Access TIFF image

Question

I am trying to read a TIFF image to perform processing. The ideal would be to be able to import this image in a OpenCV structure, but even having it accessible in a different way would be great.

If I run tiffinfo on the image I get

TIFF Directory at offset 0x2bb00 (178944)
  Subfile Type: (0 = 0x0)
  Image Width: 208 Image Length: 213
  Resolution: 1, 1
  Bits/Sample: 32
  Sample Format: IEEE floating point
  Compression Scheme: None
  Photometric Interpretation: min-is-black
  Orientation: row 0 top, col 0 lhs
  Samples/Pixel: 1
  Rows/Strip: 1
  Planar Configuration: single image plane 

I want to access single pixel values. The image is gray scale, data contained there ranges from 0.0 to 10372.471680.

I make some trials with LibTIFF, Magick++ but was not able to access single pixel values (I tried to make a loop over the pixels and to print these values on screen).

Here is a piece of code I am trying to use, I got it from an online example:

#include "tiffio.h"
#include "stdio.h"
int main()
{
    TIFF* tif = TIFFOpen("test.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++)
        {
            int n = TIFFReadScanline(tif, buf, row, 0);
        if(n==-1){
            printf("Error");
            return 0;
        }
            for (col = 0; col < scanline; col++)
                printf("%f\n", buf[col]);

            printf("\n");
        }
        printf("ScanLineSize: %d\n",scanline);
        _TIFFfree(buf);
        TIFFClose(tif);
    }
}

I compile it with

gcc test.c -ltiff -o test

when I run it, I get

test.c: In function ‘main’:
test.c:24: warning: dereferencing ‘void *’ pointer
test.c:24: error: invalid use of void expression

Any hints? Thanks for your time.

Answer 1

Look at the documentation for the function _TIFFmalloc(). If it works like the standard malloc, it returns a void pointer, which needs to be casted to a specific type if the buf[col] statement in line 24 is expected to work correctly.

Answer 2

You have to fix this with:

tdata_t *buf;
buf =(tdata_t*) _TIFFmalloc(scanline);