CODEWITHSUNDEEP
c#winformswebcam
Colin Docherty
Colin Docherty

Reputation: 111

Issue with correctly displaying a USB Camera input to winforms picturebox

I have a USB videocamera that spits out 640x480 image data frames that I'd like to put in a winforms pictureBox. When I map the data onto the pictureBox using SetPixel the image looks fine, but SetPixel is crushingly slow, so I tried this instead:

    void CreateBitmap()
    {
        int width = bitmap.Width;
        int height = bitmap.Height;
        int n = 0;

        // copy normalized data into 1D array
        lock (imageDataLocker)
        {
            for (int i = 0; i < width; ++i)
            {
                for (int j = 0; j < height; ++j)
                {
                    Color c = Colorizer.GetColor(imageData[i, j]);
                    rgbValues[n] = c.R;
                    rgbValues[n + 1] = c.G;
                    rgbValues[n + 2] = c.B;
                    n += 3;
                }
            }
        }

        // Copy image data into the bitmap
        Rectangle rect = new Rectangle(0, 0, width, height);
        BitmapData bitmapData = bitmap.LockBits(rect, ImageLockMode.WriteOnly, bitmap.PixelFormat);
        IntPtr ptr = bitmapData.Scan0;
        int bytes = rgbValues.Length;
        System.Runtime.InteropServices.Marshal.Copy(rgbValues, 0, ptr, bytes);
        bitmap.UnlockBits(bitmapData);
    }

Where rgbValues is a 1D byte array containing 3 bytes per pixel, imageData is a 2D int array supplied by the camera, and bitmap has a 24bppRgb format. I don't get any errors with this, but when I assign the bitmap to the BackgroundImage of my pictureBox there is a strange banding effect:

WEbcam

What am I missing here?

Upvotes: 0

Views: 563

Answers (1)

svenv
svenv

Reputation: 323

First of all, I think your outer loop should be j=0; j

I tested this with this simple pattern which makes a bitmap with the left half blue and the right half black.

        Bitmap bm = new Bitmap(16, 16, System.Drawing.Imaging.PixelFormat.Format24bppRgb);

        BitmapData bitmapData = bm.LockBits(new Rectangle(0,0,16,16), ImageLockMode.WriteOnly, bm.PixelFormat);
        IntPtr ptr = bitmapData.Scan0;

        byte[] rgbValues = new byte[16 * 16 * 3];

        int b = 0;

        for (int y = 0; y < bm.Height; y++)
        {
            for (int x = 0; x < bm.Width; x++)
            {
                if (x < 7)
                {
                    rgbValues[b++] = 255; // BLUE, not red!
                    rgbValues[b++] = 0; // g
                    rgbValues[b++] = 0; // r
                }
                else
                {
                    rgbValues[b++] = 0; // r
                    rgbValues[b++] = 0; // g
                    rgbValues[b++] = 0; // b

                }
            }
        }

        int bytes = rgbValues.Length;
        System.Runtime.InteropServices.Marshal.Copy(rgbValues, 0, ptr, bytes);
        bm.UnlockBits(bitmapData);
        pictureBox1.Image = bm;

    }

Also, note that the first byte you write should be the BLUE component, then green, then red.

Upvotes: 1

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