RGB和YUV420旋轉(zhuǎn)90/180/270度

1. 屏幕像素排列

像素點(diǎn)在屏幕上是按行和列來排列的邦危，我們看到的屏幕的像素坐標(biāo)系是這樣的：

rotate.png

接下的旋轉(zhuǎn)也會根據(jù)行列按屏幕像素坐標(biāo)系來進(jìn)行烁登。本文以順時針旋轉(zhuǎn)4：3 的RGB圖像為例。假設(shè)件相，有存儲原RGB圖像像素點(diǎn)的數(shù)組src, 存儲旋轉(zhuǎn)后的像素點(diǎn)的數(shù)組dst衰倦，兩個數(shù)組長度一致发侵。

2. 原圖

按照屏幕的像素坐標(biāo)系，坐標(biāo)（y, x ）的像素點(diǎn)即為第y行枫浙，第x列的像素點(diǎn)刨肃。進(jìn)行旋轉(zhuǎn)時可以根據(jù)原坐標(biāo)（y, x ）計算出新坐標(biāo)（y', x'），將所有像素點(diǎn)的坐標(biāo)逐個映射就可以得到旋轉(zhuǎn)后的圖像箩帚。

rotate0.png

3. 旋轉(zhuǎn)90度

rotate90.png

對比原圖和上圖的像素排列可知真友，像素點(diǎn)的原坐標(biāo)為（y, x），圖像的height為3紧帕，width為4盔然。旋轉(zhuǎn)90度之后，新坐標(biāo)為（x, height - y - 1）是嗜，并且圖像寬高也互換了愈案，height為4，width為3鹅搪。

因此站绪，旋轉(zhuǎn)90度就是將像素點(diǎn)從 src[y * width + x] 映射到 dst[x* height + height - y - 1]。

4. 旋轉(zhuǎn)180度

rotate180.png

對比原圖和上圖的像素排列可知丽柿，像素點(diǎn)的原坐標(biāo)為（y, x）恢准，圖像的height為3，width為4甫题。旋轉(zhuǎn)180度之后馁筐，新坐標(biāo)為（height - y - 1, width - x - 1），圖像寬高不變幔睬。

因此眯漩，旋轉(zhuǎn)180度就是將像素點(diǎn)從 src[y * width + x] 映射到 dst[ (height - y - 1) * width + width - x - 1]。

5. 旋轉(zhuǎn)270度

270.png

對比原圖和上圖的像素排列可知，像素點(diǎn)的原坐標(biāo)為（y, x）赦抖，圖像的height為3舱卡，width為4。旋轉(zhuǎn)270度之后队萤，新坐標(biāo)為（width - x - 1, y）轮锥，并且圖像寬高也互換了，height為4要尔，width為3舍杜。

因此，旋轉(zhuǎn)270度就是將像素點(diǎn)從 src[y * width + x] 映射到 dst[ (width - x - 1) * height + y]赵辕。

6. RGB及RGBA旋轉(zhuǎn)

RGB和RGBA的旋轉(zhuǎn)原理是一樣的既绩，只不過RGB為3個字節(jié)(24位)，RGBA為4個字節(jié)(32位)还惠，旋轉(zhuǎn)時需要使用不同的步長饲握。代碼實現(xiàn)：

    static inline void
    rotateRGB90(unsigned char *src, unsigned char *dst, int width, int height, int bpp) {
        int dstIndex = 0;
        int srcIndex = 0;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                //(y, x) -> (x, height - y - 1)
                //y * width + x, -> x* height + height - y - 1
                dstIndex = (x * height + height - y - 1) * bpp;
                for (int i = 0; i < bpp; i++) {
                    dst[dstIndex + i] = src[srcIndex++];
                }
            }
        }
    }

    static inline void rotateRGB90(int *src, int *dst, int width, int height) {
        int dstIndex = 0;
        int srcIndex = 0;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                //(y, x) -> (x, height - y - 1)
                //y * width + x, -> x* height + height - y - 1
                dstIndex = x * height + height - y - 1;
                dst[dstIndex] = src[srcIndex++];
            }
        }
    }

    static inline void
    rotateRGB180(unsigned char *src, unsigned char *dst, int width, int height, int bpp) {
        int dstIndex = 0;
        int srcIndex = 0;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                //(y, x) -> (height - y - 1, width - x - 1)
                //y * width + x, -> (height - y - 1) * width + width - x - 1
                dstIndex = ((height - y - 1) * width + width - x - 1) * bpp;
                for (int i = 0; i < bpp; i++) {
                    dst[dstIndex + i] = src[srcIndex++];
                }
            }
        }
    }

