Image processing in C++

Question

I am opening a 3.5 MB file in C reading it into an unsigned char array Image data which I have initialized as follows:

unsigned char *** Imagedata; Imagedata = new unsigned char**[1278]; for(int i=0; i<1278; i++){ Imagedata[i]= new unsigned char*[968]; for(int j=0; j<968; j++){ Imagedata[i][j]= new unsigned char[3]; } }

Now i open the file and read it into the array as:

ifstream ifile; ifile.open("abcde.raw", ios::in|ios::binary); for(int i=0; i<1278; i++){ for(int j=0; j<968; j++){ for(int k=0; k<3; k++){ ifile>>Imagedata[i][j][k]; } } } ifile.close();

The next step is to just rewrite the bytes into a new file.. which i call rawfile.. I have tried to achieve it like this:

ofstream myfile; myfile.open("rawfile.raw", ios::out|ios::binary); for(int i=0; i<1278; i++){ for(int j=0; j<968; j++){ myfile.write((char *)Imagedata[i][j],3*sizeof(unsigned char)); } } myfile.close();

It somehow doesn seem to work.. the image file that i get is garbage.. what could be the problem?

You know, of course, that you should use const variables or #defines instead of the literal numbers 1278 and 968. — Tom Zych
– Tom Zych, Commented Sep 10, 2011 at 20:13
Yeah I usually do that.. its just for this sample code.. Thanks for mentioning it anyways.. — PROC_HACKER
– PROC_HACKER, Commented Sep 10, 2011 at 20:40
Always worthwhile pointing it out to any newbies who happen to read it too. — Tom Zych
– Tom Zych, Commented Sep 10, 2011 at 20:41

Yakov Galka · Accepted Answer · 2011-09-10 20:15:33Z

ifile>>Imagedata[i][j][k];

This is formatted input, it eats 'whitespace' characters even though you specified ios::binary. Use

Imagedata[i][j][k] = ifile.get();

Even better, allocate one big chunk of memory for the whole file and read it by one read call. What you do now is allocating a pointer for each pixel, which is very wasteful especially for 64-bit systems.

Thanks! this works.. also.. i found another way that worked.. i removed the third looping during the reading.. for(int i=0; i<1278; i++){ for(int j=0; j<968; j++){ ifile.read((char*)Imagedata[i][j],3); } }

K-ballo · Accepted Answer · 2011-09-10 20:13:18Z

0

I would bet this is because the skipws flag is set by default in file streams. Right after opening your fstreams, add file.unsetf( std::ios_base::skipws );

answered Sep 10, 2011 at 20:13

K-ballo

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3 Comments

Tom Zych Over a year ago

Would that be set even for a binary stream? That seems silly.

K-ballo Over a year ago

Yes, it does. I am not aware of the rationale, but has bitten me many times.

K-ballo Over a year ago

I wouldn't be able to tell if it needs fixing, without knowing the rationale for it.

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