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

Also what is this `imageData` you speak of, its not referenced anywhere in the code or information you supplied — TheGeneral, Feb 14 '18 at 02:27
Also `FromHbitmap` converts form GDI bitmap handle, of type` HBITMAP` does the documentation say this is what is returned — TheGeneral, Feb 14 '18 at 02:29
Also the Title Description is innately broad. Who knows what that intPtr points to, it could be a Goldfish for all we know — TheGeneral, Feb 14 '18 at 02:31
FromHBitmap didn’t work because the fingerprint image pointer probably lacks the bitmap header. Try the [Bitmap constructor](https://msdn.microsoft.com/de-de/library/zy1a2d14(v=vs.110).aspx) where PixelFormat would need to be derived from IBSU_ImageFormat and the stride could be the (positive) Pitch or can be calculated as Width*BitsPerPixel/8+additional padding — ckuri, Feb 14 '18 at 02:39

Nyerguds · Answer 1 · 2018-02-14T09:11:34.663

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;
}

C# Convert IntPtr to Bitmap

1 Answers1