Converting 24 bit bmp to 8 bit grayscale

[keepjumpin]

Hello! I am trying to write a bmp class. I became interested while studying pattern matching in artificial intelligence. For class, we had to write an algorithm that would detect edges in an image. The algorithm did not need to actually be implemented but I decided to implement it anyways for learning purposes. I realize that there are various libraries already written which will do what I'm trying to do but again this is for learning purposes. The problem I'm having is in converting a 24 bit color bmp to an 8 bit grayscale image. In my code I've made a note of the function I'm struggling with. The problem I'm having is that the file created by SendGrayScale is 264246 bytes when it should be 263222 bytes and of course it won't open...

gs.dat is my RGB palette for the 8 bit image. I created it by reading a grayscale image, actually a grayscale version of the color image I'm working with. I read it using this class. At this point, the class correctly copies both color and grayscale images so I believe that gs.dat has been created properly.

Any help would be greatly appreciated.

The following post is my entire class. Thanks...

[keepjumpin]

#include "bmpclass.h"

BitMapClass::BitMapClass(char *fileName)
{
	clrPalette = NULL;
	fin.open(fileName, ios::in | ios::binary);
	
	GetFileHeader();
	GetImgInfo();
	GetRGBPalette();
	GetPixelData();
}
	
void BitMapClass::GetFileHeader()
{
	if (!fin.is_open()) throw string("File Read Error");
	else
	{
		fin.read((char*)&fileHeader.bfType, sizeof(fileHeader.bfType));
		if (fileHeader.bfType != 19778) throw string("Invalid Filetype");
		else
		{
			fin.read((char*)&fileHeader.bfSize, sizeof(fileHeader.bfSize));
			fin.read((char*)&fileHeader.bfRes1, sizeof(fileHeader.bfRes1));
			fin.read((char*)&fileHeader.bfRes2, sizeof(fileHeader.bfRes2));
			fin.read((char*)&fileHeader.bfOffBits, sizeof(fileHeader.bfOffBits));
		}
	}
}

void BitMapClass::GetImgInfo()
{
	if (!fin.is_open()) throw string("File Read Error");
	else
	{
		fin.read((char*)&imgInfo.biSize, sizeof(imgInfo.biSize));
		fin.read((char*)&imgInfo.biWidth, sizeof(imgInfo.biWidth));
		fin.read((char*)&imgInfo.biHeight, sizeof(imgInfo.biHeight));
		fin.read((char*)&imgInfo.biPlanes, sizeof(imgInfo.biPlanes));
		fin.read((char*)&imgInfo.biBitCount, sizeof(imgInfo.biBitCount));
		fin.read((char*)&imgInfo.biCompression, sizeof(imgInfo.biCompression));
		fin.read((char*)&imgInfo.biSizeImage, sizeof(imgInfo.biSizeImage));
		fin.read((char*)&imgInfo.biXPelsPerMeter, sizeof(imgInfo.biXPelsPerMeter));
		fin.read((char*)&imgInfo.biYPelsPerMeter, sizeof(imgInfo.biYPelsPerMeter));
		fin.read((char*)&imgInfo.biClrUsed, sizeof(imgInfo.biClrUsed));
		fin.read((char*)&imgInfo.biClrImportant, sizeof(imgInfo.biClrImportant));
	}
}

void BitMapClass::GetPixelData()
{
	int size = fileHeader.bfSize - fileHeader.bfOffBits;
	char *tempPixelData = new char[size];
	
	for (int i=0; i < size; i++)
		fin.read((char*)&tempPixelData[i], 1);
	
	unsigned long byteWidth, padWidth;
	
	byteWidth = padWidth = (unsigned long)((float)imgInfo.biWidth*(float)imgInfo.biBitCount/8.0);
	while (padWidth % 4 != 0)
		padWidth++;
	
	dword diff;
	int offset;
	long height;
	
	height = imgInfo.biHeight;
	diff = height * byteWidth;
	
