2004.10.19 19:22 "[Tiff] Changing TIFF value", by Richard Edwards

Hello. I'm having some trouble successfully changing TIFF values. I have scanned some of the archives. I'm adding the functionality in a Windows DLL.

The primary problem seems to be that I cannot read my changed value successfully. Note that I am attempting to change the ARTIST field. I'm all but certain that the field does not exist in the original TIFF file.

Here's my two functions:

extern "C" __declspec (dllexport) BOOL WINAPI ReadTag(char *filename, long tag, char *result)
{
        TIFF *image;
        long returncode, counter;

        // Open the TIFF file
        if((image = TIFFOpen(filename, "r")) == NULL)
        {
                return FALSE;
        }

        returncode = TIFFGetField(image, tag, result);

        // Close the file
        TIFFClose(image);

        return TRUE;
}

extern "C" __declspec (dllexport) BOOL WINAPI ChangeTag(char *filename, long tag, char *value)
{
        TIFF *image;
        long returncode;

        // Open the TIFF file.
        if((image = TIFFOpen(filename, "a")) == NULL)
        {
                return FALSE;
        }

        returncode = TIFFSetField(image, tag, value);

        // Write data.
        returncode = TIFFRewriteDirectory(image);

        // Close the file
        TIFFClose(image);

        return TRUE;
}

Here's the body of the code:

ReadTag("C:\\tmp\\sample.tif", 315, resultbuffer);
ChangeTag("C:\\tmp\\sample.tif", 315, "RICHARD");
ReadTag("C:\\tmp\\sample.tif", 315, resultbuffer);

When I open the TIFF file after running the code in a binary editor, I see "RICHARD", which implies that ChangeTag had some success. As a matter of fact, I get an additional "RICHARD" every time I run the code, which isn't so great. The TIFFGetField call, however, returns 0 and the "result" variable remains empty.

Any thoughts? I greatly appreciate any help.

Thanks,
Richard