Question

I am trying to copy camera metadata into a Bitmap, and seing as each value in the metadata is a 16bit (or ushort) I thought it would be sensible to display it in a 16bpp garyscale Bitmap. The code I wrote is as follows:

// Getting the metadata from the device
metaData = new DepthMetaData();
dataSource.GetMetaData(metaData);

// Setting up bitmap, rect and data to use pointer
Bitmap bitmap = new Bitmap(metaData.XRes, metaData.YRes, PixelFormat.Format16bppGrayScale);
Rectangle rect = new Rectangle(0, 0, bitmap.Width, bitmap.Height);
BitmapData data = bitmap.LockBits(rect, ImageLockMode.WriteOnly, PixelFormat.Format16bppGrayScale);

// Pointer pointing to metadata
ushort* ptrMetaData = (ushort*)dataSource.DepthMapPtr.ToPointer();

lock(this)
{
    // Runs through the whole bitmap and assigns the entry in the metadata
    // to a pixel
    for (int y = 0; y < bitmap.Height; ++y)
    {
        ushort* ptrDestination = (ushort*)data.Scan0.ToPointer() + y * data.Stride;
        for (int x = 0; x < bitmap.Width; ++x, ++ptrMetaData)
        {
            ptrDestination[x] = (ushort)*ptrMetaData;
        }
    }
}

// Once done unlock the bitmap so that it can be read again
bitmap.UnlockBits(data);

When running the Metadata’s XRes = 640 and YRes = 480. The code throws a memory access exception in the for-loops on “ptrDestination[x] = (ushort)*ptrMetaData;” after only running though 240, half the total, lines.

I used this with 8bpp where I reduced the resolution and it worked nicely, so I don’t see why it should not here. Maybe someone finds the problem.

Thanks already

Answer 1

    ushort* ptrDestination = (ushort*)data.Scan0.ToPointer() + y * data.Stride;

The data.Stride value is expressed in bytes, not ushorts. So the pointer is off by a factor of 2 so it bombs at bitmap.Height/2. Your for loops are broken, swap bitmap.Width and bitmap.Height. The lock keyword doesn’t make much sense here, you are accessing thread-local data, other than dataSource. Fix:

for (int y = 0; y < bitmap.Height; ++y)
{
    ushort* ptrDestination = (ushort*)data.Scan0.ToPointer() + y * data.Stride / 2;
    for (int x = 0; x < bitmap.Width; ++x, ++ptrMetaData)
    {
        ptrDestination[x] = (ushort)*ptrMetaData;
    }
}