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Fixed the math. #64

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John Evans 2013-07-17 12:51:14 -04:00
commit 4cdef991b9
1 changed files with 48 additions and 28 deletions
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docs/source/how_do_i.rst
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@ -3,34 +3,6 @@ How do I...?
------------
Create an image with an alpha layer?
====================================
::
>>> import numpy as np
>>> import glymur
>>> rgb = glymur.Jp2k(glymur.data.goodstuff()).read()
>>> lx, ly = rgb.shape[0:2]
>>> X, Y = np.ogrid[0:lx, 0:ly]
>>> mask = (X - lx / 2) ** 2 + (Y - ly / 2) ** 2 > lx * ly / 4
>>> alpha = 255 * np.ones((lx, ly, 1), dtype=np.uint8)
>>> alpha[mask] = 0
>>> rgba = np.concatenate((rgb, alpha), axis=2)
>>> jp2 = glymur.Jp2k('tmp.jp2', 'wb')
>>> jp2.write(rgba)
::
>>> boxes = jp2.box # The box attribute is the list of JP2 boxes
>>> index = [0, 1, 2, 3]
>>> ctype = [0, 0, 0, 1]
>>> asoc = [1, 2, 3, 0]
>>> cdef = glymur.jp2box.ChannelDefinitionBox(index, ctype, asoc)
>>> boxes[2].box.append(cdef)
>>> jp2_rgba = jp2.wrap("goodstuff_rgba.jp2", boxes=boxes)
Read the lowest resolution thumbnail?
=====================================
Printing the Jp2k object should reveal the number of resolutions (look in the
@ -147,6 +119,54 @@ and add it after the JP2 header box, but before the codestream box ::
. (truncated)
.
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,
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 . ::
>>> import numpy as np
>>> import glymur
>>> from glymur import Jp2k
>>> rgb = Jp2k(glymur.data.goodstuff()).read()
>>> lx, ly = rgb.shape[0:2]
>>> X, Y = np.ogrid[0:lx, 0:ly]
>>> mask = ly**2*(X - lx / 2) ** 2 + lx**2*(Y - ly / 2) ** 2 > (lx * ly / 2)**2
>>> alpha = 255 * np.ones((lx, ly, 1), dtype=np.uint8)
>>> alpha[mask] = 0
>>> rgba = np.concatenate((rgb, alpha), axis=2)
>>> 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::
>>> 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). ::
>>> from glymur.core import RED, GREEN, BLUE, WHOLE_IMAGE
>>> asoc = [RED, GREEN, BLUE, WHOLE_IMAGE]
>>> cdef = glymur.jp2box.ChannelDefinitionBox(channel_type=ctype, association=asoc)
It's easiest to take the existing jp2 jacket and just add the channel
definition box in the appropriate spot. The channel definition box **must**
go into the jp2 header box, and then we can rewrap the image. ::
>>> boxes = jp2.box # The box attribute is the list of JP2 boxes
>>> boxes[2].box.append(cdef)
>>> jp2_rgba = jp2.wrap("goodstuff_rgba.jp2", boxes=boxes)
Work with XMP UUIDs?
====================
The example JP2 file shipped with glymur has an XMP UUID. ::