I've been experimenting with the best way to merge two images in C#. That is, paint one image on top of another with some level of transparency as opposed to using one color as a transparency mask. I tried three candidates, all included below:
SimpleBlend: 17.69 seconds
I expect ManualBlend could be optimized further but both this and MatrixBlend are an order of magnitude faster than the naive approach. I'll be using MatrixBlend as no unsafe code is required.
private static void SimpleBlend(string image1path, string image2path, byte alpha)
{
using (Bitmap image1 = (Bitmap)Bitmap.FromFile(image1path))
{
using (Bitmap image2 = (Bitmap)Bitmap.FromFile(image2path))
{
// update the alpha for each pixel of image 2
for (int x = 0; x < image2.Width; x++)
{
for (int y = 0; y < image2.Height; y++)
{
image2.SetPixel(x, y, Color.FromArgb(alpha, image2.GetPixel(x, y)));
}
}
// draw image 2 on image 1
using (Graphics g = Graphics.FromImage(image1))
{
g.CompositingMode = CompositingMode.SourceOver;
g.CompositingQuality = CompositingQuality.HighQuality;
g.DrawImageUnscaled(image2, 0, 0);
}
}
}
}
private static void MatrixBlend(string image1path, string image2path, byte alpha)
{
// for the matrix the range is 0.0 - 1.0
float alphaNorm = (float)alpha / 255.0F;
using (Bitmap image1 = (Bitmap)Bitmap.FromFile(image1path))
{
using (Bitmap image2 = (Bitmap)Bitmap.FromFile(image2path))
{
// just change the alpha
ColorMatrix matrix = new ColorMatrix(new float[][]{
new float[] {1F, 0, 0, 0, 0},
new float[] {0, 1F, 0, 0, 0},
new float[] {0, 0, 1F, 0, 0},
new float[] {0, 0, 0, alphaNorm, 0},
new float[] {0, 0, 0, 0, 1F}});
ImageAttributes imageAttributes = new ImageAttributes();
imageAttributes.SetColorMatrix(matrix);
using (Graphics g = Graphics.FromImage(image1))
{
g.CompositingMode = CompositingMode.SourceOver;
g.CompositingQuality = CompositingQuality.HighQuality;
g.DrawImage(image2,
new Rectangle(0, 0, image1.Width, image1.Height),
0,
0,
image2.Width,
image2.Height,
GraphicsUnit.Pixel,
imageAttributes);
}
}
}
}
private static void ManualBlend(string image1path, string image2path, byte alpha)
{
// percentage of destination and source image
float alphaDst = (float)alpha / 255.0F;
float alphaSrc = 1.0F - alphaDst;
using (Bitmap image1 = (Bitmap)Bitmap.FromFile(image1path))
{
Rectangle imageRect = new Rectangle(0, 0, image1.Width, image1.Height);
BitmapData image1Data = image1.LockBits(imageRect, ImageLockMode.ReadWrite,
PixelFormat.Format32bppArgb);
using (Bitmap image2 = (Bitmap)Bitmap.FromFile(image2path))
{
BitmapData image2Data = image2.LockBits(imageRect, ImageLockMode.ReadOnly,
PixelFormat.Format32bppArgb);
unsafe
{
uint* image1Raw = (uint*)image1Data.Scan0.ToPointer();
uint* image2Raw = (uint*)image2Data.Scan0.ToPointer();
int stride = image1Data.Stride / sizeof(uint);
int currentPixel;
uint image1Pixel, image2Pixel;
uint srcRed, dstRed, finRed;
uint srcGreen, dstGreen, finGreen;
uint srcBlue, dstBlue, finBlue;
for (int x = 0; x < imageRect.Width; x++)
{
for (int y = 0; y < imageRect.Height; y++)
{
currentPixel = (y * stride) + x;
image1Pixel = image1Raw[currentPixel];
image2Pixel = image2Raw[currentPixel];
srcRed = (image1Pixel >> 16) & 0xFF;
srcGreen = (image1Pixel >> 8) & 0xFF;
srcBlue = image1Pixel & 0xFF;
dstRed = (image2Pixel >> 16) & 0xFF;
dstGreen = (image2Pixel >> 8) & 0xFF;
dstBlue = image2Pixel & 0xFF;
finRed = (uint)((alphaSrc * (float)srcRed) +
(alphaDst * (float)dstRed));
finGreen = (uint)((alphaSrc * (float)srcGreen) +
(alphaDst * (float)dstGreen));
finBlue = (uint)((alphaSrc * (float)srcBlue) +
(alphaDst * (float)dstBlue));
image1Raw[currentPixel] =
(uint)(finBlue | finGreen << 8 | finRed << 16 | 0xFF << 24);
}
}
}
image2.UnlockBits(image2Data);
}
image1.UnlockBits(image1Data);
}
}Add your comment...
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