Python-OpenCV 查找矩形和裁剪图像

Question

I'm trying to make a game bot, and in the process, need to find the minimap, and crop it out so I can figure out where the player is from it.

I was able to take a screenshot of the image, crop out approximately where the minimap is. However, I can't get the exact minimap bounding box from it.

My original gray image:

Blurred and Threshed Image:

What I wished to do:

As I'm very new to OpenCV and image processing, I'm not sure what steps I need to take to accomplish this task.

What steps should I take to find the bounding box/coordinates of the minimap?

EDIT: It seens I was unclear when I meant "knew the exact bounding box". I need to exactly extract the minimap area from the images. I do not have any coordinate info except the top left of the minimap, and the size of the minimap changes depending on the size of the map, so I can't hardcode coordinates.

Answer 1

If you know the exact coordinates of the area of interest and if that area is pinned in the same location all the time you can use any of the drawing functions with the known x,y coordinates; h,w dimensions.

void cv::rectangle  (   InputOutputArray    img,
Point   pt1,
Point   pt2,
const Scalar &  color,
int     thickness = 1,
int     lineType = LINE_8,
int     shift = 0 
)

For finding the dynamic w,h: Starting with the known top left coordinates parse the image pixel by pixel and compare the color of the read pixel to the known one, first on x axes ascending until you find a pixel that doesn't match. Second on y axes descending, and so on you can find the margins of the map.

Example of value of a pixel at coordinates 100 100 (python):

img = cv2.imread('myImage.png')

px = img[100,100]
print px

For parsing read this article for fast, optimized "for" pixel loops with OpenCV and Python