	pixelData = new char[diff];
	
	if (height > 0)
	{
		int j = imgInfo.biSize - 3;
		offset = padWidth - byteWidth;
		for (int i=0; i < imgInfo.biSize; i += 3)
		{
			if ((i + 1) % padWidth == 0)
				i += offset;
			*(pixelData + j + 2) = *(tempPixelData + i);
			*(pixelData + j + 1) = *(tempPixelData + i + 1);
			*(pixelData + j) = *(tempPixelData + i + 2);
			j++;
		}
	}
	
	for (int i=0; i < size; i++)
		pixelData[i] = tempPixelData[i];

	fin.close();
}

void BitMapClass::GetRGBPalette()
{
	if (!fin.is_open()) throw string("File Read Error");
	else
	{
		int numColors=1 << imgInfo.biBitCount;
		clrPalette = new RGBPalette[numColors];

 		if (imgInfo.biBitCount < 24)
		{
			for (int i=0; i < numColors; i++)
			{
				fin.read(&clrPalette[i].rgbBlue, 1);
				fin.read(&clrPalette[i].rgbGreen, 1);
				fin.read(&clrPalette[i].rgbRed, 1);
				fin.read(&clrPalette[i].rgbReserved, 1);
			}
		}
	}
}

//
void BitMapClass::SendGrayScale(ofstream& fout)
{	
	/*	This is the method I'm having trouble with	*/
	
	word *biBitCount = new word(8);
	int numColors=1 << *biBitCount;
	dword *bfSize = new dword(54 + (4 * numColors) + (imgInfo.biWidth * imgInfo.biHeight));
	dword *size = new dword(*bfSize - fileHeader.bfOffBits);
	char *gPixelData = new char[(*size)];
	int j = 0;
	
	for (int i=0; i < (fileHeader.bfSize - fileHeader.bfOffBits); i+=3)
	{
		gPixelData[j] = (float)(((pixelData[i])*0.299) 
			                + ((pixelData[i+1])*0.587) 
			                + ((pixelData[i+2])*0.114));
		j++;
	}
	
	if (fout.is_open())
	{
		fout.write((char*)&fileHeader.bfType, sizeof(fileHeader.bfType));
		fout.write((char*)&bfSize, sizeof(dword));
		fout.write((char*)&fileHeader.bfRes1, sizeof(fileHeader.bfRes1));
		fout.write((char*)&fileHeader.bfRes2, sizeof(fileHeader.bfRes2));
		fout.write((char*)&fileHeader.bfOffBits, sizeof(fileHeader.bfOffBits));
		fout.write((char*)&size, sizeof(dword));
		fout.write((char*)&imgInfo.biWidth, sizeof(imgInfo.biWidth));
		fout.write((char*)&imgInfo.biHeight, sizeof(imgInfo.biHeight));
		fout.write((char*)&imgInfo.biPlanes, sizeof(imgInfo.biPlanes));
		fout.write((char*)&biBitCount, sizeof(imgInfo.biBitCount));
		fout.write((char*)&imgInfo.biCompression, sizeof(imgInfo.biCompression));
		fout.write((char*)&imgInfo.biSizeImage, sizeof(imgInfo.biSizeImage));
		fout.write((char*)&imgInfo.biXPelsPerMeter, sizeof(imgInfo.biXPelsPerMeter));
		fout.write((char*)&imgInfo.biYPelsPerMeter, sizeof(imgInfo.biYPelsPerMeter));
		fout.write((char*)&imgInfo.biClrUsed, sizeof(imgInfo.biClrUsed));
		fout.write((char*)&imgInfo.biClrImportant, sizeof(imgInfo.biClrImportant));

		ifstream clrIn;
		clrIn.open("gs.dat", ios::in | ios::binary);
		
		if (clrPalette)
			delete clrPalette;
		
		clrPalette = new RGBPalette[numColors];
		
