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AlphaChannel

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description

AlphaChannel[image] gives the image's opacity as a one-channel image. An image with no alpha channel answers with an all-opaque one rather than declining: "how transparent is this?" has an answer for every image, and it is "not at all". Two channels are read as grey+alpha and four as RGB+alpha.

Examples (4)

Every input below was run against the current Mathilda build and its output recorded.

Basic Examples (4)

In[1]:= a = Image[Table[N[(i + j)/32], {i, 1, 16}, {j, 1, 16}], "Real"];

In[2]:= Union[Flatten[ImageData[AlphaChannel[a]]]]
Out[2]= {1.0}

In[3]:= Union[Flatten[ImageData[AlphaChannel[SetAlphaChannel[a, 0.25]]]]]
Out[3]= {0.25}

In[4]:= ImageChannels[AlphaChannel[Image[Table[{0.2, 0.4, 0.6}, {i, 1, 8}, {j, 1, 8}], "Real"]]]
Out[4]= 1

Implementation notes

  • Protected.
  • An image with no alpha channel answers with an all-opaque one rather than declining: "how transparent is this?" has an answer for every image, and it is "not at all".
  • Two channels are read as grey+alpha, four as RGB+alpha.

Attributes: Protected.

References