c++ - FreeImage 图像颜色错误

Question

我正在尝试从使用 Gstreamer 创建的流中提取帧，并尝试使用 FreeImage 或 QImage 保存它们(这个用于测试)。

    GstMapInfo bufferInfo;
    GstBuffer *sampleBuffer;
    GstStructure *capsStruct;
    GstSample *sample;
    GstCaps *caps;

    int width, height;
    const int BitsPP = 32;

    /* Retrieve the buffer */
    g_signal_emit_by_name (sink, "pull-sample", &sample);

    if (sample) {

        sampleBuffer = gst_sample_get_buffer(sample);
        gst_buffer_map(sampleBuffer,&bufferInfo,GST_MAP_READ);

        if (!bufferInfo.data) {
            g_printerr("Warning: could not map GStreamer buffer!\n");
            throw;
        }

        caps = gst_sample_get_caps(sample);
        capsStruct= gst_caps_get_structure(caps,0);

        gst_structure_get_int(capsStruct,"width",&width);
        gst_structure_get_int(capsStruct,"height",&height);


        auto bitmap = FreeImage_Allocate(width, height, BitsPP,0,0,0);
        memcpy( FreeImage_GetBits( bitmap ), bufferInfo.data, width * height * (BitsPP/8));

//        int pitch = ((((BitsPP * width) + 31) / 32) * 4);
//        auto bitmap = FreeImage_ConvertFromRawBits(bufferInfo.data,width,height,pitch,BitsPP,0, 0, 0);

        FreeImage_FlipHorizontal(bitmap);
        bitmap = FreeImage_RotateClassic(bitmap,180);

        static int id = 0;
        std::string name = "/home/stadmin/pic/sample" + std::to_string(id++) + ".png";

#ifdef FREE_SAVE
        FreeImage_Save(FIF_PNG,bitmap,name.c_str());
#endif

#ifdef QT_SAVE
        //Format_ARGB32
        QImage image(bufferInfo.data,width,height,QImage::Format_ARGB32);
        image.save(QString::fromStdString(name));
#endif

        fibPipeline.push(bitmap);

        gst_sample_unref(sample);
        gst_buffer_unmap(sampleBuffer, &bufferInfo);

        return GST_FLOW_OK;

FreeImage 中的颜色输出完全错误，就像 Qt - Format_ARGB32 [绿色像蓝色或蓝色像橙色等。] 但是当我用 测试时>Qt - Format_RGBA8888 我可以获得正确的输出。我需要使用 FreeImage，我希望了解如何更正此问题。

Answer 1

既然你说 Qt 使用 Format_RGBA8888 成功，我只能猜测:gstreamer 帧有 RGBA 顺序的字节，而 FreeImage 需要 ARGB。

快速修复:

//have a buffer the same length of the incoming bytes
size_t length = width * height * (BitsPP/8);
BYTE * bytes = (BYTE *) malloc(length);

//copy the incoming bytes to it, in the right order:
int index = 0;
while(index < length)
{
    bytes[index]     = bufferInfo.data[index + 2];  //B
    bytes[index + 1] = bufferInfo.data[index + 1];  //G
    bytes[index + 2] = bufferInfo.data[index];      //R
    bytes[index + 3] = bufferInfo.data[index + 3];  //A
    index += 4;
}

//fill the bitmap using the buffer
auto bitmap = FreeImage_Allocate(width, height, BitsPP,0,0,0);
memcpy( FreeImage_GetBits( bitmap ), bytes, length);

//don't forget to
free(bytes);