ID: Q172565
The information in this article applies to:
If you insert a Portable Network Graphic (PNG) image in a PowerPoint slide, any semi-transparent portions of the image appear grainy (dithered). If you examine the image closely, the semi-transparent areas of the picture appear to be drawn by alternating pixels of the foreground color with pixels of the slide background color.
NOTE: You only see this effect when you view the graphics in Slide or Notes view. When you run the slide show, the graphics appear without dithering.
A PNG file is a type of bitmap. In other words, the picture data is stored as a rectangular array of dots of different colors. Each dot is described as a mixture of 256 shades of red, 256 shades of green, 256 shades of blue, and (optionally) 256 shades of transparency. The transparency component is called an alpha channel.
If you import semi-transparent images into a photo compositing program (such as Microsoft Image Composer), you can layer them to achieve various special effects. For example, if you place the image of a semi-transparent wineglass filled with red wine in front of the image of a gift box, you can still see the gift box through the wine. It just has a red tint to it.
When you are in Slide view or Notes view, PowerPoint tries to improve performance by using a coarser preview of the graphic. When you actually run the slide show, PowerPoint displays the graphic at full fidelity.
Additional query words: ppt8 ppt97 clear pattern moire interference Portable Network Graphic Alpha Mask
Keywords : kbdraw
Version : WINDOWS:97; macintosh:98
Platform : MACINTOSH WINDOWS
Hardware : MAC x86
Issue type : kbinfo
Solution Type : kbpendingLast Reviewed: December 20, 1998