rotate an image 图像旋转代码

本文详细介绍了如何使用双线性内插法实现任意角度旋转图像的算法,包括图像大小的计算、旋转矩阵的生成以及输出文件的处理。

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/****************************************************************************
* Func: rotate_pgm *
* *
* Desc: rotate an image some arbitrary angle. New pixels are generated *
* using bilinear interpolation *
* *
* Params: buffer - pointer to image in memory *
* fileout - name of output file *
* rows - number of rows in source image *
* cols - number of columns in source image *
* angle - angle of rotation (in degrees) *
****************************************************************************/

void rotate_pgm(image_ptr buffer, char *fileout, int rows, int cols, float angle)
{
float angle2; /* 90 degrees - angle */
long x,y; /* column and row indices */
int index; /* index into output line buffer */
unsigned long source_add; /* address of source pixels */
float floatx, floaty; /* floating point values of source x and y */
int intx, inty; /* integer value of source x and y */
int centerx, centery; /* center of new image */
float EWweight, NSweight; /* linear weights for interpolation */
float NW, NE, SW, SE; /* northwest, northeast, southwest, southeast*/
float top, bottom; /* interpolated top and bottom values */
float cosine, sine; /* cosine and sine of angle */
unsigned char *line_buff; /* output line buffer */
int new_rows, new_cols; /* number of rows and columns of new image */
FILE *fp; /* output file pointer */
int xdiff, ydiff; /* difference between new and old rows and cols */

/* open new output file */
if((fp=fopen(fileout, "wb")) == NULL)
{
printf("Unable to open %s for output\n",fileout);
exit(1);
}

while(angle >= 360.0)
angle -=360.0;

/* miscellaneous trig */
angle *= ((double) 3.14159265/(double) 180.0); /* convert to RADs */
angle2 = 1.570796327 - angle;
cosine = cos(angle);
sine = sin(angle);

/* determine new size of output image */
new_cols = rows * fabs(cos(angle2)) + cols * fabs(cosine);
new_rows = rows * fabs(cosine) + cols * fabs(cos(angle2));


centerx = cols/2;
centery = rows/2;
xdiff = (new_cols - cols)/2;
ydiff = (new_rows - rows)/2;

/* print out the portable bitmap header */
fprintf(fp, "P5\n%d %d\n255\n", new_cols, new_rows);

line_buff = (unsigned char *) malloc(new_cols);

for(y=-1*ydiff; y<(new_rows-ydiff); y++)
{
index = 0;
for(x=-1*xdiff; x<(new_cols-xdiff); x++)
{
floatx = (x-centerx) * cosine + (y-centery) * sine;
floatx += centerx;
floaty = (y-centery) * cosine - (x-centerx) * sine;
floaty += centery;
intx = (int) floatx;
inty = (int) floaty;

/* check if pixel is outside of source image */
if((intx < 0) || (intx >= cols-1) || (inty < 0) || (inty >= rows-1))
line_buff[index++] = 255;
else /* interpolate new value */
{
EWweight = floatx - (float) intx;
NSweight = floaty - (float) inty;
source_add = (unsigned long) inty * cols + intx;
NW = (float) buffer[source_add];
NE = (float) buffer[source_add+1];
SW = (float) buffer[source_add+cols];
SE = (float) buffer[source_add+cols+1];

top = NW + EWweight*(NE-NW);
bottom = SW + EWweight*(SE-SW);
line_buff[index++] = (char) (top + NSweight*(bottom-top));
}
}
fwrite(line_buff, 1, new_cols, fp);
}
fclose(fp);
}



### 图像旋转功能的实现 要在 PyCharm 中通过 Python 实现图像旋转功能,可以利用 `Pillow` 库(即 PIL 的增强版本)。以下是详细的说明以及代码示例。 #### Pillow 库简介 Pillow 是一个强大的图像处理库,支持多种文件格式,并提供了丰富的操作接口,包括但不限于裁剪、缩放、旋转等功能[^1]。要使用该库,需先安装它: ```bash pip install pillow ``` #### 图像旋转的核心逻辑 图像旋转可以通过调用 `Image.rotate()` 方法完成。此方法接受角度参数作为输入,并返回一个新的已旋转图像对象。需要注意的是,默认情况下,旋转是以逆时针方向进行的[^4]。 下面是一个完整的代码示例,展示如何加载一张图片并将其旋转指定的角度后保存到本地磁盘上: ```python from PIL import Image def rotate_image(input_path, output_path, angle): """ Rotate an image by a given angle. :param input_path: Path to the source image file. :param output_path: Path where the rotated image will be saved. :param angle: Angle of rotation (in degrees). """ try: with Image.open(input_path) as img: # Perform the actual rotation operation here rotated_img = img.rotate(angle, expand=True) # Save the result into disk at specified location rotated_img.save(output_path) print(f"Successfully saved {output_path}") except Exception as e: print(f"An error occurred while processing the image: {e}") if __name__ == "__main__": input_file = "path/to/your/input/image.jpg" output_file = "path/to/save/output_rotated_image.jpg" degree_angle = 90 # Specify your desired rotation angle rotate_image(input_file, output_file, degree_angle) ``` 上述代码定义了一个函数用于接收原始路径、目标存储位置及所需调整的角度三个参数;接着尝试打开给定地址下的图形资源,在成功读取之后执行相应的变换动作——这里指定了按顺时针还是逆时针对应数值正负号关系——最后把修改后的成果存回硬盘当中去。 #### 常见注意事项 当在 IDE 如 PyCharm 下运行涉及外部依赖项的应用程序时,请确认项目解释器已经正确配置好所需的第三方模块[^3]。如果遇到无法正常预览图表的情况,则可能是因为缺少某些必要的后台服务或者环境变量设置不当所致。
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