    static inline void rotateRGB180(int *src, int *dst, int width, int height) {
        int dstIndex = 0;
        int srcIndex = 0;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                //(y, x) -> (height - y - 1, width - x - 1)
                //y * width + x, -> (height - y - 1) * width + width - x - 1
                dstIndex = (height - y - 1) * width + width - x - 1;
                dst[dstIndex] = src[srcIndex++];
            }
        }
    }

    static inline void
    rotateRGB270(unsigned char *src, unsigned char *dst, int width, int height, int bpp) {
        int dstIndex = 0;
        int srcIndex = 0;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                //(y, x) -> (width - x - 1, y)
                //y * width + x, -> (width - x - 1) * height + y
                dstIndex = ((width - x - 1) * height + y) * bpp;
                for (int i = 0; i < bpp; i++) {
                    dst[dstIndex + i] = src[srcIndex++];
                }
            }
        }
    }

    static inline void rotateRGB270(int *src, int *dst, int width, int height) {
        int dstIndex = 0;
        int srcIndex = 0;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                //(y, x) -> (width - x - 1, y)
                //y * width + x, -> (width - x - 1) * height + y
                dstIndex = (width - x - 1) * height + y;
                dst[dstIndex] = src[srcIndex++];
            }
        }
    }

    void rotateRGB(unsigned char *src, unsigned char *dst, int width, int height, float degree) {
        if (degree == 90.0f) {
            rotateRGB90(src, dst, width, height, 3);
        } else if (degree == 180.0f) {
            rotateRGB180(src, dst, width, height, 3);
        } else if (degree == 270.0f) {
            rotateRGB270(src, dst, width, height, 3);
        } else {
            return;
        }
    }

    void rotateRGBA(unsigned char *src, unsigned char *dst, int width, int height, float degree) {
        if (degree == 90.0f) {
            rotateRGB90(src, dst, width, height, 4);
        } else if (degree == 180.0f) {
            rotateRGB180(src, dst, width, height, 4);
        } else if (degree == 270.0f) {
            rotateRGB270(src, dst, width, height, 4);
        } else {
            return;
        }
    }

    void rotateRGBAInt(int *src, int *dst, int width, int height, float degree) {
        if (degree == 90.0f) {
            rotateRGB90(src, dst, width, height);
        } else if (degree == 180.0f) {
            rotateRGB180(src, dst, width, height);
        } else if (degree == 270.0f) {
            rotateRGB270(src, dst, width, height);
        } else {
            return;
        }
    }

7. YUV420旋轉(zhuǎn)

YUV420分為YUV420P和YUV420SP。YUV420P每個像素的Y蚕键、U救欧、V通道分別連續(xù)存儲，根據(jù)UV通道順序不同又分為I420和YV12锣光。YUV420SP每個像素的Y通道連續(xù)存儲笆怠，UV通道交替存儲，根據(jù)UV通道順序不同又分為NV12和NV21誊爹。如果你對YUV420不是很了解蹬刷，請戳：YUV_420_888介紹及YUV420轉(zhuǎn)RGBA

7.1 YUV420P旋轉(zhuǎn)

YUV420P的Y、U替废、V通道按4:1:1分別存儲在不同矩陣中箍铭，并且Y的數(shù)量和像素點(diǎn)數(shù)量相同。因此我們只要參考RGB的旋轉(zhuǎn)椎镣，先旋轉(zhuǎn)Y诈火，再旋轉(zhuǎn)U、V就能完成YUV420P的旋轉(zhuǎn)状答。由于旋轉(zhuǎn)時我們并不關(guān)心U和V順序冷守，所以I420和YV12旋轉(zhuǎn)可以用同一種方法。

    static inline void
    rotateYUV420P90(unsigned char *srcY, unsigned char *srcU, unsigned char *srcV,
                    unsigned char *dstY, unsigned char *dstU, unsigned char *dstV,
                    int width, int height) {
        //rotate y
        int dstIndex = 0;
        int srcIndex = 0;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                dstIndex = x * height + height - y - 1;
                dstY[dstIndex] = srcY[srcIndex++];
            }
        }

