/// <summary>
/// Blends images stored in this <see cref="Blending"/> object.
/// magicSliderValue: Percentage of range? See whiteboard...[0, 1]
/// </summary>
public static HDRImage Blend(float magicSliderValue, params LDRImage[] imgs)
{
// Put that array in a list
//_imgs = new List<LDRImage>(imgs);
// Init outputs
// TODO: Get real values for height and width
/*
*
* So yeah here I guess we do the calculations
* I imagine for max multithread perf. we should
* split the pixels up by rows?
*
*/
int n = imgs.Length; //Number of Images Being Used
byte[][] imageBytes = new byte[n][]; //Row: Image Number Column: byte value
for (int i = 0; i < n; i++) //Place pixels into 2D Array
{
imageBytes[i] = imgs[i].GetBytes();
}
float[] raw = new float[imageBytes[0].Length];//Output Array
float[] xValues = new float[n];//Average Brightness of Image #j
for (int j = 0; j < xValues.Length; j++)
{
xValues[j] = AverageBrightness(imageBytes[j]);
}
for (int i = 0; i < imgs[0].GetDecoder().PixelWidth *imgs[0].GetDecoder().PixelHeight; i++) //Loop through each Pixel Position
{
float[] yValues = new float[n]; //Luminance
//Terms used in Logarithmic Regression
float sumYLnX = 0;
float sumY = 0;
float sumLnX = 0;
float sum_LnX2 = 0;
float sumLnX_2 = 0;
for (int j = 0; j < n; j++)//Find Pixel Values at Position i for each image
{
//Calculate Y Value (Luminance) for each image at Position i
//0.299 * R + 0.587 * G + 0.114 * B = Luminance
yValues[j] = (float)(0.299 * imageBytes[j][i * 4 + 0] + 0.587 * imageBytes[j][i * 4 + 1] + 0.114 * imageBytes[j][i * 4 + 2]);
sumYLnX += (float)yValues[j] * (float)Math.Log(xValues[j]);
sumY += yValues[j];
sumLnX += (float)Math.Log(xValues[j]);
sum_LnX2 += (float)Math.Log(xValues[j]) * (float)Math.Log(xValues[j]);
}
sumLnX_2 = sumLnX * sumLnX;
float b = (n * sumYLnX - sumY * sumLnX) / (n * sum_LnX2 - sumLnX_2); //Coefficient (Vertical Stretch) of Parent Function ln()
float a = (sumY - b * sumLnX) / n; //Constant term (Vertical Shift)
//Bounds for Transformation along Curve
float alpha = xValues[n / 2];
float beta = xValues[0];
//Choose either left or right bound based on size of range of Y values
if (b * Math.Abs(Math.Log(xValues[n / 2]) - Math.Log(xValues[0])) < b * Math.Abs(Math.Log(xValues[xValues.Length - 1]) - Math.Log(xValues[n / 2])))
{
beta = xValues[xValues.Length - 1];
}
float gamma = Math.Abs(alpha - beta) * magicSliderValue;//X Value of New Luminance Value for output pixel
if (beta < alpha)
{
gamma += beta;
}
else
{
gamma += alpha;
}
float newLuminance = a + b * (float)Math.Log(gamma);//New Luminance for output pixel
//Calculate chrominance channels from middle image to recover new RGB values
float cb = 128 + (float)(-0.168736 * imageBytes[n / 2][i * 4] - 0.331264 * imageBytes[n / 2][i * 4 + 1] + 0.5 * imageBytes[n / 2][i * 4 + 2]);
float cr = 128 + (float)(0.5 * imageBytes[n / 2][i * 4] - 0.418688 * imageBytes[n / 2][i * 4 + 1] - 0.081312 * imageBytes[n / 2][i * 4 + 2]);
//Recover RGB values
float newRed = newLuminance + 1.042f * (cr - 128);
float newGreen = newLuminance - 0.344136f * (cb - 128) - 0.714136f * (cr - 128);
float newBlue = newLuminance + 1.772f * (cb - 128);
//Assign to output array
// Swapped red and blue because it seemed to be flipping those - Callum
raw[i * 4] = newBlue;
raw[i * 4 + 1] = newGreen;
raw[i * 4 + 2] = newRed;
raw[i * 4 + 3] = imageBytes[n / 2][i * 4 + 3];
}
// Construct HDR image for final output
HDRImage output = new HDRImage(imgs[0].GetWidth(), raw);
return(output);
}
