Digital Signal Processing Reference
In-Depth Information
adjacent. The tiles are all the same size, and encoded using the
same procedure.
Pyramidal tiling also partitions the image into multiple tiles,
but each tile can have different levels of resolution, resulting in
a multi-resolution pyramidal JPEG image. This is known as the
JPEG Tiled Image Pyramid (JTIP) model. The JTIP image has
successive layers of the same image, but using different resolu-
tions. The top of the pyramid has an image that is one-sixteenth
of the defined screen size. It is called the vignette and it can be
used for quick displays of image contents. The next image is one-
fourth of the screen and is called the imagette
this is often used
to display multiple images simultaneously. Next is a lower-reso-
lution, full-screen image and after that are higher-resolution
images. The last image is the original image. Each of the pyra-
midal images can be JPEG encoded, either separately or together
in the same data stream. If done separately, then it can allow for
faster access of the selected image quality.
Multiple-resolution versions of images can also be stored and
displayed using composite tiling, known as a mosaic. Composite
tiling differs from pyramidal tiling in three ways: the tiles can
overlap, be different sizes, and be encoded using different
quantization scaling. Each tile is encoded independently, so they
can be easily combined.
Other JPEG extensions are detailed in the JPEG standards.
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