colorkey problem for DirectDraw

I have a 24 bit BMP image with 96x96 tiles, with a background color (which is neither black or white) for transparency. It is loaded on to a surface of smaller size so as expected the image is shrunk according to the surface size. But as a result, there was no transparency, somehow the color has changed. But if i load the image with the correct size, it works. Even by loading onto a surface half the image size, it works... I included an excerpt from my code that I used for converting the color key from RGB to the integer color value. ///

/// Counts the width of bits. ///

private byte countBitWidth( int _i ) { uint i = (uint)_i; while((i&1)==0) i>>=1; byte w=0; while(i!=0) { i >>= 1; w++; } return w; } ///

/// Converts a Color into a fill value. ///

private uint colorToFill( Color c , DirectDrawSurface7 surface) { byte widthR,widthB,widthG; // compute the bit shift width for color fill DDPIXELFORMAT pixelFormat = new DDPIXELFORMAT(); surface.GetPixelFormat( ref pixelFormat ); widthR = countBitWidth(pixelFormat.lRBitMask); widthG = countBitWidth(pixelFormat.lGBitMask); widthB = countBitWidth(pixelFormat.lBBitMask); uint x = 0; x |= ((uint)c.R)>>(8-widthR); x <<= widthG; x |= ((uint)c.G)>>(8-widthG); x <<= widthB; x |= ((uint)c.B)>>(8-widthB); return x; } Is there anyone who can solve this problem?