/// <summary>
/// Any pixel values below threshold will be changed to 0 (black).
/// Any pixel values above (or equal to) threshold will be changed to 255 (white).
/// </summary>
/// <param name="imageBytes">Image bytes</param>
/// <param name="bitmapData">Pixel depth</param>
/// <param name="threshold">Threshold value</param>
private static void ApplyDirect(byte[] imageBytes, BitmapData bitmapData, byte threshold)
{
if (bitmapData.IsColor())
{
int pixelDepth = bitmapData.GetPixelDepth();
int stride = bitmapData.Stride;
int width = bitmapData.GetStrideWithoutPadding();
int height = bitmapData.Height;
int limit = bitmapData.GetSafeArrayLimitForImage(imageBytes);
// Exclude alpha/transparency byte when averaging
int thresholdByteLength = Math.Min(pixelDepth, Constants.PixelDepthRGB);
int pixelSum;
bool belowThreshold;
// Find distribution of pixels at each level
for (int y = 0; y < height; y++)
{
// Images may have extra bytes per row to pad for CPU addressing.
// so need to ensure we traverse to the correct byte when moving between rows.
int offset = y * stride;
for (int x = 0; x < width; x += pixelDepth)
{
int i = offset + x;
if (i < limit)
{
pixelSum = 0;
// Sum each pixel component
for (int j = 0; j < thresholdByteLength && i + j < imageBytes.Length; j++)
{
pixelSum += imageBytes[i + j];
}
// Compare average to threshold
belowThreshold = (pixelSum / thresholdByteLength) < threshold;
// Apply threshold
for (int j = 0; j < thresholdByteLength && i + j < imageBytes.Length; j++)
{
imageBytes[i + j] = belowThreshold ? byte.MinValue : byte.MaxValue;
}
}
else
{
break;
}
}
}
}
else
{
// Apply threshold value to image
for (int i = 0; i < imageBytes.Length; i++)
{
imageBytes[i] = imageBytes[i] < threshold ? byte.MinValue : byte.MaxValue;
}
}
}