 
 
 
 
 
 
 
 
 
 
Transparency is usually not considered to be a blending mode, however,
it works just like one!  Transparency is just a combination of the
Multiply and Addition blending modes; it takes a
percentage of the foreground and adds it to the complementary
percentage of the background.  Thus, if you want the foreground to be
75% opaque (opacity is just the opposite of transparency), you
multiply the foreground by 0.75, the background by (1-0.75), and add
the two.  This relationship can be expressed as
 
 represents the opacity.  The percentages used in
scaling the foreground and background pixels are called complementary
because
represents the opacity.  The percentages used in
scaling the foreground and background pixels are called complementary
because 
 .
.
By the way, can you guess why the percentage of opacity is represented by the Greek letter alpha in the preceding equation? It is because the opacity of a layer is controlled by its alpha channel. The alpha channel takes values in the range [0,255] where a value of 255 represents 100% opacity, and 0 represents 100% transparency.
Different amounts of transparency/opacity can be obtained by adjusting
the value of  .
For a foreground and background pixel pair, the
effect of opacity can be illustrated in the RGB cube.
Figure 5.24
.
For a foreground and background pixel pair, the
effect of opacity can be illustrated in the RGB cube.
Figure 5.24
Figure 5.25
Transparency/opacity can also be controlled for the GIMP's painting functions. The Opacity slider for these are found in the Brush Selection dialog.
 
 
 
 
 
 
 
 
