Figure 17-1. The three Perl/Tk image types
The Bitmap image type (column one) handles XBM files commonly found on Unix systems. XBM files are usually used for desktop icons and cursor shapes and are actually C language statements that define a two-dimensional array of source bits. In their simplest forms, an “on” source bit displays a foreground color and an “off” source bit displays a background color. There is an optional bitmap array of mask bits. If a mask is specified, pixels where the mask is zero display nothing, producing a transparent effect by allowing the background to show through. If the mask bit is one, the pixel displays the foreground color if the source bit is one and the background color if the source bit is zero.
The Pixmap image type (column two) handles X11 pixmap (XPM) files. XPM files are also text files of C language statements and are suitable for colored icons and cursor shapes. This format uses ASCII characters to define a color lookup table, then encodes the picture as a series of C strings containing characters from the color table. Each string represents a row of the picture and each character of the string a pixel from that row.
The most sophisticated image type, Photo, handles various image formats. The default ...