Develop Reference

How to find GLCM matrix in python?

We are using Python 2.7.9.and scikit image library. We are not able to use skimage.feature.greycomatrix because there is no file such as greycomatrix.py in the feature folder. Their documentation seems to be wrong as it says this function is available. We get an error module attribute has no object feature. Is there any other image processing library in Python which will help us achieve this goal?

from skimage.feature import greycomatrix
This works for me, just like the instructions at http://scikit-image.org/docs/dev/auto_examples/plot_glcm.html.
Maybe you just have an old version and need to update scikit-image? Or if it was actually a bug on their behalf they have probably fixed it now.
Which version of scikit-image do you have? That is more relevant for this problem than your Python version. For me:
import skimage
print skimage.__version__
'0.11.2'
So for version 0.11.2 up atleast it should work.

In my case I use the following imports and it works for me.
I say
import skimage.feature as sk
##Then I say
glcm = sk.greycomatrix(img, [1],[0])
This should work fine.

Difference between from PIL import Image and import Image

I tried to use Python's Image Module on my Mac (new to mac)and I had trouble setting it up. I have Yosemite and some of the posts that I found online didn't work. I ended up installing Homebrew and I finally got PIL on my computer. However, instead of using import image (which I saw people doing it online), I have to use from PIL import image. Is there key difference between import Image and from PIL import Image. It's the first time that I actually use Image module.
One more question, do I actually need to install third party tools like Homebrew and Macports to set up my environment?

If you are using PIL, you might be able to use import Image.
If you are using Pillow, you must use from PIL import Image.
This is by design.

1-Pillow and PIL cannot co-exist in the same environment. Before installing Pillow, please uninstall PIL.
2-Pillow >= 1.0 no longer supports “import Image”. Please use “from PIL import Image” instead. so be careful with it
3-Pillow >= 2.1.0 no longer supports “import _imaging”. Please use “from PIL.Image import core as _imaging” instead.

In python, modules are represented by *.py files. These files can be imported using import module. That statement will first search for a build-in module, if it fails to find one it will search in a given list of directories (PYTHONPATH).
When you imported your module, you can then access names (aka functions or classes) via module.name.
However, when using from module import myFunc you can reference that function directly without using the modulename. The same goes for from module import *.
Now, to the PIL:
Image is a name (here class) in the PIL module. As, import Image searches for modules called Image. It can't find one, because Image is part of the PIL module.
You can also look at the documentation here: Modules in Python
I hope this helped you understanding modules better.

Python extension scikit-image error

I am trying to use scikit-image to do some research. The system is Windows 7 64bit, and the python version is 2.7, 64bit.
The first program I run is from: http://scikit-image.org/
The code is
from skimage import data, io, filter
image = data.coins() # or any NumPy array!
edges = filter.sobel(image)
io.imshow(edges)
io.show()
However, the problem happens, and the error message is:
C:\Python27\lib\site-packages\skimage\io_plugins\null_plugin.py:14:
RuntimeWarning: No plugin has been loaded. Please refer to
skimage.io.plugins()
for a list of available plugins.
warnings.warn(RuntimeWarning(message))
I believe that both Python and scikit-image are correctly installed. So, may I know what is wrong with it?
Any suggestion is appreciated. Many thanks.

Just had precisely the same issue on amazon linux. The issue is that skimage requires PIL, and PIL is not installed. In the latest skimage they added the dependency, but the version that I got installed with pip didn't have it yet.
The solution is
pip install Pillow
EDIT: and after that you will probably immediately face another issue, with skimage loading image, but not being able to read it (in particular, shape being empty tuple). Here's the solution
Why does scipy.ndimage.io.imread return PngImageFile, not an array of values

Exif reading library

Is there an exif library out there for Python 3.x? It seems every exif library I run into is for Python 2.x only. I don't need anything too fancy. Just reading the values is enough.

