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This post will be helpful in learning OpenCV using Python programming. Here I will show how to implement OpenCV functions and apply them in various aspects using some great examples. Then the output will be visualized along with the comparisons.

We will also discuss the basic of image processing and provide the detail explanation related to the OpenCV functions.

Requirements:

• OpenCV 3.4+
• Python 3.6+
• Numpy
• Image, Webcam or Video input
• Documentation Source: OpenCV Official Documentation

First, you need to setup your Python Environment with OpenCV. You can easily do it by following Life2Coding’s tutorial on YouTube: Linking OpenCV with Python 3

Goals:

The goal is to make you understand how to draw text watermark on images using Python OpenCV.

Documentation:

imread()

Loads an image from a file.

Parameters

filename	Name of file to be loaded.
flags	Flag that can take values of cv::ImreadModes

putText()

Draws a text string.

Parameters

img	Image.
text	Text string to be drawn.
org	Bottom-left corner of the text string in the image.
fontFace	Font type, see HersheyFonts.
fontScale	Font scale factor that is multiplied by the font-specific base size.
color	Text color.
thickness	Thickness of the lines used to draw a text.
lineType	Line type. See LineTypes
bottomLeftOrigin	When true, the image data origin is at the bottom-left corner. Otherwise, it is at the top-left corner.

addWeighted()

Calculates the weighted sum of two arrays.

Parameters

src1	first input array.
alpha	weight of the first array elements.
src2	second input array of the same size and channel number as src1.
beta	weight of the second array elements.
gamma	scalar added to each sum.
dst	output array that has the same size and number of channels as the input arrays.
dtype	optional depth of the output array; when both input arrays have the same depth, dtype can be set to -1, which will be equivalent to src1.depth().

imshow()

Displays an image in the specified window.

Parameters

winname	Name of the window.
mat	Image to be shown.

waitKey()

Waits for a pressed key.

Parameters

delay

Delay in milliseconds. 0 is the special value that means “forever”.

Steps:

• Load a face image using cv2.imread()
• Load the image using cv2.imread()
• Create the overlay copy of the image using copy()
• Draw the watermark text using cv2.putText() on the overlay image
• Then blend the images using cv2.addWeighted()
• Display the image using cv2.imshow()
• Wait for keyboard button press using cv2.waitKey()
• Exit window and destroy all windows using cv2.destroyAllWindows()

Example Code:

# import the necessary packages
from __future__ import print_function
import numpy as np
import cv2

# load the image
image = cv2.imread("./hanif.jpg")

def addWaterMark(text,opacity,BGRColor):
    opacity=opacity/100
    overlay = image.copy()
    output = image.copy()

    cv2.putText(overlay, text, (0,int(2*(image.shape[1])/3)), cv2.FONT_HERSHEY_SIMPLEX, 1.0, BGRColor, 2)
    # apply the overlay
    cv2.addWeighted(overlay, opacity, output, 1 - opacity,
                    0, output)
    # show the output image
    cv2.imshow("Output", output)
    cv2.waitKey(0)

if __name__ == '__main__':
    #put the text , Opacity, BGR Color
    addWaterMark("Life2Coding",50,(255,0,255))

Output:

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