Transparency and PNG format

[Glenn E. Fisher]

Graham,
On November 29, 2005 4:05:09 PM CST you wrote:
> (GraphicConverter on the Mac is really good for this - a lot simpler 
> than Photoshop Elements... but I digress). However when I import a PNG 
> as an image, the transparency disappears and the figure therefore 
> appears in a white rectangle.

Here's how I create an alpha channel using GraphicConverter.  Maybe 
this will help.

To add an alpha channel to an image file using GraphicConverter.

1) Open the file with GraphicConverter.

2) Do a "Save As" under the "File" menu and select "PNG" for the output 
file type.
I usually select another output folder to hold my converted images.

3) Select "Select Picture Content" under the Edit menu.

4) Select "Copy>" and "Copy" under the Edit menu.

5) Select "Add Alpha/Mask Channel" under the "Effect" menu.

6) Select "Show Alpha/Mask Channel" under the "Effect" menu.

7) Select "Paste>" and "Paste" under the "Edit" menu.
This will paste a grey scale of your image into the alpha channel.

8) Select "Threshold..." under the "Effect" menu and adjust the level 
until you get a reasonable black and white mask.
I sometimes have to use the eraser tool to remove some left over areas 
that I do not want in the mask.

9) Depending upon the image, you may need to select "Invert" under the 
"Picture" menu to get the right mask.
You can change it with invert later if it diplays wrong.

10) Select "Hide Alpha/Mack Channel" under the "Effect" menu.

11) Select "Save" under the "File" menu.

HTH,
Glenn
--
Glenn E. Fisher	University of Houston - Retired
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