Option 1. Use pyexiv2. See: pyexiv2 Bug #824440: Python 3 support You need boost-python for py3k and also to manually apply the patch posted at the end of the bug above, but aside from that it works. Probably easiest to get up and running under latest Ubuntu.
Option 2. Use PIL Downside: this branch/fork doesn't seem to be actively developed.
from PIL import Image
from PIL.ExifTags import TAGS
image = Image.open("test.jpg")
exif = image._getexif()
# decode exif using TAGS
Option 3. Use PythonMagick
from PythonMagick import Image
img = Image("image.jpg")
print img.attribute("EXIF:Orientation")
See also: Exif manipulation library for python

For reference, the pyexiv2 homepage now has a deprecation warning which points to Gexiv2, a GObject-introspection based wrapper around libexiv2 (the same library pyexiv2 wraps) specifically for the purpose of Python 3.x support.
Unfortunately, at the time of writing, installation of Gexiv2 is still painful and thus far I've been unable to get it working on Ubuntu Precise (looks like the libs are out of date - probably serves me right for sticking around on an LTS...), so PIL is still the best option for reading EXIF tags in Python 3.

Image library for Python 3

What is python-3 using instead of PIL for manipulating Images?

The "friendly PIL fork" Pillow works on Python 2 and 3. Check out the Github project for support matrix and so on.

Christoph Gohlke managed to build PIL (for Windows only) for python versions up to 3.3: http://www.lfd.uci.edu/~gohlke/pythonlibs/
I tried his version of PIL with Python 3.2, and image open/create/pixel manipulation/save all work.

Qt works very well with graphics. In my opinion it is more versatile than PIL.
You get all the features you want for graphics manipulation, but there's also vector graphics and even support for real printers. And all of that in one uniform API, QPainter.
To use Qt you need a Python binding for it: PySide or PyQt4.
They both support Python 3.
Here is a simple example that loads a JPG image, draws an antialiased circle of radius 10 at coordinates (20, 20) with the color of the pixel that was at those coordinates and saves the modified image as a PNG file:
from PySide.QtCore import *
from PySide.QtGui import *
app = QCoreApplication([])
img = QImage('input.jpg')
g = QPainter(img)
g.setRenderHint(QPainter.Antialiasing)
g.setBrush(QColor(img.pixel(20, 20)))
g.drawEllipse(QPoint(20, 20), 10, 10)
g.end()
img.save('output.png')
But please note that this solution is quite 'heavyweight', because Qt is a large framework for making GUI applications.

As of March 30, 2012, I have tried and failed to get the sloonz fork on GitHub to open images. I got it to compile ok, but it didn't actually work. I also tried building gohlke's library, and it compiled also but failed to open any images. Someone mentioned PythonMagick above, but it only compiles on Windows. See PythonMagick on the wxPython wiki.
PIL was last updated in 2009, and while it's website says they are working on a Python 3 port, it's been 3 years, and the mailing list has gone cold.
To solve my Python 3 image manipulation problem, I am using subprocess.call() to execute ImageMagick shell commands. This method works.
See the subprocess module documentation.

You can use my package mahotas on Python 3. It is numpy-based rather than PIL based.

You want the Pillow library, here is how to install it on Python 3:
pip3 install Pillow
If that does not work for you (it should), try normal pip:
pip install Pillow

Depending on what is needed, scikit-image may be the best choice, with manipulations going way beyond PIL and the current version of Pillow. Very well-maintained, at least as much as Pillow. Also, the underlying data structures are from Numpy and Scipy, which makes its code incredibly interoperable. Examples that pillow can't handle:
You can see its power in the gallery. This paper provides a great intro to it. Good luck!

If you are on Python3 you can also use the library PILasOPENCV which works in Python 2 and 3. Function api calls are the same as in PIL or pillow but internally it works with OpenCV and numpy to load, save and manipulate images. Have a look at https://github.com/bunkahle/PILasOPENCV or install it with pip install PILasOPENCV. Not all PIL functions have been simulated but the most common functions work.