Extracting color from image in C# using lockbits method.

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C#

.NET

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image

I want to extract blue color from image, I wrote code for it. I am using lockbits method in C#.
24 bit image - BGR
[0] = Blue
[1] = Green
[2] = Red
Here is code -

BitmapData bitmapdata = bitmap.LockBits (
                            new Rectangle(
                                0,
                                0,
                                bitmap.Width,
                                bitmap.Height),
                            ImageLockMode.ReadWrite,
                            PixelFormat.Format24bppRgb );
IntPtr                  ptr = bitmapdata.Scan0;
                                     // declare  an array to hold
                                     // the bytes of bitmap
int                     bytes = Math.Abs ( bitmapdata.Stride ) *
                                bitmap.Height;
byte [ ]                values = new byte [ bytes ];

System.Runtime.InteropServices.Marshal.Copy ( ptr, values, 0, bytes );

for ( int i = 0; ( i < values.Length ); i += 3 )
    {
                                     // Comparing blue and green and
                                     // blue and red. if blue is greater
                                     // than both pixel than make it
                                     // more intensive otherwise make white
    if ( ( values [ i ] - values [ i + 1 ] > 9 ) &&
         ( values [ i ] - values [ i + 2 ] > 9 )
        {
        values [ i ] = 255;
        values [ i + 1 ] = 0;
        values [ i + 2 ] = 0;
        }
    else
        {
        values [ i ] =  255;
        values [ i + 1 ] =  255;
        values [ i + 2 ] =   255;
        }
    }
bitmap.Save("bitmap.jpg");

This code is working fine but in one image I got problem, it was extracting red color instead of blue when the image has no color.
This image should be white when I run this code.
I don't want to use getpixel or setpixel method.
Image attached.