I have an image of a signature I am trying to save as 1 bpp bitmap to save file space. The full .NET Framework has the enum PixelFormat.Format1bppIndexed, but the .NET Compact Framework does not supported it.
Has any one discovered a way to accomplish this in Windows Mobile?
Creating and saving a bitonal bitmap is problematic even in the full framework.
I previously authored an article on this issues involved.
http://www.codeproject.com/KB/GDI-plus/BitonalImageConverter.aspx
I revisited this code in the context of the compact framework and discovered as you did that the enum value does not exist, so you can't create a bitonal image from scratch.
I'd be interested to know if you can load pre-existing bitonal images in the compact framework. If you can load pre-existing bitonal bitmaps, then it might be possible to go lower level and write the bitmap image format to disk or a memory stream directly, rather than use the GDI+ objects, but it would be non-trivial to do so.
I had to do this in the past for generating black & white reports printed via Bluetooth (color or greyscale images were too large for the printer's buffer). Turned out I had to create the images using native code.
Here's a snippet:
private void CreateUnmanagedResources()
{
// for safety, clean up anything that was already allocated
ReleaseUnmanagedResources();
bih = new BITMAPINFOHEADER();
bih.biBitCount = 1;
bih.biClrImportant = 0;
bih.biClrUsed = 0;
bih.biCompression = 0;
bih.biHeight = m_cy;
bih.biPlanes = 1;
bih.biSize = (uint)(Marshal.SizeOf(typeof(BITMAPINFOHEADER)) - 8);
bih.biSizeImage = 0;
bih.biWidth = m_cx;
bih.biXPelsPerMeter = 0;
bih.biYPelsPerMeter = 0;
bih.clr2 = 0xffffff;
bih.clr1 = 0x0;
hDC = Win32.CreateCompatibleDC(IntPtr.Zero);
pBits = IntPtr.Zero;
hBitmap = Win32.CreateDIBSection(hDC, bih, 1, ref pBits, IntPtr.Zero, 0);
hbmOld = Win32.SelectObject(hDC, hBitmap);
}
private void ReleaseUnmanagedResources()
{
if (hbmOld != IntPtr.Zero)
Win32.SelectObject(hDC, hbmOld);
if(hBitmap != IntPtr.Zero)
Win32.DeleteObject(hBitmap);
if (hDC != IntPtr.Zero)
Win32.DeleteDC(hDC);
}
I then used Graphics.FromHdc to get a managed graphics object that I could paint the report onto.
I did saving with a BinaryWriter, but that was in CF 1.0 days when the Bitmap class didn't have a Save, so you're free and clear there.
Thanks for pointing me in the right direction, ctacke.
I was unable to use the Bitmap class to save the image data. It continually threw an OutOfMemoryException. I resorted to writing the bitmap out using a BinaryWriter, like you suggested.
My end solution returns a byte array, with which you can choose to write to disk, save to a database, transmit, etc.
class ImageHelper
{
[StructLayout(LayoutKind.Sequential)]
public struct BITMAPINFOHEADER
{
public BITMAPINFOHEADER(ushort bpp, int height, int width)
{
biBitCount = bpp;
biWidth = width;
biHeight = height;
biSize = (uint)Marshal.SizeOf(typeof(BITMAPINFOHEADER));
biPlanes = 1; // must be 1
biCompression = 0; // no compression
biSizeImage = 0; // no compression, so can be 0
biXPelsPerMeter = 0;
biYPelsPerMeter = 0;
biClrUsed = 0;
biClrImportant = 0;
}
public void Store(BinaryWriter bw)
{
Store(bw, null);
}
public void Store(BinaryWriter bw, uint[] colorPalette)
{
// Must maintain order for file writing
bw.Write(biSize);
bw.Write(biWidth);
bw.Write(biHeight);
bw.Write(biPlanes);
bw.Write(biBitCount);
bw.Write(biCompression);
bw.Write(biSizeImage);
bw.Write(biXPelsPerMeter);
