1602882000

# OpenCV: Complete Beginners Guide To Master the Basics Of Computer Vision With Code!

Computer Vision is perhaps the most intriguing and fascinating concept in artificial intelligence. Computer Vision is an interdisciplinary field that deals with how computers or any software can learn a high-level understanding of the visualizations in the surroundings. After obtaining this conceptual perspective, it can be useful to automate tasks or perform the desired action.

The tasks that are obvious to the human brain are not so intuitive to the computers as they need to be trained specifically on these jobs to produce effective results. This process involves complicated steps like acquiring the data from the real world, processing the acquired data in a suitable format, analyzing the processed images, and finally teaching and training the model to perform the complex task with very high accuracy.

To understand computer vision more intuitively, let us consider an example. Assume you have to teach a computer to differentiate between the various colors. Consider, you have three objects with the following colors, namely red, blue, and green, and you want to differentiate these colors accordingly. This job is an extremely simple task for the human brain to perform, but it is quite a complicated task for the computer to perform.

The task mentioned above is one of the most basic actions that can be performed by using computer vision. We will learn about how images in the digital world work and also try to understand the image and how these stacked layers exactly work. . We will also learn in-depth about the basics of the open-cv module. Finally, we will also be implementing some hands on basic level projects with this library. So, without further ado let us dive into understanding all the aspects required for mastering the basic computer vision skills.

## Dealing With Images:

Screenshot By Author

The composition of these three colors, namely red, green, and blue can be used to compose almost any other color. Mixing them in the right proportion allows us to frame any other desired color. This concept has existed since the cathode ray televisions a few decades ago. So how does this exactly work?

Each of these colors has an 8 bit integer value. This means a matrix of these could range from 0 to 255. The reasoning for this is because 2⁸ is 256 and 0–255 consist of 256 values. Each of these colors will have a value of this range and since we have a 3-Dimensional image, we can stack each of these upon each other. This might be a slightly more complex example, so let us switch over to the grayscale images which only consists of black and white and that would be easier to understand. Below is the grayscale representation.

Screenshot By Author

This grayscale representation shown above should be a good starting point to understand the concept of how images work in computer vision better. The below figure shows how the level change starts to happen as we move from the 0th mark to the 255th mark. After 256 levels of changing we go from a completely black shade to a fully white shade.

#programming #machine-learning #computer-vision #data-science #opencv

1675304280

## Introduction

We are back with another exciting and much-talked-about Rails tutorial on how to use Hotwire with the Rails application. This Hotwire Rails tutorial is an alternate method for building modern web applications that consume a pinch of JavaScript.

Rails 7 Hotwire is the default front-end framework shipped with Rails 7 after it was launched. It is used to represent HTML over the wire in the Rails application. Previously, we used to add a hotwire-rails gem in our gem file and then run rails hotwire: install. However, with the introduction of Rails 7, the gem got deprecated. Now, we use turbo-rails and stimulus rails directly, which work as Hotwire’s SPA-like page accelerator and Hotwire’s modest JavaScript framework.

## What is Hotwire?

Hotwire is a package of different frameworks that help to build applications. It simplifies the developer’s work for writing web pages without the need to write JavaScript, and instead sending HTML code over the wire.

Introduction to The Hotwire Framework:

### 1. Turbo:

It uses simplified techniques to build web applications while decreasing the usage of JavaScript in the application. Turbo offers numerous handling methods for the HTML data sent over the wire and displaying the application’s data without actually loading the entire page. It helps to maintain the simplicity of web applications without destroying the single-page application experience by using the below techniques:

Turbo Frames: Turbo Frames help to load the different sections of our markup without any dependency as it divides the page into different contexts separately called frames and updates these frames individually.
Turbo Drive: Every link doesn’t have to make the entire page reload when clicked. Only the HTML contained within the tag will be displayed.
Turbo Streams: To add real-time features to the application, this technique is used. It helps to bring real-time data to the application using CRUD actions.

### 2. Stimulus

It represents the JavaScript framework, which is required when JS is a requirement in the application. The interaction with the HTML is possible with the help of a stimulus, as the controllers that help those interactions are written by a stimulus.

Not much information is available about Strada as it has not been officially released yet. However, it works with native applications, and by using HTML bridge attributes, interaction is made possible between web applications and native apps.

Simple diagrammatic representation of Hotwire Stack:

## Prerequisites For Hotwire Rails Tutorial

As we are implementing the Ruby on Rails Hotwire tutorial, make sure about the following installations before you can get started.

