Drawing on images (lines, rectangles, circles, text) in Computer Vision - Cheat Sheet & Quick Revision

Recall & Review

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What is the purpose of drawing shapes like lines, rectangles, and circles on images in computer vision?

Drawing shapes helps highlight or mark important parts of an image, like objects or areas of interest, making it easier to understand or analyze the image.

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Which function is commonly used to draw a line on an image in OpenCV?

The function cv2.line() is used to draw a line by specifying the start and end points, color, and thickness.

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How do you specify the position and size of a rectangle when drawing it on an image?

You provide the top-left corner and bottom-right corner coordinates of the rectangle to define its position and size.

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What parameters are needed to draw text on an image?

You need the text string, position coordinates, font type, font scale (size), color, and thickness to draw text on an image.

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Why is it important to choose contrasting colors when drawing on images?

Contrasting colors make the drawn shapes or text stand out clearly against the image background, improving visibility and understanding.

Which OpenCV function draws a circle on an image?

A cv2.circle()

B cv2.rectangle()

C cv2.line()

D cv2.putText()

cv2.circle() is used to draw circles by specifying the center, radius, color, and thickness.

What does the thickness parameter control when drawing shapes on images?

A The width of the shape's border

B The color of the shape

C The size of the shape

D The transparency of the shape

Thickness controls how wide or thick the border or line of the shape will be.

To draw text on an image, which parameter specifies the font style?

A fontScale

B thickness

C color

D fontFace

fontFace specifies the font style, such as cv2.FONT_HERSHEY_SIMPLEX.

Which coordinate system is used when drawing on images?

A Polar coordinates

B Cartesian coordinates with origin at top-left

C Cartesian coordinates with origin at center

D Spherical coordinates

Images use Cartesian coordinates with the origin (0,0) at the top-left corner.

What happens if you set thickness to -1 when drawing a rectangle in OpenCV?

A The rectangle is drawn with default thickness

B The rectangle border is invisible

C The rectangle is filled with color

D An error occurs

Setting thickness to -1 fills the rectangle with the specified color.

Explain how to draw a rectangle and add text on an image using OpenCV.

Think about the functions cv2.rectangle() and cv2.putText() and their key parameters.

Why is drawing shapes and text on images useful in computer vision projects?

Consider how marking parts of an image helps people or algorithms.