Does anyone have experience using OpenCV in Lazarus?

[xiyi0616]

I'm using Lazarus 3.9 on Ubuntu 22.04.5 LTS. I installed OpenCV version 4.5.4 using apt-get install libopencv-dev.

The code is as simple as:

unit OpenCVDisplayMain;

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, LCLType,
  ctypes, LCLIntf, ExtCtrls;

type

  { TForm1 }

  TForm1 = class(TForm)
    Image1: TImage;
    procedure FormCreate(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;

  TSize = record
    width, height: Integer;
  end;
  PSize = ^TSize;

var
  Form1: TForm1;

implementation

{$R *.lfm}

function cv_imread(filename: PAnsiChar; flags: Integer): Pointer; cdecl; external 'libopencv_imgcodecs.so.4.5.4d';
function cv_GetSize(img: Pointer): PSize; cdecl; external 'libopencv_core.so.4.5';
procedure cv_releaseImage(img: PPointer); cdecl; external 'libopencv_core.so.4.5'; /
function cvCvtColor(src, dst: Pointer; code: Integer): Integer; cdecl; external 'libopencv_imgproc.so.4.5';
function cvCreateImage(size: PSize; depth: Integer; channels: Integer): Pointer; cdecl; external 'libopencv_core.so.4.5';


{ TForm1 }

procedure TForm1.FormCreate(Sender: TObject);
var
  OpenCVImage, ConvertedImage: Pointer;
  Size: PSize;
  Filename: string;
  OpenCVImagePtr: PPointer;
  Bitmap: TBitmap;
begin
  Filename := 'test.jpg';

  OpenCVImage := cv_imread(PAnsiChar(AnsiString(Filename)), 1);

  if OpenCVImage <> nil then
  begin
    Size := cv_GetSize(OpenCVImage);

    ConvertedImage := cvCreateImage(Size, 8, 3); // 8 bits per channel, 3 channels (BGR)

    cvCvtColor(OpenCVImage, ConvertedImage, 6); // COLOR_BGR2BGR = 6

    Bitmap := TBitmap.Create;
    try
      Bitmap.PixelFormat := pf24bit;
      Bitmap.Width := Size^.width;
      Bitmap.Height := Size^.height;

      Move(Pointer(ConvertedImage)^, Bitmap.ScanLine[0]^, Bitmap.Width * Bitmap.Height * 3);

      Image1.Picture.Assign(Bitmap);

    finally
      Bitmap.Free;
    end;

    OpenCVImagePtr := @OpenCVImage;
    cv_releaseImage(OpenCVImagePtr);

    OpenCVImagePtr := @ConvertedImage;
    cv_releaseImage(OpenCVImagePtr);

  end else
    ShowMessage('Failed to load image: ' + Filename);
end;

end.

However, I keep getting the following compile-time error: Error: opencvdisplaymain.pas:(.text.n_opencvdisplaymain$_$tform1_$__$$_formcreate$tobject+0x7e): undefined reference to \cv_imread'`.

I've already tried asking AI for help, but haven't been able to resolve the issue. Does anyone have experience with this?

『
ls /usr/lib/x86_64-linux-gnu/ | grep libopencv_imgcodecs
libopencv_imgcodecs.a
libopencv_imgcodecs.so
libopencv_imgcodecs.so.4.5.4d
libopencv_imgcodecs.so.4.5d
』

[Gustavo 'Gus' Carreno]

Hey xiyi0616,

Not trying to answer your question, just providing a better display of your code.
It's better on the eyes and will probably capture the attention of more people,

Code: Pascal  [Select][+][-]

