opencv基本操作(五)

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imencodeimdecode

图片的编码与解码

void valueChanged(int changeCount) {        this->setAlgorithm([=](const QImage & arg)->QImage {            if (changeCount<1) { return arg; }            auto i=changeCount;            try {                QImage image=arg.copy();                const auto imageData=const_cast<uchar*>(image.constBits());                const auto lineStep=image.bytesPerLine();                const auto imageHeight=image.height();                const auto imageWidth3=image.width()*3;                const auto lineEnd=imageData+imageHeight*lineStep;                std::vector<std::uint8_t> buffer;                const std::vector<int> par={                    CV_IMWRITE_JPEG_QUALITY,77,                };                cv::Mat input(imageHeight,image.width(),CV_8UC3,                    imageData,lineStep);                /*opencv架构级错误，导致大量无用运算*/                cv::cvtColor(input,input,cv::COLOR_RGB2BGR);                /*参考:*/                /*view-source:https://m13253.github.io/JPEGreen/*/                auto clamp=[](const auto & x)->std::uint8_t {                    return (x>=0)?(x<=255)?                        std::uint8_t(x):std::uint8_t(255)                        :std::uint8_t(0);                };                auto clampuv=[](const auto & x)->std::int8_t {                    return (x>=-128)?(x<=127)?                        std::int8_t(x):std::int8_t(127)                        :std::int8_t(-128);                };                while ((--i)>=0) {                    /*RGB 与 YUV 低精度转换*/                    auto line=imageData;                    for (; line<lineEnd; line+=lineStep) {                        auto p=line; auto pend=p+imageWidth3;                        for (; p<pend; p+=3) {                            auto &b=p[0];                            auto &g=p[1];                            auto &r=p[2];                            const auto y=clamp((77*r+150*g+29*b)>>8);                            const auto u=clampuv(((-43*r-85*g+128*b)>>8)-1);                            const auto v=clampuv(((128*r-107*g-21*b)>>8)-1);                            r=clamp((65536*y+91881*v)>>16);                            g=clamp((65536*y-22553*u-46802*v)>>16);                            b=clamp((65536*y+116130*u)>>16);                        }                    }                    /*opencv架构级别错误，导致大量无用运算，                    尤其是save/load图片过程中，第三方库一般是按照rgb设计的，                    于是opencv要先将bgr转rgb，浪费大量时间                    可以自行查看opencv源代码验证*/                    cv::imencode(".jpeg",input,buffer,par);                    input=cv::imdecode(buffer,CV_LOAD_IMAGE_COLOR,&input);                    assert(imageData==input.data);                }                /*opencv架构级错误，导致大量无用运算*/                cv::cvtColor(input,input,cv::COLOR_RGB2BGR);                return std::move(image);            }            catch (...) { CPLUSPLUS_EXCEPTION(false); }            return arg;        });    }

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