SVG Image Masking by Stephen Bucaro

Masking is a similar to clipping, except that clipping defines an area of a graphic element that will be visible and makes a sharp boarder between the visible and clipped areas. A mask defines an area where each pixel of the mask has a degree of transparency and opaqueness that lets some of the graphic element show through, making a blurry boundary between the visible and masked areas.

In the example shown above, a radial gradient is defined and given an id of "fade". A mask is defined and given an id of "fademask". The radial gradient is then used as the fill of the mask. The image leaves.jpg is then loaded with xlink:href and the mask is used with the mask attribute in the leaves image tag.

A mask works by using its alpha channel to allow or block pixels of the image from showing through. The less opaque a part of the mask is, the less visible that part of the image will be. you can make the mask stop-colors any color you like, but it will turn out white in the result because mask uses only the transparency bits of the mask.

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