How can I simply load a greyscale tiff in libtiff and get an array of pixel intensities?

Question

I am trying to understand images some more, and I'm having a great deal of trouble. From using matlab, I have experience in using imread('test.tif'), and getting a beautiful matrix of rows vs. columns, where you have the intensity of each pixel as an integer. So, a 720 x 250 image will give a 720 x 250 matrix, where each cell contains the intensity of the pixel, on a scale from 0-255 (depending on the data type). So, 0 was black, 255 was white.

It was so simple and made so much sense. Now I am attempting to use libtiff, and I am really struggling. I want to do the same thing--access those pixels, and I just can't get it.

I have the following code:

int main(int argc, char *argv[]){
  TIFF* tif = TIFFOpen( argv[1], "r");
    FILE *fp = fopen("test2.txt", "w+");

  if (tif) {
      int * buf;
      tstrip_t strip;
      uint32* bc;
      uint32 stripsize;
  TIFFGetField( tif, TIFFTAG_STRIPBYTECOUNTS, &bc);
  stripsize = bc[0];
  buf   = _TIFFmalloc(stripsize);
  for(strip = 0; strip < TIFFNumberOfStrips(tif); strip++ ) {
      if( bc[strip] > stripsize) {
          buf = _TIFFrealloc(buf, bc[strip]);
          stripsize = bc[strip];
      }
      TIFFReadRawStrip(tif, strip, buf, bc[strip]);
  }
  int i;
  for (i=0; i<stripsize; i++) {
      if ( i % 960 ==0 )
          fprintf(fp, "\n");
      fprintf(fp,"%d ",  buf[i]);
  }
  _TIFFfree(buf);
  TIFFClose(tif);
  }
  exit(0);
}

But I get completely meaningless results--just completely wacked out numbers. Nothing like the numbers I see when I load the image in matlab.

How can I simply access the pixel values, and look at them?

Thanks so much.

Answer 1

I think you should read Using The TIFF Library article. It contains enough information to get started with libtiff.

Here is some code to read image scanlines and print values of each sample.

main()
{
    TIFF* tif = TIFFOpen("myfile.tif", "r");
    if (tif) {
        uint32 imagelength;
        tsize_t scanline;
        tdata_t buf;
        uint32 row;
        uint32 col;

        TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imagelength);
        scanline = TIFFScanlineSize(tif);
        buf = _TIFFmalloc(scanline);
        for (row = 0; row < imagelength; row++)
        {
            TIFFReadScanline(tif, buf, row);
            for (col = 0; col < scanline; col++)
                printf("%d ", buf[col]);

            printf("\n");
        }
        _TIFFfree(buf);
        TIFFClose(tif);
    }
}