• Ruby on Rails
• Hotwire gem
• PostgreSQL/SQLite (choose any one database)
• Turbo Rails
• Stimulus.js

Looking for an enthusiastic team of ROR developers to shape the vision of your web project?
Contact Bacancy today and hire Ruby developers to start building your dream project!

## Create a new Rails Project

Find the following commands to create a rails application.

``````mkdir ~/projects/railshotwire
cd ~/projects/railshotwire
echo "source 'https://rubygems.org'" > Gemfile
echo "gem 'rails', '~> 7.0.0'" >> Gemfile
bundle install
bundle exec rails new . --force -d=postgresql``````

Now create some files for the project, up till now no usage of Rails Hotwire can be seen.
Fire the following command in your terminal.

• For creating a default controller for the application
``````echo "class HomeController < ApplicationController" > app/controllers/home_controller.rb
echo "end" >> app/controllers/home_controller.rb``````
• For creating another controller for the application
``````echo "class OtherController < ApplicationController" > app/controllers/other_controller.rb
echo "end" >> app/controllers/home_controller.rb``````
• For creating routes for the application
``````echo "Rails.application.routes.draw do" > config/routes.rb
echo '  get "home/index"' >> config/routes.rb
echo '  get "other/index"' >> config/routes.rb
echo '  root to: "home#index"' >> config/routes.rb
echo 'end' >> config/routes.rb``````
• For creating a default view for the application
``````mkdir app/views/home
echo '<h1>This is Rails Hotwire homepage</h1>' > app/views/home/index.html.erb
echo '<div><%= link_to "Enter to other page", other_index_path %></div>' >> app/views/home/index.html.erb
``````
• For creating another view for the application
``````mkdir app/views/other
echo '<h1>This is Another page</h1>' > app/views/other/index.html.erb
``````
• For creating a database and schema.rb file for the application
``````bin/rails db:create
bin/rails db:migrate``````
• For checking the application run bin/rails s and open your browser, your running application will have the below view.

Additionally, you can clone the code and browse through the project. Here’s the source code of the repository: Rails 7 Hotwire application

Now, let’s see how Hotwire Rails can work its magic with various Turbo techniques.

## Hotwire Rails: Turbo Drive

Now click on go to another page link that appears on the home page to redirect from the home page to another page. In our Network tab, we can see that this action of navigation is achieved via XHR. It appears only the part inside HTML is reloaded, here neither the CSS is reloaded nor the JS is reloaded when the navigation action is performed.

By performing this action we can see that Turbo Drive helps to represent the HTML response without loading the full page and only follows redirect and reindeer HTML responses which helps to make the application faster to access.

## Hotwire Rails: Turbo Frame

This technique helps to divide the current page into different sections called frames that can be updated separately independently when new data is added from the server.
Below we discuss the different use cases of Turbo frame like inline edition, sorting, searching, and filtering of data.

Let’s perform some practical actions to see the example of these use cases.

Make changes in the app/controllers/home_controller.rb file

#CODE

``````class HomeController < ApplicationController
def turbo_frame_form
end

def turbo_frame submit
extracted_anynumber = params[:any][:anynumber]
render :turbo_frame_form, status: :ok, locals: {anynumber: extracted_anynumber,      comment: 'turbo_frame_submit ok' }
end
end``````

Add app/views/home/turbo_frame_form.html.erb file to the application and add this content inside the file.

#CODE

``````<section>

<%= turbo_frame_tag 'anyframe' do %>

<div>
<h2>Frame view</h2>
<%= form_with scope: :any, url: turbo_frame_submit_path, local: true do |form| %>
<%= form.label :anynumber, 'Type an integer (odd or even)', 'class' => 'my-0  d-inline'  %>
<%= form.text_field :anynumber, type: 'number', 'required' => 'true', 'value' => "#{local_assigns[:anynumber] || 0}",  'aria-describedby' => 'anynumber' %>
<%= form.submit 'Submit this number', 'id' => 'submit-number' %>
<% end %>
</div>
<div>
<h2>Data of the view</h2>
<pre style="font-size: .7rem;"><%= JSON.pretty_generate(local_assigns) %></pre>
</div>

<% end %>

</section>``````

#CODE

``````Rails.application.routes.draw do
get 'home/index'
get 'other/index'

get '/home/turbo_frame_form' => 'home#turbo_frame_form', as: 'turbo_frame_form'
post '/home/turbo_frame_submit' => 'home#turbo_frame_submit', as: 'turbo_frame_submit'

root to: "home#index"
end``````
• Next step is to change homepage view in app/views/home/index.html.erb