		for (int i=0; i < numColors; i++)
		{
			clrIn.read(&clrPalette[i].rgbBlue, 1);
			clrIn.read(&clrPalette[i].rgbGreen, 1);
			clrIn.read(&clrPalette[i].rgbRed, 1);
			clrIn.read(&clrPalette[i].rgbReserved, 1);
			fout.write(&clrPalette[i].rgbBlue, 1);
			fout.write(&clrPalette[i].rgbGreen, 1);
			fout.write(&clrPalette[i].rgbRed, 1);
			fout.write(&clrPalette[i].rgbReserved, 1);
		}
		
		for (int i=0; i < (*size); i++)
		{
			fout.write(&gPixelData[i], 1);
		}
		
	}
}
//

void BitMapClass::SendToFile(ofstream& fout)
{
	dword size = fileHeader.bfSize - fileHeader.bfOffBits;
	int numColors=1 << imgInfo.biBitCount;
	
	if (fout.is_open())
	{
		fout.write((char*)&fileHeader.bfType, sizeof(fileHeader.bfType));
		fout.write((char*)&fileHeader.bfSize, sizeof(fileHeader.bfSize));
		fout.write((char*)&fileHeader.bfRes1, sizeof(fileHeader.bfRes1));
		fout.write((char*)&fileHeader.bfRes2, sizeof(fileHeader.bfRes2));
		fout.write((char*)&fileHeader.bfOffBits, sizeof(fileHeader.bfOffBits));
		fout.write((char*)&imgInfo.biSize, sizeof(imgInfo.biSize));
		fout.write((char*)&imgInfo.biWidth, sizeof(imgInfo.biWidth));
		fout.write((char*)&imgInfo.biHeight, sizeof(imgInfo.biHeight));
		fout.write((char*)&imgInfo.biPlanes, sizeof(imgInfo.biPlanes));
		fout.write((char*)&imgInfo.biBitCount, sizeof(imgInfo.biBitCount));
		fout.write((char*)&imgInfo.biCompression, sizeof(imgInfo.biCompression));
		fout.write((char*)&imgInfo.biSizeImage, sizeof(imgInfo.biSizeImage));
		fout.write((char*)&imgInfo.biXPelsPerMeter, sizeof(imgInfo.biXPelsPerMeter));
		fout.write((char*)&imgInfo.biYPelsPerMeter, sizeof(imgInfo.biYPelsPerMeter));
		fout.write((char*)&imgInfo.biClrUsed, sizeof(imgInfo.biClrUsed));
		fout.write((char*)&imgInfo.biClrImportant, sizeof(imgInfo.biClrImportant));
		if (imgInfo.biBitCount < 24)
		{
			for (int i=0; i < numColors; i++)
			{
				fout.write(&clrPalette[i].rgbBlue, 1);
				fout.write(&clrPalette[i].rgbGreen, 1);
				fout.write(&clrPalette[i].rgbRed, 1);
				fout.write(&clrPalette[i].rgbReserved, 1);
			}
		}
		for (int i=0; i < size; i++)
		{
			fout.write(&pixelData[i], 1);
		}
		
	}
}

void BitMapClass::TextDumpFileHeader(ostream& out)
{
	if (!out) throw string("Invalid Output Stream");
	else
	{
		cout << fileHeader.bfType << endl;
		cout << fileHeader.bfSize << endl;
		cout << fileHeader.bfRes1 << endl;
		cout << fileHeader.bfRes2 << endl;
		cout << fileHeader.bfOffBits << endl;
	}
}

void BitMapClass::TextDumpImgInfo(ostream& out)
{
	if (!out) throw string("Invalid Output Stream");
	else
	{
		cout << imgInfo.biSize << endl;
		cout << imgInfo.biWidth << endl;
		cout << imgInfo.biHeight << endl;
		cout << imgInfo.biPlanes << endl;
		cout << imgInfo.biBitCount << endl;
		cout << imgInfo.biCompression << endl;
		cout << imgInfo.biSizeImage << endl;
		cout << imgInfo.biXPelsPerMeter << endl;
		cout << imgInfo.biYPelsPerMeter << endl;
		cout << imgInfo.biClrUsed << endl;
		cout << imgInfo.biClrImportant << endl;
	}
}

