The canvas component method getImageData() will not release the frame buffer from system memory.

import QtQuick 2.0

Item {
    width: 400
    height: 400

    Canvas {
        id: canvas
        renderStrategy: Canvas.Immediate
        anchors.fill: parent
        onPaint: { }
    }

    Timer {
        running: true
        interval: 100
        repeat: true
        onTriggered: canvas.getContext("2d").getImageData(0, 0, canvas.width, canvas.height)
    }
}