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Added screenshot, more description of rgba process, #64

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John Evans 2013-07-17 18:17:04 -04:00
commit 32a145eb32
2 changed files with 15 additions and 7 deletions
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docs/source/how_do_i.rst
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@ -123,12 +123,14 @@ Create an image with an alpha layer?
====================================
OpenJPEG can create JP2 files with more than 3 components, but by default, any
extra components are not described. In order to specify an alpha layer as such,
extra components are not described as such. In order to do so,
we need to rewrap such an image in a set of boxes that includes a channel
definition box.
This example is based on SciPy example code found at
http://scipy-lectures.github.io/advanced/image_processing/#basic-manipulations . ::
http://scipy-lectures.github.io/advanced/image_processing/#basic-manipulations .
Instead of a circular mask, however, we'll make it an ellipse since the source
image isn't square.
>>> import numpy as np
>>> import glymur
@ -143,16 +145,18 @@ http://scipy-lectures.github.io/advanced/image_processing/#basic-manipulations .
>>> jp2 = Jp2k('tmp.jp2', 'wb')
>>> jp2.write(rgba)
The first three channels are color channels, but the fourth will be identified
as an alpha channel::
Next we need to specify what types of channels we have.
The first three channels are color channels, but we identify the fourth as
an alpha channel::
>>> from glymur.core import COLOR, OPACITY
>>> ctype = [COLOR, COLOR, COLOR, OPACITY]
And finally we have to specify just exactly how each channel is to be
interpreted. The color channels are straightforward, but the alpha channel
in this case is to be applied against the entire image (it is possible to
apply an alpha channel to a single color channel, but we aren't doing that). ::
interpreted. The color channels are straightforward, they correspond to R-G-B,
but the alpha (or opacity) channel in this case is to be applied against the
entire image (it is possible to apply an alpha channel to a single color
channel, but we aren't doing that). ::
>>> from glymur.core import RED, GREEN, BLUE, WHOLE_IMAGE
>>> asoc = [RED, GREEN, BLUE, WHOLE_IMAGE]
@ -166,6 +170,10 @@ go into the jp2 header box, and then we can rewrap the image. ::
>>> boxes[2].box.append(cdef)
>>> jp2_rgba = jp2.wrap("goodstuff_rgba.jp2", boxes=boxes)
Here's how the Preview application on the mac shows the RGBA image.
.. image:: goodstuff_alpha.png
Work with XMP UUIDs?
====================