B4A Library OpenCV 3.x

JordiCP · May 22, 2017

OpenCV (Open Source Computer Vision Library) is a really huge project/framework actively developed, mainly written in C++ . It is released under a BSD license.

Read more here: http://opencv.org/

OpenCV versions: https://opencv.org/releases/

OpenCV library for B4A: wraps the official OpenCV 3.x release for Android (in fact not all, about 95% of it)

Feel free to test and use it. You can even
License: You can use it for your projects, but you are not allowed to distribute nor sell this library. Of course you can distribute apps that use it (remember that OpenCV itself has BSD license as stated before)
Supported hardware is: armeabi-v7a and arm64-v8
Versions
- 1.04 (2020/05/17)
  - This version wraps OpenCV 3.4.1 Android release and fixes some bugs (mostly some instance methods and some not exposed classes) of the previous version.
  - One of the major additions is the DNNmodule and related classes.
    - LINK to example (too large to be uploaded here)
    - Result video
  - Link to the B4A library files: HERE
- 1.00 (2017/09/27)
  - First B4A library wrapper (OpenCv320forB4A V1.00) which replicates (95%) the official OpenCV 3.20 Java API for Android.
  - (removed link. Use 1.04)

Please note that my support will be limited to issues with the wrapper itself, not to help translating OpenCV code from other languages to B4A ?‍

========================================================================

(There may be some inaccuracies in what I expose in this post, related to the OpenCV project, since I am relatively new to it and don't know all about its internals. If you find any, please let me know and I will correct it)

A bit of explanation

There exist 'official' OpenCV wrappers for different languages and platforms. Android is one of them.
The official OpenCV 3.20 for Android API includes a lot of classes, organized in modules. But it does not include "all" the original OpenCV modules (since there are other 'experimental', non-free, or platform specific modules which may be present in other platforms but not for Android). Also, there are build options to "tune" it...

I have played quite a lot with it this last year, with a huge project which I started with inline Java, and also translating examples or testing features. But what I have used is just a small percent of the classes and methods exposed. So, there may be some (let's hope not too many) things to fix.

How to learn OpenCVforB4A

If you have worked before with OpenCV, the learning curve will be easy.
If it was using Java with OpenCV for Android, then it will be immediate, since all the methods have exactly the same syntax (except for initializers, polimorphism, and some special cases where simply I did my best).
Anyhow, the ways that I can think of, are (will add links later, also suggestions as online tutorials,.. are welcome)

Attached examples.
B4A OpenCV Tutorials. I will write a couple of them with what I consider the most important building pieces (for instance the Mat class, which in B4A is OCVMat) and modules
Internet examples: there are A LOT of examples over there, written in C++, Java, Python, JavaCV. I would look for examples in the language that is easier to understand for you and then try to translate. Some tips about it (based on my experience)

OpenCV syntax has changed as new versions. So there is an 'old' syntax in which nearly everything started with "cv...". Since version 3.X, there was 'cleaner' organization (project was written in C++ instead of C), and there were major syntax changes.
JavaCV: Translating from JavaCV to OpenCV should be quite easy but not always direct. JavaCV uses a mix of the old OpenCV syntax with some of its own, and at the beginning it can be a bit confusing, but then it is also easy.
Python: there is a lot of material...

First steps. Prepare for some crashes...

In OpenCV nearly everything takes part in the native code.
When we call a Sub/method/algorithm, it performs some internal checks to see if all the input data is correct. This check is perfomed in the native side. If something is not correct (wrong OCVMat dimensions, some incoherent parameters,...) it throws an exception and crashes. If we are lucky, perhaps we see in the log some clues about the check that made it crash.
On the good side, it is very easy to achieve results with OpenCV (check the examples). The real difficult part, as with many other things, is to fine-tune it: OpenCV has a collection of really powerful 'primitive' objects and operations, and really complex algorithms that can do many things. But it is the user who has to glue all of them to achieve the desired results.

(from the previous Beta announcement)

IMPORTANT: you must take this into account:

OpenCV (the included binary modules) is a free(*) project, but subject to license terms as described here: http://opencv.org/
- (*): There are some modules in the OpenCV project which are on-free, but here I am refering to the ones included in the library
My work: (the B4A library) is free to test and use, but you can

for it . I'll keep donators updated with "advanced" material and examples
If you are interested, please PM me with your mail address and I will send you a link with the library and some basic examples. (be patient if you don't receive it immediately, I'll do it as soon as possible).

