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Quick search for a small image in a larger image

I need to get the coordinates of a small place of an image located on a large image (say, I need to find a specific tree inside a forest photo. If a sub-image is found, the result will be something like this: x=120 y=354for example).

Is there a quick algorithm I could use?

I use Delphi (can also use Java if necessary)

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6 answers

Edit: A few things about theory:

"" : . (freq , : (). , , " ". , , . , . . ( , - .) - ( formular :() "" " " ( , img.), matlab, . , , : FT ([f ° g] (m, n)) = F (u, v) * G ° (u, v). F - fft, G ° - G (G - fft )

, .:) , , fft, , , , , . "I_ausschnitt" "".

Matlab . , .:)

I = im2double(imread('Textiltextur.tif')); // This is our reference image
I_model = imcrop( I, [49 36 42 28] ); // Our model - what we want so search in I

[X Y] = size( I ); // Get the size of the reference image. 
f = fft2(I); // Perform the fast fourier transform->put the image into frequency space. 
f_model = fft2(I_model ,X,Y); // Perform the fft of the model but do this in the size of the original image. matlab will center I_model and set other pixel to zero
w = conj(model ); // Complex conjugated
g = real( ifft2(w.*f)); // .* will perform a komponent wise multiplicaion e.g. [0][0]*[0][0], [0][1]*[0][1] and not a matrix mul. 
gs =im2uint8(mat2gray(g)); // Convert the resulting correlation into an grayscale image with larger values->higher correlation

// Rest of the code is for displaying only
figure(1);
imshow(gs);
colormap hsv

figure;
[ XX YY] = meshgrid(1:Y,1:X );
colormap hsv 
surfc(XX,YY,double(gs)), title('3D Korrelation') 
min_corr = min(min(gs))
max_corr = max(max(gs))
%axis([1 X 1 Y min_corr max_corr])
colorbar

: .

+4

.

. , . , ( ) .

( / ), - . , SIFT SURF.

, : , 1D (Boyer-Moore) , . , , , , , , .

+1

( 160 , 90 1600x900) , . . 24- Win7/Win10 x64, XE2, XE5.

uses
  System.Generics.Collections;

type
  TSubImageInfo = record
    X: integer;
    Y: integer;
    Color: integer;
  end;

function ImageSearch(const ASubimageFile: string): TRect;
var
  X, Y, K, _Color: integer;
  _SubImageInfo: TSubImageInfo;
  _SubImageInfoList: TList<TSubImageInfo>;
  _SmallWidth, _SmallHeight, _BigWidth, _BigHeight: integer;
  _MatchingPixels: integer;
  _LTColor, _RTColor, _LBColor, _RBColor: integer;
  _FirstPixels: TList<TSubImageInfo>;
  _Offset: TPoint;
  _Desktop: HDC;
  _ScreenBitmap: TBitmap;
  _SubimageBitmap: TPNGImage;
  _Pos: TPoint;
begin
  Result.Left := -1;
  Result.Top := Result.Left;
  Result.Height := Result.Left;
  Result.Width := Result.Left;

  if not FileExists(ASubimageFile) then
    Exit;

  _SubImageInfoList := TList<TSubImageInfo>.Create;
  _ScreenBitmap := TBitmap.Create;
  _SubimageBitmap := TPNGImage.Create;
  _FirstPixels := TList<TSubImageInfo>.Create;
  try
    _SubimageBitmap.LoadFromFile(ASubimageFile);

    if (_SubimageBitmap.Height < 3) or (_SubimageBitmap.Width < 3) then
      Exit; // Image is too small

    X := 0;
    Y := _SubimageBitmap.Height div 2;
    while X < _SubimageBitmap.Width - 1 do
    begin
      _SubImageInfo.X := X;
      _SubImageInfo.Y := Y;
      _Color := _SubimageBitmap.Canvas.Pixels[X, Y];
      _SubImageInfo.Color := _Color;
      _SubImageInfoList.Add(_SubImageInfo);
      X := X + 3;
    end;

    Y := 0;
    X := _SubimageBitmap.Width div 2;
    while Y < _SubimageBitmap.Height - 1 do
    begin
      _SubImageInfo.X := X;
      _SubImageInfo.Y := Y;
      _Color := _SubimageBitmap.Canvas.Pixels[X, Y];
      _SubImageInfo.Color := _Color;
      _SubImageInfoList.Add(_SubImageInfo);
      Y := Y + 3;
    end;

    X := 0;
    Y := _SubimageBitmap.Height div 4;
    while X < _SubimageBitmap.Width - 1 do
    begin
      _SubImageInfo.X := X;
      _SubImageInfo.Y := Y;
      _Color := _SubimageBitmap.Canvas.Pixels[X, Y];
      _SubImageInfo.Color := _Color;
      _SubImageInfoList.Add(_SubImageInfo);
      X := X + 3;
    end;

    Y := 0;
    X := _SubimageBitmap.Width div 4;
    while Y < _SubimageBitmap.Height - 1 do
    begin
      _SubImageInfo.X := X;
      _SubImageInfo.Y := Y;
      _Color := _SubimageBitmap.Canvas.Pixels[X, Y];
      _SubImageInfo.Color := _Color;
      _SubImageInfoList.Add(_SubImageInfo);
      Y := Y + 3;
    end;

