Hi All,
I had also faced a similar issue while loading 32 bit bitmaps with alpha channel.I had overcome this issue by creating a new memory bitmap with alpha channel(32bppArgb) and copying the rgb values of original bitmap via a BitmapData object.
using (MemoryStream ms = new MemoryStream(File.ReadAllBytes(@"C:\test32.bmp")))
{
using (bitmapImage = (Bitmap)Bitmap.FromStream(ms, true, false))
{
if (Bitmap.GetPixelFormatSize(bitmapImage.PixelFormat) == 32)
{
// Allocate the destination bitmap in ARGB format
Bitmap bitmapARGBImage = new Bitmap(bitmapImage.Width, bitmapImage.Height, PixelFormat.Format32bppArgb);
// Lock the original bitmap's bits
BitmapData bmpData = bitmapImage.LockBits(new Rectangle(0, 0, bitmapImage.Width, bitmapImage.Height),
ImageLockMode.WriteOnly, bitmapImage.PixelFormat);
// Declare an array to hold the bytes of the original bitmap
byte[] rgbValues = new byte[bmpData.Stride * bitmapImage.Height];
// Copy the RGB values into the array
// bmpData.Scan0 is the address of the first pixel data in the bitmap
Marshal.Copy(bmpData.Scan0, rgbValues, 0, bmpData.Stride * bitmapImage.Height);
// Unlock the bits from the system memory
bitmapImage.UnlockBits(bmpData);
// Release bitmap data
if (bmpData != null) bmpData = null;
// Lock the new memory bitmap with alphachannel bitmap's bits
bmpData = bitmapARGBImage.LockBits(new Rectangle(0, 0, bitmapARGBImage.Width, bitmapARGBImage.Height),
ImageLockMode.WriteOnly, bitmapARGBImage.PixelFormat);
// Copy the RGB values of original bitmap back to the new bitmap with alpha channel
Marshal.Copy(rgbValues, 0, bmpData.Scan0, bmpData.Stride * bitmapARGBImage.Height);
// Unlock the bits from the system memory
bitmapARGBImage.UnlockBits(bmpData);
// Save the image to the memory stream and convert it to Png format
bitmapARGBImage.Save(ms, ImageFormat.Png);
// Set the page's content type
context.Response.ContentType = "image/png";
// Send the image to the browser
ms.WriteTo(context.Response.OutputStream);
// Release resources
if (bmpData != null) bmpData = null;
if (rgbValues != null) rgbValues = null;
}
}
}
Hope this helps!
Thanks,
Vinay \m/
