Question

Is an SVG image purely vectorial or can we combine bitmap images into an SVG image ?
How about transforms applied on the bitmap images (perspective, mappings, etc.) ?

Edit: Images may be included in an SVG by link reference. See http://www.w3.org/TR/SVG/struct.html#ImageElement. My question was in fact if bitmap images may be included inside the svg so that the svg image would be self contained. Otherwise, whenever the svg image is displayed the link must be followed and the image downloaded. Apparently .svg files are simply xml files.

Answer 1

Yes, you can reference any image from the image element. And you can use data URIs to make the SVG self-contained. An example:

<svg xmlns="http://www.w3.org/2000/svg"
     xmlns:xlink="http://www.w3.org/1999/xlink">

    ...
    <image
        width="100" height="100"
        xlink:href="data:image/png;base64,IMAGE_DATA"
        />
    ...
</svg>

The svg element attribute xmlns:xlink declares xlink as a namespace prefix and says where the definition is. That then allows the SVG reader to know what xlink:href means.

The IMAGE_DATA is where you’d add the image data as base64-encoded text. Vector graphics editors that support SVG usually have an option for saving with images embedded. Otherwise there are plenty of tools around for encoding a byte stream to and from base64.

Here’s a full example from the SVG testsuite.