mirror of
https://github.com/python-pillow/Pillow.git
synced 2024-12-25 09:26:16 +03:00
535 lines
16 KiB
ReStructuredText
535 lines
16 KiB
ReStructuredText
Tutorial
|
||
========
|
||
|
||
Using the Image class
|
||
---------------------
|
||
|
||
The most important class in the Python Imaging Library is the
|
||
:py:class:`~PIL.Image.Image` class, defined in the module with the same name.
|
||
You can create instances of this class in several ways; either by loading
|
||
images from files, processing other images, or creating images from scratch.
|
||
|
||
To load an image from a file, use the :py:func:`~PIL.Image.open` function
|
||
in the :py:mod:`~PIL.Image` module::
|
||
|
||
>>> from PIL import Image
|
||
>>> im = Image.open("lena.ppm")
|
||
|
||
If successful, this function returns an :py:class:`PIL.Image.Image` object. You
|
||
can now use instance attributes to examine the file contents::
|
||
|
||
>>> print im.format, im.size, im.mode
|
||
PPM (512, 512) RGB
|
||
|
||
The :py:attr:`~PIL.Image.Image.format` attribute identifies the source of an
|
||
image. If the image was not read from a file, it is set to None. The size
|
||
attribute is a 2-tuple containing width and height (in pixels). The
|
||
:py:attr:`~PIL.Image.Image.mode` attribute defines the number and names of the
|
||
bands in the image, and also the pixel type and depth. Common modes are “L”
|
||
(luminance) for greyscale images, “RGB” for true color images, and “CMYK” for
|
||
pre-press images.
|
||
|
||
If the file cannot be opened, an :py:exc:`IOError` exception is raised.
|
||
|
||
Once you have an instance of the :py:class:`~PIL.Image.Image` class, you can use
|
||
the methods defined by this class to process and manipulate the image. For
|
||
example, let’s display the image we just loaded::
|
||
|
||
>>> im.show()
|
||
|
||
.. note::
|
||
|
||
The standard version of :py:meth:`~PIL.Image.Image.show` is not very
|
||
efficient, since it saves the image to a temporary file and calls the
|
||
:command:`xv` utility to display the image. If you don’t have :command:`xv`
|
||
installed, it won’t even work. When it does work though, it is very handy
|
||
for debugging and tests.
|
||
|
||
The following sections provide an overview of the different functions provided in this library.
|
||
|
||
Reading and writing images
|
||
--------------------------
|
||
|
||
The Python Imaging Library supports a wide variety of image file formats. To
|
||
read files from disk, use the :py:func:`~PIL.Image.open` function in the
|
||
:py:mod:`~PIL.Image` module. You don’t have to know the file format to open a
|
||
file. The library automatically determines the format based on the contents of
|
||
the file.
|
||
|
||
To save a file, use the :py:meth:`~PIL.Image.Image.save` method of the
|
||
:py:class:`~PIL.Image.Image` class. When saving files, the name becomes
|
||
important. Unless you specify the format, the library uses the filename
|
||
extension to discover which file storage format to use.
|
||
|
||
Convert files to JPEG
|
||
^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
import os, sys
|
||
from PIL import Image
|
||
|
||
for infile in sys.argv[1:]:
|
||
f, e = os.path.splitext(infile)
|
||
outfile = f + ".jpg"
|
||
if infile != outfile:
|
||
try:
|
||
Image.open(infile).save(outfile)
|
||
except IOError:
|
||
print "cannot convert", infile
|
||
|
||
A second argument can be supplied to the :py:meth:`~PIL.Image.Image.save`
|
||
method which explicitly specifies a file format. If you use a non-standard
|
||
extension, you must always specify the format this way:
|
||
|
||
Create JPEG thumbnails
|
||
^^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
import os, sys
|
||
from PIL import Image
|
||
|
||
size = (128, 128)
|
||
|
||
for infile in sys.argv[1:]:
|
||
outfile = os.path.splitext(infile)[0] + ".thumbnail"
|
||
if infile != outfile:
|
||
try:
|
||
im = Image.open(infile)
|
||
im.thumbnail(size)
|
||
im.save(outfile, "JPEG")
|
||
except IOError:
|
||
print "cannot create thumbnail for", infile
|
||
|
||
|
||
It is important to note that the library doesn’t decode or load the raster data
|
||
unless it really has to. When you open a file, the file header is read to
|
||
determine the file format and extract things like mode, size, and other
|
||
properties required to decode the file, but the rest of the file is not
|
||
processed until later.