There is no documentation. In short, the syntax is nearly-exactly the same as the OpenCV3.20 Java API, adding "OCV" prefix and only the minimum modifications to adapt to B4A, For reference (taking into account described syntax changes) you can look at http://docs.opencv.org/java/3.1.0/ (which is not the latest one, but the API is nearly the same).
It would be preferable if you have worked before with OpenCV and/or can translate examples from Java/C++ and/or simply are interested in it.
I recommend starting with the examples and try to understand what is done. Just experimenting can lead to crash after crash of the native libraries with nearly no useful information, and can be very discouraging.
I forgot, the included binaries are for ameabi-v7a and arm64-v8 devices

---------------------------------------------------------------------
Some screenshots taken from the examples

Canny operator - Features2D - Color space conversion

2D-FFT

Color Blob detection

JordiCP · Jun 22, 2020

wang xue feng said:
I want to complete the function of green screen button image, can it be realized? colorkey? thank you!

Not sure to understand. What do you mean exactly?

VittorioBarile · Jun 24, 2020

how could I run CameraOpenCvTest on a USB Camera?

JordiCP · Jun 24, 2020

VittorioBarile said:
how could I run CameraOpenCvTest on a USB Camera?

It won't work directly on a USB camera, sorry ?‍
CameraOpenCvTest example uses JavaCameraView, which relies on the Android Camera API. As it is, this class only has access to the device's internal cameras.

If you can get the USB camera (UVC?) to work with B4A by itself, and get its preview, then the example can be easily ported to process that preview instead of the JavaCameraview input

VittorioBarile · Jun 24, 2020

JordiCP said:
If you can get the USB camera (UVC?) to work with B4A by itself, and get its preview, then the example can be easily ported to process that preview instead of the JavaCameraview input

It's a webcam with usb cable. However it doesn't work with B4A, with USB library too

fernando.oliboni · Jul 11, 2020

Olá Jordi Gostaria de testar uma biblioteca para trabalhar com textos. Você poderia me enviar o link para download?
fernando.oliboni@gmail.com

gezueb · Aug 6, 2020

Hi Jordi, I am refering to your Example ImageManipulation2 where the points of a circle are detected. This is the part of your code:

B4X:

        Dim circles As OCVMatOfPoint3f
        circles.Initialize   
        'dp=1 --> scaling factor of the algorith. 1=start with the original image
        'minDistance --> to prevent false positives. But if circles are concentrical, leave this factor as small as possible
        'mImgProc.HoughCircles1(    tmpMatGray,circles,mImgProc.HOUGH_GRADIENT,1,10)
        mImgProc.HoughCircles(tmpMatGray,circles,mImgProc.HOUGH_GRADIENT,1.0d,10,150,100,20,240)
        'The function HoughCircles returns an array of 3-points (x,y,radius)
        Log(circles.rows&" "&circles.cols&" "&circles.depth)
        Dim allCircles() As OCVPoint3= circles.toArray()
        For k=0 To allCircles.Length-1

            Log("Detected circle: x="&allCircles(k).x &" y="& allCircles(k).y &" radius="& allCircles(k).z)

I would like to detect lines instead of circles, but I cannot figure out the necessary declarations for a line. There is no OCVMatOfPoint4f (for begin and end coordinates) or OCVMatOfLine. Can you help me with the declarations?
Thank you!

VittorioBarile · Sep 25, 2020

Hi,
i got UnsatisfiedLinkError exception with serial lib. I made a topic for help

UnsatisfiedLinkError: Serial lib mismatch with OpenCV3

Hello, i have a big issue and i don't know how to deal with UnsatisfiedLinkError exception. I'm using my own library wrapped from FriendlyThings API for communicate with serial - PWM - I2C - GPIO for NanoPC T2 When i call some methods from this library it will mismatch with OpenCV3 library...

www.b4x.com

could you help me?

cesarcm · Dec 2, 2020

JordiCP,

Congrats! Your OpenCV is GREAT!

BTW => donation is done

Question:
- which are the parameters for PutText2 ??? (OCVpoint, fontFace and fontScale)

Thanks
Regards,
Cesar

gezueb · Dec 3, 2020

OpenCV PutText fontscale is not in pixels. It is something like 0=tiny,1=small,2=reasonable, 3=big etc. Fontface: no idea, but 1 gives a reasonable character.

cesarcm · Dec 3, 2020

Gezueb,

Thanks!
Cesar

gezueb · Dec 3, 2020

You are welcome! I forgot that you asked for points too. They must be declared as ocvpoints. Use a code like this to create an ocv point:

B4X:

sub CreatePoint(X As Double, Y As Double) As OCVPoint
    Dim p As OCVPoint
    p.Initialize(X, Y)
    Return p
End Sub

and call this sub with x and y bitmap coordinates.

cesarcm · Dec 3, 2020

Gezub,

You rock
Thanks a lot

BUT, just two more questions

a) how to split RGB channels to independent arrays (probablu cvMat), since I have to calculate something on each channel ???

b) is there a function for Optical Flow since aI have to track an object motion?