    X := 0;
    Y := (_SubimageBitmap.Height div 4) + (_SubimageBitmap.Height div 2);
    while X < _SubimageBitmap.Width - 1 do
    begin
      _SubImageInfo.X := X;
      _SubImageInfo.Y := Y;
      _Color := _SubimageBitmap.Canvas.Pixels[X, Y];
      _SubImageInfo.Color := _Color;
      _SubImageInfoList.Add(_SubImageInfo);
      X := X + 3;
    end;

    Y := 0;
    X := (_SubimageBitmap.Width div 4) + (_SubimageBitmap.Width div 2);
    while Y < _SubimageBitmap.Height - 1 do
    begin
      _SubImageInfo.X := X;
      _SubImageInfo.Y := Y;
      _Color := _SubimageBitmap.Canvas.Pixels[X, Y];
      _SubImageInfo.Color := _Color;
      _SubImageInfoList.Add(_SubImageInfo);
      Y := Y + 3;
    end;

    _Desktop := GetDC(0);
    _ScreenBitmap.PixelFormat := pf32bit;
    _ScreenBitmap.Width := Screen.Width;
    _ScreenBitmap.Height := Screen.Height;
    BitBlt(_ScreenBitmap.Canvas.Handle, 0, 0, _ScreenBitmap.Width,
      _ScreenBitmap.Height, _Desktop, 0, 0, SRCCOPY);
    _MatchingPixels := 0;
    _SmallWidth := _SubimageBitmap.Width - 1;
    _SmallHeight := _SubimageBitmap.Height - 1;
    _BigWidth := _ScreenBitmap.Width;
    _BigHeight := _ScreenBitmap.Height;

    _LTColor := _SubimageBitmap.Canvas.Pixels[0, 0];
    _RTColor := _SubimageBitmap.Canvas.Pixels[_SmallWidth, 0];
    _LBColor := _SubimageBitmap.Canvas.Pixels[0, _SmallHeight];
    _RBColor := _SubimageBitmap.Canvas.Pixels[_SmallWidth, _SmallHeight];

    for X := 1 to 3 do
    begin
      for Y := 1 to 3 do
      begin
        _SubImageInfo.X := X;
        _SubImageInfo.Y := Y;
        _SubImageInfo.Color := _SubimageBitmap.Canvas.Pixels[X, Y];
        _FirstPixels.Add(_SubImageInfo);
      end;
    end;

    X := 0;
    while X < _BigWidth - _SmallWidth do
    begin
      Y := 0;
      while Y < _BigHeight - _SmallHeight do
      begin
        _Color := _ScreenBitmap.Canvas.Pixels[X, Y];
        _Offset.X := 0;
        _Offset.Y := 0;
        for K := 0 to _FirstPixels.Count - 1 do
        begin
          if (_Color = _FirstPixels[K].Color) then
          begin
            _Offset.X := _FirstPixels[K].X;
            _Offset.Y := _FirstPixels[K].Y;
            Break;
          end;
        end;

        // Check if all corners matches of smaller image
        if ((_Offset.X <> 0) or (_Color = _LTColor)) and
          (_ScreenBitmap.Canvas.Pixels[X + _SmallWidth, Y] = _RTColor) and
          (_ScreenBitmap.Canvas.Pixels[X, Y + _SmallHeight] = _LBColor) and
          (_ScreenBitmap.Canvas.Pixels[X + _SmallWidth, Y + _SmallHeight]
          = _RBColor) then
        begin
          // Checking if content matches
          for K := 0 to _SubImageInfoList.Count - 1 do
          begin
            _Pos.X := X - _Offset.X + _SubImageInfoList[K].X;
            _Pos.Y := Y - _Offset.Y + _SubImageInfoList[K].Y;
            if (_ScreenBitmap.Canvas.Pixels[_Pos.X, _Pos.Y] = _SubImageInfoList
              [K].Color) then
              _MatchingPixels := _MatchingPixels + 1
            else
            begin
              _Pos.X := X - _Offset.X - 1 + _SubImageInfoList[K].X;
              _Pos.Y := Y - _Offset.Y + 1 + _SubImageInfoList[K].Y;
              if (_ScreenBitmap.Canvas.Pixels[_Pos.X, _Pos.Y]
                = _SubImageInfoList[K].Color) then
                _MatchingPixels := _MatchingPixels + 1
              else
              begin
                _MatchingPixels := 0;
                Break;
              end;
            end;
          end;
          if (_MatchingPixels - 1 = _SubImageInfoList.Count - 1) then
          begin
            Result.Left := X - _Offset.X;
            Result.Top := Y - _Offset.Y;

            Result.Width := _SubimageBitmap.Width;
            Result.Height := _SubimageBitmap.Height;
            Exit;
          end;
        end;
        Y := Y + 3;
      end;
      X := X + 3;
    end;

  finally
    FreeAndNil(_FirstPixels);
    FreeAndNil(_ScreenBitmap);
    FreeAndNil(_SubimageBitmap);
    FreeAndNil(_SubImageInfoList);
  end;
end;

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enter image description here

E PDF.

+1

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-1

Source: https://habr.com/ru/post/1750788/

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