如何在 MATLAB 中实现鱼眼镜头效果(桶形变换)? [英] How can I implement a fisheye lens effect (barrel transformation) in MATLAB?

问题描述

如何实现该图像中所示的鱼眼镜头效果:

可以尝试使用 Google 的徽标:

顺便说一句，它的术语是什么?

解决方案

我相信这通常被称为鱼眼镜头"效果或桶形变换".以下是我找到的两个演示链接:

• 您可以通过更改options 数组中的第三个值来调整失真程度，该值是用于图像点径向变形的指数幂.

  How can one implement the fisheye lens effect illustrated in that image:

  One can use Google's logo for a try:

  BTW, what's the term for it?

  解决方案

  I believe this is typically referred to as either a "fisheye lens" effect or a "barrel transformation". Here are two links to demos that I found:

  • Sample code for how you can apply fisheye distortions to images using the 'custom' option for the function maketform from the Image Processing Toolbox.

  • An image processing demo which performs a barrel transformation using the function tformarray.

  Example

  In this example, I started with the function radial.m from the first link above and modified the way it relates points between the input and output spaces to create a nice circular image. The new function fisheye_inverse is given below, and it should be placed in a folder on your MATLAB path so you can use it later in this example:

  function U = fisheye_inverse(X, T)
  
    imageSize = T.tdata(1:2);
    exponent = T.tdata(3);
    origin = (imageSize+1)./2;
    scale = imageSize./2;
  
    x = (X(:, 1)-origin(1))/scale(1);
    y = (X(:, 2)-origin(2))/scale(2);
    R = sqrt(x.^2+y.^2);
    theta = atan2(y, x);
  
    cornerScale = min(abs(1./sin(theta)), abs(1./cos(theta)));
    cornerScale(R < 1) = 1;
    R = cornerScale.*R.^exponent;
  
    x = scale(1).*R.*cos(theta)+origin(1);
    y = scale(2).*R.*sin(theta)+origin(2);
    U = [x y];
  
  end
  

  The fisheye distortion looks best when applied to square images, so you will want to make your images square by either cropping them or padding them with some color. Since the transformation of the image will not look right for indexed images, you will also want to convert any indexed images to RGB images using ind2rgb. Grayscale or binary images will also work fine. Here's how to do this for your sample Google logo:

  [X, map] = imread('logo1w.png');  % Read the indexed image
  rgbImage = ind2rgb(X, map);       % Convert to an RGB image
  [r, c, d] = size(rgbImage);       % Get the image dimensions
  nPad = (c-r)/2;                   % The number of padding rows
  rgbImage = cat(1, ones(nPad, c, 3), rgbImage, ones(nPad, c, 3));  % Pad with white
  

  Now we can create the transform with maketform and apply it with imtransform (or imwarp as recommended in newer versions):

  options = [c c 3];  % An array containing the columns, rows, and exponent
  tf = maketform('custom', 2, 2, [], ...  % Make the transformation structure
                 @fisheye_inverse, options);
  newImage = imtransform(rgbImage, tf);   % Transform the image
  imshow(newImage);                       % Display the image
  

  And here's the image you should see:

  You can adjust the degree of distortion by changing the third value in the options array, which is the exponential power used in the radial deformation of the image points.

  这篇关于如何在 MATLAB 中实现鱼眼镜头效果(桶形变换)?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！