#CODE

``````<h1>This is Rails Hotwire home page</h1>
<div><%= link_to "Enter to other page", other_index_path %></div>

<%= turbo_frame_tag 'anyframe' do %>
<div>
<h2>Home view</h2>
<%= form_with scope: :any, url: turbo_frame_submit_path, local: true do |form| %>
<%= form.label :anynumber, 'Type an integer (odd or even)', 'class' => 'my-0  d-inline'  %>
<%= form.text_field :anynumber, type: 'number', 'required' => 'true', 'value' => "#{local_assigns[:anynumber] || 0}",  'aria-describedby' => 'anynumber' %>
<%= form.submit 'Submit this number', 'id' => 'submit-number' %>
<% end %>
<div>
<% end %>``````

After making all the changes, restart the rails server and refresh the browser, the default view will appear on the browser.

Now in the field enter any digit, after entering the digit click on submit button, and as the submit button is clicked we can see the Turbo Frame in action in the below screen, we can observe that the frame part changed, the first title and first link didn’t move.

## Hotwire Rails: Turbo Streams

Turbo Streams deliver page updates over WebSocket, SSE or in response to form submissions by only using HTML and a series of CRUD-like operations, you are free to say that either

• Update the piece of HTML while responding to all the other actions like the post, put, patch, and delete except the GET action.
• Transmit a change to all users, without reloading the browser page.

This transmit can be represented by a simple example.

• Make changes in app/controllers/other_controller.rb file of rails application

#CODE

``````class OtherController < ApplicationController

def post_something
respond_to do |format|
format.turbo_stream {  }
end
end

end``````

Add the below line in routes.rb file of the application

#CODE

``post '/other/post_something' => 'other#post_something', as: 'post_something'``

Superb! Rails will now attempt to locate the app/views/other/post_something.turbo_stream.erb template at any moment the ‘/other/post_something’ endpoint is reached.

For this, we need to add app/views/other/post_something.turbo_stream.erb template in the rails application.

#CODE

``````<turbo-stream action="append" target="messages">
<template>
<div id="message_1">This changes the existing message!</div>
</template>
</turbo-stream>
``````

This states that the response will try to append the template of the turbo frame with ID “messages”.

Now change the index.html.erb file in app/views/other paths with the below content.

#CODE

``````<h1>This is Another page</h1>

<div style="margin-top: 3rem;">
<%= form_with scope: :any, url: post_something_path do |form| %>
<%= form.submit 'Post any message %>
<% end %>
<turbo-frame id="messages">
<div>An empty message</div>
</turbo-frame>
</div>``````
• After making all the changes, restart the rails server and refresh the browser, and go to the other page.

• Once the above screen appears, click on the Post any message button

This action shows that after submitting the response, the Turbo Streams help the developer to append the message, without reloading the page.

Another use case we can test is that rather than appending the message, the developer replaces the message. For that, we need to change the content of app/views/other/post_something.turbo_stream.erb template file and change the value of the action attribute from append to replace and check the changes in the browser.

#CODE

``````<turbo-stream action="replace" target="messages">
<template>
<div id="message_1">This changes the existing message!</div>
</template>
</turbo-stream>``````

When we click on Post any message button, the message that appear below that button will get replaced with the message that is mentioned in the app/views/other/post_something.turbo_stream.erb template

## Stimulus

There are some cases in an application where JS is needed, therefore to cover those scenarios we require Hotwire JS tool. Hotwire has a JS tool because in some scenarios Turbo-* tools are not sufficient. But as we know that Hotwire is used to reduce the usage of JS in an application, Stimulus considers HTML as the single source of truth. Consider the case where we have to give elements on a page some JavaScript attributes, such as data controller, data-action, and data target. For that, a stimulus controller that can access elements and receive events based on those characteristics will be created.

