Hello everyone, today I will introduce you to the Opencv2 library, a very powerful library used in image processing, this is also the library I use mainly in the next article. And here I will code in python 3 on jupyter notebook school.

Setup

I encourage you to use anaconda there will jupyter notebook settup way you can refer to the following link here .

Install opencv2 library:

Check the version:

Or if you don’t want to waste time you can use colab

Read and display image

The picture I will use will be the following:

The output of img will now be a three-dimensional matrix but in the theory of RGB. We will have a command to view the shape and size of the image:

When displaying images, there are 2 ways:

• Method 1 uses the function available in cv2:
  
  <span class="token comment"># cv2.imshow(window_name, image)</span> cv2 <span class="token punctuation">.</span> imshow <span class="token punctuation">(</span> <span class="token string">'test'</span> <span class="token punctuation">,</span> img <span class="token punctuation">)</span>

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  <span class="token comment"># cv2.imshow(window_name, image)</span> cv2 <span class="token punctuation">.</span> imshow <span class="token punctuation">(</span> <span class="token string">'test'</span> <span class="token punctuation">,</span> img <span class="token punctuation">)</span>

• Option 2 uses the matplotlib library.
  
  <span class="token comment">#to display at jupyter notebook</span> <span class="token keyword">import</span> matplotlib <span class="token punctuation">.</span> pyplot <span class="token keyword">as</span> plt <span class="token comment">#Note cv2 read BGR as default</span> plt <span class="token punctuation">.</span> imshow <span class="token punctuation">(</span> image <span class="token punctuation">)</span>

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  <span class="token comment">#to display at jupyter notebook</span> <span class="token keyword">import</span> matplotlib <span class="token punctuation">.</span> pyplot <span class="token keyword">as</span> plt <span class="token comment">#Note cv2 read BGR as default</span> plt <span class="token punctuation">.</span> imshow <span class="token punctuation">(</span> image <span class="token punctuation">)</span>

  
  If the code as above, the output image will be as follows:

  Because cv2 defaults to reading color images in the order of BGR (blue, green and red). Therefore, if you want to display correctly, you must write:

  <span class="token comment">#display rgb image</span> plt <span class="token punctuation">.</span> imshow <span class="token punctuation">(</span> image <span class="token punctuation">[</span> <span class="token punctuation">:</span> <span class="token punctuation">,</span> <span class="token punctuation">:</span> <span class="token punctuation">,</span> <span class="token punctuation">:</span> <span class="token punctuation">:</span> <span class="token operator">-</span> <span class="token number">1</span> <span class="token punctuation">]</span> <span class="token punctuation">)</span>

  1 2 3

  <span class="token comment">#display rgb image</span> plt <span class="token punctuation">.</span> imshow <span class="token punctuation">(</span> image <span class="token punctuation">[</span> <span class="token punctuation">:</span> <span class="token punctuation">,</span> <span class="token punctuation">:</span> <span class="token punctuation">,</span> <span class="token punctuation">:</span> <span class="token punctuation">:</span> <span class="token operator">-</span> <span class="token number">1</span> <span class="token punctuation">]</span> <span class="token punctuation">)</span>

Accessing image data with numpy.array

The operations we are familiar with using numpy are also used in image data. For example:

Crop out part of the image and display them:

Result:

Change the color of the area we have cropped to green:

Result:

Resizing images

We want to resize the image into an image of size 200, 200 will do the following:

Write images

Save the image file using the following command:

summary

All the code you can see here: here

Above I introduced you on how to read, display and save an image file