How can I scale an image using tcpdf?

I've got an image of size 490 x 630 that was drawn in corel. It's supposed to have 41.3 mm (wide) and 52.3 mm .

The unit I'm using in my TCPDF class is "mm".

I'm having trouble trying to acomplish this.

What value should I put on setImageScale() ?

Thanks !