用libtiff如何将cmyk四张分色图合并成一张tiff，并保存一张bmp缩略图？

以下是使用libtiff库将CMYK四张分色图合并成一张TIFF，并保存一张BMP缩略图的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <tiffio.h>

int main(int argc, char** argv)
{
    if (argc < 6) {
        printf("Usage: %s c.tif m.tif y.tif k.tif out.tif out.bmp\n", argv[0]);
        return 0;
    }

    // Open input files
    TIFF* c_tiff = TIFFOpen(argv[1], "r");
    TIFF* m_tiff = TIFFOpen(argv[2], "r");
    TIFF* y_tiff = TIFFOpen(argv[3], "r");
    TIFF* k_tiff = TIFFOpen(argv[4], "r");

    if (!c_tiff || !m_tiff || !y_tiff || !k_tiff) {
        printf("Error: Failed to open input files\n");
        return 0;
    }

    // Get image width and height
    uint32_t width, height;
    TIFFGetField(c_tiff, TIFFTAG_IMAGEWIDTH, &width);
    TIFFGetField(c_tiff, TIFFTAG_IMAGELENGTH, &height);

    // Create output TIFF file
    TIFF* out_tiff = TIFFOpen(argv[5], "w");
    if (!out_tiff) {
        printf("Error: Failed to create output TIFF file\n");
        return 0;
    }

    // Set TIFF tags
    TIFFSetField(out_tiff, TIFFTAG_IMAGEWIDTH, width);
    TIFFSetField(out_tiff, TIFFTAG_IMAGELENGTH, height);
    TIFFSetField(out_tiff, TIFFTAG_SAMPLESPERPIXEL, 4);
    TIFFSetField(out_tiff, TIFFTAG_BITSPERSAMPLE, 8);
    TIFFSetField(out_tiff, TIFFTAG_PHOTOMETRIC, PHOTOMETRIC_SEPARATED);
    TIFFSetField(out_tiff, TIFFTAG_PLANARCONFIG, PLANARCONFIG_CONTIG);
    TIFFSetField(out_tiff, TIFFTAG_ROWSPERSTRIP, TIFFDefaultStripSize(out_tiff, width * 4));

    // Allocate memory for image data
    uint8_t* data = (uint8_t*)malloc(width * height * 4 * sizeof(uint8_t));
    if (!data) {
        printf("Error: Failed to allocate memory for image data\n");
        return 0;
    }

    // Read image data from input files
    TIFFReadRGBAImage(c_tiff, width, height, (uint32_t*)data, 0);
    TIFFReadRGBAImage(m_tiff, width, height, (uint32_t*)(data + width * height * 4), 0);
    TIFFReadRGBAImage(y_tiff, width, height, (uint32_t*)(data + width * height * 8), 0);
    TIFFReadRGBAImage(k_tiff, width, height, (uint32_t*)(data + width * height * 12), 0);

    // Write image data to output file
    TIFFWriteEncodedStrip(out_tiff, 0, data, width * height * 4);

    // Create BMP thumbnail
    TIFF* bmp_tiff = TIFFOpen(argv[6], "w");
    if (!bmp_tiff) {
        printf("Error: Failed to create BMP thumbnail\n");
        return 0;
    }

    // Set TIFF tags for BMP
    TIFFSetField(bmp_tiff, TIFFTAG_IMAGEWIDTH, width);
    TIFFSetField(bmp_tiff, TIFFTAG_IMAGELENGTH, height);
    TIFFSetField(bmp_tiff, TIFFTAG_PHOTOMETRIC, PHOTOMETRIC_RGB);
    TIFFSetField(bmp_tiff, TIFFTAG_PLANARCONFIG, PLANARCONFIG_CONTIG);
    TIFFSetField(bmp_tiff, TIFFTAG_BITSPERSAMPLE, 8);
    TIFFSetField(bmp_tiff, TIFFTAG_SAMPLESPERPIXEL, 3);
    TIFFSetField(bmp_tiff, TIFFTAG_ROWSPERSTRIP, height);

    // Write BMP data
    uint8_t* bmp_data = (uint8_t*)malloc(width * height * 3 * sizeof(uint8_t));
    for (uint32_t i = 0; i < height; i++) {
        for (uint32_t j = 0; j < width; j++) {
            uint8_t* pixel = data + (i * width + j) * 4;
            bmp_data[(i * width + j) * 3] = 255 - pixel[0];
            bmp_data[(i * width + j) * 3 + 1] = 255 - pixel[1];
            bmp_data[(i * width + j) * 3 + 2] = 255 - pixel[2];
        }
    }
    TIFFWriteEncodedStrip(bmp_tiff, 0, bmp_data, width * height * 3);

    // Close files and free memory
    TIFFClose(c_tiff);
    TIFFClose(m_tiff);
    TIFFClose(y_tiff);
    TIFFClose(k_tiff);
    TIFFClose(out_tiff);
    TIFFClose(bmp_tiff);
    free(data);
    free(bmp_data);

    return 0;
}

该程序需要传入四个CMYK分色图的文件名，一个输出TIFF文件名和一个输出BMP缩略图的文件名。程序首先打开输入文件并获取图像的宽度和高度。然后，它创建一个新的TIFF文件并设置必要的标记，例如图像宽度，高度，样本数，位数和颜色模型。接下来，程序将分配足够的内存来存储图像数据，并从四个输入文件中读取RGBA数据。最后，程序将此数据写入输出TIFF文件和BMP缩略图。请注意，BMP缩略图是将CMYK颜色转换为RGB并反相的结果。程序成功完成后，它将关闭所有文件并释放分配的内存。

希望这可以帮助你！