On Fri, 2008-10-17 at 21:26 -0500, Eric P wrote:
> Check out this png.  I'm not sure if it is editable in the GIMP.
> http://i34.tinypic.com/rtzshs.png
> First of all it's an indexed image.  You'll see two white arrows on the right 
> hand side.  Switch the mode to RGB and
> you'll see two new alpha transparent arrows appear on the left hand side (!?)
> Checking the header of the image I see Adobe Fireworks in there.  Any ideas 
> what this anomaly of a png is?

  Image Width: 20 Image Length: 110
  Bitdepth (Bits/Sample): 2
  Channels (Samples/Pixel): 1
  Pixel depth (Pixel Depth): 2
  Colour Type (Photometric Interpretation):
    PALETTED COLOUR with alpha (3 colours, 3 transparent) 
  Image filter: Single row per byte filter 
  Interlacing: No interlacing 
  Compression Scheme: Deflate method 8, 32k window
  Resolution: 2834, 2834 (pixels per meter)
  FillOrder: msb-to-lsb
  Byte Order: Network (Big Endian)
  Number of text strings: 1 of 9
    Software (xTXt deflate compressed): Adobe Fireworks CS3
  Offsets: 0, 0

This image uses an indexed palette with transparency information. This
is not fully supported in GIMP. The PNG loader seems to handle it
nicely, but the GIMP image display has some special code that thresholds
the alpha channel for images in indexed mode. This is because the code
was written for GIF images. The projection in indexed mode simulates the
alpha capabilities of the GIF format, where a pixel is either fully
transparent or opaque.


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