how to enable pinch zoom to images in fullscreen?

i am trying to enable pinch zoom during full screen mode.

I called the full screen mode trough my modal element as below. I would like to allow the pinch zoom only to the image, not to the buttons and others elements.... I couldn't find anything helpful.

HTML meta:

<meta name="viewport"
        content="width=device-width, initial-scale=1., maximum-scale=12.0, minimum-scale=.25, user-scalable=yes" />

if (document.fullscreenEnabled) {
        document.getElementById("myModal").requestFullscreen();
}