/// <summary>
/// Histogram Equalization will enhance general contrast
/// by distributing grey levels wider and more evenly.
/// </summary>
/// <param name="imageBytes">Image bytes</param>
/// <param name="pixelDepth">Pixel depth of image</param>
/// <param name="imageWidth">Image width</param>
/// <param name="imageHeight">Image height</param>
public static void HistogramEqualizationDirect(byte[] imageBytes, int pixelDepth, int imageWidth, int imageHeight)
{
int[] histogram = ImageHistogram.GetHistogramValues(imageBytes, pixelDepth);
double numberOfPixels = imageWidth * imageHeight;
double numberOfLevels = histogram.Length;
int cumulativeFrequency = 0;
int equalizedValue;
// Calculate cumulative distribution for histogram
for (int i = 0; i < histogram.Length; i++)
{
cumulativeFrequency += histogram[i];
// Calculate equalized value
equalizedValue = (int)Math.Round((numberOfLevels * cumulativeFrequency) / numberOfPixels) - 1;
// Ensure +ve value
histogram[i] = Math.Max(0, equalizedValue);
}
bool isColor = BitmapDataExt.IsColorPixelDepth(pixelDepth);
int limit = BitmapDataExt.GetSafeArrayLimitForImage(isColor, pixelDepth, imageBytes);
// Apply distribution to image to equalize
if (isColor)
{
// Exclude alpha/transparency byte
int pixelDepthWithoutAlpha = Math.Min(pixelDepth, Constants.PixelDepthRGB);
for (int i = 0, j; i < limit; i += pixelDepth)
{
for (j = 0; j < pixelDepthWithoutAlpha; j++)
{
imageBytes[i + j] = (byte)histogram[imageBytes[i + j]];
}
}
}
else
{
for (int i = 0; i < limit; i++)
{
imageBytes[i] = (byte)histogram[imageBytes[i]];
}
}
}
/// <summary>
/// Obtains threshold value for image using Otsu's Method.
/// </summary>
/// <param name="imageBytes">Image bytes</param>
/// <param name="pixelDepth">Pixel depth</param>
/// <returns>Threshold value</returns>
public static byte GetByOtsuMethod(byte[] imageBytes, int pixelDepth)
{
int[] histValues = ImageHistogram.GetHistogramValues(imageBytes, pixelDepth);
return(GetByOtsuMethod(histValues));
}
