10 PyX focuses on the creation of scaleable vector graphics. However, PyX also
11 allows for the output of bitmap images. Still, the support for creation and
12 handling of bitmap images is quite limited. On the other hand the interfaces are
13 built that way, that its trivial to combine PyX with the "Python Image Library",
16 The creation of a bitmap can be performed out of some unpacked binary data by
17 first creating image instances::
20 image_bw = bitmap.image(2, 2, "L", "\0\377\377\0")
21 image_rgb = bitmap.image(3, 2, "RGB", "\77\77\77\177\177\177\277\277\277"
22 "\377\0\0\0\377\0\0\0\377")
24 Now ``image_bw`` is a :math:`2\times2` grayscale image. The bitmap data is
25 provided by a string, which contains two black (``"\0" == chr(0)``) and two
26 white (``"\377" == chr(255)``) pixels. Currently the values per (colour) channel
27 is fixed to 8 bits. The coloured image ``image_rgb`` has :math:`3\times2` pixels
28 containing a row of 3 different gray values and a row of the three colours red,
31 The images can then be wrapped into ``bitmap`` instances by::
33 bitmap_bw = bitmap.bitmap(0, 1, image_bw, height=0.8)
34 bitmap_rgb = bitmap.bitmap(0, 0, image_rgb, height=0.8)
36 When constructing a ``bitmap`` instance you have to specify a certain position
37 by the first two arguments fixing the bitmaps lower left corner. Some optional
38 arguments control further properties. Since in this example there is no
39 information about the dpi-value of the images, we have to specify at least a
40 ``width`` or a ``height`` of the bitmap.
42 The bitmaps are now to be inserted into a canvas::
47 c.writeEPSfile("bitmap")
49 Figure :ref:`fig:bitmap` shows the resulting output.
57 .. centered:: An introductory bitmap example.
64 :synopsis: Bitmap support
68 .. class:: image(width, height, mode, data, compressed=None)
70 This class is a container for image data. *width* and *height* are the size of
71 the image in pixel. *mode* is one of ``"L"``, ``" RGB"`` or ``"CMYK"`` for
72 grayscale, rgb, or cmyk colours, respectively. *data* is the bitmap data as a
73 string, where each single character represents a colour value with ordinal range
74 ``0`` to ``255``. Each pixel is described by the appropriate number of colour
75 components according to *mode*. The pixels are listed row by row one after the
76 other starting at the upper left corner of the image.
78 *compressed* might be set to ``" Flate"`` or ``"DCT"`` to provide already
79 compressed data. Note that those data will be passed to PostScript without
80 further checks, *i.e.* this option is for experts only.
83 .. class:: jpegimage(file)
85 This class is specialized to read data from a JPEG/JFIF-file. *file* is either
86 an open file handle (it only has to provide a :meth:`read` method; the file
87 should be opened in binary mode) or a string. In the latter case
88 :class:`jpegimage` will try to open a file named like *file* for reading.
90 The contents of the file is checked for some JPEG/JFIF format markers in order
91 to identify the size and dpi resolution of the image for further usage. These
92 checks will typically fail for invalid data. The data are not uncompressed, but
93 directly inserted into the output stream (for invalid data the result will be
94 invalid PostScript). Thus there is no quality loss by recompressing the data as
95 it would occur when recompressing the uncompressed stream with the lossy jpeg
99 .. class:: bitmap(xpos, ypos, image, width=None, height=None, ratio=None, storedata=0, maxstrlen=4093, compressmode="Flate", flatecompresslevel=6, dctquality=75, dctoptimize=1, dctprogression=0)
101 *xpos* and *ypos* are the position of the lower left corner of the image. This
102 position might be modified by some additional transformations when inserting the
103 bitmap into a canvas. *image* is an instance of :class:`image` or
104 :class:`jpegimage` but it can also be an image instance from the "Python Image
107 *width*, *height*, and *ratio* adjust the size of the image. At least *width* or
108 *height* needs to be given, when no dpi information is available from *image*.
110 *storedata* is a flag indicating, that the (still compressed) image data should
111 be put into the printers memory instead of writing it as a stream into the
112 PostScript file. While this feature consumes memory of the PostScript
113 interpreter, it allows for multiple usage of the image without including the
114 image data several times in the PostScript file.
116 *maxstrlen* defines a maximal string length when *storedata* is enabled. Since
117 the data must be kept in the PostScript interpreters memory, it is stored in
118 strings. While most interpreters do not allow for an arbitrary string length (a
119 common limit is 65535 characters), a limit for the string length is set. When
120 more data need to be stored, a list of strings will be used. Note that lists are
121 also subject to some implementation limits. Since a typical value is 65535
122 entries, in combination a huge amount of memory can be used.
124 Valid values for *compressmode* currently are ``"Flate"`` (zlib compression),
125 ``"DCT"`` (jpeg compression), or ``None`` (disabling the compression). The zlib
126 compression makes use of the zlib module as it is part of the standard Python
127 distribution. The jpeg compression is available for those *image* instances
128 only, which support the creation of a jpeg-compressed stream, *e.g.* images from
129 the "Python Image Library" with jpeg support installed. The compression must be
130 disabled when the image data is already compressed.
132 *flatecompresslevel* is a parameter of the zlib compression. *dctquality*,
133 *dctoptimize*, and *dctprogression* are parameters of the jpeg compression.
134 Note, that the progression feature of the jpeg compression should be turned off
135 in order to produce valid PostScript. Also the optimization feature is known to
136 produce errors on certain printers.