Histogram Equalization, Stretching, origin histo compare and example source code

Example source code for histogram equalization
and compare with origin histogram and stretching histogram.

result is like that:

origin image & histogram




stretching image and histogram






Equalization image and histogram
 

<gist>

</gist>


tags:
equalizeHist, cvtColor, normalize, calcHist

python list, numpy slicing

Oh.. I seem to be old.. I need a memo everything..
This is memo for me about list slicing.

nums = list(range(5))
print(nums)      #[0, 1, 2, 3, 4]
print(nums[2:4]) #[2, 3]
print(nums[2:])  #[2, 3, 4] 
print(nums[:2])  #[0, 1]
print(nums[:])   #[0, 1, 2, 3, 4]
print(nums[:-1]) #[0, 1, 2, 3]
nums[2:4] = [8,9]
print(nums)      #[0, 1, 8, 9, 4]

result
[0, 1, 2, 3, 4]
[2, 3]
[2, 3, 4]
[0, 1]
[0, 1, 2, 3, 4]
[0, 1, 2, 3]
[0, 1, 8, 9, 4]


numpy slicing

import numpy as np

a = np.array([1, 2, 3, 4, 5])
print(a[1:3]) #array [2 3]
print(a[-1]) #5
a[0:2] = 9
print(a) #array [9 9 3 4 5]
b = np.array([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]])
print(b)
#array
#[[ 1  2  3  4]
# [ 5  6  7  8]
# [ 9 10 11 12]]

print(b[:,1]) #array [2 6 10]
print(b[-1])      #array [9 10 11 12]
print(b[-1,:])    #array [9 10 11 12]
print(b[-1, ...]) #array [9 10 11 12]

print(b[0:2, :])
#array#[[1 2 3 4]# [5 6 7 8]]

😀

Making virtualenv using mkvirtualenv or virtualenv, simple command memo.

- create virtual env wrapper & deactivate

mkvirtualenv env-py2 -p python2 #(or python3)
workon env-py2
deactivate

- create virtual env & deactivate

sudo pip install virtualenv
virtualenv env
sourse env/bin/activate
source deactivate

- delete virtual env

rmvirtualenv envname

- virtualenv dependencies save and install

#On the first, save
pip freeze > requirements.txt

#On the second, install(note! after activating target env)
pip install -r requirements.txt

-show all virtualenv names

lsvirtualenv -l

- PyCharm virtualenv wrapper setting
We have to set directory path manually in preference setting page.
The path is like this in my case.

And then you can select this virtualenv on run/debug configuration.

opencv histogram stretching, example source code.

Histogram stretching
It's just adjusting the range with the same ratio.

For example, there is a range of numbers.
60, 61, 62, 63, 64, 65
Stretching is to extent other range, such as 0~255.
So, if we stitching 60~65 to 0~255, numbers will be like that.
60 -> 0
61 -> 51
62 -> 102
63 -> 153
64 -> 204
65 -> 255

so, in case of histogram, origin histogram will be stretched like that

image source : https://stackoverflow.com/questions/41118808/difference-between-contrast-stretching-and-histogram-equalization

then, let's look at code and result with real image.

origin input image


histogram


stretched image


histogram of stretched image


source code
<gist start>

<gist end>

Django + install rich html text editor (WYSIWYG, ckeditor)

I recommend you do this on virtual-env.

1. install packages

pip install django-ckeditor
pip install image (optional)

2. Set settings.py

Add ckeditor in INSTALLED_APPS

INSTALLED_APPS = [ 'django.contrib.admin',                   

                   'django.contrib.auth',                   

                    ... 
                   'ckeditor',]

Add this contents end of settings.py

CKEDITOR_UPLOAD_PATH = "uploads/" 

CKEDITOR_CONFIGS = { 
    'default': { 'toolbar': None, },

}

3. Set url.py

Add "url(r'^ckeditor/', include('ckeditor_uploader.urls'))," in urlpatterns

urlpatterns = [ url(r'^admin/', admin.site.urls),                

               ... 
                url(r'^ckeditor/', include('ckeditor_uploader.urls')),                

]

4. set models.py

Add import RichTextField
change "models.TextField()" to "RichTextField()"

from ckeditor.fields import RichTextField 
# Create your models here 

class OpenCV_Post(models.Model): 
    author = models.ForeignKey('auth.User') 
    title = models.CharField(max_length=200)
    # text = models.TextField()    

    text = RichTextField()

5. migration!

>>python manage.py makemigrations
>>python manage.py migrate

The Result on Admin






reference
https://www.youtube.com/watch?v=W8PTD7SszDI

Hue histogram example opencv source code

Hue histogram example source code.

input


Hue histogram output


source code
<gist start>

<gist end>

calcHist for RGB image, opencv histogram example

A Example source code for rgb histogram, the source code uses calcHist function in opencv.

Important things in the source code are the part of split rgb mat to vector[3] and drawing part.
Read the code carefully, so then you can understand easliy. ^^

input


the result of rgb histogram


<gist code start>

<gist code end>



reference : https://docs.opencv.org/2.4/doc/tutorials/imgproc/histograms/histogram_calculation/histogram_calculation.html