THREE.TextureLoader load the image fail with imageprovider

[qintxwd]

in my main.cpp

QQmlApplicationEngine engine;
engine.addImageProvider("imageProvider", imageProvider);

then i can use image in my qml like this(it run ok):

        Image {
                id: zoomout_img
                source: "image://imageProvider/map.png"                    
            }

also I use threejs in my code like this(it run ok) :

var geometry = new THREE.PlaneGeometry( 0.4, 0.4, 0.4, 0.4 );
var textureLoader = new THREE.TextureLoader();
var textureCase= textureLoader.load("qrc:/img/xxx.png");
var material = new THREE.MeshBasicMaterial({ map: textureCase , transparent: true});
var mesh = new THREE.Mesh( geometry, material );

however,when i load image by imageprovider,it fail:

var geometry = new THREE.PlaneGeometry( 0.4, 0.4, 0.4, 0.4 );
var textureLoader = new THREE.TextureLoader();
var textureCase= textureLoader.load("image://imageProvider/map.png");
var material = new THREE.MeshBasicMaterial({ map: textureCase , transparent: true});
var mesh = new THREE.Mesh( geometry, material );

any one know why?the image provider is like this:

class BkgImgProvider : public QQuickImageProvider
{
public:
    explicit BkgImgProvider():QQuickImageProvider(QQuickImageProvider::Pixmap){

    }
    virtual QPixmap requestPixmap(const QString &id, QSize *size, const QSize& requestedSize)
    {
        QImage img;
        if(id == "map.png")
            img = QImage::fromData(qba_map,format.toStdString().c_str());

        if(!img.isNull()){
            if (requestedSize.isValid()) {
                img.scaledToWidth(requestedSize.width());
                img.scaledToHeight(requestedSize.height());
            }else{
                //                    img.scaledToWidth(bkg->getWidth());
                //                    img.scaledToHeight(bkg->getHeight());
            }
            *size = img.size();
        }

        QPixmap pix = QPixmap::fromImage(img);
        return pix;
    }
    void setMapData(const QByteArray &qba){qba_map = qba;};
private:
    QByteArray qba_map;
}