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primarykey
Id
12404384
data
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0
AnswerCount
0
ClosedDate
CommentCount
1
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CreationDate
2012-09-13T10:38:16.563
FavoriteCount
0
LastActivityDate
2018-03-22T09:29:44.827
LastEditDate
2018-03-22T09:29:44.827
LastEditorUserId
141253
OwnerUserId
141253
ParentId
12373489
PostTypeId
2
Score
1
ViewCount
0
LastEditorDisplayName
text
Body
<p>I finally managed to convert the image respecting the original alpha using NumPy. I asked in the cairo mailing lists, but the only alternative that I got had the same problem that my version had (ie, it didn't respect the original alpha channel).</p> <p>Here is my solution:</p> <pre><code>import cairo import numpy import sys def convert_to_grayscale(img_in): """Convert an image to grayscale. Arguments: img_in: (cairo.ImageSurface) input image. Return: (cairo.ImageSurface) image in grayscale, in ARGB32 mode. Timing: ~100ms to convert an image of 800x800 Examples: # returns a B&W image >>> convert_to_grayscale(cairo.ImageSurface.create_from_png('test.png')) """ a = numpy.frombuffer(img_in.get_data(), numpy.uint8) w, h = img_in.get_width(), img_in.get_height() a.shape = (w, h, 4) assert sys.byteorder == 'little', ( 'The luminosity vector needs to be switched if we\'re in a big endian architecture. ' 'The alpha channel will be at position 0 instead of 3.') alpha = a[:, :, 3] alpha.shape = (w, h, 1) luminosity_float = numpy.sum(a * numpy.array([.114, .587, .299, 0]), axis=2) luminosity_int = numpy.array(luminosity_float, dtype=numpy.uint8) luminosity_int.shape = (w, h, 1) grayscale_gbra = numpy.concatenate((luminosity_int, luminosity_int, luminosity_int, alpha), axis=2) stride = cairo.ImageSurface.format_stride_for_width(cairo.FORMAT_ARGB32, w) assert stride == 4 * w, 'We need to modify the numpy code if the stride is different' img_out = cairo.ImageSurface.create_for_data(grayscale_gbra, cairo.FORMAT_ARGB32, w, h, stride) return img_out </code></pre>
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1. POHow to convert an image to grayscale with Cairo
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1. USJoaquin Cuenca Abela
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1. USJoaquin Cuenca Abela
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1. POHow to convert an image to grayscale with Cairo
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