Specifications

Image Architecture

2-9

This section gives a short overview of image tiling in the Image Processing

Library. In Chapter 4 you will find more information about tiling, namely,

the descriptions of the

TileInfo structure, the imageID parameter, and the

functions CreateTileInfo, SetTileInfo,andDeleteTileInfo.

Tile Size

In the Image Processing Library, all tiles must be of the same size,

including those on the edge of an image. The tiles on the edge of an image

must contain valid data up to the border of the image; beyond that, the

pixels are ignored, and the border mode is used instead.

The size of the image tiles is contained within the

IplTileInfo structure.

It is restricted to being an even multiple of 8 in each dimension. Typical

tile sizes are 32x32 and 64x64.

For functions that take more than one source image, either all source

images must be tiled with equally-sized tiles or they must all be non-tiled.

The source and destination images tiling and tile sizes need not be the

same.

Call-backs

For tiled images, the IplImage structure does not contain a pointer to

image data; therefore, functions operating on tiled images must acquire

data tile-by-tile. To do this, the library uses a system of call-backs, in

which the functions request pointers to individual tiles based on need.

The call-back system is implemented (by the library user) as a single

function, the prototype and behavior of which are specified below. When

called by the library, this function must provide or release one tile’s worth

of data. The function is specified to the library in the

callBack field of the

IplTileInfo structure. The prototype is as follows:

void (*IplCallBack) (const IplImage* img, int xIndex,

int yIndex, int mode);

where img is the header of the parent image;

xIndex and yIndex are the indices of the requested tile; they refer to the