1. unit OpenCVDisplayMain;
2.  
3. interface
4.  
5. uses
6.   Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, LCLType,
7.   ctypes, LCLIntf, ExtCtrls;
8.  
9. type
10.  
11.   { TForm1 }
12.  
13.   TForm1 = class(TForm)
14.     Image1: TImage;
15.     procedure FormCreate(Sender: TObject);
16.   private
17.     { private declarations }
18.   public
19.     { public declarations }
20.   end;
21.  
22.   TSize = record
23.     width, height: Integer;
24.   end;
25.   PSize = ^TSize;
26.  
27. var
28.   Form1: TForm1;
29.  
30. implementation
31.  
32. {$R *.lfm}
33.  
34. function cv_imread(filename: PAnsiChar; flags: Integer): Pointer; cdecl; external 'libopencv_imgcodecs.so.4.5.4d';
35. function cv_GetSize(img: Pointer): PSize; cdecl; external 'libopencv_core.so.4.5';
36. procedure cv_releaseImage(img: PPointer); cdecl; external 'libopencv_core.so.4.5'; /
37. function cvCvtColor(src, dst: Pointer; code: Integer): Integer; cdecl; external 'libopencv_imgproc.so.4.5';
38. function cvCreateImage(size: PSize; depth: Integer; channels: Integer): Pointer; cdecl; external 'libopencv_core.so.4.5';
39.  
40.  
41. { TForm1 }
42.  
43. procedure TForm1.FormCreate(Sender: TObject);
44. var
45.   OpenCVImage, ConvertedImage: Pointer;
46.   Size: PSize;
47.   Filename: string;
48.   OpenCVImagePtr: PPointer;
49.   Bitmap: TBitmap;
50. begin
51.   Filename := 'test.jpg';
52.  
53.   OpenCVImage := cv_imread(PAnsiChar(AnsiString(Filename)), 1);
54.  
55.   if OpenCVImage <> nil then
56.   begin
57.     Size := cv_GetSize(OpenCVImage);
58.  
59.     ConvertedImage := cvCreateImage(Size, 8, 3); // 8 bits per channel, 3 channels (BGR)
60.  
61.     cvCvtColor(OpenCVImage, ConvertedImage, 6); // COLOR_BGR2BGR = 6
62.  
63.     Bitmap := TBitmap.Create;
64.     try
65.       Bitmap.PixelFormat := pf24bit;
66.       Bitmap.Width := Size^.width;
67.       Bitmap.Height := Size^.height;
68.  
69.       Move(Pointer(ConvertedImage)^, Bitmap.ScanLine[0]^, Bitmap.Width * Bitmap.Height * 3);
70.  
71.       Image1.Picture.Assign(Bitmap);
72.  
73.     finally
74.       Bitmap.Free;
75.     end;
76.  
77.     OpenCVImagePtr := @OpenCVImage;
78.     cv_releaseImage(OpenCVImagePtr);
79.  
80.     OpenCVImagePtr := @ConvertedImage;
81.     cv_releaseImage(OpenCVImagePtr);
82.  
83.   end else
84.     ShowMessage('Failed to load image: ' + Filename);
85. end;
86.  
87. end.

Cheers,
Gus

[Gustavo 'Gus' Carreno]

Hey xiyi0616,

Now that I had a look at your code, can I suggest that you use:

• libopencv_core.so instead of libopencv_core.so.4.5
• libopencv_imgcodecs.so instead of libopencv_imgcodecs.so.4.5.4d
• libopencv_imgproc.so instead of libopencv_imgproc.so.4.5

Usually the .so is a symlink to the correct versioned file. Please confirm what it points at. It's also future proof that you use the .so, since after future updates of the package, it will point to the correct versioned one.

From the little that I could perceive from the error, it looks like you're linking to the incorrect library and you're trying to use definitions that don't exist in the lib that you're linking to. Maybe using the .so instead of the versioned one might solve the issue.

If not, please confirm that the functions that you need are exported. You can use objdump, readelf or nm to confirm that:

• Example on using objdump, readelf: https://www.baeldung.com/linux/shared-library-exported-functions
• Example on using nm: https://stackoverflow.com/questions/4514745/how-do-i-view-the-list-of-functions-a-linux-shared-library-is-exporting

Give it a try and then report back please.

