Defined in pyglet.extlibs.png
fromarray
(a, mode=None, info={})¶Create a PNG Image
object from a 2- or 3-dimensional
array. One application of this function is easy PIL-style saving:
png.from_array(pixels, 'L').save('foo.png')
.
Unless they are specified using the info parameter, the PNG’s
height and width are taken from the array size. For a 3 dimensional
array the first axis is the height; the second axis is the width;
and the third axis is the channel number. Thus an RGB image that is
16 pixels high and 8 wide will use an array that is 16x8x3. For 2
dimensional arrays the first axis is the height, but the second axis
is width*channels
, so an RGB image that is 16 pixels high and 8
wide will use a 2-dimensional array that is 16x24 (each row will be
8*3==24 sample values).
mode is a string that specifies the image colour format in a PIL-style mode. It can be:
'L'
'LA'
'RGB'
'RGBA'
The mode string can also specify the bit depth (overriding how this
function normally derives the bit depth, see below). Appending
';16'
to the mode will cause the PNG to be 16 bits per channel;
any decimal from 1 to 16 can be used to specify the bit depth.
When a 2-dimensional array is used mode determines how many channels the image has, and so allows the width to be derived from the second array dimension.
The array is expected to be a numpy
array, but it can be any
suitable Python sequence. For example, a list of lists can be used:
png.from_array([[0, 255, 0], [255, 0, 255]], 'L')
. The exact
rules are: len(a)
gives the first dimension, height;
len(a[0])
gives the second dimension; len(a[0][0])
gives the
third dimension, unless an exception is raised in which case a
2-dimensional array is assumed. It’s slightly more complicated than
that because an iterator of rows can be used, and it all still
works. Using an iterator allows data to be streamed efficiently.
The bit depth of the PNG is normally taken from the array element’s
datatype (but if mode specifies a bitdepth then that is used
instead). The array element’s datatype is determined in a way which
is supposed to work both for numpy
arrays and for Python
array.array
objects. A 1 byte datatype will give a bit depth of
8, a 2 byte datatype will give a bit depth of 16. If the datatype
does not have an implicit size, for example it is a plain Python
list of lists, as above, then a default of 8 is used.
The info parameter is a dictionary that can be used to specify
metadata (in the same style as the arguments to the
:class:png.Writer
class). For this function the keys that are
useful are:
Generally anything specified in the
info dictionary will override any implicit choices that this
function would otherwise make, but must match any explicit ones.
For example, if the info dictionary has a greyscale
key then
this must be true when mode is 'L'
or 'LA'
and false when
mode is 'RGB'
or 'RGBA'
.