|
||
|
||
This means that opening an image file is a fast operation, which is independent
|
||
of the file size and compression type. Here’s a simple script to quickly
|
||
identify a set of image files:
|
||
|
||
Identify Image Files
|
||
^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
import sys
|
||
from PIL import Image
|
||
|
||
for infile in sys.argv[1:]:
|
||
try:
|
||
im = Image.open(infile)
|
||
print infile, im.format, "%dx%d" % im.size, im.mode
|
||
except IOError:
|
||
pass
|
||
|
||
Cutting, pasting, and merging images
|
||
------------------------------------
|
||
|
||
The :py:class:`~PIL.Image.Image` class contains methods allowing you to
|
||
manipulate regions within an image. To extract a sub-rectangle from an image,
|
||
use the :py:meth:`~PIL.Image.Image.crop` method.
|
||
|
||
Copying a subrectangle from an image
|
||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
box = (100, 100, 400, 400)
|
||
region = im.crop(box)
|
||
|
||
The region is defined by a 4-tuple, where coordinates are (left, upper, right,
|
||
lower). The Python Imaging Library uses a coordinate system with (0, 0) in the
|
||
upper left corner. Also note that coordinates refer to positions between the
|
||
pixels, so the region in the above example is exactly 300x300 pixels.
|
||
|
||
The region could now be processed in a certain manner and pasted back.
|
||
|
||
Processing a subrectangle, and pasting it back
|
||
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
region = region.transpose(Image.ROTATE_180)
|
||
im.paste(region, box)
|
||
|
||
When pasting regions back, the size of the region must match the given region
|
||
exactly. In addition, the region cannot extend outside the image. However, the
|
||
modes of the original image and the region do not need to match. If they don’t,
|
||
the region is automatically converted before being pasted (see the section on
|
||
:ref:`color-transforms` below for details).
|
||
|
||
Here’s an additional example:
|
||
|
||
Rolling an image
|
||
^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
def roll(image, delta):
|
||
"Roll an image sideways"
|
||
|
||
xsize, ysize = image.size
|
||
|
||
delta = delta % xsize
|
||
if delta == 0: return image
|
||
|
||
part1 = image.crop((0, 0, delta, ysize))
|
||
part2 = image.crop((delta, 0, xsize, ysize))
|
||
image.paste(part2, (0, 0, xsize-delta, ysize))
|
||
image.paste(part1, (xsize-delta, 0, xsize, ysize))
|
||
|
||
return image
|
||
|
||
For more advanced tricks, the paste method can also take a transparency mask as
|
||
an optional argument. In this mask, the value 255 indicates that the pasted
|
||
image is opaque in that position (that is, the pasted image should be used as
|
||
is). The value 0 means that the pasted image is completely transparent. Values
|
||
in-between indicate different levels of transparency.
|
||
|
||
The Python Imaging Library also allows you to work with the individual bands of
|
||
an multi-band image, such as an RGB image. The split method creates a set of
|
||
new images, each containing one band from the original multi-band image. The
|
||
merge function takes a mode and a tuple of images, and combines them into a new
|
||
image. The following sample swaps the three bands of an RGB image:
|
||
|
||
Splitting and merging bands
|
||
^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
r, g, b = im.split()
|
||
im = Image.merge("RGB", (b, g, r))
|
||
|
||
Note that for a single-band image, :py:meth:`~PIL.Image.Image.split` returns
|
||
the image itself. To work with individual color bands, you may want to convert
|
||
the image to “RGB” first.
|
||
|
||
Geometrical transforms
|
||
----------------------
|
||
|
||
The :py:class:`PIL.Image.Image` class contains methods to
|
||
:py:meth:`~PIL.Image.Image.resize` and :py:meth:`~PIL.Image.Image.rotate` an
|
||
image. The former takes a tuple giving the new size, the latter the angle in
|
||
degrees counter-clockwise.
|
||
|
||
Simple geometry transforms
|
||
^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
out = im.resize((128, 128))
|
||
out = im.rotate(45) # degrees counter-clockwise
|
||
|
||
To rotate the image in 90 degree steps, you can either use the
|
||
:py:meth:`~PIL.Image.Image.rotate` method or the
|
||
:py:meth:`~PIL.Image.Image.transpose` method. The latter can also be used to
|
||
flip an image around its horizontal or vertical axis.
|
||
|
||
Transposing an image
|
||
^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
out = im.transpose(Image.FLIP_LEFT_RIGHT)
|
||
out = im.transpose(Image.FLIP_TOP_BOTTOM)
|
||
out = im.transpose(Image.ROTATE_90)
|
||
out = im.transpose(Image.ROTATE_180)
|
||
out = im.transpose(Image.ROTATE_270)
|
||
|
||
There’s no difference in performance or result between ``transpose(ROTATE)``
|
||
and corresponding :py:meth:`~PIL.Image.Image.rotate` operations.
|
||
|
||
A more general form of image transformations can be carried out via the
|
||
:py:meth:`~PIL.Image.Image.transform` method.
