如何使用OpenGL模拟OpenCV的warpPerspective功能(透视变换) [英] How to use OpenGL to emulate OpenCV's warpPerspective functionality (perspective transform)

问题描述

我已经在Python和C ++中使用OpenCV进行了图像变形，看到可口可乐徽标在我选择的角落变形了:

I've done image warping using OpenCV in Python and C++, see the Coca Cola logo warped in place in the corners I had selected:

使用以下图像:

和这个:

完整的专辑，上面有过渡图片和说明

我需要精确地做到这一点，但是在OpenGL中.我将拥有:

I need to do exactly this, but in OpenGL. I'll have:

• 必须在其中映射变形图像的角落

• Corners inside which I've to map the warped image

一个单应矩阵，用于映射徽标图像的变换 进入您在最终图像中看到的徽标图像(使用OpenCV的 warpPerspective)，如下所示:

A homography matrix that maps the transformation of the logo image into the logo image you see inside the final image (using OpenCV's warpPerspective), something like this:

[[  2.59952324e+00,   3.33170976e-01,  -2.17014066e+02],
[  8.64133587e-01,   1.82580111e+00,  -3.20053715e+02],
[  2.78910149e-03,   4.47911310e-05,   1.00000000e+00]]

主图像(此处为跑道图像)

Main image (the running track image here)

重叠图像(此处为可口可乐图像)

Overlay image (the Coca Cola image here)

有可能吗?我已经阅读了很多书，并开始了OpenGL基础教程，但是仅凭我的能力就能做到吗? OpenGL实现会更快吗，比如大约10ms?

Is it possible ? I've read a lot and started OpenGL basics tutorials, but can it be done from just what I have? Would the OpenGL implementation be faster, say, around ~10ms?

我目前正在这里学习本教程: http://ogldev.atspace.co.uk/www/tutorial12/tutorial12. html 我朝着正确的方向前进吗?这里共有OpenGL新手，请耐心等待.谢谢.

I'm currently playing with this tutorial here: http://ogldev.atspace.co.uk/www/tutorial12/tutorial12.html Am I going in the right direction? Total OpenGL newbie here, please bear. Thanks.

推荐答案

在尝试了此处和其他地方提出的许多解决方案后，我通过编写片段着色器来复制此问题，该片段着色器复制了"warpPerspective"的功能.

After trying a number of solutions proposed here and elsewhere, I ended solving this by writing a fragment shader that replicates what 'warpPerspective' does.

片段着色器代码类似于:

The fragment shader code looks something like:

varying highp vec2 textureCoordinate;

uniform sampler2D inputImageTexture;

// NOTE: you will need to pass the INVERSE of the homography matrix, as well as 
// the width and height of your image as uniforms!
uniform highp mat3 inverseHomographyMatrix;
uniform highp float width;
uniform highp float height;

void main()
{
   // Texture coordinates will run [0,1],[0,1];
   // Convert to "real world" coordinates
   highp vec3 frameCoordinate = vec3(textureCoordinate.x * width, textureCoordinate.y * height, 1.0);

   // Determine what 'z' is
   highp vec3 m = inverseHomographyMatrix[2] * frameCoordinate;
   highp float zed = 1.0 / (m.x + m.y + m.z);
   frameCoordinate = frameCoordinate * zed;

   // Determine translated x and y coordinates
   highp float xTrans = inverseHomographyMatrix[0][0] * frameCoordinate.x + inverseHomographyMatrix[0][1] * frameCoordinate.y + inverseHomographyMatrix[0][2] * frameCoordinate.z;
   highp float yTrans = inverseHomographyMatrix[1][0] * frameCoordinate.x + inverseHomographyMatrix[1][1] * frameCoordinate.y + inverseHomographyMatrix[1][2] * frameCoordinate.z;

   // Normalize back to [0,1],[0,1] space
   highp vec2 coords = vec2(xTrans / width, yTrans / height);

   // Sample the texture if we're mapping within the image, otherwise set color to black
   if (coords.x >= 0.0 && coords.x <= 1.0 && coords.y >= 0.0 && coords.y <= 1.0) {
       gl_FragColor = texture2D(inputImageTexture, coords);
   } else {
       gl_FragColor = vec4(0.0,0.0,0.0,0.0);
   }
}

请注意，我们在此处传递的单应性矩阵是反同构矩阵！！您必须将要传递给"warpPerspective"的单应性矩阵求反，否则此代码将无法工作.

Note that the homography matrix we are passing in here is the INVERSE HOMOGRAPHY MATRIX! You have to invert the homography matrix that you would pass into 'warpPerspective'- otherwise this code will not work.

顶点着色器除了通过坐标外什么也不做:

The vertex shader does nothing but pass through the coordinates:

// Vertex shader
attribute vec4 position;
attribute vec4 inputTextureCoordinate;

varying vec2 textureCoordinate;

void main() {
   // Nothing happens in the vertex shader
   textureCoordinate = inputTextureCoordinate.xy;
   gl_Position = position;
}

传入未更改的纹理坐标和位置坐标(即textureCoordinates = [(0,0)，(0,1)，(1,0)，(1,1)]和positionCoordinates = [(-1，-1 )，(-1,1)，(1，-1)，(1,1)]，用于三角形条)，这应该可以工作！

Pass in unaltered texture coordinates and position coordinates (i.e. textureCoordinates = [(0,0),(0,1),(1,0),(1,1)] and positionCoordinates = [(-1,-1),(-1,1),(1,-1),(1,1)], for a triangle strip), and this should work!

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