Cheers,
Gus

[gidesa]

Hello,
you are using the C API of Opencv, it's abandoned and deprecated from Opencv version 2.4, although retained until now. And it expose only a fraction of Opencv functions/classes (it's written in C++).
You can use ocvWrapper46 for Opencv version 4.6, that exposes all C++ classes. For FPC and Delphi, on Windows, Linux, Macos.

https://github.com/gidesa/ocvWrapper46


 

[Gustavo 'Gus' Carreno]

Hey Gidesa,

you are using the C API of Opencv, it's abandoned and deprecated from Opencv version 2.4, although retained until now. And it expose only a fraction of Opencv functions/classes (it's written in C++).
You can use ocvWrapper46 for Opencv version 4.6, that exposes all C++ classes. For FPC and Delphi, on Windows, Linux, Macos.

https://github.com/gidesa/ocvWrapper46

This is valuable information indeed!!!
Thanks for that!!

EDIT
And thanks for the monumental effort in producing the C wrapper and the Object Pascal ones !!!

I'm gonna guess that if he used the tools to search for the functions, they would not return what he expected !!

Cheers,
Gus

[gidesa]

Using ocvWrapper46, the code is as simple as this:
(Note that Opencv 4.6 is required, so first you have to remove Opencv 4.5, and then install Opencv 4.6 and ocvWrapper 46 using the instructions for Linux)

Code: Pascal  [Select][+][-]

1. unit frmtxocvimage;
2.  
3. {$mode Delphi}{$H+}
4. interface
5.  
6. uses
7.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls, ExtCtrls,
8.   unOCVImage;
9.  
10. type
11.  
12.   { TForm1 }
13.  
14.   TForm1 = class(TForm)
15.     btStart: TButton;
16.     Image1: TImage;
17.     procedure btStartClick(Sender: TObject);
18.   private
19.  
20.   public
21.  
22.   end;
23.  
24.  
25. var
26.   Form1: TForm1;
27.  
28. implementation
29.  
30. {$R *.lfm}
31.  
32. procedure testOcvImage();
33. var
34.   ocvimg: TOCVImage;
35.   filename: string;
36. begin
37.   filename:='xxx.jpg';
38.   ocvimg:=TOCVImage.Create(filename);
39.   ocvimg.showInImage(form1.image1);
40.  
41.   ocvimg.Free;
42.  
43. end;
44.  
45.  
46. { TForm1 }
47.  
48. procedure TForm1.btStartClick(Sender: TObject);
49. begin
50.   testOcvImage();
51. end;
52.  
53. end.
54.  

[xiyi0616]

Hey， Gustavo 'Gus' Carreno
First, thank you for your suggestion regarding the code demonstration. It seems you're right, and I'm not very proficient in that area. The reason I need to use OpenCV is that the current version of Lazarus's built-in controls are not good at decoding Tiff Group 4 format. Additionally, I need to analyze lines in images. I'm not very familiar with unOCVImage, and I'm unsure if it can perform these functions, but I will give it a try. Thank you for your advice.

[xiyi0616]

Hello gidesa, thank you for your suggestion,  I will give it a try.

[xiyi0616]

Also, I initially used libopencv_core.so, and then, based on AI's suggestion, I tried libopencv_core.so.4.5.

[Gustavo 'Gus' Carreno]

Hey xiyi0616,

Hey， Gustavo 'Gus' Carreno

Please just call me Gus

First, thank you for your suggestion regarding the code demonstration. It seems you're right, and I'm not very proficient in that area. The reason I need to use OpenCV is that the current version of Lazarus's built-in controls are not good at decoding Tiff Group 4 format. Additionally, I need to analyze lines in images. I'm not very familiar with unOCVImage, and I'm unsure if it can perform these functions, but I will give it a try. Thank you for your advice.

