PNG alpha-Transparency

The alpha-channel in PNG graphics is used to control transparency of an image. To the three 8bit RGB- channels a forth 8bit alpha-channel is added producing 32bit images. Thus this channel allows 256 levels of transparency.

The examples below shows a building of the castle complex of Burghausen [DE] in Bavaria. The first picture is the original (24bit) without any transparency set, the second one has a fully transparent background, the third picture is semi-transparent, and the forth picture has increasing transparency from the center of the image to the outside.

Hovering over each picture changes the background colour of the <img /> element, thus emphasising the effect of alpha transparency.

Picture 1: no transparency

Picture 2: background (sky) fully transparent

Picture 3: whole image semitransparent

Picture 4: semitransparent with outwards increasing transparency