将图像旋转90度的算法？ （无额外记忆） [英] Algorithm to rotate an image 90 degrees in place? (No extra memory)

问题描述

在嵌入式C应用程序中，我想要旋转90度的大图像。目前，我使用着名的简单算法来做到这一点。但是，该算法需要我制作图像的另一个副本。我想避免为副本分配内存，我宁愿在原位旋转它。由于图像不是方形，这是棘手的。有没有人知道一个合适的算法？

In an embedded C app, I have a large image that I'd like to rotate by 90 degrees. Currently I use the well-known simple algorithm to do this. However, this algorithm requires me to make another copy of the image. I'd like to avoid allocating memory for a copy, I'd rather rotate it in-place. Since the image isn't square, this is tricky. Does anyone know of a suitable algorithm?

编辑添加澄清，因为人们问：

Edited to add clarification, because people are asking:

我存储通常格式的图像：

I store an image in the usual format:

// Images are 16 bpp
struct Image {
    int width;
    int height;
    uint16_t * data;
};

uint16_t getPixel(Image *img, int x, int y)
{
    return img->data[y * img->width + x];
}

我希望移动数据数组，然后交换 width 和 height 成员变量。所以如果我从一个9x20像素的图像开始，然后旋转它，我会得到一个20x9像素的图像。这会改变图像的大步，这使算法复杂化了很多。

I'm hoping to move the contents of the data array around, then swap over the width and height member variables. So if I start with a 9x20 pixel image, then rotate it, I'll end up with a 20x9 pixel image. This changes the stride of the image, which complicates the algorithm a lot.

推荐答案

这可能有助于：就地矩阵转置。

（你也可以必须在转置后做一些镜像，如rlbond提到）。

(You might also have to do some mirroring after the transposition, as rlbond mentions).

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