I am trying to generate 16bit grayscale Bitmap in C# from a random data.But it crashed on Marshal.Copy.
Here is my code:
Bitmap b16bpp;
private void GenerateDummy16bitImage()
{
b16bpp = new Bitmap(IMAGE_WIDTH, IMAGE_HEIGHT, System.Drawing.Imaging.PixelFormat.Format16bppGrayScale);
var rect = new Rectangle(0, 0, IMAGE_WIDTH, IMAGE_HEIGHT);
var bitmapData = b16bpp.LockBits(rect, ImageLockMode.WriteOnly, b16bpp.PixelFormat);
// Calculate the number of bytes required and allocate them.
var numberOfBytes = bitmapData.Stride * IMAGE_HEIGHT * 2;
var bitmapBytes = new short[numberOfBytes];
// Fill the bitmap bytes with random data.
var random = new Random();
for (int x = 0; x < IMAGE_WIDTH; x++)
{
for (int y = 0; y < IMAGE_HEIGHT; y++)
{
var i = ((y * IMAGE_WIDTH) + x) * 2; // 16bpp
// Generate the next random pixel color value.
var value = (short)random.Next(5);
bitmapBytes[i] = value; // BLUE
bitmapBytes[i + 1] = value; // GREEN
bitmapBytes[i + 2] = value; // RED
// bitmapBytes[i + 3] = 0xFF; // ALPHA
}
}
// Copy the randomized bits to the bitmap pointer.
var ptr = bitmapData.Scan0;
Marshal.Copy(bitmapBytes, 0, ptr, numberOfBytes);//crashes here
// Unlock the bitmap, we're all done.
b16bpp.UnlockBits(bitmapData);
b16bpp.Save("random.bmp", ImageFormat.Bmp);
Debug.WriteLine("saved");
}
The exception is:
An unhandled exception of type 'System.AccessViolationException' occurred in mscorlib.dll
This is not my code.I found it in relation to 32bit Bitmaps and modified.But I guess I have missed something as I am pretty new to C#.
Basically,all I need is to wrap into BitmapData an arrays of shorts.
Solved
I have corrected some of your mistakes (mostly wrong sizes). But it will still crash on b16bpp.Save(), because GDI+ does not support saving 16bit grayscale images.
Bitmap b16bpp;
private void GenerateDummy16bitImage()
{
b16bpp = new Bitmap(IMAGE_WIDTH, IMAGE_HEIGHT, System.Drawing.Imaging.PixelFormat.Format16bppGrayScale);
var rect = new Rectangle(0, 0, IMAGE_WIDTH, IMAGE_HEIGHT);
var bitmapData = b16bpp.LockBits(rect, ImageLockMode.WriteOnly, b16bpp.PixelFormat);
// Calculate the number of bytes required and allocate them.
var numberOfBytes = bitmapData.Stride * IMAGE_HEIGHT;
var bitmapBytes = new short[IMAGE_WIDTH * IMAGE_HEIGHT];
// Fill the bitmap bytes with random data.
var random = new Random();
for (int x = 0; x < IMAGE_WIDTH; x++)
{
for (int y = 0; y < IMAGE_HEIGHT; y++)
{
var i = ((y * IMAGE_WIDTH) + x); // 16bpp
// Generate the next random pixel color value.
var value = (short)random.Next(5);
bitmapBytes[i] = value; // GRAY
}
}
// Copy the randomized bits to the bitmap pointer.
var ptr = bitmapData.Scan0;
Marshal.Copy(bitmapBytes, 0, ptr, bitmapBytes.Length);
// Unlock the bitmap, we're all done.
b16bpp.UnlockBits(bitmapData);
b16bpp.Save("random.bmp", ImageFormat.Bmp);
Debug.WriteLine("saved");
}
Explanation of my changes:
bitmapData.Stride is already IMAGE_WIDTH * BytesPerPixel so you don't need to multiply by 2- as you declared
bitmapBytes as short[] it has to have the size of the image in pixels not in bytes
- that means you also do not need to multiply
i by 2
- since you have a grayscale image it does not have a blue, green and red channel, but one single 16bit gray channel
- Marshal.Copy takes the length in "array units" not in bytes
All in all you tried to copy an array 8 times to large into the bitmap.
This works for System.Drawing.Imaging.PixelFormat.Format16bppGrayScale:
private static void SaveBmp(Bitmap bmp, string path)
{
Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height);
BitmapData bitmapData = bmp.LockBits(rect, ImageLockMode.ReadOnly, bmp.PixelFormat);
var pixelFormats = ConvertBmpPixelFormat(bmp.PixelFormat);
BitmapSource source = BitmapSource.Create(bmp.Width,
bmp.Height,
bmp.HorizontalResolution,
bmp.VerticalResolution,
pixelFormats,
null,
bitmapData.Scan0,
bitmapData.Stride * bmp.Height,
bitmapData.Stride);
bmp.UnlockBits(bitmapData);
FileStream stream = new FileStream(path, FileMode.Create);
TiffBitmapEncoder encoder = new TiffBitmapEncoder();
encoder.Compression = TiffCompressOption.Zip;
encoder.Frames.Add(BitmapFrame.Create(source));
encoder.Save(stream);
stream.Close();
}
private static System.Windows.Media.PixelFormat ConvertBmpPixelFormat(System.Drawing.Imaging.PixelFormat pixelformat)
{
System.Windows.Media.PixelFormat pixelFormats = System.Windows.Media.PixelFormats.Default;
switch (pixelformat)
{
case System.Drawing.Imaging.PixelFormat.Format32bppArgb:
pixelFormats = PixelFormats.Bgr32;
break;
case System.Drawing.Imaging.PixelFormat.Format8bppIndexed:
pixelFormats = PixelFormats.Gray8;
break;
case System.Drawing.Imaging.PixelFormat.Format16bppGrayScale:
pixelFormats = PixelFormats.Gray16;
break;
}
return pixelFormats;
}
