C++ 使用 OpenCV 将图像旋转 90 度的最简单方法？
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Easiest way to rotate by 90 degrees an image using OpenCV?
提问by Ben H
What is the best way (in c/c++) to rotate an IplImage/cv::Mat by 90 degrees? I would assume that there must be something better than transforming it using a matrix, but I can't seem to find anything other than that in the API and online.
将 IplImage/cv::Mat 旋转 90 度的最佳方法是什么（在 c/c++ 中）？我认为一定有比使用矩阵转换它更好的东西，但我似乎无法在 API 和在线中找到除此之外的任何东西。
回答by sastanin
Rotation is a composition of a transpose and a flip.
旋转是转置和翻转的组合。
Which in OpenCV can be written like this (Python example below):
在 OpenCV 中可以这样写（下面的 Python 示例）：
img = cv.LoadImage("path_to_image.jpg")
timg = cv.CreateImage((img.height,img.width), img.depth, img.channels) # transposed image
# rotate counter-clockwise
cv.Transpose(img,timg)
cv.Flip(timg,timg,flipMode=0)
cv.SaveImage("rotated_counter_clockwise.jpg", timg)
# rotate clockwise
cv.Transpose(img,timg)
cv.Flip(timg,timg,flipMode=1)
cv.SaveImage("rotated_clockwise.jpg", timg)
回答by Morris Franken
As of OpenCV3.2, life just got a bit easier, you can now rotate an image in a single line of code:
从 OpenCV3.2 开始，生活变得更轻松了，您现在可以在一行代码中旋转图像：
cv::rotate(image, image, cv::ROTATE_90_CLOCKWISE);
For the direction you can choose any of the following:
对于方向，您可以选择以下任何一项：
ROTATE_90_CLOCKWISE
ROTATE_180
ROTATE_90_COUNTERCLOCKWISE
回答by Jacob
Update for transposition:
换位更新：
You should use cvTranspose()or cv::transpose()because (as you rightly pointed out) it's more efficient. Again, I recommend upgrading to OpenCV2.0 since most of the cvXXXfunctions just convert IplImage*structures to Matobjects (no deep copies). If you stored the image in a Matobject, Mat.t()would return the transpose.
您应该使用cvTranspose()orcv::transpose()因为（正如您正确指出的那样）它更有效。同样，我建议升级到 OpenCV2.0，因为大多数cvXXX函数只是将IplImage*结构转换为Mat对象（没有深拷贝）。如果您将图像存储在Mat对象中，Mat.t()将返回转置。
Any rotation:
任意旋转：
You should use cvWarpAffine by defining the rotation matrix in the general framework of the transformation matrix. I would highly recommend upgrading to OpenCV2.0which has several features as well as a Matclass which encapsulates matrices and images. With 2.0 you can use warpAffineto the above.
您应该通过在转换矩阵的一般框架中定义旋转矩阵来使用 cvWarpAffine。我强烈建议升级到OpenCV2.0，它有几个特性以及一个Mat封装矩阵和图像的类。使用 2.0 你可以使用warpAffine到上面。
回答by Eran W
Here is my python cv2implementation:
这是我的pythoncv2实现：
import cv2
img=cv2.imread("path_to_image.jpg")
# rotate ccw
out=cv2.transpose(img)
out=cv2.flip(out,flipCode=0)
# rotate cw
out=cv2.transpose(img)
out=cv2.flip(out,flipCode=1)
cv2.imwrite("rotated.jpg", out)
回答by Andres Hurtis
This is an example without the new C++ interface (works for 90, 180 and 270 degrees, using param = 1, 2 and 3). Remember to call cvReleaseImageon the returned image after using it.
这是一个没有新 C++ 接口的示例（适用于 90、180 和 270 度，使用 param = 1、2 和 3）。使用后记得调用cvReleaseImage返回的图像。
IplImage *rotate_image(IplImage *image, int _90_degrees_steps_anti_clockwise)
{
IplImage *rotated;
if(_90_degrees_steps_anti_clockwise != 2)
rotated = cvCreateImage(cvSize(image->height, image->width), image->depth, image->nChannels);
else
rotated = cvCloneImage(image);
if(_90_degrees_steps_anti_clockwise != 2)
cvTranspose(image, rotated);
if(_90_degrees_steps_anti_clockwise == 3)
cvFlip(rotated, NULL, 1);
else if(_90_degrees_steps_anti_clockwise == 1)
cvFlip(rotated, NULL, 0);
else if(_90_degrees_steps_anti_clockwise == 2)
cvFlip(rotated, NULL, -1);
return rotated;
}
回答by mpen
Here's my EmguCV (a C# port of OpenCV) solution:
这是我的 EmguCV（OpenCV 的 C# 端口）解决方案：
public static Image<TColor, TDepth> Rotate90<TColor, TDepth>(this Image<TColor, TDepth> img)
where TColor : struct, IColor
where TDepth : new()
{
var rot = new Image<TColor, TDepth>(img.Height, img.Width);
CvInvoke.cvTranspose(img.Ptr, rot.Ptr);
rot._Flip(FLIP.HORIZONTAL);
return rot;
}
public static Image<TColor, TDepth> Rotate180<TColor, TDepth>(this Image<TColor, TDepth> img)
where TColor : struct, IColor
where TDepth : new()
{
var rot = img.CopyBlank();
rot = img.Flip(FLIP.VERTICAL);
rot._Flip(FLIP.HORIZONTAL);
return rot;
}
public static void _Rotate180<TColor, TDepth>(this Image<TColor, TDepth> img)
where TColor : struct, IColor
where TDepth : new()
{
img._Flip(FLIP.VERTICAL);
img._Flip(FLIP.HORIZONTAL);
}
public static Image<TColor, TDepth> Rotate270<TColor, TDepth>(this Image<TColor, TDepth> img)
where TColor : struct, IColor
where TDepth : new()
{
var rot = new Image<TColor, TDepth>(img.Height, img.Width);
CvInvoke.cvTranspose(img.Ptr, rot.Ptr);
rot._Flip(FLIP.VERTICAL);
return rot;
}
Shouldn't be too hard to translate it back into C++.
将它翻译回 C++ 应该不会太难。
回答by Artem
Well I was looking for some details and didn't find any example. So I am posting a transposeImagefunction which, I hope, will help others who are looking for a direct way to rotate 90° without losing data:
好吧，我正在寻找一些细节，但没有找到任何示例。所以我发布了一个transposeImage函数，我希望它能帮助那些正在寻找一种直接旋转 90° 而不丢失数据的方法的人：
IplImage* transposeImage(IplImage* image) {
IplImage *rotated = cvCreateImage(cvSize(image->height,image->width),
IPL_DEPTH_8U,image->nChannels);
CvPoint2D32f center;
float center_val = (float)((image->width)-1) / 2;
center.x = center_val;
center.y = center_val;
CvMat *mapMatrix = cvCreateMat( 2, 3, CV_32FC1 );
cv2DRotationMatrix(center, 90, 1.0, mapMatrix);
cvWarpAffine(image, rotated, mapMatrix,
CV_INTER_LINEAR + CV_WARP_FILL_OUTLIERS,
cvScalarAll(0));
cvReleaseMat(&mapMatrix);
return rotated;
}
Question : Why this?
问题：为什么会这样？
float center_val = (float)((image->width)-1) / 2;
Answer : Because it works :) The only center I found that doesn't translate image. Though if somebody has an explanation I would be interested.
答：因为它有效:) 我发现的唯一一个不翻译图像的中心。虽然如果有人有解释，我会感兴趣。
