f * *(srcPtr + 4 * i) + 0.7152f *
            *(srcPtr + 4 * i + 1) + 0.0722f * *(srcPtr + 4 * i + 2)) / 255;
        total += lumArray[i];
    }
    const float avg = total / numPixels;
    float sum = 0;

    for (int i = 0; i < numPixels; i++) {
        sum += (lumArray[i] - avg) * (lumArray[i] - avg);
    }
    delete[] lumArray;
    return ((float) sqrt(sum / numPixels));
}