Using Canny edge detection in OpenCV

• http://sourceforge.net/apps/mediawiki/pyvision/index.php?title=Quick_Start_1
• http://www.opencv.org.cn/index.php/Canny边缘检测2

The second Python example works on my MacBook. So HighGUI does work on the Mac OS X.

Batch Image Processing with Python

Adapted from http://www.coderholic.com/batch-image-processing-with-python/

If you want to make changes to a single image, such as resizing or converting from one file format to another, then you’ll probably load up the image in an editor and manually make the required changes. This approach is great for a single image, but it doesn’t really scale past more than a few images, at which point it becomes time consuming, not to mention boring!

This is where Python and the Python Imaging Library (or PIL) come in, allowing you to write scripts that process images in batch.

Batch Processing

No matter what processing we want to do on our images the script outline will be the same: loop over all provided arguments, and perform the processing. The code to do this is shown below:

#!/usr/bin/env python
import sys
import Image

# Loop through all provided arguments
for i in range(1, len(sys.argv)):
try:
  # Attempt to open an image file
  filepath = sys.argv[i]
  image = Image.open(filepath)
except IOError, e:
  # Report error, and then skip to the next argument
  print "Problem opening", filepath, ":", e
  continue
  # Perform operations on the image here

This will allow our script to be called in all of the following ways:

$ batch_process.py image.gif
$ batch_process.py image1.png image2.gif image3.jpg
$ batch_process.py *.png
$ batch_process.py image1.gif, *.png

With the help of PIL the image processing is really simple. Below is a collection of just some of the operations we could perform. For more details see the PIL documentation.

#Resize an image
image = image.resize((width, height), Image.ANTIALIAS)

# Convert to greyscale
image = image.convert('L')

# Blur
image = image.filter(ImageFilter.BLUR)

# Sharpen
image = image.filter(ImageFilter.SHARPEN)

Saving

Once we’ve processed the image we need to save the changes. In some instances we might just want to save over the original filename. If that’s the case we can just call the save method of image with its original filename. If we want to save the file under a different name, or as a different filetype we need to do a little more work:

# Split our original filename into name and extension
(name, extension) = os.path.splitext(filepath)

# Save with "_changed" added to the filename
image.save(name + '_changed' + extension)

# Save the image as a JPG
image.save(name + '.jpg')

Notice in the last example how PIL takes care of the conversion to JPG for us. All we do is provide the file extension and PIL does the rest for us.

A Complete Example

Each of the steps above can easily be put together to create a batch image processing script. Below is a complete script which creates thumbnails of all provided images, and saves them as PNG images, not matter what their original format:

!/usr/bin/env python
# Batch thumbnail generation script using PIL

import sys
import os.path
import Image

thumbnail_size = (28, 28)

# Loop through all provided arguments
for i in range(1, len(sys.argv)):
try:
  # Attempt to open an image file
  filepath = sys.argv[i]
  image = Image.open(filepath)
except IOError, e:
  # Report error, and then skip to the next argument
  print "Problem opening", filepath, ":", e
  continue

  # Resize the image
  image = image.resize(thumbnail_size, Image.ANTIALIAS)

  # Split our original filename into name and extension
  (name, extension) = os.path.splitext(filepath)

  # Save the thumbnail as "(original_name)_thumb.png"
  image.save(name + '_thumb.png')

Instaling Eclipse for Python

Be default, we all can use python interpreter to test smaller codes but really, it is not a feasible way to write fast code so you can use Eclipse, probably the best open source IDE in the market and create and manage python programs using it.

IBM's Eclipse project was a veritable breath of fresh air, at a moment when it was most needed. The development of open source IDEs seemed to have stopped – with a lot of users sticking to emacs and vi, despite spectacular (but unfruitful) development from Kdevelop and Anjuta.

Eclipse is very extensible and able to work with just about any programming language. In this short tutorial, we will talk about how to set up a Python development environment, using Eclipse and PyDev. The reference distribution is Ubuntu, but aside from the command to install packages, everything will be identical on any distribution.

Step 1.

Obtain and install the Java Runtime Environment (JRE). In most cases, there is a package readily available for most distributions, and it is a dependency for Eclipse. You only need to install JRE manually if there is no readily-available package, or if your package manager does not resolve dependencies automatically (and unless you are using plain RPM, without Yum, or Slackware's package manager without a tool like slapt-get, chances are it does)

Step 2.

Install Python. The version you use depends on your needs. PyDev has a rather wide support.

Step 3.

Install Eclipse and PyDev. Most distributions have a separate package for Eclipse and PyDev. However, there are a lot of distributions which do not provide a PyDev package, since Eclipse can install it itself.

If PyDev cannot be installed by using the distribution's package manager, it can be installed by using Eclipse's Update Manager. To install PyDev from Eclipse, go to Help, Software Updates and click Find and Install.

In the wizard window that appears, choose “Search for new features to install” and click Next. This will open a new window. Click “New Remote Site”, and in the dialog box that appears, enter “PyDev Extensions” in the Name text box, and http://www.pydev.com.br/updates in the URL text box. Click Ok and follow the subsequent on-screen instructions.

Step 4.

Configure the Python interpreter. After you have installed PyDev, open Eclipse and go to Window, Preferences, PyDev, Interpretor – Python (or Jython if you use it instead of Python). Near the Python interpreters list box, click New and navigate to the Python executable on your system (it's usually /usr/bin/python. If it's not there, run the command 'which python' without quotes, and use the path it returns). PyDev will automatically detect some required settings. Once this is over, you are ready to go.

You can now use Eclipse to work on your Python projects. Most project management functions should be familiar to you, and PyDev has a wide range of features, from code completion to refactoring tools.

Installing Java on Ubuntu 9.04

Currently Ubuntu has the following Java packages

sun-java6-bin – Contains the binaries

sun-java6-demo – Contains demos and examples

sun-java6-doc – Contains the documentation

sun-java6-fonts – Contains the Lucida TrueType fonts from the JRE

sun-java6-jdk – Contains the metapackage for the JDK

sun-java6-jre – Contains the metapackage for the JRE

sun-java6-plugin – Contains the plug-in for Mozilla-based browsers

sun-java6-source – Contains source files for the JDK

Use the following command from a terminal

sudo apt-get install sun-java6-jre sun-java6-plugin sun-java6-fonts

MacPorts commonly used commands

As usual, this blog is for keeping notes, as I, like, keep forgetting commands.

Installing a port (example given is for php):

port search php

port info php5

port variants php5 sudo

port -v install php5 +apache2 +mysql5

Upgrade all outdated packages:

sudo port selfupdate

sudo port upgrade outdated

Use the upgrade command with care. In the case of Python 2.5, it will update some of the libraries to 2.6, breaking half of the modules.

For a complete list of all installed ports:

sudo port installed

Why Python?

Oldie but goodie.

ExifTool: It really saved my day

Problem 1: My Coolpix has the year set to 2009, and we took close to a hundred pictures before we realized the error.

Problem 2: This is really a Canon vs Nikon thing. I like my Nikon camera but I like the Canon software better which creates folders according to the picture creation date. If the Canon software would just download data from a Nikon camera, this wouldn't be problem.

So today I discovered ExifTool, installed in on MacBook and voila! Windows users have to install Perl first.

Of course, first you have to navigate to the folder containing the pictures.

To solve problem #1, give this command.

exiftool "-AllDates-=1:: 0" *.jpg

To solve problem 2, give this command:

exiftool -d %Y_%m_%d "-directory<datetimeoriginal" jpg="">