        //rotate uv
        int uvHeight = height / 2;
        int uvWidth = width / 2;
        int dstUVIndex = 0;
        int srcUVIndex = 0;
        for (int y = 0; y < uvHeight; y++) {
            for (int x = 0; x < uvWidth; x++) {
                dstUVIndex = x * uvHeight + uvHeight - y - 1;
                dstU[dstUVIndex] = srcU[srcUVIndex];
                dstV[dstUVIndex] = srcV[srcUVIndex];
                srcUVIndex++;
            }
        }
    }

    static inline void
    rotateYUV420P180(unsigned char *srcY, unsigned char *srcU, unsigned char *srcV,
                     unsigned char *dstY, unsigned char *dstU, unsigned char *dstV,
                     int width, int height) {
        //rotate y
        int dstIndex = 0;
        int srcIndex = 0;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                dstIndex = (height - y - 1) * width + width - x - 1;
                dstY[dstIndex] = srcY[srcIndex++];
            }
        }

        //rotate uv
        int uvHeight = height / 2;
        int uvWidth = width / 2;
        int dstUVIndex = 0;
        int srcUVIndex = 0;
        for (int y = 0; y < uvHeight; y++) {
            for (int x = 0; x < uvWidth; x++) {
                dstUVIndex = (uvHeight - y - 1) * uvWidth + uvWidth - x - 1;
                dstU[dstUVIndex] = srcU[srcUVIndex];
                dstV[dstUVIndex] = srcV[srcUVIndex];
                srcUVIndex++;
            }
        }
    }

    static inline void
    rotateYUV420P270(unsigned char *srcY, unsigned char *srcU, unsigned char *srcV,
                     unsigned char *dstY, unsigned char *dstU, unsigned char *dstV,
                     int width, int height) {
        //rotate y
        int dstIndex = 0;
        int srcIndex = 0;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                dstIndex = (width - x - 1) * height + y;
                dstY[dstIndex] = srcY[srcIndex++];
            }
        }

        //rotate uv
        int uvHeight = height / 2;
        int uvWidth = width / 2;
        int dstUVIndex = 0;
        int srcUVIndex = 0;
        for (int y = 0; y < uvHeight; y++) {
            for (int x = 0; x < uvWidth; x++) {
                dstUVIndex = (uvWidth - x - 1) * uvHeight + y;
                dstU[dstUVIndex] = srcU[srcUVIndex];
                dstV[dstUVIndex] = srcV[srcUVIndex];
                srcUVIndex++;
            }
        }
    }

    void
    rotateYUV420P(unsigned char *src, unsigned char *dst, int width, int height, float degree) {
        unsigned char *pSrcY = src;
        unsigned char *pSrcU = src + width * height;
        unsigned char *pSrcV = src + width * height / 4 * 5;

        unsigned char *pDstY = dst;
        unsigned char *pDstU = dst + width * height;
        unsigned char *pDstV = dst + width * height / 4 * 5;

        if (degree == 90.0f) {
            rotateYUV420P90(pSrcY, pSrcU, pSrcV, pDstY, pDstU, pDstV, width, height);
        } else if (degree == 180.0f) {
            rotateYUV420P180(pSrcY, pSrcU, pSrcV, pDstY, pDstU, pDstV, width, height);
        } else if (degree == 270.0f) {
            rotateYUV420P270(pSrcY, pSrcU, pSrcV, pDstY, pDstU, pDstV, width, height);
        } else {
            return;
        }
    }

需要注意的是惊科，如果是旋轉(zhuǎn)90度或者270度拍摇，由于旋轉(zhuǎn)后寬和高互換了，旋轉(zhuǎn)后轉(zhuǎn)換RGB時yRowStride和uvRowStride也要相應(yīng)的由 width 和 width/2 改為 height 和 height/2馆截。

if (rotationDegree == 90.0f || rotationDegree == 270.0f) {
    NativeUtils.I420ToRGBAInt(rotatedYUV420, rgba, height, width, height, height / 2, 1);
    ImageUtils.RGBAToJPEG(context, rgba, height, width, parent, fileName);
} else if (rotationDegree == 180.0f) {
    NativeUtils.I420ToRGBAInt(rotatedYUV420, rgba, width, height, width, width / 2, 1);
    ImageUtils.RGBAToJPEG(context, rgba, width, height, parent, fileName);
} else {
    NativeUtils.I420ToRGBAInt(yuv420, rgba, width, height, width, width / 2, 1);
    ImageUtils.RGBAToJPEG(context, rgba, width, height, parent, fileName);
}