Welp, in the end, it looks like @gidesa is the REAL expert in this, so it's awesome he dropped his pearls of wisdom!!

Cheers,
Gus

[Gustavo 'Gus' Carreno]

Hey xiyi0616,

Also, I initially used libopencv_core.so, and then, based on AI's suggestion, I tried libopencv_core.so.4.5.

Yeah... The bots sometimes have some hallucinations

Like I said: The .so is usually a symlink to the versioned file. So best use that, cuz if and when you upgrade your package from the repo, there could be a new versioned file and then your program won't work.
But now, with @gidesa's wrapper, you don't have to care about any of that, as long as you update the wrapper from @gidesa's repo !!

All the luck in your project!!

Cheers,
Gus

[gidesa]

Hello xiyi0616,
here a code adapted for your task, reading a TIFF image. For display, there is a conversion from BGRA format (4 channels) to the 3 channels format required by TImage.

Code: Pascal  [Select][+][-]

1. unit frmtxocvimage;
2.  
3. {$mode Delphi}{$H+}
4. interface
5.  
6. uses
7.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls, ExtCtrls,
8.   unOCVImage,
9.   OPENCVWrapper;
10.  
11. type
12.  
13.   { TForm1 }
14.  
15.   TForm1 = class(TForm)
16.     btStart: TButton;
17.     Image1: TImage;
18.     procedure btStartClick(Sender: TObject);
19.   private
20.  
21.   public
22.  
23.   end;
24.  
25.  
26. var
27.   Form1: TForm1;
28.  
29. implementation
30.  
31. {$R *.lfm}
32.  
33.  
34. procedure testOcvImage();
35. var
36.   ocvimg: TOCVImage;
37.   ocvimg2: TOCVImage;
38.   filename: string;
39. begin
40.   filename:='..\..\Sample-Tiff-File.tif';
41.   ocvimg:=TOCVImage.Create(filename);
42.   if ocvimg.nchannels>3 then
43.   begin
44.        ocvimg2:=TOCVImage.Create(ocvimg.width, ocvimg.height, 3);
45.        pCvcvtColor(ocvimg.PCvMatPtr, ocvimg2.PCvMatPtr, ord(COLOR_BGRA2BGR));
46.   end else
47.       ocvimg2:= ocvimg.clone();
48.   ocvimg2.showInImage(form1.image1);
49.  
50.   ocvimg2.Free;
51.   ocvimg.Free;
52. end;
53.  
54.  
55. { TForm1 }
56.  
57. procedure TForm1.btStartClick(Sender: TObject);
58. begin
59.   testOcvImage();
60. end;
61.  
62. end.
63.  

[xiyi0616]

Okay, Gus.

With Lazarus's version upgrades, it feels better and better to use. I'm happy to see this trend.

Cheers,
xiyi0616

[xiyi0616]

Hello gidesa

Thank you for your time.

I believe unOCVImage is not included in the standard Lazarus installation. I will need to research, install, and familiarize myself with it. In the meantime, I'm temporarily using libtiff for reading images., which seems to be working.

Code: Pascal  [Select][+][-]

1.        LibHandle := LoadLibrary('libtiff.so');
2.        if LibHandle = NilHandle then
3.           raise Exception.Create('Failed to load libtiff');
4.  
5.        Pointer(TIFFOpen) := GetProcAddress(LibHandle, 'TIFFOpen');
6.        Pointer(TIFFClose) := GetProcAddress(LibHandle, 'TIFFClose');
7.        Pointer(TIFFGetField) := GetProcAddress(LibHandle, 'TIFFGetField');
8.  

Cheers,
xiyi0616

[Gustavo 'Gus' Carreno]

Hey Y'All,

Ermmm, isn't TIFF one of the image formats supported natively by Lazarus?!

I was under the impression it was, but again, most of the times my assumptions end with me inserting foot in mouth... So... dunno...

Cheers,
Gus