Confuse with camera Orientation

tham

The orientation of Camera is weird

1 : on desktop, orientation 0, the image is top down like following

alt text

But on mobile(android), topDown orientation become 270

2 : When I save the image access by QAbstractVideoFilter, the image become upside down,but it is topDown on the screen(orientation is 0)

Image become topDown

alt text

How should I understand orientation value?Thanks

Codes :

ApplicationWindow {
    id: win
    visible: true
    //width: 640
    //height: 480
    title: qsTr("Hello World")       

    Camera{
        id: camera
    }

    SSDFilter {
        id: ssd_filter

        onMessageChanged: {
            console.log("msg is:" + msg)
            msg_text.text = "msg is:" + msg
        }

        orientation: video.orientation
    }

    Column{
        VideoOutput {
            id: video
            source: camera
            width: win.width
            height: win.height - 20
            autoOrientation: true
            filters: [ ssd_filter ]

            onOrientationChanged: {
                msg_text.text = "phone orientation:" + video.orientation
            }
        }

        Text{
            id: msg_text            
        }
    }
}

tham

I found the answer of the orientation, all I need to do is check the direction of scanline

surfaceFormat.scanLineDirection()

In object recognition task, topToBottom or bottomToTop is crucial