Make a change in app/views/other/index.html.erb template file in rails application

#CODE

``````<h1>This is Another page</h1>

<div style="margin-top: 2rem;">
<%= form_with scope: :any, url: post_something_path do |form| %>
<%= form.submit 'Post something' %>
<% end %>
<turbo-frame id="messages">
<div>An empty message</div>
</turbo-frame>
</div>

<div style="margin-top: 2rem;">
<h2>Stimulus</h2>
<div data-controller="hello">
<input data-hello-target="name" type="text">
<button data-action="click->hello#greet">
Greet
</button>
<span data-hello-target="output">
</span>
</div>
</div>``````

Make changes in the hello_controller.js in path app/JavaScript/controllers and add a stimulus controller in the file, which helps to bring the HTML into life.

#CODE

``````import { Controller } from "@hotwired/stimulus"

export default class extends Controller {
static targets = [ "name", "output" ]

greet() {
this.outputTarget.textContent =
`Hello, \${this.nameTarget.value}!`
}
}``````

Go to your browser after making the changes in the code and click on Enter to other page link which will navigate to the localhost:3000/other/index page there you can see the changes implemented by the stimulus controller that is designed to augment your HTML with just enough behavior to make it more responsive.

With just a little bit of work, Turbo and Stimulus together offer a complete answer for applications that are quick and compelling.

Using Rails 7 Hotwire helps to load the pages at a faster speed and allows you to render templates on the server, where you have access to your whole domain model. It is a productive development experience in ROR, without compromising any of the speed or responsiveness associated with SPA.

## Conclusion

We hope you were satisfied with our Rails Hotwire tutorial. Write to us at service@bacancy.com for any query that you want to resolve, or if you want us to share a tutorial on your query.

For more such solutions on RoR, check out our Ruby on Rails Tutorials. We will always strive to amaze you and cater to your needs.

Original article source at: https://www.bacancytechnology.com/

1602882000

## OpenCV: Complete Beginners Guide To Master the Basics Of Computer Vision With Code!

Computer Vision is perhaps the most intriguing and fascinating concept in artificial intelligence. Computer Vision is an interdisciplinary field that deals with how computers or any software can learn a high-level understanding of the visualizations in the surroundings. After obtaining this conceptual perspective, it can be useful to automate tasks or perform the desired action.

The tasks that are obvious to the human brain are not so intuitive to the computers as they need to be trained specifically on these jobs to produce effective results. This process involves complicated steps like acquiring the data from the real world, processing the acquired data in a suitable format, analyzing the processed images, and finally teaching and training the model to perform the complex task with very high accuracy.

To understand computer vision more intuitively, let us consider an example. Assume you have to teach a computer to differentiate between the various colors. Consider, you have three objects with the following colors, namely red, blue, and green, and you want to differentiate these colors accordingly. This job is an extremely simple task for the human brain to perform, but it is quite a complicated task for the computer to perform.

The task mentioned above is one of the most basic actions that can be performed by using computer vision. We will learn about how images in the digital world work and also try to understand the image and how these stacked layers exactly work. . We will also learn in-depth about the basics of the open-cv module. Finally, we will also be implementing some hands on basic level projects with this library. So, without further ado let us dive into understanding all the aspects required for mastering the basic computer vision skills.

## Dealing With Images:

Screenshot By Author

The composition of these three colors, namely red, green, and blue can be used to compose almost any other color. Mixing them in the right proportion allows us to frame any other desired color. This concept has existed since the cathode ray televisions a few decades ago. So how does this exactly work?

Each of these colors has an 8 bit integer value. This means a matrix of these could range from 0 to 255. The reasoning for this is because 2⁸ is 256 and 0–255 consist of 256 values. Each of these colors will have a value of this range and since we have a 3-Dimensional image, we can stack each of these upon each other. This might be a slightly more complex example, so let us switch over to the grayscale images which only consists of black and white and that would be easier to understand. Below is the grayscale representation.

Screenshot By Author

This grayscale representation shown above should be a good starting point to understand the concept of how images work in computer vision better. The below figure shows how the level change starts to happen as we move from the 0th mark to the 255th mark. After 256 levels of changing we go from a completely black shade to a fully white shade.

#programming #machine-learning #computer-vision #data-science #opencv

1621137960

## Guidelines for Java Code Reviews

#### Get a jump-start on your next code review session with this list.

Having another pair of eyes scan your code is always useful and helps you spot mistakes before you break production. You need not be an expert to review someone’s code. Some experience with the programming language and a review checklist should help you get started. We’ve put together a list of things you should keep in mind when you’re reviewing Java code. Read on!

### 5. Handle Exceptions With Care

#java #code quality #java tutorial #code analysis #code reviews #code review tips #code analysis tools #java tutorial for beginners #java code review

1604008800

## Static Code Analysis: What It Is? How to Use It?

Static code analysis refers to the technique of approximating the runtime behavior of a program. In other words, it is the process of predicting the output of a program without actually executing it.

