C# Convert IntPtr to Bitmap

Question

I am trying to get a Bitmap image from a fingerprint device SDK. The SDK provided a struct for preview image, I failed to convert it to Bitmap:

public struct IBSU_ImageData
{
    /* Pointer to image buffer.  If this structure is supplied by a callback function, this pointer 
     * must not be retained; the data should be copied to an application buffer for any processing
     * after the callback returns. */
    public IntPtr Buffer;

    /* Image horizontal size (in pixels). */
    public uint Width;

    /* Image vertical size (in pixels). */
    public uint Height;

    /* Horizontal image resolution (in pixels/inch). */
    public double ResolutionX;

    /* Vertical image resolution (in pixels/inch). */
    public double ResolutionY;

    /* Image acquisition time, excluding processing time (in seconds). */
    public double FrameTime;

    /* Image line pitch (in bytes).  A positive value indicates top-down line order; a negative 
     * value indicates bottom-up line order. */
    public int Pitch;

    /* Number of bits per pixel. */
    public byte BitsPerPixel;

    /* Image color format. */
    public IBSU_ImageFormat Format;

    /* Marks image as the final processed result from the capture.  If this is FALSE, the image is
     * a preview image or a preliminary result. */
    public bool IsFinal;

    /* Threshold of image processing. */
    public uint ProcessThres;
}

public enum IBSU_ImageFormat
{
    IBSU_IMG_FORMAT_GRAY,                                    /* Gray scale image. */
    IBSU_IMG_FORMAT_RGB24,                                   /* 24 bit RGB color image. */
    IBSU_IMG_FORMAT_RGB32,                                   /* True color RGB image. */
    IBSU_IMG_FORMAT_UNKNOWN                                  /* Unknown format. */
}

I've tried use Image.FromHbitmap(imageData) but not work.

I debug and give the IBSU_ImageData content:

Buffer : 0x1741d020
Width : 1600
Height : 1500
ResolutionX : 500
ResolutionY : 500
FrameTime : 0.100421
Pitch : -1600
BitsPerPixel : 8
Format : IBSU_IMG_FORMAT_GRAY
IsFinal : false
ProcessThres : 2

Answer 1

You have all the data you need. Simply construct the image from that data. I wrote a function before that can build a Bitmap from a byte array and the relevant information.

You can copy the buffer contents from the Buffer pointer using Marshal.Copy, into an array of pitch * height bytes. You just need to be careful with the negative pitch, though; it indicates BMP-style bottom-to-top lines.

public static Bitmap GetBitmapFromIBSU(IBSU_ImageData imageData)
{
    // Can't handle this.
    if (imageData.Format == IBSU_ImageFormat.IBSU_IMG_FORMAT_UNKNOWN)
        throw new NotSupportedException();
    Byte[] data = new byte[imageData.Width * Math.Abs(imageData.Pitch)];
    Marshal.Copy(imageData.Buffer, data, 0, data.Length);
    // Write this function yourself. They're both enums so a simple switch-case should do.
    // GRAY probably needs to be seen as indexed 8bpp; then you need to give a generated
    // 256-entry black-to-white colour fade palette to BuildImage in the next step.
    PixelFormat format = ConvertPixelformat(imageData.Format);
    // The function I linked in the description.
    Bitmap image = BuildImage(data, imageData.Width, imageData.Height, imageData.Pitch, format, null, null);
    bitmap.SetResolution(imageData.ResolutionX, imageData.ResolutionY);
    return bitmap;
}

Answer 2

        public static Bitmap toBitmap(this IBSU_ImageData imageData)
    {
        int w = (int)imageData.Width;
        int h = (int)imageData.Height;

        byte[] pixels = new byte[w * h];

        Marshal.Copy(imageData.Buffer, pixels, 0, pixels.Length);

        var bitmap = new Bitmap(w, h, PixelFormat.Format8bppIndexed);

        //bitmap.SetResolution((float)imageData.ResolutionY,
        //                     (float)imageData.ResolutionX);

        ///////////////////////////////////////
        // Set grayscale palette
        ///////////////////////////////////////
        ColorPalette colorPalette = bitmap.Palette;
        for (int i = 0; i < colorPalette.Entries.Length; i++)
        {
            colorPalette.Entries[i] = Color.FromArgb(i, i, i);
        }

        bitmap.Palette = colorPalette;

        var _imageData = bitmap.LockBits(new Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed);

        Marshal.Copy(pixels, 0, _imageData.Scan0, pixels.Length);

        bitmap.UnlockBits(_imageData);
        return bitmap;
    }