To fix the pixel shift or discoloration issue search for
data[dataOffset + 0] = pixels[pixelOffset + 0];
data[dataOffset + 1] = pixels[pixelOffset + 1];
data[dataOffset + 2] = pixels[pixelOffset + 2];
data[dataOffset + 3] = pixels[pixelOffset + 3];
if (y > 0)
{
int lastOffset = ((y - 1) * _image.PixelWidth + x) * 4;
data[dataOffset + 0] -= pixels[lastOffset + 0];
data[dataOffset + 1] -= pixels[lastOffset + 1];
data[dataOffset + 2] -= pixels[lastOffset + 2];
data[dataOffset + 3] -= pixels[lastOffset + 3];
}
data[dataOffset + 0] = pixels[pixelOffset + 2];
data[dataOffset + 1] = pixels[pixelOffset + 1];
data[dataOffset + 2] = pixels[pixelOffset + 0];
data[dataOffset + 3] = pixels[pixelOffset + 3];
if (y > 0)
{
int lastOffset = ((y - 1) * _image.PixelWidth + x) * 4;
data[dataOffset + 0] -= pixels[lastOffset + 2];
data[dataOffset + 1] -= pixels[lastOffset + 1];
data[dataOffset + 2] -= pixels[lastOffset + 0];
data[dataOffset + 3] -= pixels[lastOffset + 3];
}