|
||
|
||
.. _color-transforms:
|
||
|
||
Color transforms
|
||
----------------
|
||
|
||
The Python Imaging Library allows you to convert images between different pixel
|
||
representations using the :py:meth:`~PIL.Image.Image.convert` method.
|
||
|
||
Converting between modes
|
||
^^^^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
im = Image.open("lena.ppm").convert("L")
|
||
|
||
The library supports transformations between each supported mode and the “L”
|
||
and “RGB” modes. To convert between other modes, you may have to use an
|
||
intermediate image (typically an “RGB” image).
|
||
|
||
Image enhancement
|
||
-----------------
|
||
|
||
The Python Imaging Library provides a number of methods and modules that can be
|
||
used to enhance images.
|
||
|
||
Filters
|
||
^^^^^^^
|
||
|
||
The :py:mod:`~PIL.ImageFilter` module contains a number of pre-defined
|
||
enhancement filters that can be used with the
|
||
:py:meth:`~PIL.Image.Image.filter` method.
|
||
|
||
Applying filters
|
||
~~~~~~~~~~~~~~~~
|
||
|
||
::
|
||
|
||
from PIL import ImageFilter
|
||
out = im.filter(ImageFilter.DETAIL)
|
||
|
||
Point Operations
|
||
^^^^^^^^^^^^^^^^
|
||
|
||
The :py:meth:`~PIL.Image.Image.point` method can be used to translate the pixel
|
||
values of an image (e.g. image contrast manipulation). In most cases, a
|
||
function object expecting one argument can be passed to the this method. Each
|
||
pixel is processed according to that function:
|
||
|
||
Applying point transforms
|
||
~~~~~~~~~~~~~~~~~~~~~~~~~
|
||
|
||
::
|
||
|
||
# multiply each pixel by 1.2
|
||
out = im.point(lambda i: i * 1.2)
|
||
|
||
Using the above technique, you can quickly apply any simple expression to an
|
||
image. You can also combine the :py:meth:`~PIL.Image.Image.point` and
|
||
:py:meth:`~PIL.Image.Image.paste` methods to selectively modify an image:
|
||
|
||
Processing individual bands
|
||
~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
||
|
||
::
|
||
|
||
# split the image into individual bands
|
||
source = im.split()
|
||
|
||
R, G, B = 0, 1, 2
|
||
|
||
# select regions where red is less than 100
|
||
mask = source[R].point(lambda i: i < 100 and 255)
|
||
|
||
# process the green band
|
||
out = source[G].point(lambda i: i * 0.7)
|
||
|
||
# paste the processed band back, but only where red was < 100
|
||
source[G].paste(out, None, mask)
|
||
|
||
# build a new multiband image
|
||
im = Image.merge(im.mode, source)
|
||
|
||
Note the syntax used to create the mask::
|
||
|
||
imout = im.point(lambda i: expression and 255)
|
||
|
||
Python only evaluates the portion of a logical expression as is necessary to
|
||
determine the outcome, and returns the last value examined as the result of the
|
||
expression. So if the expression above is false (0), Python does not look at
|
||
the second operand, and thus returns 0. Otherwise, it returns 255.
|
||
|
||
Enhancement
|
||
^^^^^^^^^^^
|
||
|
||
For more advanced image enhancement, you can use the classes in the
|
||
:py:mod:`~PIL.ImageEnhance` module. Once created from an image, an enhancement
|
||
object can be used to quickly try out different settings.
|
||
|
||
You can adjust contrast, brightness, color balance and sharpness in this way.
|
||
|
||
Enhancing images
|
||
~~~~~~~~~~~~~~~~
|
||
|
||
::
|
||
|
||
from PIL import ImageEnhance
|
||
|
||
enh = ImageEnhance.Contrast(im)
|
||
enh.enhance(1.3).show("30% more contrast")
|
||
|
||
Image sequences
|
||
---------------
|
||
|
||
The Python Imaging Library contains some basic support for image sequences
|
||
(also called animation formats). Supported sequence formats include FLI/FLC,
|
||
GIF, and a few experimental formats. TIFF files can also contain more than one
|
||
frame.
|
||
|
||
When you open a sequence file, PIL automatically loads the first frame in the
|
||
sequence. You can use the seek and tell methods to move between different
|
||
frames:
|
||
|
||
Reading sequences
|
||
^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
from PIL import Image
|
||
|
||
im = Image.open("animation.gif")
|
||
im.seek(1) # skip to the second frame
|
||
|
||
try:
|
||
while 1:
|
||
im.seek(im.tell()+1)
|
||
# do something to im
|
||
except EOFError:
|
||
pass # end of sequence
|
||
|
||
As seen in this example, you’ll get an :py:exc:`EOFError` exception when the
|
||
sequence ends.
