Harika-BV / OpenCV-Python

Basics of OpenCV using python

Basics of OpenCV with Python

What will be covered in this post

1. Image Fundamentals - Image Read, Image Write, Drawing circle, Rectangle, Line, Text
2. Image Processing - Image Transforms, Rotate, Scaling, Image Thresholding
3. Image Filtering - Blur, Bilateral filtering, Gaussian Blur, Median Blur
4. Feature Detection - Canny Edge Detector
5. Video Analysis - Video read, Video write, Webcam initialization
6. Applications - Face detection, Real time face detection, Real time eye detection

Image Fundamentals

1. How to read an image?

cv2.imread(file_path, flag)

file_path : Path of the image to be loaded
flag : Specifies the way in which the image should be read. (0 - Grayscale, greater than 0 - RGB Colored)

2. How to write/ save an image in other format?

cv2.imwrite(new_file_path, original_image)

new_file_path : Path to which image has to be uploaded

3. How to draw a rectangle?

cv2.rectangle(image, start_point, end_point, color, thickness)

image : Image on which rectangle is to be drawn
start_point : Starting coordinates of rectangle (X1,Y1)
end_point : Ending coordinates of rectangle (X2,Y2) 
color : BGR Colors - (255,0,0)
Thickness : thickness border line in px. -1 : Fill the rectangle shape by specified color

4. How to draw a line?

cv2.line(image, start_point, end_point, color, thickness)

image : Image on which line is to be drawn
start_point : Starting coordinates of rectangle (X1,Y1)
end_point : Ending coordinates of rectangle (X2,Y2) 
color : BGR Colors - (255,0,0)
Thickness : thickness border line in px. -1 : Fill the rectangle shape by specified color

5. How to draw a circle?

cv2.circle(image, start_point, radius, color, thickness)

image : Image on which circle is to be drawn
start_point : Starting coordinates of rectangle (X1,Y1)
radius : radious of circle
color : BGR Colors - (255,0,0)
Thickness : thickness border line in px. -1 : Fill the rectangle shape by specified color

6. How to put text on an image?

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

image : Image on which text is to be written
text : text string to be written
origin : bottom left corner of the text string
font : denotes font type
color : BGR Colors - (255,0,0)
Thickness : thickness border line in px. -1 : Fill the rectangle shape by specified color
lineType : Gives type of the line to be drawn

Image Processing

7. Image Shifting / Rotating

M = cv2.getRotationMatrix2D(center, angle, 1)
rotate = cv2.warpAffine(pic, M, (cols,rows))

8. Image Thresholding

(T_value,binary_threshold) = cv2.threshold(pic, threshold_value, 255, cv2.THRESH_BINARY)

Image Filtering

9. How to apply Gaussian Blur

cv2.GaussianBlur(pic, matrix,0)

10. How to apply Median Blur

cv2.medianBlur(pic, matrix)

11. How to Bilateral Blur

cv2.bilateralFilter(pic,dimpixel,color,space)

Feature Detection

12. Canny edge detector

cv2.Canny(pic, thresholdval1, thresholdval2)

Video Processing

13. How to read a video?

cv2.VideoCapture('sampleVideo.mp4')