void BitMapClass::TextDumpClrPalette(ostream& out)
{
	int numColors=1 << imgInfo.biBitCount;
	
	for (int i=0; i < numColors; i++)
	{
		cout << (int)clrPalette[i].rgbBlue << '\t';
		cout << (int)clrPalette[i].rgbGreen << '\t';
		cout << (int)clrPalette[i].rgbRed << '\t';
		cout << (int)clrPalette[i].rgbReserved << endl;
	}
}

BitMapClass::~BitMapClass()
{
}

[PiMaster]

The formula for grayscale is:

S=(R*0.3+G*0.59+B*0.11)

or with only integers:

S=(R*30+G*59+B*11)/10

Where:
S=shade of gray (intensity)
R=red
G=green
B=blue


Source:
http://en.wikipedia.org/wiki/Grayscale#Converting_color_to_grayscale

[keepjumpin]

did you look at my code?

[ne555]

Check for memory leaks (everything that is allocated with new should be deallocated with delete)

	dword *bfSize = new dword(54 + (4 * numColors) + (imgInfo.biWidth * imgInfo.biHeight));
	dword *size = new dword(*bfSize - fileHeader.bfOffBits);

Maybe those could be avoided

char *gPixelData = new char[(*size)];
for (int K=0, L=0; L < size; K+=3, L++) //maybe out of bounds
	gPixelData[L] = (float)(((pixelData[K])*0.299) //gPixel is char, why are you casting to float?
			                + ((pixelData[K+1])*0.587) 
			                + ((pixelData[K+2])*0.114));

//dword *bfSize;
fout.write((char*)&bfSize, sizeof(dword));

bfSize is a pointer, saving its content is futile (also you dimension is incorrect).
Maybe you want fout.write( (char *)bfSize, sizeof(*bfSize) );

[keepjumpin]

lol.. As I was copying my code into my post I thought "I wonder if anyone will say anything about not cleaning up my memory..." For the moment I'm not too worried about memory leaks. :)

I cast gPixel to float so that I can get the numerical value for the colors...
Perhaps I don't need to...

I see what you're saying about bfSize being a pointer...
bfSize is a dword pointer so I don't see how the dimension is wrong.

I will play around with your suggestions. I'm thinking it may be the for loop as you said it may be out of bounds.

Thank you

[ne555]

bfSize is a dword pointer so I don't see how the dimension is wrong.

If you save a pointer the size must be the one of the pointer fout.write((char*)&bfSize, sizeof(bfSize) );. However saving a pointers makes no sense.

/*for (int i=0; i < size; i++){
	fout.write(&pixelData[i], 1);
}*/
fout.write( pixelData, sizeof(pixelData) ); //if is not dynamical allocated
fout.write( pixelData, sizeof(pixelData[0])*size ); //maybe there is a way without dereferencing 

for (int i=0; i < numColors; i++)
			{
				fout.write(&clrPalette[i].rgbBlue, 1);
				fout.write(&clrPalette[i].rgbGreen, 1);
				fout.write(&clrPalette[i].rgbRed, 1);
				fout.write(&clrPalette[i].rgbReserved, 1);
			}

If you change your structure, you could use the same trick

[keepjumpin]

My understanding about write is that it takes a pointer to a block of memory then the size of the block so it's not saving the pointer but the data starting at the pointer and ending at the end of the block size... Maybe I'm missing something here?

I had initially tried saving the whole block at one time as you have shown but I didn't take into account that the array was dynamically allocated. I see now why it didn't work. I will give that a try again...

Thanks.

[ne555]

My understanding about write is that it takes a pointer to a block of memory

Yes, but you were doing &bfSize (a pointer to the pointer)

[keepjumpin]

ah, yep... I see it now... Thanks. Things are starting to clear up now.