2.3 OpenCV中的绘图功能.ipynb

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    "# OpenCV中的绘图功能\n",
    "\n",
    "### 目标\n",
    "\n",
    "- 学习使用OpenCV绘制不同的几何形状\n",
    "- 您将学习以下功能：**cv.line()**，**cv.circle()**，**cv.rectangle()**，**cv.ellipse()**，**cv.putText**()等。\n",
    "\n",
    "### 代码\n",
    "在上述所有功能中，您将看到一些常见的参数，如下所示：\n",
    "\n",
    "- img：您要绘制形状的图像\n",
    "- color：形状的颜色。对于BGR，将其作为元组传递，例如：(255,0,0)对于蓝色。对于灰度，只需传递标量值即可。\n",
    "- 厚度：线或圆等的粗细。如果对闭合图形（如圆）传递`-1` ，它将填充形状。*默认厚度= 1*\n",
    "- lineType：线的类型，是否为8连接线，抗锯齿线等。*默认情况下*，为8连接线。**cv.LINE_AA**给出了抗锯齿的线条，看起来非常适合曲线。\n",
    "\n",
    "#### 画线\n",
    "要绘制一条线，您需要传递线的开始和结束坐标。我们将创建一个黑色图像，并从左上角到右下角在其上绘制一条蓝线。"
   ]
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     "execution_count": 1,
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   ],
   "source": [
    "import numpy as np\n",
    "import cv2 as cv\n",
    "\n",
    "# 创建黑色的图像\n",
    "img = np.zeros((512,512,3), np.uint8)\n",
    "\n",
    "# 绘制一条厚度为5的蓝色对角线\n",
    "cv.line(img,(0,0),(511,511),(255,0,0),5)"
   ]
  },
  {
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   "source": [
    "#### 画矩形\n",
    "\n",
    "要绘制矩形，您需要矩形的左上角和右下角。这次，我们将在图像的右上角绘制一个绿色矩形。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
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       "        [255,   0,   0]]], dtype=uint8)"
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     },
     "execution_count": 2,
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     "output_type": "execute_result"
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   ],
   "source": [
    "cv.rectangle(img,(384,0),(510,128),(0,255,0),3)"
   ]
  },
  {
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   "metadata": {},
   "source": [
    "#### 画圆圈\n",
    "要绘制一个圆，需要其中心坐标和半径。我们将在上面绘制的矩形内绘制一个圆。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
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       "array([[[255,   0,   0],\n",
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       "        [255,   0,   0]]], dtype=uint8)"
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     },
     "execution_count": 3,
     "metadata": {},
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    }
   ],
   "source": [
    "cv.circle(img,(447,63), 63, (0,0,255), -1)"
   ]
  },
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   "source": [
    "#### 画椭圆\n",
    "要绘制椭圆，我们需要传递几个参数。一个参数是中心位置（x，y）。下一个参数是轴长度（长轴长度，短轴长度）。angle是椭圆沿逆时针方向旋转的角度。startAngle和endAngle表示从主轴沿顺时针方向测量的椭圆弧的开始和结束。即给出0和360给出完整的椭圆。有关更多详细信息，请参阅**cv.ellipse**的文档。下面的示例在图像的中心绘制一个椭圆形。\n"
   ]
  },
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   "execution_count": 4,
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       "        [255,   0,   0]]], dtype=uint8)"
      ]
     },
     "execution_count": 4,
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    }
   ],
   "source": [
    "cv.ellipse(img,(256,256),(100,50),0,0,180,255,-1)"
   ]
  },
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   "source": [
    "#### 画多边形\n",
    "\n",
    "要绘制多边形，首先需要顶点的坐标。将这些点组成形状为`ROWSx1x2`的数组，其中`ROWS`是顶点数，并且其类型应为int32。在这里，我们绘制了一个带有四个顶点的黄色小多边形。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
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       "array([[[255,   0,   0],\n",
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     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "pts = np.array([[10,5],[20,30],[70,20],[50,10]], np.int32)\n",
    "pts = pts.reshape((-1,1,2))\n",
    "cv.polylines(img,[pts],True,(0,255,255))"
   ]
  },
  {
   "attachments": {},
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "> **注意**\n",
    "  如果第三个参数为False，您将获得一条连接所有点的折线，而不是闭合形状。\n",
    "  **cv.polylines**()可用于绘制多条线。只需创建要绘制的所有线条的列表，然后将其传递给函数即可。所有线条将单独绘制。与为每条线调用**cv.line**相比，绘制一组线是一种更好，更快的方法。\n",
    "\n",
    "#### 向图像添加文本：\n",
    "\n",
    "要将文本放入图像中，需要指定以下内容。\n",
    "- 您要写入的文字数据\n",
    "- 您要放置它的位置坐标（即数据开始的左下角）。\n",
    "- 字体类型（检查**cv.putText**文档以获取受支持的字体）\n",
    "- 字体比例（指定字体大小）\n",
    "- 常规的内容，例如颜色，厚度，线条类型等。为了获得更好的外观，建议使用lineType = **cv.LINE_AA**。\n",
    "\n",
    "我们将在白色图像上写入**OpenCV**。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
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      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "font = cv.FONT_HERSHEY_SIMPLEX\n",
    "cv.putText(img,'OpenCV',(10,500), font, 4,(255,255,255),2,cv.LINE_AA)"
   ]
  },
  {
   "attachments": {},
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### 结果\n",
    "现在是时候查看我们绘图的最终结果了。正如您在以前的文章中学习的那样，显示图像以查看它。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [],
   "source": [
    "cv.imshow('image', img)\n",
    "cv.waitKey(0)\n",
    "cv.destroyAllWindows()"
   ]
  },
  {
   "attachments": {},
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 其他资源\n",
    "\n",
    "1. 椭圆函数中使用的角度不是我们的圆角。有关更多详细信息，请访问此讨论：http://answers.opencv.org/question/14541/angles-in-ellipse-function/。\n",
    "\n",
    "### 练习题\n",
    "\n",
    "1. 尝试使用OpenCV中可用的绘图功能创建OpenCV的徽标。"
   ]
  }
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