bw.Write(biYPelsPerMeter);
bw.Write(biClrUsed);
bw.Write(biClrImportant);
// write color palette if 8 bpp or less
if (biBitCount <= 8)
{
if (colorPalette == null)
throw new ArgumentNullException("bpp is 8 or less, color palette is required");
uint paletteCount = BITMAPFILEHEADER.CalcPaletteSize(biBitCount) / 4;
if (colorPalette.Length < paletteCount)
throw new ArgumentException(string.Format("bpp is 8 or less, color palette must contain {0} colors", paletteCount));
foreach (uint color in colorPalette)
bw.Write(color);
}
}
public uint biSize;
public int biWidth;
public int biHeight;
public ushort biPlanes;
public ushort biBitCount;
public uint biCompression;
public uint biSizeImage;
public int biXPelsPerMeter;
public int biYPelsPerMeter;
public uint biClrUsed;
public uint biClrImportant;
}
[StructLayout(LayoutKind.Sequential)]
public struct BITMAPFILEHEADER
{
public BITMAPFILEHEADER(BITMAPINFOHEADER info, out uint sizeOfImageData)
{
bfType = 0x4D42; // Microsoft supplied value to indicate Bitmap 'BM'
bfReserved1 = 0;
bfReserved2 = 0;
// calculate amount of space needed for color palette
uint paletteSize = CalcPaletteSize(info.biBitCount);
bfOffBits = 54 + paletteSize; // default value + paletteSize
// calculate size of image
sizeOfImageData = (uint)(CalcRowSize(info.biWidth * info.biBitCount) * info.biHeight);
bfSize = sizeOfImageData + bfOffBits;
}
private static int CalcRowSize(int bits)
{
return ((((bits) + 31) / 32) * 4);
}
public static uint CalcPaletteSize(int bpp)
{
// 8 bpp or less, needs an uint per color
if (bpp <= 8)
return 4 * (uint)Math.Pow(2, bpp);
// no palette needed for 16bpp or higher
return 0;
}
public void Store(BinaryWriter bw)
{
// Must maintain order for file writing
bw.Write(bfType);
bw.Write(bfSize);
bw.Write(bfReserved1);
bw.Write(bfReserved2);
bw.Write(bfOffBits);
}
public ushort bfType;
public uint bfSize;
public short bfReserved1;
public short bfReserved2;
public uint bfOffBits;
}
public static byte[] GetByteArray(Bitmap image)
{
IntPtr hbmOld;
IntPtr hBitmap;
IntPtr hDC;
// create infoheader
BITMAPINFOHEADER bih = new BITMAPINFOHEADER(1, image.Height, image.Width);
// set black and white for 1 bit color palette
// create fileheader and get data size
uint sizeOfImageData;
BITMAPFILEHEADER bfh = new BITMAPFILEHEADER(bih, out sizeOfImageData);
// create device context in memory
hDC = Win32.CreateCompatibleDC(IntPtr.Zero);
// create a 1 bpp DIB
IntPtr pBits = IntPtr.Zero;
hBitmap = Win32.CreateDIBSection(hDC, ref bih, 1, ref pBits, IntPtr.Zero, 0);
// selet DIB into device context
hbmOld = Win32.SelectObject(hDC, hBitmap);
using (Graphics g = Graphics.FromHdc(hDC))
{
g.DrawImage(image, 0, 0);
}
byte[] imageData = new byte[sizeOfImageData];
byte[] fileData;
using (MemoryStream ms = new MemoryStream((int)bfh.bfSize))
{
using (BinaryWriter w = new BinaryWriter(ms))
{
bfh.Store(w);
// store bitmapinfoheader with 1 bpp color palette for black and white
bih.Store(w, new uint[] { (uint)0x0, (uint)0xffffff });
// copy image data into imageData buffer
Marshal.Copy(pBits, imageData, 0, imageData.Length);
// write imageData to stream
w.Write(imageData);
w.Close();
}
fileData = ms.GetBuffer();
ms.Close();
}
// select old object
if (hbmOld != IntPtr.Zero)
Win32.SelectObject(hDC, hbmOld);
// delete memory bitmap
if (hBitmap != IntPtr.Zero)
Win32.DeleteObject(hBitmap);
// delete memory device context
if (hDC != IntPtr.Zero)
Win32.DeleteDC(hDC);
return fileData;
}
}