CODEWITHSUNDEEP
c++zlibifstreamtiffinflate
user8137073
user8137073

Reputation:

Decompressing TIFF data prints random character

So I have this TIFF, with compression 32946, which is COMPRESSION_DEFLATE.

I am reading it by hand:

ifstream istream;
std::string line;
TIFHEAD header;
istream.open("pic.tif",ios::binary|ios::in);
istream.read((char*)&header, sizeof(TIFHEAD));
istream.seekg(header.IFDOffset);

WORD numEntries1;
istream.read((char *)&numEntries1, sizeof(WORD));
cout<<numEntries1<<endl;

DWORD tagOffset;
DWORD stripByte;

for(int i=0; i<numEntries1; i++) {
    TIFTAG tag;
    istream.read((char *)&tag, sizeof(TIFTAG));
}

and found all the TIFF hex values.

I now have a value, data3.txt, which contains all hex values from the hexdump. Here it is pasted into docs:

This is my zlib code so far, and for most of the data, it prints correctly (for some reason, partway through, it starts printing 000 and a newline repeatedly, then goes into non-ASCII characters).

int main(int argc, char **argv) {
    gzFile inFileZ = gzopen("data3.txt", "rb");
    unsigned char unzipBuffer[4];
    uint8_t unzippedBytes;
    while (true) {
        unzippedBytes = gzread(inFileZ, unzipBuffer, 4);
        std::cout<<std::hex<<unzipBuffer<<std::endl;
        z_stream stream;
        stream.next_in = unzipBuffer;
        inflate(&stream, 1);
        std::cout<<stream.next_in<<std::endl;
    }
    gzclose(inFileZ);
}

and the second thing that's printed out are partly the values and partly non-ASCII characters. Why is this?

if it's not clear, my end goal is to read a TIFF by hand which has floating points at each pixel. I want to just get all those floats.

EDIT: Also, even when data3.txt only contains 12 characters, there is an infinite loop. Why?

Upvotes: 0

Views: 74

Answers (1)

Malcolm McLean
Malcolm McLean

Reputation: 6404

As far as I can tell you're decompressing binary floating point values and treating them as ASCII,which creates something which looks like garbage.

Upvotes: 1

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