旋转cv :: Mat使用cv :: warpAffine偏移目标图像 [英] Rotate cv::Mat using cv::warpAffine offsets destination image

问题描述

我想使用OpenCV的 C ++ API 旋转 1296x968 图片， 90度我遇到了一些问题。

I'm trying to rotate a 1296x968 image by 90 degrees using the C++ API of OpenCV and I'm facing a few problems.

输入：

旋转：

如您所见，旋转后的图片有几个问题。首先，它具有与原始大小相同的大小，即使我专门创建了目标 Mat 与原始的倒置大小。因此，目标图像被裁剪。

As you can see, the rotated image has a few problems. First, it has the same size of the original, even though I specifically create the destination Mat with the inverted size of the original. As a result, the destination image gets cropped.

我怀疑这是因为我调用 warpAffine（），并传递原始的大小 Mat 而不是目标的大小 Mat 。但我这样做是因为我遵循此答案 ，但现在我怀疑答案可能是错误的。所以这是我的第一个疑问/问题。

I suspect this is happening because I'm calling warpAffine() and passing the size of the original Mat instead of the size of destination Mat. But I'm doing this because I followed this answer, but now I suspect that the answer may be wrong. So this is my first doubt/problem.

第二个是 warpAffine（）到某个偏移的目的地（可能要将旋转的数据复制到图像的中间），此操作会在图像周围留下一个可怕的和大的黑色边框。

The second, is that warpAffine() is writing to the destination at a certain offset (probably to copy the rotated data to the middle of the image) and this operation leaves a horrible and large black border around the image.

如何解决这些问题？

代码如下：

#include <cv.h>
#include <highgui.h>
#include <iostream>

using namespace cv;
using namespace std;

void rotate(Mat& image, double angle)
{
    Point2f src_center(image.cols/2.0F, image.rows/2.0F);

    Mat rot_matrix = getRotationMatrix2D(src_center, angle, 1.0);

    Mat rotated_img(Size(image.size().height, image.size().width), image.type());

    warpAffine(image, rotated_img, rot_matrix, image.size());
    imwrite("rotated.jpg", rotated_img);
}

int main(int argc, char* argv[])
{
    Mat orig_image = imread(argv[1], 1);
    if (orig_image.empty())
    {
        cout << "!!! Couldn't load " << argv[1] << endl;
        return -1;
    }

    rotate(orig_image, 90);

    return 0;
}

推荐答案

找到了解决方案，但不涉及 warpAffine（） 。

I've found a solution that doesn't involve warpAffine().

但在此之前，我需要说明（以后参考）我的怀疑是正确的，你需要通过调用 warpAffine（）时目标的大小：

But before that, I need to state (for future references) that my suspicion was right, you needed to pass the size of the destination when calling warpAffine():

warpAffine(image, rotated_img, rot_matrix, rotated_img.size());

据我所知，黑色边框功能似乎是它的标准行为。我注意到这与C接口，并与在Mac和Linux上运行的OpenCV的C + +接口，使用版本2.3.1a和2.3.0。

As far as I can tell, the black border (caused by writing at an offset) drawed by this function seems to be it's standard behavior. I've noticed this with the C interface and also with the C++ interface of OpenCV running on Mac and Linux, using the versions 2.3.1a and 2.3.0.

解决方案我最终使用比所有这些 warp事情更简单。您可以使用 cv :: transpose（） 和 cv :: flip（） 将图像旋转90度。这里是：

The solution I ended up using is much simpler than all this warp thing. You can use cv::transpose() and cv::flip() to rotate an image by 90 degrees. Here it is:

Mat src = imread(argv[1], 1);

cv::Mat dst;
cv::transpose(src, dst);
cv::flip(dst, dst, 1);

imwrite("rotated90.jpg", dst);

---- I>

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