Lately, however, the term “Static Code Analysis” is more commonly used to refer to one of the applications of this technique rather than the technique itself — program comprehension — understanding the program and detecting issues in it (anything from syntax errors to type mismatches, performance hogs likely bugs, security loopholes, etc.). This is the usage we’d be referring to throughout this post.

“The refinement of techniques for the prompt discovery of error serves as well as any other as a hallmark of what we mean by science.”

• J. Robert Oppenheimer

### Outline

We cover a lot of ground in this post. The aim is to build an understanding of static code analysis and to equip you with the basic theory, and the right tools so that you can write analyzers on your own.

We start our journey with laying down the essential parts of the pipeline which a compiler follows to understand what a piece of code does. We learn where to tap points in this pipeline to plug in our analyzers and extract meaningful information. In the latter half, we get our feet wet, and write four such static analyzers, completely from scratch, in Python.

Note that although the ideas here are discussed in light of Python, static code analyzers across all programming languages are carved out along similar lines. We chose Python because of the availability of an easy to use `ast` module, and wide adoption of the language itself.

### How does it all work?

Before a computer can finally “understand” and execute a piece of code, it goes through a series of complicated transformations:

As you can see in the diagram (go ahead, zoom it!), the static analyzers feed on the output of these stages. To be able to better understand the static analysis techniques, let’s look at each of these steps in some more detail:

### Scanning

The first thing that a compiler does when trying to understand a piece of code is to break it down into smaller chunks, also known as tokens. Tokens are akin to what words are in a language.

A token might consist of either a single character, like `(`, or literals (like integers, strings, e.g., `7``Bob`, etc.), or reserved keywords of that language (e.g, `def` in Python). Characters which do not contribute towards the semantics of a program, like trailing whitespace, comments, etc. are often discarded by the scanner.

Python provides the `tokenize` module in its standard library to let you play around with tokens:

Python

1

``````import io
``````

2

``````import tokenize
``````

3

4

``````code = b"color = input('Enter your favourite color: ')"
``````

5

6

``````for token in tokenize.tokenize(io.BytesIO(code).readline):
``````

7

``````    print(token)
``````

Python

1

``````TokenInfo(type=62 (ENCODING),  string='utf-8')
``````

2

``````TokenInfo(type=1  (NAME),      string='color')
``````

3

``````TokenInfo(type=54 (OP),        string='=')
``````

4

``````TokenInfo(type=1  (NAME),      string='input')
``````

5

``````TokenInfo(type=54 (OP),        string='(')
``````

6

``````TokenInfo(type=3  (STRING),    string="'Enter your favourite color: '")
``````

7

``````TokenInfo(type=54 (OP),        string=')')
``````

8

``````TokenInfo(type=4  (NEWLINE),   string='')
``````

9

``````TokenInfo(type=0  (ENDMARKER), string='')
``````

(Note that for the sake of readability, I’ve omitted a few columns from the result above — metadata like starting index, ending index, a copy of the line on which a token occurs, etc.)

#code quality #code review #static analysis #static code analysis #code analysis #static analysis tools #code review tips #static code analyzer #static code analysis tool #static analyzer

1624332357

## Morse Code Translator Detect Blinks — Python, OpenCV, MediaPipe

Hello everyone,

It has been a while since the last time I posted a tutorial, or something in general. Basically life happened and I decided not to share rather than sharing low quality content. Today, I’ll walk you through a computer vision project that takes your live video input and translates your blinks into Morse Alphabet so you can blink short and long to write messages.

The source code for the project is here, I also used this awesome tutorial as a boiler plate to start with, if you want to learn more about Computer Vision applications you can check the channel owner’s channel from the link I posted. So without further ado let’s dive right into it.

As for the beginning I want to explain MediaPipe library a little bit, “MediaPipe offers open source cross-platform, customizable ML solutions for live and streaming media.”, this definition is from their own website and explains what you can do with that library shortly and cleanly, they offer several other solutions that can run on different platforms and I’ll explain all of them in a different post in the future. The feature that we’ll use today is called “Face Mesh”, this solution provides us a face landmark map with the most important 468 landmarks that can be seen in a human’s face. Using that map we’ll calculate the ratio between some particular points in the face and with that information we’ll detect if the person on the camera blinked or not.

#python #opencv #mediapipe #computer-vision #morse code translator detect blinks — python, opencv, mediapipe #morse code translator detect blinks