Why i get bad image result from my webcamera?

Question

I am getting wrong image result from SampleGrabber filter. Instead of colourfull image, image is in grayscale with red/green pixels between and image is repeated twice horizontaly.

I had to forget something important.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using DirectShowLib;
using System.Runtime.InteropServices;
using System.Drawing.Imaging;

namespace WindowsFormsApplication3
{
    public partial class Form1 : Form
    {
        public IGraphBuilder gb;
        public ICaptureGraphBuilder2 cgb;
        public IBaseFilter filter;
        static SampleGrabberCallback cb;
        VideoInfoHeader header;
        static Form1 thisform;

        public class SampleGrabberCallback : ISampleGrabberCB
        {

            int ISampleGrabberCB.SampleCB(Double SampleTime, IMediaSample sample)
            {
                return 0;
            }

            int ISampleGrabberCB.BufferCB(Double SampleTime, IntPtr dataPtr, Int32 BufferLen)
            {
                Bitmap bitmap = new Bitmap(640, 480, 640 * 3, PixelFormat.Format24bppRgb, dataPtr);

                Graphics g = thisform.panel1.CreateGraphics();
                g.DrawImageUnscaled(bitmap, 0, 0, 640, 480);

                return 0;
            }
        }

        public Form1()
        {
            InitializeComponent();
            thisform = this;

            DsDevice[] videoInputDevices = DsDevice.GetDevicesOfCat(FilterCategory.VideoInputDevice);
            object obj = null; Guid iid = typeof(IBaseFilter).GUID;
            videoInputDevices[1].Mon.BindToObject(null, null, ref iid, out obj);
            filter = (IBaseFilter)obj;
            ISampleGrabber grabberFilter = (ISampleGrabber)new SampleGrabber();
            IBaseFilter baseGrabber = (IBaseFilter)grabberFilter;

            ((IAMCameraControl)filter).Set(CameraControlProperty.Exposure, 0, CameraControlFlags.Auto);

            gb = (IGraphBuilder)new FilterGraph();
            cgb = (ICaptureGraphBuilder2)new CaptureGraphBuilder2();

            cgb.SetFiltergraph(gb);

            IEnumPins pins;
            IPin[] inputPin = { null };
            IPin[] outputPin = { null };

            filter.EnumPins(out pins);
            pins.Next(1, outputPin, IntPtr.Zero);

            baseGrabber.EnumPins(out pins);
            pins.Next(1, inputPin, IntPtr.Zero);

            gb.AddFilter(filter, "First Filter");
            gb.AddFilter(baseGrabber, "Grabber Filter");
            gb.Connect(outputPin[0], inputPin[0]);

            grabberFilter.SetBufferSamples(true);

            AMMediaType media = new AMMediaType();
            media.majorType = MediaType.Video;
            media.subType = MediaSubType.RGB24;
            media.formatPtr = IntPtr.Zero;

            grabberFilter.SetMediaType(media);
            grabberFilter.GetConnectedMediaType(media);
            header = (VideoInfoHeader)Marshal.PtrToStructure(media.formatPtr, typeof(VideoInfoHeader));

            cb = new SampleGrabberCallback();

            grabberFilter.SetCallback(cb, 1);

            cgb.RenderStream(PinCategory.Preview, MediaType.Video, filter, null, null);
            ((IMediaControl)gb).Run();
        }
    }
}

This is my code. I enumerated all video devices. My device has ID 1. I created filter where webcam data is passed then i connected samplegrabber filter to the previous filter. Callback function is called when image is ready.

Unfortunately, image output is wrong and i have no idea why.

Also callback says bufferlen is 614 400 bytes. Strange as it means that pixel has only 16 bits. (640*480*2). Does it mean, buffer has different colorspace ? YUV ? Most examples does not care about color space and it's working fine. Also i specified RGB24 in mediaType.

Thank you very much for helping me.

Answer 1

You are supposed to set your Sample Grabber up before connecting its input. Your request to make it 24-bit RGB is late and your actual connection and media type is different. You are still ignoring this on your callback and hence the broken picture.