7.2 YUV420SP旋轉(zhuǎn)

與YUV420P一樣充活，YUV420SP的旋轉(zhuǎn)蜂莉，也是先旋轉(zhuǎn)Y，再旋轉(zhuǎn)U混卵、V映穗。旋轉(zhuǎn)時也不關(guān)心U和V順序，NV12和NV21可以用同一種方法幕随。
區(qū)別在于YUV420SP的UV通道是交替存儲的蚁滋，所以我們像RGB旋轉(zhuǎn)時一樣，設(shè)置一個步長2赘淮。

    static inline void
    rotateYUV420SP90(unsigned char *srcY, unsigned char *srcUV, unsigned char *dstY,
                     unsigned char *dstUV, int width, int height) {
        //rotate y
        int dstIndex = 0;
        int srcIndex = 0;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                dstIndex = x * height + height - y - 1;
                dstY[dstIndex] = srcY[srcIndex++];
            }
        }

        //rotate uv
        int uvHeight = height >> 1;
        int uvWidth = width >> 1;
        int dstUVIndex = 0;
        int srcUVIndex = 0;
        for (int y = 0; y < uvHeight; y++) {
            for (int x = 0; x < uvWidth; x++) {
                dstUVIndex = (x * uvHeight + uvHeight - y - 1) << 1;
                dstUV[dstUVIndex] = srcUV[srcUVIndex++];
                dstUV[dstUVIndex + 1] = srcUV[srcUVIndex++];
            }
        }
    }

    static inline void
    rotateYUV420SP180(unsigned char *srcY, unsigned char *srcUV, unsigned char *dstY,
                      unsigned char *dstUV, int width, int height) {
        //rotate y
        int dstIndex = 0;
        int srcIndex = 0;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                dstIndex = (height - y - 1) * width + width - x - 1;
                dstY[dstIndex] = srcY[srcIndex++];
            }
        }

        //rotate uv
        int uvHeight = height >> 1;
        int uvWidth = width >> 1;
        int dstUVIndex = 0;
        int srcUVIndex = 0;
        for (int y = 0; y < uvHeight; y++) {
            for (int x = 0; x < uvWidth; x++) {
                dstUVIndex = ((uvHeight - y - 1) * uvWidth + uvWidth - x - 1) << 1;
                dstUV[dstUVIndex] = srcUV[srcUVIndex++];
                dstUV[dstUVIndex + 1] = srcUV[srcUVIndex++];
            }
        }
    }

    static inline void
    rotateYUV420SP270(unsigned char *srcY, unsigned char *srcUV, unsigned char *dstY,
                      unsigned char *dstUV, int width, int height) {
        //rotate y
        int dstIndex = 0;
        int srcIndex = 0;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                dstIndex = (width - x - 1) * height + y;
                dstY[dstIndex] = srcY[srcIndex++];
            }
        }

        //rotate uv
        int uvHeight = height >> 1;
        int uvWidth = width >> 1;
        int dstUVIndex = 0;
        int srcUVIndex = 0;
        for (int y = 0; y < uvHeight; y++) {
            for (int x = 0; x < uvWidth; x++) {
                dstUVIndex = ((uvWidth - x - 1) * uvHeight + y) << 1;
                dstUV[dstUVIndex] = srcUV[srcUVIndex++];
                dstUV[dstUVIndex + 1] = srcUV[srcUVIndex++];
            }
        }
    }

    void
    rotateYUV420SP(unsigned char *src, unsigned char *dst, int width, int height, float degree) {
        unsigned char *pSrcY = src;
        unsigned char *pSrcUV = src + width * height;

        unsigned char *pDstY = dst;
        unsigned char *pDstUV = dst + width * height;

        if (degree == 90.0f) {
            rotateYUV420SP90(pSrcY, pSrcUV, pDstY, pDstUV, width, height);
        } else if (degree == 180.0f) {
            rotateYUV420SP180(pSrcY, pSrcUV, pDstY, pDstUV, width, height);
        } else if (degree == 270.0f) {
            rotateYUV420SP270(pSrcY, pSrcUV, pDstY, pDstUV, width, height);
        } else {
            return;
        }
    }

同樣需要注意的是辕录，如果是旋轉(zhuǎn)90度或者270度，旋轉(zhuǎn)后寬和高互換了梢卸，轉(zhuǎn)換RGB時需要使用旋轉(zhuǎn)后的寬高走诞。

測試效果：

測試效果.png

本文中的代碼已經(jīng)上傳到github：https://github.com/qiuxintai/YUV420Converter

8. 本文參考

http://www.reibang.com/p/7e602dea3ca1
感謝原作者的辛勤付出。