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我有一个程序，它具有以下功能来写入 tiff 文件。但是，任何图片查看软件都无法识别生成的文件。这段代码有什么问题，为什么它没有生成正确的 tiff 文件？请注意，它使用libtiff库。

long WriteGrayscaleTIFF(char *filename, long width, 
        long height, long scanbytes, unsigned char *data)
{
    long y;
    double factor;
    long c;
    unsigned long cmap[256];           /* output color map */
    TIFF *outimage;                     /* TIFF image handle */

    /* create a grayscale ramp for the output color map */
    factor = (double)((1 << 16) - 1) / (double)((1 << 8) - 1);
    for (c = 0; c < 256; c++)
        cmap[c] = (long)(c * factor);

    /* open and initialize output file */
    if ((outimage = TIFFOpen(filename, "w")) == NULL)
        return(0);
    TIFFSetField(outimage, TIFFTAG_IMAGEWIDTH, width);
    TIFFSetField(outimage, TIFFTAG_IMAGELENGTH, height);
    TIFFSetField(outimage, TIFFTAG_BITSPERSAMPLE, 8);
    TIFFSetField(outimage, TIFFTAG_SAMPLESPERPIXEL, 1);
    TIFFSetField(outimage, TIFFTAG_PLANARCONFIG, PLANARCONFIG_CONTIG);
    TIFFSetField(outimage, TIFFTAG_COMPRESSION, COMPRESSION_LZW);
    TIFFSetField(outimage, TIFFTAG_ORIENTATION, ORIENTATION_BOTLEFT);
    TIFFSetField(outimage, TIFFTAG_PHOTOMETRIC, PHOTOMETRIC_PALETTE);
    TIFFSetField(outimage, TIFFTAG_COLORMAP, cmap, cmap, cmap);

    /* write the image data */
    printf( "height = %d, width = %d!\n", height, width );
    for (y = 0; y < height; y++) {
        if (!TIFFWriteScanline(outimage, data, y, 0)) 
        {
            printf( "TIFFClose!\n" );
            TIFFClose(outimage);
            return(0);
        }
        data += scanbytes;
    }

    /* close the file */
    TIFFClose(outimage);
    return(1);
}
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