Thanks a lot.
Regards,
Cesar

gezueb · Dec 3, 2020

Split rgb channel is easy, there are 4 byte values packed into a float value in a bitmap(see many examples). You will have to get the rgb pixel in a x,y nested loop with .getpixels and write the values extracted with bit.and and unsigned right shift with the setpixels method from the btmpex library into an empty 8bit bitmap (UCV8) of same size. Upmost byte is transparency (rarely used on camera pictures, the others are rgb in descending order. For conversion from rgb to grey values there is a separate function but I do not think there is one for each color.
Dont know about flow but I found that the OpenCV stuff is surprisingly fast, maybe you can use simple functions in loop.

JordiCP · Dec 3, 2020

cesarcm said:
BTW => donation is done

Thanks! ?

cesarcm said:
a) how to split RGB channels to independent arrays (probablu cvMat), since I have to calculate something on each channel ???

Something similar to this

B4X:

Dim channels As List
channels.Initialize
mCore.split( myMat, channels)     '<-- Statically declare mCore as OCVCore 
Dim blueChannel As OCVMat = channels.Get(2)
...

cesarcm said:
b) is there a function for Optical Flow since aI have to track an object motion?

Classes OCVDenseOpticalFlow, OCVDualTLV1OpticalFlow, OCVFarnebackOpticalFlow, OCVSparseOpticalFlow...are implemented.
I've never used them, so there are may be wrapper errors for those classes. If you find something strange, pls report.

cesarcm · Dec 3, 2020

JordiCP said:
Thanks! ?

Something similar to this

B4X:

Dim channels As List channels.Initialize mCore.split( myMat, channels) '<-- Statically declare mCore as OCVCore Dim blueChannel As OCVMat = channels.Get(2) ...

Classes OCVDenseOpticalFlow, OCVDualTLV1OpticalFlow, OCVFarnebackOpticalFlow, OCVSparseOpticalFlow...are implemented.
I've never used them, so there are may be wrapper errors for those classes. If you find something strange, pls report.

PERFECT!!!
Thanks a lot.
Regards,
Cesar

cesarcm · Dec 3, 2020

JordiCP,

We are migrating our project (partially written in Python and Javascript) to B4A / OpenCV.

If everything works fine you will have a good bonu$ (donation) as well.

Thanks.
Regards,
Cesar

cesarcm · Dec 4, 2020

JordiCP,

One more question:

Does the library have a denoising function / method? for Rgb image ...

In OpenCV we can use:

cv.fastNlMeansDenoising() - works with a single grayscale images
cv.fastNlMeansDenoisingColored() - works with a color image.
cv.fastNlMeansDenoisingMulti() - works with image sequence captured in short period of time (grayscale images)
cv.fastNlMeansDenoisingColoredMulti() - same as above, but for color images.

Thanks.
Regards,
Cesar

JordiCP · Dec 4, 2020

cesarcm said:
Does the library have a denoising function / method? for Rgb image ...

They are under the Photo (OCVPhoto) module class.

B4X:

Dim mPhoto as OCVPhoto
mPhoto.fastNIMeansDenoising(..)     '<-- see variants with subindex 1,2,3 that allow for different parameters
mPhoto.fastNIMeansDenoisingColored(..)   '<-- also has a variant with suffix 1
mPhoto.fastNIMeansDenoisingColoredMulti(..)   '<-- also has a variant with suffix 1
mPhoto.fastNIMeansDenoisingMulti(..)   '<-- also has variants with suffix 1,2,3

Take into account that depending on the parameters (searchwindowsize), it may take a while since there are a lot of convolutions involved.

cesarcm · Dec 5, 2020

Perfect! You rock!

Everything is included ... I really have to dig deeper into to discover all features inside ..

??

cesarcm · Dec 5, 2020

JordiCP,

Sorry to ask you many questions but until I find everything by myself I am sure that your your tips are valuable and indispensable at all.

In my project I have to split the RGB frame into channels; for each channel I have to:

PS: please just help to inform in which OCV object there is each function below! Thanks a lot!

a) cv.Mat.zeros
b) cv.Mat.eye
c) cv.Mat.ones
d) cv.matFromArray

*** copied from my Javascript code

Thanks.
Regards,
Cesar

B4A Library OpenCV 3.x

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