PhD: Portable Network Graphics Lose Transparency in Web Browser (265221)


The information in this article applies to:

  • Microsoft Internet Explorer 5.0 for Windows 98
  • Microsoft Internet Explorer 4.0 for Windows 95
  • Microsoft PhotoDraw 2000
  • Microsoft PhotoDraw 2000 2.0
This article was previously published under Q265221

SYMPTOMS

If you save an image with a transparent background in Portable Network Graphics (PNG) format and then open the image inside Microsoft Internet Explorer or another Web browser, the image background may appear to be gray rather than transparent.

NOTE: The image background appears to be transparent when you open the image inside Microsoft Picture It! 2000, Microsoft PhotoDraw 2000, or Microsoft Photo Editor.

CAUSE

This behavior can occur if you enable the True Color option when you save an image in PNG format in PhotoDraw 2000.

Internet Explorer versions 4.0 and later support transparent backgrounds in PNG images only if you save the image with a 256 color palette.

RESOLUTION

To preserve the transparent image background in Internet Explorer:

  1. Start PhotoDraw 2000.
  2. Create or open an image.
  3. On the File menu, click Save As.
  4. In the Save as Type box, click Portable Network Graphics.
  5. Click Options.
  6. In the Convert to box, click Palette.
  7. In the Color palette box, click Optimal palette.
  8. Click to select the Save transparency check box, and then click OK.
  9. Click Save.
NOTE: If you open an image that you saved by using this procedure in Netscape Navigator, the quality of the image may appear degraded, and the image background may not be transparent.

STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

MORE INFORMATION

Transparencies in PNG images are achieved by using an alpha channel.

The PNG alpha channel can associate a variable level of transparency with each pixel in a PNG picture, known as per-pixel-transparency. Any area of the picture can be fully or partially transparent, or fully opaque.

Internet Explorer 4.0 or later does not support per-pixel-transparency for PNG pictures. Transparency can only be applied to the picture as a whole or through the use of colormap or palette-based images (where the color of a pixel is defined by a lookup table). This provides equivalent results as can be achieved with GIF-based pictures.

There is a workaround available that is recommended for developers who are creating Windows-specific content or applications through CSS Filters and Transitions. For more information, visit the following Microsoft Web site:

http://msdn.microsoft.com/library/default.asp?url=/workshop/author/filter/reference/filters/AlphaImageLoader.asp

NOTE: The PNG file specification was released as a World Wide Web Consortium (W3C) recommendation on October 1, 1996.

For more information on the PNG file format, visit the following W3C Web site:

http://www.w3.org/Graphics/PNG/

Modification Type:MinorLast Reviewed:8/18/2005
Keywords:kbbug kbconversion kbdisplay kbpending KB265221
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