Drawing and Writing on Images using OpenCV

In this story we are going to go through some functions of OpenCV that can help us draw shapes and place texts on Images according to our will.

First things first, lets show this image using matplotlib in jupyter using the following code:

import cv2 as cv
import matplotlib.pyplot as plt

image1=cv.imread(“catto2.png”,1)
image2=cv.cvtColor(image1, cv.COLOR_BGR2RGB)
plt.imshow(image2)

If these steps seem unfamiliar , check out my previous blog

DRAWING RECTANGLES:

Method used for drawing Rectangles:

cv2.rectangle()

Syntax: cv2.rectangle(img, startingPoint, endingPoint, colour, thickness)

Example:

image3=cv.rectangle(image2,(40,40),(200,200),(0,0,0),10)
plt.imshow(image3)

Output for this code is :

Explanation:

Here we are drawing a black rectangle of dimensions (200,200) starting from co-ordinates(40,40) having a thickness of 10px.

DRAWING CIRCLES:

Method used for drawing Circles:

cv2.circle()

Syntax: cv2.circle(img, co-ordinates, radius, colour, thickness)

Code snippet for drawing circles

DRAWING LINES:

Method used for drawing Lines:

cv2.line()

Syntax: cv2.line(img, startingPoint, endingPoint, colour, thickness)

Code snippet for drawing lines

PLACING TEXTS ON IMAGES

The method for placing texts on images expects a lot of parameters, we’ll go over them all one by one.

Syntax:

image = cv2.putText(image, text, org, font, fontScale, color, thickness, lineType)

Parameter description:

image: The image to place a text on

text: The text to be placed on the image

org: The coordinates of the bottom-left corner of the text string in the image. The coordinates are represented as tuples of two values i.e. (X coordinate value, Y coordinate value).

font: The font family used for the text

fontScale: The font scale factor that is multiplied by the font-specific base size.

color: The color of the text

thickness: Thickness of the text

lineType: An optional parameter. It gives the type of the line to be used. Example : cv2.line_AA

Code snippet for putting text on an image

See some actual applications of drawing Shapes on images in this blog.