Tag: android

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Image Filtering Using Fourier Transform

In Machine Vision there is a magical trick that involves Fourier transformation of an image and I would like to share it with you today. I learned this long ago from a professor of mine but I remember back then there was not much experience and information about this on the web. Also there was no program that allowed experimenting with Fourier transformation of Images, until I developed an Android application titled Image Transformer, using OpenCV and Qt, which allows you to do just that.

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How to get screen size in Qt

Qt includes a very simple method to get the size of the screen (width and height). Here it is:

QSize size = qApp->screens()[0]->size();

Note that this function works perfectly in Android and iOS too.

Another thing to note is that if you replace [0] with 1, 2, 3, … you can access other monitors (if there are any) on desktop computers.

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How to Open Android Image Gallery in Qt

This article describes how to open default Android Gallery in Qt using a mixture of Android’ Java and Qt (C++) code. It is specially useful if you are working with images, for example if you want to open a Mat Image in OpenCV using imread function or if you are just writing some kind of image viewer program. Unfortunately Qt does not offer this (yet) by default so I thought I could share it with you.

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How To Mix C++ And Java Code (In Qt For Android)

Qt allows you to use Java code in your Android applications. This is the same code that Android Studio (or Eclipse etc.) users use when they are writing applications for Android. In Qt, by default, you are limited to C++ code and what the Qt modules have to offer (which in most cases are enough) but there are certain situations where you need to use something from Android API which is not provided in Qt. An obvious example for this can be using the default Android Galley to open a picture, or using Text-To-Speech engine or any other API that you can think of. If you don’t want to be limited to what is provided by Qt while writing Android apps then follow the steps below to be able to add Java code to your Qt project.

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Download Template Project – Qt for Android (with OpenCV)

I start Qt for Android projects all the time and setting up all the required folders and including libraries can take some time, assuming that I don’t make any mistakes during the initialization of the project. Previously I had posted this about how to add OpenCV libraries to your Qt for Android project but it proved to be not enough and I also receive questions about how to create a correct project with OpenCV all the time.

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How to add Permissions to your Qt Android app

Whether you want to use GPS or Compass, Camera or the Internet, you will need to add permissions to your Qt app for Android because Android API uses a permission system for security reasons. It actually has other benefits such as helping with monitoring and app statistics and so on but I’m not going to discus that in this post.

If you need to add permissions to your Qt Android app then follow these steps.

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