Two image compare using win32 api c#

EDN Admin · Dec 11, 2012

i have two images and i want to compare two image and want to get difference. i search google and found a link from where i copy paste the code for image comparison using win32 api. so this is the url http://blog.bobcravens.com/2009/04/create-a-remote-desktop-viewer-using-c-and-wcf/ 
 
here i am pasting the code. 
 
private void button1_Click(object sender, EventArgs e) 
{ 
Bitmap _prevBitmap = new Bitmap(@"d

rev.jpg"); 
Bitmap _newBitmap = new Bitmap(@"d:current.jpg"); 
 
Rectangle bounds = GetBoundingBoxForChanges(_prevBitmap, _newBitmap); 
if (bounds == Rectangle.Empty) 
{ 
} 
 
Bitmap diff = new Bitmap(bounds.Width, bounds.Height); 
Graphics g = Graphics.FromImage(diff); 
g.DrawImage(_newBitmap, 0, 0, bounds, GraphicsUnit.Pixel); 
g.Dispose(); 
 
// Set the current bitmap as the previous to prepare 
// for the next screen capture. 
// 
diff.Save(@"d:diff.bmp"); 
 
//return diff; 
} 
 
private Rectangle GetBoundingBoxForChanges(Bitmap _prevBitmap, Bitmap _newBitmap) 
{ 
// The search algorithm starts by looking 
// for the top and left bounds. The search 
// starts in the upper-left corner and scans 
// left to right and then top to bottom. It uses 
// an adaptive approach on the pixels it 
// searches. Another pass is looks for the 
// lower and right bounds. The search starts 
// in the lower-right corner and scans right 
// to left and then bottom to top. Again, an 
// adaptive approach on the search area is used. 
// 
 
// Note: The GetPixel member of the Bitmap class 
// is too slow for this purpose. This is a good 
// case of using unsafe code to access pointers 
// to increase the speed. 
// 
 
// Validate the images are the same shape and type. 
// 
if (_prevBitmap.Width != _newBitmap.Width || 
_prevBitmap.Height != _newBitmap.Height || 
_prevBitmap.PixelFormat != _newBitmap.PixelFormat) 
{ 
// Not the same shape...cant do the search. 
// 
return Rectangle.Empty; 
} 
 
// Init the search parameters. 
// 
int width = _newBitmap.Width; 
int height = _newBitmap.Height; 
int left = width; 
int right = 0; 
int top = height; 
int bottom = 0; 
 
BitmapData bmNewData = null; 
BitmapData bmPrevData = null; 
try 
{ 
// Lock the bits into memory. 
// 
bmNewData = _newBitmap.LockBits( 
new Rectangle(0, 0, _newBitmap.Width, _newBitmap.Height), 
ImageLockMode.ReadOnly, _newBitmap.PixelFormat); 
bmPrevData = _prevBitmap.LockBits( 
new Rectangle(0, 0, _prevBitmap.Width, _prevBitmap.Height), 
ImageLockMode.ReadOnly, _prevBitmap.PixelFormat); 
 
// The images are ARGB (4 bytes) 
// 
int numBytesPerPixel = 4; 
 
// Get the number of integers (4 bytes) in each row 
// of the image. 
// 
int strideNew = bmNewData.Stride / numBytesPerPixel; 
int stridePrev = bmPrevData.Stride / numBytesPerPixel; 
 
// Get a pointer to the first pixel. 
// 
// Note: Another speed up implemented is that I dont 
// need the ARGB elements. I am only trying to detect 
// change. So this algorithm reads the 4 bytes as an 
// integer and compares the two numbers. 
// 
System.IntPtr scanNew0 = bmNewData.Scan0; 
System.IntPtr scanPrev0 = bmPrevData.Scan0; 
 
// Enter the unsafe code. 
// 
unsafe 
{ 
// Cast the safe pointers into unsafe pointers. 
// 
int* pNew = (int*)(void*)scanNew0; 
int* pPrev = (int*)(void*)scanPrev0; 
 
// First Pass - Find the left and top bounds 
// of the minimum bounding rectangle. Adapt the 
// number of pixels scanned from left to right so 
// we only scan up to the current bound. We also 
// initialize the bottom & right. This helps optimize 
// the second pass. 
// 
// For all rows of pixels (top to bottom) 
// 
for (int y = 0; y < _newBitmap.Height; ++y) 
{ 
// For pixels up to the current bound (left to right) 
// 
for (int x = 0; x < left; ++x) 
{ 
// Use pointer arithmetic to index the 
// next pixel in this row. 
// 
if ((pNew + x)[0] != (pPrev + x)[0]) 
{ 
// Found a change. 
// 
if (x < left) 
{ 
left = x; 
} 
if (x > right) 
{ 
right = x; 
} 
if (y < top) 
{ 
top = y; 
} 
if (y > bottom) 
{ 
bottom = y; 
} 
} 
} 
 
// Move the pointers to the next row. 
// 
pNew += strideNew; 
pPrev += stridePrev; 
} 
 
// If we did not find any changed pixels 
// then no need to do a second pass. 
// 
if (left != width) 
{ 
// Second Pass - The first pass found at 
// least one different pixel and has set 
// the left & top bounds. In addition, the 
// right & bottom bounds have been initialized. 
// Adapt the number of pixels scanned from right 
// to left so we only scan up to the current bound. 
// In addition, there is no need to scan past 
// the top bound. 
// 
 
// Set the pointers to the first element of the 
// bottom row. 
// 
pNew = (int*)(void*)scanNew0; 
pPrev = (int*)(void*)scanPrev0; 
pNew += (_newBitmap.Height - 1) * strideNew; 
pPrev += (_prevBitmap.Height - 1) * stridePrev; 
 
// For each row (bottom to top) 
// 
for (int y = _newBitmap.Height - 1; y > top; y--) 
{ 
// For each column (right to left) 
// 
for (int x = _newBitmap.Width - 1; x > right; x--) 
{ 
// Use pointer arithmetic to index the 
// next pixel in this row. 
// 
if ((pNew + x)[0] != (pPrev + x)[0]) 
{ 
// Found a change. 
// 
if (x > right) 
{ 
right = x; 
} 
if (y > bottom) 
{ 
bottom = y; 
} 
} 
} 
 
// Move up one row. 
// 
pNew -= strideNew; 
pPrev -= stridePrev; 
} 
} 
} 
} 
catch (Exception ex) 
{ 
int xxx = 0; 
} 
finally 
{ 
// Unlock the bits of the image. 
// 
if (bmNewData != null) 
{ 
_newBitmap.UnlockBits(bmNewData); 
} 
if (bmPrevData != null) 
{ 
_prevBitmap.UnlockBits(bmPrevData); 
} 
} 
 
// Validate we found a bounding box. If not 
// return an empty rectangle. 
// 
int diffImgWidth = right - left + 1; 
int diffImgHeight = bottom - top + 1; 
if (diffImgHeight < 0 || diffImgWidth < 0) 
{ 
// Nothing changed 
return Rectangle.Empty; 
} 
 
// Return the bounding box. 
// 
return new Rectangle(left, top, diffImgWidth, diffImgHeight); 
} 
 
when GetBoundingBoxForChanges() call then i am getting error and error message is Attempted to read or write protected memory. This is often an indication that other memory is corrupt. 
 
error occur at this code if ((pNew + x)[0] != (pPrev + x)[0]) 
 
so i am not being able to find out the reason. how to fix this error. please guide. thanks 

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Two image compare using win32 api c#

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