Abstract
The images on a dot-matrix hologram consist of many 2-D grating dots with different pitches and orientations. Only some specified pitches and 256 specified orientations are usually employed. The difference between any two pitches to show different colors is more than 0.1 µm; therefore, it is possible to hide several extra pitches in a specified pitch. If all the extra pitches are almost equal to the specified pitch, grating dots with extra pitches will be of nearly the same color as the specified pitch. When a laser beam is incident on the dot-matrix hologram with hidden pitches, data for the hidden pitches will be decoded by the diffraction pattern of the grating dots of the hologram. A specified grating orientation can be used to hide extra grating orientations similarly. What's better, mixing the above two hiding techniques is possible.
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