一、简介
1 概念
在图像处理中的空间变换(spatial transformation)分成两种情况,有仿射变换(Affine Transformation)及投影变换(Perspective Transformation)。
仿射变换是从一个二维坐标变换到另一个二维坐标,它是一种线性变换,保持了图像的平行性和平直性,即在变换之后,原先图像中的直线与平行线还是保持一致。只是位置存在变化。仿射变换包括平移(Translation)、缩放(Scale)、翻转(Flip)、旋转(Rotation)和剪切(Shear)。
而投影变换则是指利用投影光束映射图像到投影面上,原始图像与变换后的图像存在着投影变换的关系。
对于数学上的表示而言,这两者都是一样的,始终存在着一个变换矩阵使得原图像与变换后的图像能够互相转换。
2 举个例子
如上图所示,假设f为原图像,g为变换后图像。
通过一定的变换关系,使得f变换到g。如果我们知道对应角点的坐标,则可以通过以下的式子进行推算。
二、源代码
function varargout = affine_trans(varargin)
% AFFINE_TRANS M-file for affine_trans.fig
% AFFINE_TRANS, by itself, creates a new AFFINE_TRANS or raises the existing
% singleton*.
%
% H = AFFINE_TRANS returns the handle to a new AFFINE_TRANS or the handle to
% the existing singleton*.
%
% AFFINE_TRANS('CALLBACK',hObject,eventData,handles,...) calls the local
% function named CALLBACK in AFFINE_TRANS.M with the given input arguments.
%
% AFFINE_TRANS('Property','Value',...) creates a new AFFINE_TRANS or raises the
% existing singleton*. Starting from the left, property value pairs are
% applied to the GUI before affine_trans_OpeningFunction gets called. An
% unrecognized property name or invalid value makes property application
% stop. All inputs are passed to affine_trans_OpeningFcn via varargin.
%
% *See GUI Options on GUIDE's Tools menu. Choose "GUI allows only one
% instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES
% Edit the above text to modify the response to help affine_trans
% Last Modified by GUIDE v2.5 21-May-2009 16:53:05
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name', mfilename, ...
'gui_Singleton', gui_Singleton, ...
'gui_OpeningFcn', @affine_trans_OpeningFcn, ...
'gui_OutputFcn', @affine_trans_OutputFcn, ...
'gui_LayoutFcn', [] , ...
'gui_Callback', []);
if nargin & isstr(varargin{1})
gui_State.gui_Callback = str2func(varargin{1});
end
if nargout
[varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT
% --- Executes just before affine_trans is made visible.
function affine_trans_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject handle to figure
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% varargin command line arguments to affine_trans (see VARARGIN)
f = checkerboard(50);
axes(handles.axes1);
imshow(f);
s = 0.8;
theta = pi/6;
T = [s*cos(theta) s*sin(theta) 0
-s*sin(theta) s*cos(theta) 0
0 0 1];
tform = maketform('affine',T);
g = imtransform(f,tform,'nearest');
axes(handles.axes2);
imshow(g);
set(handles.theta_edit,'string',30);
% Choose default command line output for affine_trans
handles.output = hObject;
% Update handles structure
guidata(hObject, handles);
% UIWAIT makes affine_trans wait for user response (see UIRESUME)
% uiwait(handles.figure1);
% --- Outputs from this function are returned to the command line.
function varargout = affine_trans_OutputFcn(hObject, eventdata, handles)
% varargout cell array for returning output args (see VARARGOUT);
% hObject handle to figure
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Get default command line output from handles structure
varargout{1} = handles.output;
% --- Executes during object creation, after setting all properties.
function theta_edit_CreateFcn(hObject, eventdata, handles)
% hObject handle to θ_edit (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles empty - handles not created until after all CreateFcns called
% Hint: edit controls usually have a white background on Windows.
% See ISPC and COMPUTER.
if ispc
set(hObject,'BackgroundColor','white');
else
set(hObject,'BackgroundColor',get(0,'defaultUicontrolBackgroundColor'));
end
function theta_edit_Callback(hObject, eventdata, handles)
% hObject handle to θ_edit (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Hints: get(hObject,'String') returns contents of θ_edit as text
% str2double(get(hObject,'String')) returns contents of θ_edit as a double
% --- Executes during object creation, after setting all properties.
function interpolate_pop_menu_CreateFcn(hObject, eventdata, handles)
% hObject handle to interpolate_pop_menu (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles empty - handles not created until after all CreateFcns called
% Hint: popupmenu controls usually have a white background on Windows.
% See ISPC and COMPUTER.
if ispc
set(hObject,'BackgroundColor','white');
else
set(hObject,'BackgroundColor',get(0,'defaultUicontrolBackgroundColor'));
end
% --- Executes on selection change in interpolate_pop_menu.
function interpolate_pop_menu_Callback(hObject, eventdata, handles)
% hObject handle to interpolate_pop_menu (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Hints: contents = get(hObject,'String') returns interpolate_pop_menu contents as cell array
% contents{get(hObject,'Value')} returns selected item from interpolate_pop_menu- 1.
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三、运行结果

四、备注
版本:2014a
1137

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