问题

Traceback (most recent call last): File “alg_face_occlusion/ky.py”,
line 1360, in ky.run File “alg_face_occlusion/ky.py”, line 119, in
ky.process_red_region_invasion File “alg_face_occlusion/ky.py”, line
850, in ky.handle_alarm cv2.error: OpenCV(4.11.0) 👎 error: (-5:Bad
argument) in function ‘polylines’

Overload resolution failed:

• img marked as output argument, but provided NumPy array marked as readonly
• Expected Ptrcv::UMat for argument ‘img’

except info : OpenCV(4.11.0) 👎 error: (-5:Bad argument) in
function ‘polylines’

Overload resolution failed:

• img marked as output argument, but provided NumPy array marked as readonly
• Expected Ptrcv::UMat for argument ‘img’

2025-03-06 11:20:56.822258 except info: OpenCV(4.11.0) 👎 error:
(-5:Bad argument) in function ‘polylines’

Overload resolution failed:

• img marked as output argument, but provided NumPy array marked as readonly
• Expected Ptrcv::UMat for argument ‘img’

Traceback (most recent call last):
  File "alg_face_occlusion/ky.py", line 1360, in ky.run
  File "alg_face_occlusion/ky.py", line 119, in ky.process_red_region_invasion
  File "alg_face_occlusion/ky.py", line 850, in ky.handle_alarm
cv2.error: OpenCV(4.11.0) :-1: error: (-5:Bad argument) in function 'polylines'
> Overload resolution failed:
>  - img marked as output argument, but provided NumPy array marked as readonly
>  - Expected Ptr<cv::UMat> for argument 'img'

except info :  OpenCV(4.11.0) :-1: error: (-5:Bad argument) in function 'polylines'
> Overload resolution failed:
>  - img marked as output argument, but provided NumPy array marked as readonly
>  - Expected Ptr<cv::UMat> for argument 'img'

2025-03-06 11:20:56.822258 except info: OpenCV(4.11.0) :-1: error: (-5:Bad argument) in function 'polylines'
> Overload resolution failed:
>  - img marked as output argument, but provided NumPy array marked as readonly
>  - Expected Ptr<cv::UMat> for argument 'img'

分析&解决方案

这是什么问题？怎么解决？

这个OpenCV的polylines函数错误通常发生在以下情况：

问题原因：
当尝试在只读的NumPy数组上使用绘图函数时（比如从某些不可变数据源加载的图像），而OpenCV需要可写缓冲区来绘制图形。常见于：

1. 使用cv2.imread()加载图像时设置了cv2.IMREAD_UNCHANGED等只读标志
2. 图像数据来自不可修改的缓存区
3. 数组被显式设置为flags.writeable = False

解决方案：

# ... existing code ...
# 在调用polylines之前确保图像可写
if not img.flags.writeable:
    img = np.copy(img)  # 创建可写副本

# 确保使用正确的数据类型
img = img.astype(np.uint8)

# 现在可以安全调用polylines
cv2.polylines(img, [pts], isClosed, color, thickness)
# ... existing code ...

关键修改点：

1. 检查并确保图像数组的flags.writeable属性为True
2. 必要时使用np.copy()创建可写副本
3. 显式指定图像数据类型为np.uint8

参考链接：OpenCV官方文档 - polylines

这是文件目录无法写入图片吗，还是什么原因？

这不是文件目录写入权限问题，而是内存中的图像数据不可修改导致的。具体来说：

根本原因在于：

1. 你正在操作的图像数组被OpenCV识别为"只读内存"
2. 常见于以下场景：
   • 从视频流或网络摄像头获取的原始帧数据
   • 使用cv2.imread()时未正确设置读取模式
   • 图像数据来自不可变的缓存区(如某些深度学习框架的预处理输出)

典型错误代码示例：

# 错误方式：可能返回只读数组
img = cv2.imread('image.jpg', cv2.IMREAD_UNCHANGED) 

# 直接在此img上绘图会报错
cv2.polylines(img, ...)  # ❌ 触发只读错误

正确修复方式：

# ... existing code ...
# 读取时强制可写
img = cv2.imread('image.jpg', cv2.IMREAD_COLOR)  # ✅ 使用标准读取模式

# 或者在处理前显式创建副本
working_img = np.ascontiguousarray(img)  # ✅ 创建连续可写副本
cv2.polylines(working_img, ...)  # ✅ 现在可安全操作
# ... existing code ...

建议在调用polylines前添加数组验证：

assert img.flags.writeable, "图像数组不可写！"
assert img.dtype == np.uint8, "需要uint8数据类型！"