problem with image processing

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i have 3 code!!they have no error but i dont know a problem!!time to run code1 and code2 is slower than code3 and the result image is not true but i think code1 and code2 are better than code 3!!Can you explain me for this problem??

Code 1:

public static void chinhdosang(Bitmap bm, int dosang)
        {
            Rectangle rec = new Rectangle(0, 0, bm.Width, bm.Height);
            BitmapData bmdata = bm.LockBits(rec, ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
            IntPtr ptr = bmdata.Scan0;
            int stride = bmdata.Stride;
            int offset = stride - bm.Width * 3;
            int n = stride * bm.Height;
            byte[] rgbvalue = new byte[n];
            System.Runtime.InteropServices.Marshal.Copy(ptr, rgbvalue, 0, n);
            int temp,x,y;
            for (y = 0; y < bm.Height; y++)
            {
                for (x = 0; x < bm.Width; x++)
                {
                    int i;
                    i = y * stride + x;
                    temp = (int)rgbvalue[i] + dosang;
                    if (temp < 0) temp = 0;
                    if (temp > 255) temp = 255;
                    rgbvalue[i] = (byte)temp;

                }
            }
            System.Runtime.InteropServices.Marshal.Copy(rgbvalue, 0, ptr, n);
            bm.UnlockBits(bmdata);
            

 
        }

Code 2:

public static void chinhdosang(Bitmap bm, double dosang)
        {
            Rectangle rec = new Rectangle(0, 0, bm.Width, bm.Height);
            BitmapData bmdata = bm.LockBits(rec, ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
            int stride = bmdata.Stride;
            IntPtr ptr = bmdata.Scan0;
            int offset = stride - bm.Width * 3;
            unsafe
            {
                byte* p = (byte*)ptr;
                int x, y;
                double value;
                for (y =0;y<bm.Height;y++)
                {
                    for (x = 0; x < bm.Width; x++)
                    {
                        value = (double)(p[0]) + dosang;
                        if (value < 0) value = 0;
                        if (value > 255) value = 255;
                        p[0] = (byte) value;
                        ++p;


                    }
                    p += offset;
                }

            }
            bm.UnlockBits(bmdata);
}

Code 3:

public static void chinhdosang(Bitmap bm, int dosang)
        {
            Rectangle rec = new Rectangle(0, 0, bm.Width, bm.Height);
            BitmapData bmdata = bm.LockBits(rec, ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
            IntPtr ptr = bmdata.Scan0;
            int stride = bmdata.Stride;
            int offset = stride - bm.Width * 3;
            int n = bm.Width * bm.Height * 3;
            byte[] rgbvalue = new byte[n];
            System.Runtime.InteropServices.Marshal.Copy(ptr, rgbvalue, 0, n);
            int temp,x,y;
            
                for ( int i = 0; i < n; i++)
                {
                    
                    //i = y * stride + x;
                    temp = (int)rgbvalue[i] + dosang;
                    if (temp < 0) temp = 0;
                    if (temp > 255) temp = 255;
                    rgbvalue[i] = (byte)temp;

                }
            
            System.Runtime.InteropServices.Marshal.Copy(rgbvalue, 0, ptr, n);
            bm.UnlockBits(bmdata);
            

 
        }

Posted 26-Sep-10 16:43pm

chuot chui

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E.F. Nijboer · Answer 1 · 2010-09-27T06:57:00

You need to keep in mind that you have an image with a pixel format of 24bit. This means that each pixel is using 3 bytes of color information horizontally. This is not the case for vertically,

First of all, your calculation is not correct:
int n = bm.Width * bm.Height * 3;

When for example take a width of 10 and height of 100 the calculation would be 10*100*3 and is 3000. This isn't correct and should be height * (width * 30) which would be 100 * (10 * 3) and is 300.

Second, the loop needs to process each color information byte of each pixel, so horizontally you need to multiply by 3 (not vertically).

C#

for (y =0;y<bm.Height;y++)
{
   for (x = 0; x < bm.Width * 3; x++)
...

Good luck!

chuot chui · Answer 2 · 2010-09-27T08:45:00

Solution 2

thanks!i knew what mistake is!haha!thanks again!

Posted 27-Sep-10 8:45am