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Chapter 1 ■ Practical Aspects of a Vision System 3

image = cvLoadImage( ˝ C:\AIPCV\image1.jpg˝, 1 );
if( image )
{
cvNamedWindow( ˝ Input Image˝, 1 );
cvShowImage( ˝ Input Image˝, image );
printf( ˝ Press a key to exit\n˝);
cvWaitKey(0);
cvDestroyWindow( ˝ String˝);
}
else
fprintf( stderr, ˝ Error reading image\n˝ );
return 0;
}

This is similar to many example programs on the Internet. It reads in an
image (C:\AIPCV\image1.jpg is a string giving the path name of the image)
and displays it in a window on the screen. When the user presses a key, the
program terminates after destroying the display window.
Before anyone can modify this code in a knowledgeable way, the data
structures and functions need to be explained.

1.2.1 The IplImage Data Structure

The IplImage structure is the in-memory data organization for an image.
Images in IplImage form can be converted into arrays of pixels, but IplImage
also contains a lot of structural information about the image data, which can
have many forms. For example, an image read from a GIF file could be 256
grey levels with an 8-bit pixel size, or a JPEG file could be read into a 24-bit
per pixel color image. Both files can be represented as an IplImage.
An IplImage is much like other internal image representations in its basic
organization. The essential fields are as follows:

width An integer holding the width of the image in pixels

height An integer holding the height of the image in pixels
imageData A pointer to an array of characters, each one an actual pixel or color value

If each pixel is one byte, this is really all we need. However, there are many
data types for an image within OpenCV; they can be bytes, ints, floats, or
doubles in type, for instance. They can be greys (1 byte) or 3-byte color (RGB),
4 bytes, and so on. Finally, some image formats may have the origin at the
upper left (most do, in fact) and some use the lower left (only Microsoft).