// -------------- Average and Maximum --------------
// This method that takes YData instead of YDataFloat is by far the fastest method.
public static void CalculateAverageAndMaximumCPU(YData imageData, out float average, out float maximum)
{
const float LOW_ACCURACY_THRESHOLD = 64.0f;
const int LOW_ACCURACY_DIVISOR = 8;
int width = imageData.Width;
int height = imageData.Height;
// Calculate average and maximum
average = 0.0f;
maximum = 0.0f;
var averageSlices = new int[height];
var averageCounts = new int[height];
var maximumSlices = new byte[height];
int loopCount = height / LOW_ACCURACY_DIVISOR;
Parallel.For(0, loopCount, (loop, state) =>
{
for (int y = loop * LOW_ACCURACY_DIVISOR; y < (loop + 1) * LOW_ACCURACY_DIVISOR && (y < height); y++)
{
unsafe
{
fixed(byte *pDataByte = imageData.Data)
{
var pData = (int *)pDataByte; // Tried long* instead of int* and it made little difference
int ySrcOffset = (y * imageData.Stride) / sizeof(int);
int xMax = width / sizeof(int);
int avg = 0;
int count = 0;
byte max = 0;
for (int x = 0; x < xMax; x++)
{
var color = pData[ySrcOffset++];
byte value;
value = (byte)(color & 0xFF);
avg += value;
if (max < value)
{
max = value;
}
value = (byte)((color >> 8) & 0xFF);
avg += value;
if (max < value)
{
max = value;
}
value = (byte)((color >> 16) & 0xFF);
avg += value;
if (max < value)
{
max = value;
}
value = (byte)((color >> 24) & 0xFF);
avg += value;
if (max < value)
{
max = value;
}
count += 4;
if (max > LOW_ACCURACY_THRESHOLD)
{
x += 7;
ySrcOffset += 7;
}
}
averageSlices[y] = avg;
averageCounts[y] = count;
maximumSlices[y] = max;
if (max > LOW_ACCURACY_THRESHOLD)
{
break;
}
}
}
}
});
average = averageSlices.AsParallel().Sum();
var totalCount = averageCounts.AsParallel().Sum();
average /= (float)totalCount;
maximum = maximumSlices.AsParallel().Max();
}
// -------------- Standard Deviation --------------
public static void CalculateStandardDeviationCPU(YData imageData, float average, out float stdDev)
{
const float LOW_ACCURACY_THRESHOLD = 48.0f;
const int LOW_ACCURACY_DIVISOR = 16;
int width = imageData.Width;
int height = imageData.Height;
// Calculate standard deviation
stdDev = 0.0f;
float[] totalSlices = new float[height];
int[] countSlices = new int[height];
int loopCount = height;
if (average > LOW_ACCURACY_THRESHOLD)
{
loopCount = height / LOW_ACCURACY_DIVISOR;
}
//for (int y = 0; y < height; y++)
Parallel.For(0, loopCount, (y) =>
{
if (average > LOW_ACCURACY_THRESHOLD)
{
y *= LOW_ACCURACY_DIVISOR;
}
unsafe
{
fixed(byte *pDataByte = imageData.Data)
{
var pData = (int *)pDataByte; // Tried long* instead of int* and it was far worse performance
int ySrcOffset = (y * imageData.Stride) / sizeof(int);
int xMax = width / sizeof(int);
float total = 0.0f;
int count = 0;
for (int x = 0; x < xMax; x++)
{
var color = pData[ySrcOffset++];
float value;
value = (float)(color & 0xFF);
value = (value - average) * (value - average);
total += value;
value = (float)((color >> 8) & 0xFF);
value = (value - average) * (value - average);
total += value;
value = (float)((color >> 16) & 0xFF);
value = (value - average) * (value - average);
total += value;
value = (float)((color >> 24) & 0xFF);
value = (value - average) * (value - average);
total += value;
count += 4;
if (average > LOW_ACCURACY_THRESHOLD)
{
x += (LOW_ACCURACY_DIVISOR - 1);
ySrcOffset += (LOW_ACCURACY_DIVISOR - 1);
}
}
totalSlices[y] = total;
countSlices[y] = count;
}
}
});
stdDev = totalSlices.AsParallel().Sum();
var totalCount = countSlices.AsParallel().Sum();
stdDev /= (float)totalCount;
stdDev = (float)Math.Sqrt(stdDev);
}