|
||
|
||
Note that most drivers in the current version of the library only allow you to
|
||
seek to the next frame (as in the above example). To rewind the file, you may
|
||
have to reopen it.
|
||
|
||
The following iterator class lets you to use the for-statement to loop over the
|
||
sequence:
|
||
|
||
A sequence iterator class
|
||
^^^^^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
class ImageSequence:
|
||
def __init__(self, im):
|
||
self.im = im
|
||
def __getitem__(self, ix):
|
||
try:
|
||
if ix:
|
||
self.im.seek(ix)
|
||
return self.im
|
||
except EOFError:
|
||
raise IndexError # end of sequence
|
||
|
||
for frame in ImageSequence(im):
|
||
# ...do something to frame...
|
||
|
||
|
||
Postscript printing
|
||
-------------------
|
||
|
||
The Python Imaging Library includes functions to print images, text and
|
||
graphics on Postscript printers. Here’s a simple example:
|
||
|
||
Drawing Postscript
|
||
^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
from PIL import Image
|
||
from PIL import PSDraw
|
||
|
||
im = Image.open("lena.ppm")
|
||
title = "lena"
|
||
box = (1*72, 2*72, 7*72, 10*72) # in points
|
||
|
||
ps = PSDraw.PSDraw() # default is sys.stdout
|
||
ps.begin_document(title)
|
||
|
||
# draw the image (75 dpi)
|
||
ps.image(box, im, 75)
|
||
ps.rectangle(box)
|
||
|
||
# draw centered title
|
||
ps.setfont("HelveticaNarrow-Bold", 36)
|
||
w, h, b = ps.textsize(title)
|
||
ps.text((4*72-w/2, 1*72-h), title)
|
||
|
||
ps.end_document()
|
||
|
||
More on reading images
|
||
----------------------
|
||
|
||
As described earlier, the :py:func:`~PIL.Image.open` function of the
|
||
:py:mod:`~PIL.Image` module is used to open an image file. In most cases, you
|
||
simply pass it the filename as an argument::
|
||
|
||
im = Image.open("lena.ppm")
|
||
|
||
If everything goes well, the result is an :py:class:`PIL.Image.Image` object.
|
||
Otherwise, an :exc:`IOError` exception is raised.
|
||
|
||
You can use a file-like object instead of the filename. The object must
|
||
implement :py:meth:`~file.read`, :py:meth:`~file.seek` and
|
||
:py:meth:`~file.tell` methods, and be opened in binary mode.
|
||
|
||
Reading from an open file
|
||
^^^^^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
fp = open("lena.ppm", "rb")
|
||
im = Image.open(fp)
|
||
|
||
To read an image from string data, use the :py:class:`~StringIO.StringIO`
|
||
class:
|
||
|
||
Reading from a string
|
||
^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
import StringIO
|
||
|
||
im = Image.open(StringIO.StringIO(buffer))
|
||
|
||
Note that the library rewinds the file (using ``seek(0)``) before reading the
|
||
image header. In addition, seek will also be used when the image data is read
|
||
(by the load method). If the image file is embedded in a larger file, such as a
|
||
tar file, you can use the :py:class:`~PIL.ContainerIO` or
|
||
:py:class:`~PIL.TarIO` modules to access it.
|
||
|
||
Reading from a tar archive
|
||
^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
from PIL import TarIO
|
||
|
||
fp = TarIO.TarIO("Imaging.tar", "Imaging/test/lena.ppm")
|
||
im = Image.open(fp)
|
||
|
||
Controlling the Decoder
|
||
-----------------------
|
||
|
||
Some decoders allow you to manipulate the image while reading it from a file.
|
||
This can often be used to speed up decoding when creating thumbnails (when
|
||
speed is usually more important than quality) and printing to a monochrome
|
||
laser printer (when only a greyscale version of the image is needed).
|
||
|
||
The :py:meth:`~PIL.Image.Image.draft` method manipulates an opened but not yet
|
||
loaded image so it as closely as possible matches the given mode and size. This
|
||
is done by reconfiguring the image decoder.
|
||
|
||
Reading in draft mode
|
||
^^^^^^^^^^^^^^^^^^^^^
|
||
|
||
::
|
||
|
||
im = Image.open(file)
|
||
print "original =", im.mode, im.size
|
||
|
||
im.draft("L", (100, 100))
|
||
print "draft =", im.mode, im.size
|
||
|
||
This prints something like:
|
||
|
||
original = RGB (512, 512)
|
||
draft = L (128, 128)
|
||
|
||
Note that the resulting image may not exactly match the requested mode and
|
||
size. To make sure that the image is not larger than the given size, use the
|
||
thumbnail method instead.
|