How to draw a rectangle around a region of interest in python

please don't try with the old cv module, use cv2:

import cv2cv2.rectangle(img, (x1, y1), (x2, y2), (255,0,0), 2)x1,y1 ------|          ||          ||          |--------x2,y2

[edit] to append the follow-up questions below:

cv2.imwrite("my.png",img)cv2.imshow("lalala", img)k = cv2.waitKey(0) # 0==wait forever

You can use cv2.rectangle():

cv2.rectangle(img, pt1, pt2, color, thickness, lineType, shift)Draws a simple, thick, or filled up-right rectangle.The function rectangle draws a rectangle outline or a filled rectanglewhose two opposite corners are pt1 and pt2.Parameters    img   Image.    pt1   Vertex of the rectangle.    pt2    Vertex of the rectangle opposite to pt1 .    color Rectangle color or brightness (grayscale image).    thickness  Thickness of lines that make up the rectangle. Negative values,    like CV_FILLED , mean that the function has to draw a filled rectangle.    lineType  Type of the line. See the line description.    shift   Number of fractional bits in the point coordinates.

I have a PIL Image object and I want to draw rectangle on this image. I want to use opencv2 and draw rectangle, and then convert back to PIL Image object. Here is how I do it:

# im is a PIL Image objectim_arr = np.asarray(im)# convert rgb array to opencv's bgr formatim_arr_bgr = cv2.cvtColor(im_arr, cv2.COLOR_RGB2BGR)# pts1 and pts2 are the upper left and bottom right coordinates of the rectanglecv2.rectangle(im_arr_bgr, pts1, pts2,              color=(0, 255, 0), thickness=3)im_arr = cv2.cvtColor(im_arr_bgr, cv2.COLOR_BGR2RGB)# convert back to Image objectim = Image.fromarray(im_arr)

As the other answers said, the function you need is cv2.rectangle(), but keep in mind that the coordinates for the bounding box vertices need to be integers if they are in a tuple, and they need to be in the order of (left, top) and (right, bottom). Or, equivalently, (xmin, ymin) and (xmax, ymax).